# Review of a neat bench power supply from MPJA.com



## milkyspit (Jul 11, 2003)

I found a nifty regulated bench power supply at MPJA.com, a surplus electronics distributor that I've bought from several times in the past. My much-anticipated power supply came by UPS today, and... it's quite nice! It includes digital readouts for both voltage and current, and allows adjustment of both, making it perfect for testing LEDs at specific voltage/current combinations.







As a quick test, I hooked a single Nichia 9200mcd white LED to the power supply, turned the voltage knob to max, and slowly increased the current from 0 to about 200mA. All the while I kept the leads of the LED close to the head gripped between my thumb and index finger, so that as I felt the leads get warm I could back off the current -- low tech but effective! /ubbthreads/images/graemlins/grin.gif I learned more about the nature of Nichia LEDs in one minute of tinkering with the bench power supply than I have from all my previous reading and modding.

Anyway, I really think this would make a great power supply for a flashaholic's workbench. The range of 0-18V and 0-2A should work well for such uses, and the supply is certainly user friendly! The ability to vary voltage OR current is great.

There's even some good heatsinking on the outside back of the power supply to help dissipate the heat of its own electronics.

I paid $59.95 for this little puppy and would heartily recommend it to anyone here... and no, I don't have any connection with MPJA, just a satisfied customer. /ubbthreads/images/graemlins/blush.gif Here's a link to their product page for this power supply.

Downsides? I think the primary one is that the current readout only goes to two decimal places, which can be annoying when testing extremely low current circuits. For example, a Nichia driven at 20mA would show as "0.02" on the readout. I suppose one could hook a DMM to the circuit to get greater precision, though, and the actual current adjustment knob still offers sufficient "granularity" even at low current output to make small adjustments.

Incidentally, one really cool thing I did with the Nichia was to turn the current down until it ALMOST went out, then look directly into the top of the LED. At this minimal brightness I could clearly see the traces and a small pool of photons collecting between them. Very very cool. /ubbthreads/images/graemlins/smirk.gif


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## ElectroCaver (Jul 11, 2003)

Great find Scott. I've been looking for a reasonably priced power supply for a long time. I ordered one. Thanks for sharing the info.


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## Tweek (Jul 11, 2003)

MPJA is my favorite place to look first when I need a power supply... /ubbthreads/images/graemlins/smile.gif


Chris


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## snuffy (Jul 12, 2003)

Nice find Scott. /ubbthreads/images/graemlins/thumbsup.gif
Is this a linear or switching supply and does it come with a schematic? 
At 6.2 lbs I guess it's a linear supply /ubbthreads/images/graemlins/banghead.gif, long day /ubbthreads/images/graemlins/icon23.gif


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## milkyspit (Jul 12, 2003)

[ QUOTE ]
*snuffy said:*
Nice find Scott. /ubbthreads/images/graemlins/thumbsup.gif
Is this a linear or switching supply and does it come with a schematic? 
At 6.2 lbs I guess it's a linear supply /ubbthreads/images/graemlins/banghead.gif, long day /ubbthreads/images/graemlins/icon23.gif 

[/ QUOTE ]

To be honest, I couldn't tell you which type of supply it is. I can tell you, though, that the heatsink on the outside back of the unit also incorporates what looks like a power transistor (is that the name of those things? large metallic circle sitting on a pointed oval base).

I was about to grab the small manual that came with the power supply, then realized that my baby is asleep on the bed in that room and I'd have a deathwish to risk waking him up. /ubbthreads/images/graemlins/banghead.gif From memory, I don't remember seeing much in the way of schematics.

For what it's worth, the voltage and current controls seem to be variable resistors, speaking solely on the basis of their actions and the way they stop at an extreme left and extreme right point when turning. (That was my confusing way of saying they don't turn around endlessly, but instead have limits just like variable resistors would.)

Does this give enough circumstantial evidence to guess what type of supply it is?


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## Gman (Jul 12, 2003)

Looks like a switcher. A good CC supply is useful for lots of things, including troubleshooting electronics and manual battery charging. Btw, you don't need to turn the voltage to max, only a little more than you need to keep in CC mode.


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## snuffy (Jul 12, 2003)

Scott, thanks for all the info.
It sounds like a linear supply to me, at 6.2 lbs a switcher would be capable of 20-25 amps output.
That's the pass transistor on the heatsink alright. 
I'd appreciate it if, after your baby wakes up, you can tell me if it has a schematic with it.
Thanks, Jim


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## milkyspit (Jul 13, 2003)

Snuffy, I'll definitely check on the schematic, although it might not happen until sometime tomorrow. Stay tuned...


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## James S (Jul 13, 2003)

What does it really matter if it's linear or switching? Does that affect somehow the circuit you're running from it? I know that the linear circuit will generate more heat and such, but you're running mains and not battery /ubbthreads/images/graemlins/smile.gif


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## snuffy (Jul 13, 2003)

[ QUOTE ]
*James S said:*
What does it really matter if it's linear or switching? 

[/ QUOTE ]
I'm a ham radio op and some inexpensive switching supplies generate an excessive amount of radio frequency interference. With that in mind I try to avoid having a lot of RFI floating around. /ubbthreads/images/graemlins/grin.gif 

Scott: I'm "tuned" -- thanks /ubbthreads/images/graemlins/grinser2.gif


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## James S (Jul 13, 2003)

Ah, so in your case linear would be better. For some reason I was thinking the implication in the above messages was that switching was better for some reason.

In any case I've ordered one too as it's something thats been on my list for a long time and the price is right. Type of regulation is less important for me as I am not (yet) involved with any ham radios.

Thanks


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## star882 (Jul 13, 2003)

"Is this a linear or switching supply and does it come with a schematic? 
At 6.2 lbs I guess it's a linear supply"
I have a 200w computer PSU that weighs close to 5lbs, and I'm sure it's a switcher.
It's a high quality PSU(Dell), though, and the heatsinks inside are pretty big.
I think it's to allow the use of a slow, quiet fan.


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## milkyspit (Jul 15, 2003)

[ QUOTE ]
*snuffy said:*
Scott, thanks for all the info.
It sounds like a linear supply to me, at 6.2 lbs a switcher would be capable of 20-25 amps output.
That's the pass transistor on the heatsink alright. 
I'd appreciate it if, after your baby wakes up, you can tell me if it has a schematic with it.
Thanks, Jim 

[/ QUOTE ]

Jim, I looked through the not-very-long manual, and unfortunately there is no schematic. /ubbthreads/images/graemlins/frown.gif


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## snuffy (Jul 15, 2003)

[/ QUOTE ]unfortunately there is no schematic. /ubbthreads/images/graemlins/frown.gif 

[/ QUOTE ]
Thanks for looking Scott. /ubbthreads/images/graemlins/icon23.gif


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## Doug Owen (Jul 15, 2003)

Gents, 

A couple of thoughts. First off, while I've never seen the power supply in question, I've 'modded' a fair number of similar ones by replacing the 'single turn' (really 270 degrees) pots that control voltage and current with ten turn units of the same value. This makes precision adjustmets easy.

Those that were interested if it had a schematic are encouraged to check out the LM723. It's the IC that most 'open frame linear' supplies are based on. Add an external transistor, and a few other parts and you're 'good to go'. A full featured (voltage or current limited) supply.

Doug Owen


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## milkyspit (Jul 16, 2003)

Doug, interesting info as I've not heard of 10-turns variable resistors before. /ubbthreads/images/graemlins/cool.gif

Incidentally -- and straying off topic ever so briefly -- what's your background; are you an electrical engineer? You seem from this post and some others to have good knowledge of some fairly technical issues.


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## eluminator (Jul 16, 2003)

I like this one at $88. It has course and fine adjustment knobs for current and voltage. Limits are 30 volts and 3 amps. LED meters instead of LCD. Like yours they only show hundredths of volts and amps. 

http://www.elexp.com/tst_3003.htm


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## milkyspit (Jul 16, 2003)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*eluminator said:*
I like this one at $88. It has course and fine adjustment knobs for current and voltage. Limits are 30 volts and 3 amps. LED meters instead of LCD. Like yours they only show hundredths of volts and amps. 

http://www.elexp.com/tst_3003.htm 

[/ QUOTE ]

Nice find. /ubbthreads/images/graemlins/smile.gif I think they are made by the same company, based on similarities in appearance (such as the knobs and binding posts, and the similar model numbering scheme); yours is model "HY3003" and mine is "HY1802D." This line of bench power supplies seems to come in several models, with higher price models extending to higher volt/amp combinations. For my purposes, the lower-end model serves my needs fine, but of course that's a personal decision.

Incidentally, have you bought from http://elexp.com before, and are they a reputable company? I've not heard of them...

The coarse and fine adjustment is a nice touch. /ubbthreads/images/graemlins/thumbsup.gif


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## eluminator (Jul 17, 2003)

*Re: Review of a neat bench power supply from MPJA.*

Yes, I have bought several items from them in the last 3 years. I haven't had any problems. Their website is bad, but the merchandise seems good. Half the time I look for something on their site I can't find it, and I know they sell it. You have to call them on the phone to order, but deliveries are fast.

I am also the proud owner of this $46 multimeter with PC interface.

http://www.elexp.com/tst_s345.htm


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## milkyspit (Jul 17, 2003)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*eluminator said:*
I am also the proud owner of this $46 multimeter with PC interface.

http://www.elexp.com/tst_s345.htm 

[/ QUOTE ]

Dang you! You're gonna make me purchase my THIRD DMM in the past 12 months. /ubbthreads/images/graemlins/ooo.gif (Actually, one of the existing two was free.) My present two DMMs don't have a PC interface, which I could see being helpful with things such as flashlight brightness vs. runtime graphs, or perhaps temperature over time.

This is straying off-topic, but have you used the PC interface? What software do you use for data capture and charting?


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## N2UK (Jul 17, 2003)

*Re: Review of a neat bench power supply from MPJA.*

I received my MPJA 18 volt 2 amp power supply today and found out that it has a linear design. Because of this, it should not radiate any radio frequency interfernce.

Thanks,

Ken


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## Doug Owen (Jul 17, 2003)

[ QUOTE ]
*milkyspit said:*
Doug, interesting info as I've not heard of 10-turns variable resistors before. /ubbthreads/images/graemlins/cool.gif

Incidentally -- and straying off topic ever so briefly -- what's your background; are you an electrical engineer? You seem from this post and some others to have good knowledge of some fairly technical issues.


[/ QUOTE ]

Yup, they're out there, a bit pricey, but well worth it in some uses. Very linear, not that we need that in this case. Speak up if you have trouble finding them.

Engineer? Yeah, I been called that (and worse). I've been fiddling around with this stuff for hobby and pay for a lot of years. Traveled the world on other people's money doing Field Circus (really service and installations) as well when I was younger. A fair bit of design, development and production of lots of keen stuff. The last 15 or so years as a 'Research Specialist' for the Material Science division of Lawrence Berkeley Labs (Electron Microscopes specifically); Wanna see pictures of atoms?

I've also taught Electronics part time at the local community college for the last 20 years or so (even did a few gigs teaching computer repair at the local Federal Woman's prison......). $45 an hour for that, all I could afford at the time.....

Doug Owen


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## star882 (Jul 17, 2003)

"I am also the proud owner of this $46 multimeter with PC interface.

http://www.elexp.com/tst_s345.htm"
Now, if only it can connect via USB.


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## PaulW (Jul 17, 2003)

*Re: Review of a neat bench power supply from MPJA.*

Eliminator,

I like what's at the Electronix Express link you shared. I am very tempted by the 30V, 5 A model at $105. I need to be able to generate 3.5 Amps.

Has anyone had experience with Electronix Express (division of R.S.R. Electronics)?

Paul


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## Doug Owen (Jul 18, 2003)

[ QUOTE ]
*star882 said:*
"I am also the proud owner of this $46 multimeter with PC interface.

http://www.elexp.com/tst_s345.htm"
Now, if only it can connect via USB. 

[/ QUOTE ]

Such a gizzie exists, I looked into it a year or so back when we changed computers at home. Bummer they cost about as much as the meter, and didn't support the latest USB standard (although plenty good for serial port use). A couple of models out there, Jameco (again) has one that looked good at the time.

I ended up buying a dual port serial card for far less (and got it 'down the street').

FWIW, the meter is indeed tempting. I smell my third such purchace (neither of my other two PC interfaced meters have software of any real value). This software looks useful, at least it saves excell sheets. Oh well, third time and all that.....

Have you used the software? Opinions?

Doug Owen


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## James S (Jul 18, 2003)

I got mine last night delivered from MPJA and I'm very happy with it! It's not too big, will fit easily on my shelf by the work desk. For the price I'm quite happy.

Running a single LED from it is not all that useful as it doesn't have a lot of resolution on the current, so 30ma is just .03 but thats OK, I'll not need to use it to supply such small currents often.

Cheers to MPJA!


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## milkyspit (Jul 18, 2003)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*James S said:*
I got mine last night delivered from MPJA and I'm very happy with it! It's not too big, will fit easily on my shelf by the work desk. For the price I'm quite happy.

Running a single LED from it is not all that useful as it doesn't have a lot of resolution on the current, so 30ma is just .03 but thats OK, I'll not need to use it to supply such small currents often.

Cheers to MPJA! 

[/ QUOTE ]

James, congratulations on joining the club. /ubbthreads/images/graemlins/grin.gif Given 10mA resolution of the current readout, I'd hook a DMM to the circuit whenever I needed more precise information. As for actually *adjusting* the current, maybe I had unusually steady hands when I tested a single LED on the power supply, but I was able to fine-tune it to the point JUST before the LED stopped producing visible light (as mentioned in my original post) and was treated to a way cool look at the LED's guts, teeny tiny traces, little pool o' photons and all. Highly recommended diversion. /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif

Enjoy the power supply!


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## Darell (Jul 18, 2003)

*Re: Review of a neat bench power supply from MPJA.*

Just what I was looking for! I think we need to start a user's club now. Of course I couldn't get out of there without loading up my cart with hundreds of other little things that I didn't know I needed.


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## milkyspit (Jul 18, 2003)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*Darell said:*
Just what I was looking for! I think we need to start a user's club now. Of course I couldn't get out of there without loading up my cart with hundreds of other little things that I didn't know I needed. 

[/ QUOTE ]

Darell, if you mean MPJA, I've bought a few large boxes o' goods from them myself, including 30 Panaflo 8cm fans about a year ago for my other hobby, modding my PCs to make them totally silent. /ubbthreads/images/graemlins/buttrock.gif (SilentPCreview.com is the equivalent of CPF for that crowd.) Incidentally, those fans either single or in arrays would be great for other ventilation needs, such as venting crawlspaces, making a cheap table fan, etc. They are super quiet, run as low as 5V, and draw about 100mA. But I digress. /ubbthreads/images/graemlins/grin.gif

Regarding the power supply, I used it to test my Camry dome light frame with your Luxeon regulator drop-in board. Saved me lots of trial-and-error cramped in the back seat of my car! /ubbthreads/images/graemlins/thumbsup.gif


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## eluminator (Jul 21, 2003)

*Re: Review of a neat bench power supply from MPJA.*

milkyspit, sorry to be so tardy. I tried out the PC interface for the Mastech 345 multimeter a few times when I first got it. I used the software that comes with it. It's called Masview version 1.1. It seemed okay, but I've been busy doing other things and haven't used it much.


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## eluminator (Jul 21, 2003)

*Re: Review of a neat bench power supply from MPJA.*

star882, I looked for a USB connected multimeter a year ago and couldn't find any.

I do have a device that can measure voltage etc. that connects via USB. It costs $120. I haven't used it much. It seems I spend all my time writing software.

This thing has 8 analog inputs, 2 analog outputs and 20 digital I/O.

http://www.labjack.com/labjack_u12.html


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## **DONOTDELETE** (Jul 25, 2003)

*Re: Review of a neat bench power supply from MPJA.*

Milky, great find, I may have to get one -- always wanted a digital readout..
I was posting about using a power supply for battery charging back when... the string's called 'charging video camera battery' by Craig, it's exhausting to read it again, but really wrangles out the truth in the end! /ubbthreads/images/graemlins/smile.gif 
power supply charging of batteries cpf link /ubbthreads/images/graemlins/rolleyes.gif /ubbthreads/images/graemlins/grin.gif

only now they have become cheap as dirt - I spent about $160 on a one-station analog meter 0-30 volt 0-3 amp "EZ" supply from elexp -- for the same money lookit what you can get now - a THREE station digital! wow!

http://www.elexp.com/tst_0033.htm


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## IlluminatingBikr (Aug 20, 2003)

Does the power supply come with leads? I am looking at the picture and just see two spots for them. Are they alligator clip leads?


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## milkyspit (Aug 20, 2003)

*IlluminatingBikr*, the two spots you see in the photo are binding posts. You can unscrew them, slide bare wires into the openings, and screw the caps down over them... or you can insert banana plugs into the end... or (what I usually do) you can unscrew the caps completely and clip alligator clips onto the bare posts. I have some alligator clip jumpers (also got them at MPJA, same as the power supply) that work nicely for this purpose. Just don't forget which post is which when the caps are off!


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## IlluminatingBikr (Aug 20, 2003)

Milkyspit,

I have the tpi 120 digital mulitmeter.
Could I take the leads out of it, and put them over the binding posts of the power supply?

Here is a picture of a different multimeter, but has the connections on the top so you can see what type of ends the leads on my multimeter have.


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## milkyspit (Aug 20, 2003)

*Aaron*, it's tough to say if it would work, but I wouldn't count on it. Sorry to poke a hole in the idea.
/ubbthreads/images/graemlins/icon23.gif

What you could do instead, though, would be to remove the caps from the binding posts on the power supply, attach a couple alligator clip jumper cables, and clip the other end of the cables to your test leads. Or just clip the other end directly to whatever you wanted to supply with power. Both methods should work.

As far as the cables themselves, the ones I'm describing are shown over here. I'm sure you could buy them anywhere, though.


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## IlluminatingBikr (Aug 20, 2003)

Thanks Scott. I actually do have some of those alligator clips that I got from radio shack, so finding a way to connect the power supply to my test subject won't be a problem. I was just wondering if those would work, and maybe make things a tad bit easier.


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## Darell (Aug 20, 2003)

Well, my PS is here, and I've actually used it. Both constructively and destructively (oops). For the price it seems great. I do wish it had a few more features and higher resolution... but that's just icing. For what I use 'em for, this will work fine. Thanks again for the great find!

- Darell


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## milkyspit (Aug 20, 2003)

*Aaron*, You sound like things are under control. For a minor investment you could buy some banana jacks and test lead wire from Radio Shack, then make your own leads. The banana jacks should plug into the hole in those binding posts nicely. Good luck to you!

Come to think of it, I might make some homemade leads myself next time I've got some free time...

*Darell*, glad to hear it. /ubbthreads/images/graemlins/smile.gif Uh, I hope you didn't "destruct" the PS itself! Mine came in handy when I was fashioning a LS dome light for my car and wanted to test the module before stuffing it into place. Good thing, too, because it (the dome light module) didn't work the first time!

Now that I've got a decent source of power, I've been upgrading my measurement capabilities. Bought a Fluke DMM on ebay, and have an order in for another. Sweet. /ubbthreads/images/graemlins/grin.gif


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## milkyspit (Oct 3, 2003)

*A Worthwhile Accessory!*

The other night I was wasting time in a Radio Shack and FINALLY got around to buying some banana plug test leads. As suspected, they fit into the holes down the centers of the power supply terminals perfectly! /ubbthreads/images/graemlins/smile.gif

Specifically, I paid $3.99 for a pair of test leads, and they're Radio Shack part #278-704A. These make it really convenient to apply power to something for a quick-n-dirty test.


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## robk (Jan 30, 2004)

I bought one of these power supplies, and it works great, but the adjustment at low current values was scratchy,so I decided to replace the 270° pots with 10 turn units. I found a couple of cheap pots here: Circuit Specialists .The original pots are 6.8K, I replaced them with 5K pots (I couldn't find 10 turn 6.8K cheap), the drawback is now it goes to max 15VDC and 1.8A instead of 18VDC and 2A, not a problem for me.
First you need to cut 1/8" off the shafts, drill the plastic faceplate to 3/8" and then drill the knobs to 1/4" (as they are designed to fit a splined shaft). What you end up with is a real precise PS that allows fine adjustment of current or voltage. Now I have to figure out how to display mA in three digits on the stock mA LCD!
Rob

PS- here's the pots I used:


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## milkyspit (Jan 31, 2004)

*robk*, THANK YOU! /ubbthreads/images/graemlins/bowdown.gif

I've been wondering about the 10-turns pot since I first started this thread. I didn't really know which one to buy, or what the specs were on the stock ones, etc. You've provided some valuable info here! /ubbthreads/images/graemlins/smile.gif

One question: do the stock pots sit on some kind of circuit board, or are they just bolted onto the case?


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## robk (Jan 31, 2004)

Scott-
They are panel mounted, with wire leads from a harness, so they are real easy to replace. I forgot to mention the threaded bushing is a little longer on the 10 turn units, I had to use (3) 3/8" flat washers behind the panel so the knobs would fit properly (not stick out too far).
Rob


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## Doug Owen (Jan 31, 2004)

I seriously doubt you'll find 6.8 K 10 turns (or any other 'oddball' value for that matter) at any price (sort of custom).

The traditional 'fix' is to shunt a higher value down. If, for instance, you used the 10 K with 20 K of external resistor across it, you'd have 6.66 K, no doubt close enough for jazz. Used as a potentiometer, there is no difference, used as a rheostat linearity is a little funny, but you'd never notice it without 10 turn knobs.

This is what I had in mind when I suggested this 'mod' in this thread back in July. As I said then, I've done it a number of times over the years. Recommended.

As far as adding another digit to the display, you're probably SOL. You might be able to add a lower range by changing the sense shunt (resistor in the current path monitored by the meter), but the meter itself doesn't led itself to hacking in another digit. You might replace the whole unit, Jameco sells 3.5 Digit panel meters for about $12 but you have to cobble up 9 volts (floating) to run them.

Doug Owen


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## springnr (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Another option is to just add a smaller value pot for fine adjustment.


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## robk (Jan 31, 2004)

Doug,
That's why I went with 5K, easily available, although they limit the maximum settings a little. I'd rather have the linearity than the full 18V, 2A.
About the display, it has a "1" that qualifies it as a 3 1/2 digit display, it can be seen briefly on power up. There don't appear to be any jumpers to move the decimal point over one position, as I've seen on some standalone panel meters. I suppose I could find new ones that would fit the cutouts, but that's sort of defeating the low price of this PS. It does have 2 isolated secondary windings solely for each LCD meter, they are on the same board but have separate full wave bridges and regulators.
Rob


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## milkyspit (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

I wonder if the only thing limiting this particular model to 18V and 2A is the value of the adjustment pots themselves. If they were replaced with *higher* value ones, would the supply operate with slightly higher limits, like maybe 20-something volts and 3 amps, for example?


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## Doug Owen (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Again, in the way these are no doubt used, potentiometers (3 leads), not rheostats (two leads) there is no linearity issue. And even if there were (in the case of a rheostat), without a turns counting knob capable of resolving sub percents of range changes you'll never notice it. What happens is the first few turns would give you a bit more than 1.8 volts per turn, the last few a *bit* less. Unless you have a scale on the knob fine enough to show this level of precision (it needs 3 places of resolution) you'd never notice (or care) that two complete turns gave you 3.8 Volts not 3.6. As designed (turn the knob until the *meter* says what you want) you don't even have a scale to start with. When you dial up say 12 Volts you've no idea how many turns you've gone, what does linearity mean?

There's a reason why this is the traditional trim for potentiometers.

As far as Scott's suggestion that a little higher voltage or current is as easy as boosting the resistance a bit, no way Charlie. You're sure to run into ripple problems, especially at low line. It's safe to assume the engineers thought about this idea....... If you really need to try it, there's probably a series resistor on the high side of the pot, find it and shunt it with say ten times it's value, that should shift things up. But expect trouble if you try for more than the maker intended, sound design says there's not much margin in there.

Doug Owen


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## robk (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

The pots are wired as rheostats in the PS, wiper jumpered to the CW tab on the pot. Does that make a difference? There's no scale on the knobs or counters, it's "turn till you get what you want"! The 5K 10 turn pots work great, just don't allow the max output of the PS.
Rob


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## milkyspit (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

*Doug*, thanks. I would be a little scared to try "overdriving" the top end voltage and/or current as I suggested. Wouldn't want to blow up my workshop! /ubbthreads/images/graemlins/mad.gif

If the marketing guys had their way with this product, though, it might actually be a crippled version of a higher-powered bench supply. I seem to recall the same manufacturer also selling another unit with higher limits, that looked pretty much identical to this unit from the outside. It would be typical marketer behavior to reason along the lines of: "Gee, our PSU costs $79.95, but focus group research shows a ready hobbyist market for a unit priced at $59.95. So let's save R&D and manufacturing costs by taking units off the same line and selling some of them at the $59.95 price. But so as not to cannibalize sales of our higher end product, we'll limit the output of the $59.95 one to lower outputs."

I know in the software world, Windows 2000 Workstation (at the time maybe $150) and Windows 2000 Server ($600 and up) were THE SAME PIECE OF CODE, with some flags set one way or the other in the Windows Registry. It gets done in software, and I imagine it gets done in electronics, too.

But you're right, if the engineers were in control of things, this unit probably isn't capable of going much higher.

/ubbthreads/images/graemlins/icon23.gif


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## gwbaltzell (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Milkyspit

When I was writing directions for setting up a bench supply I didn't realize you were using the same as my only "store bought" one. Of course it was the reason I remembered to warn of meter accuracy! Had thought about replacing the pots, will likely go ahead with it.

George


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## nomrah (Jan 31, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Interesting thread. If it were my money I'd go for the 30v 3A model also as there are just too many things to play with that are 24V and 2 A is just a little light to have some headroom. If you are really lucky and shop around surplus, sometimes you can find some outstanding buys. My preference for a bench supply is Lambda because I've only seen 2 broken ones in some 30 years in electronics. I did find some Lambda lab supplies 40v 4A new, programable, digital read out for about $125. It was technically still in warranty and listed for about $1700.00! Only down side was it didn't have BP jack on the front, it had a terminal strip on the rear, minor problem. By the way it IS a SWITCHER. Ripple was a little higher than I would have liked to see 50-75 mv max but most of the newer supplies, even lab supplies are switchers. Another time I picked up a couple of Lambdas(NIB) built for a special purpose in a rack with digital volt and current readouts for $80.00. So long story short you can find some really good suplies if you shop around and are patient. As you can tell I prefer Lambda power supplies with the exception of the little Kikusui 32v 3A supplies of years ago. they were such a nice little plug in baqttery! While I'm on the soapbox, I prefer Fluke voltmeters, but HP also makes some nice ones, Tektronix scopes and Hp does a pretty good job at freq counters and signal generators(RF) Fluke makes some calibrators that are 30 years old and still in use today.
Well that's my .02 for now, thanks for being patient!


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## Doug Owen (Feb 1, 2004)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*robk said:*
The pots are wired as rheostats in the PS, wiper jumpered to the CW tab on the pot. Does that make a difference? There's no scale on the knobs or counters, it's "turn till you get what you want"! The 5K 10 turn pots work great, just don't allow the max output of the PS.


[/ QUOTE ]

Interesting configuration. You should be able to go 'up stream' from one end of the pot (not the grounded end, the other one) and find the input to the error amp and a series resistor (that forms the voltage divider with the front panel pot) to the source (either reference or feedback, depending). Look for a resistor hooked to it then try adding another in parallel to it, try say ten times it's value. Look for the maximum voltage (or current depending) to go up a bit, about a third of what we need. I think you're looking for three times the value, expecting to recover the 36% of the range lost based on pot value change or five times to correct for the 20% drop in actual voltage. Hard to say what's up, but the numbers don't quite match??? Anyway, start out low and sneak up on it.

Doug Owen


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## Doug Owen (Feb 1, 2004)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*milkyspit said:*
*Doug*, thanks. I would be a little scared to try "overdriving" the top end voltage and/or current as I suggested. Wouldn't want to blow up my workshop! /ubbthreads/images/graemlins/mad.gif

If the marketing guys had their way with this product, though, it might actually be a crippled version of a higher-powered bench supply. I seem to recall the same manufacturer also selling another unit with higher limits, that looked pretty much identical to this unit from the outside. It would be typical marketer behavior to reason along the lines of: "Gee, our PSU costs $79.95, but focus group research shows a ready hobbyist market for a unit priced at $59.95. So let's save R&D and manufacturing costs by taking units off the same line and selling some of them at the $59.95 price. But so as not to cannibalize sales of our higher end product, we'll limit the output of the $59.95 one to lower outputs."

I know in the software world, Windows 2000 Workstation (at the time maybe $150) and Windows 2000 Server ($600 and up) were THE SAME PIECE OF CODE, with some flags set one way or the other in the Windows Registry. It gets done in software, and I imagine it gets done in electronics, too.

But you're right, if the engineers were in control of things, this unit probably isn't capable of going much higher.

/ubbthreads/images/graemlins/icon23.gif


[/ QUOTE ]

I doubt you will do any real harm trying to boost the voltage, it's just that when you run the regulator out of headroom, ripple happens. It'll be OK at low current, but will pick up ripple, eventually to several volts. Hey, it's your supply (and house), go for it......

It's highly unlikely that there is more capacity is available, marketing decisions aside, it takes a higher voltage cap and transformer to make the raw supply higher so the output can go up. This means the transformer is also bigger, has to carry more iron and copper. The physical size of the cap needs to get bigger as well or we need to accept lower ripple performance due to less capacity. Adding 50% to the current capacity means a 50% increase in the transformer (again we need more iron and copper) and a 50% increase in the capacitor of the main storage cap. And probably more heatsink, if not a better pass element as well. This makes it heavier, sometimes bigger and cost more.

Anyway, you probably won't get into too much trouble hot rodding the voltage (although technical performance will fall apart), but stay away from current unless you know what you're doing.

And I know what you mean by frimware selected options, hey, I've been around long enough to recall them set by DIP switches (read at startup....).

Doug Owen


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## drs2000 (Feb 7, 2004)

*Re: Review of a neat bench power supply from MPJA.*

I got mine from Circuit Specialists, at the same price, and it includes a $30 DMM if you type XYZZY (<-- That goes back a ways. /ubbthreads/images/graemlins/smile.gif at the promotional code box on the order form.

Also ordered the 10K 10 turn pots:
10K ohm 10 turn ww panel 2010-10K 2 6.95

And this at $40:
Intelligent DMM w RS-232 CSI345 1 39.95

Anyway, the stuff showed up the other day and I ripped into the P/S after verifying it worked. Fairly clean inside, very linear, multi-wind transformer. Nice LCDs and rather accurate. Dropped in the 10 turn 10K pots, and took some measurements. The output voltage will go over 25V (27.3 in my case) and will hold that output voltage to at least 2.3A! That's with 118VAC in to the power cord.
The filter cap was holding at 30.5V. The cap sits at 36V when idle and output over 10V. (Cap is rated 35V 4700ufd. Bit close on both counts.) With output set to 10V or less, relay drops to a lower winding on the 'former, making it about 21V on the cap.

The max current limit is now 2.8A. The 2N3055 and the 3A rectifiers start to show the pain, but hold. I'm planning to change the input cap and check the output cap voltage, as well as pull the 2N3055 and put some heatsink paste on it, as it gets hot fast, but the sink does not.. /ubbthreads/images/graemlins/grin.gif

I'm going to leave it at these maxes, but only use it to 25V and 2.5A under supervised and short-term conditions. Still haven't checked ripple but it seems pretty solid.

The transformer's definitely not huge, and I'm sure would overheat if pushed long at high current. (Over 2A) But, all in all, it's a really cute little box. i'm working on the current scaling thing as well. 
Will test further and post any mods that look useful. 

Thanks for the tip, Milky. I decided to get it all at Circuit Specialists, especially after I found the DMM deal. Will be testing the rs-232 DMM soon, I hope. By the way, the person that wanted the USB DMM? I'll test and see if this works thru the USB-rs232 converters we've got spare, and report back.

My unit came set for 220V, by the way. Those of you with under 18V output might check the recessed switch on the back. I couldn't get over 17.5V, and the filter cap only had 18V on it. Found and flipped the switch, much better..

Back to torturing Luxeons..

yours, drs the crazed..


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## Doug Owen (Feb 8, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Yer right, 4700 ain't many microfarads. That's what, almost two volts ripple per amp?

You might consider putting a 100K or so trim pot across those 10K pots and trim them down so the maximum voltage and current are a mite lower?

Otherwise, good hacking.

Doug Owen


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## drs2000 (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

Been poking at this box some more. Tested it's capabilities with the 10K /10 turn pots. After adding another 4700mfd 35V cap in parallel with the existing cap, I tested it under duress.. The supply at 117V in was able to maintain with good regulation, 25V at 2.5A for 20 minutes. Ripple at input cap about .4VAC. That's the max time I wanted to push the transformer. Got warm, but held OK. Clean, stable output..

The max stress for the unit, modded or unmodded, is to be set to about 12V at 2A+. Then it has to blow off about 20V at 2A in the transistor out back. (40 watts.) Used real paste, helped. After measuring things, I may move the Hi-low tap relay switchpoint up from 10ish to 14ish volts. There's still about 6V of headroom at that level, and it stays clean to about 2.6V headroom, and it'd cut the hell out of the dissipation at the voltages I use..


Good for over 27Vdc at over an amp cleanly. (headroom about 6V)

I thot someone had mentioned that they'd wanted an indicator that would tell them when the supply was in current or voltage limit mode. (??) Can't find that post. Anyway, I came up with a two transistor, 1 diode, two leds, 6 resistor drop-in that attaches to 3 points on the board, and gives a Green led indication for voltage control, and Red for current control. Easy to add, and you instantly know what mode it's running in. Can post scheme and pick-off points if interested. I'm working on a bunch of stuff currently, and plan to have a photoshoot of the mes(ses) all at once, so could shoot these mods as well. Still working on the current display one, as well. (1 Ma resolution for those of us that really wanna squeeze the last photons out.. /ubbthreads/images/graemlins/grin.gif)

On another note: Finally got to play with the $39.95 DMM with RS-232 from Circuit Specialists that I picked up.
Intelligent DMM w RS-232 CSI345 1 39.95

It's a 3-3/4 digit unit, Mastech MAS-345. Has the usual stuff, as well as an included thermocouple (K-type), and capacitance measurements. Comes with Masview 1.1 software. Simple, but works and allows saving results and Excelling them.. /ubbthreads/images/graemlins/grin.gif. Did a bit of sniffing and comparision, and based on specs and looks, I tried Metex's scopeview. (For the economy line, set for the 30 series.) It also talked to the meter and ran fine.. (Win2000 box, BTW.) Now i'm thinking of another evyyyll scheme to come up with a box to allow the one meter and software package to run multiple readings on a time basis of Light output, voltage in, voltage out, current in and current out. Plug the meter into the box, plug all the other test leads into the box, set a couple things and start the program. Feed the file into Excel and process.

Anyway, a progress report of something..

Yours, drs the crazed..


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## Doug Owen (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

[ QUOTE ]
*drs2000 said:*
Now i'm thinking of another evyyyll scheme to come up with a box to allow the one meter and software package to run multiple readings on a time basis of Light output, voltage in, voltage out, current in and current out. Plug the meter into the box, plug all the other test leads into the box, set a couple things and start the program. Feed the file into Excel and process.



[/ QUOTE ]

You might want to consider Labjack:

Labjack 

Doug Owen


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## drs2000 (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

Well, it isn't as much fun and skullsweat as rolling your own, but it sure looks like a nice box for the $$. (Isn't electronics supposed to hurt your head??) Thanks for the referral. /ubbthreads/images/graemlins/grin.gif Bookmarked. Have you used it?

By the way, got the ammeter on the P/S scaling now. Definitely 3-1/2 digit meter. 1Ma resolution. Still tweaking the rest. Side note: The front trimpot on the PC board sets the voltage pot's top range, and the one behind it the current range..

Again, thanks for the note. Better go sell those Coke cans, so I can buy more stuff!!

Yours, drs the solder fumed.. "For that smooooth smoke... Kester, with a Weller iron..." drs


Still messin..

Yours, drs the crazed..


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## milkyspit (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

/ubbthreads/images/graemlins/popcorn.gif


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## robk (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

drs2000,
How did you get the display to show mA to three digits? Change a resistor?
Thanks, Rob


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## drs2000 (Feb 15, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

The quick version of the answer is yes. Added a switch and a .27ish ohm resistor in series with the .03ish shunt, and the switch picks up either the .03 tap or the .3 total. Still messing, tho. Haven't switched the decimal point, and the extra 'burden' is throwing off the current setting high end. (Can only go to 1.4A at the moment. Should have addressed by tomorrow, if the weather holds..)

Will post total 'tweaks' when finished. So far, everything's fairly easy and cheap. Except the 10 turn pots. Those are still $14 the pair.. But nice..

Schematic and hook-up instructions are done for the current/voltage limit indicator mod. Will add in the other bits and neaten up for posting.. Also need to take pix.. But, so far, it's been fun and rewarding. A good brain stretch.

Yours, drs the shuttin' down..


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## robk (Feb 16, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

Sounds great! Looking forward to your post. I already did the 10-turn pot mod, works great.
Rob


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## milkyspit (Feb 16, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

*Drs2000*, PM sent on a few issues, one of which involves these PSU mods...


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## LEDmodMan (Feb 17, 2004)

*BK Precision supplies*

http://www.bkprecision.com/



 /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif
Good for up to 30v and 3A.
Coarse and Fine adjustment knobs.
CC and CV indicator leds
digital readout
/ubbthreads/images/graemlins/grinser2.gif

They also have a lot of other types of supplies too!
Single Output
Switching
Low Cost
RS-232 Programmable

All Products Index


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## LitFuse (Feb 17, 2004)

*Re: BK Precision supplies*

Nice PS, but at $336.00 and up, (with a quick search), not really the same type of thing that's being discussed in this thread. More for professional use than "tinkering around" with I think.


Peter


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## LEDmodMan (Feb 17, 2004)

*Re: BK Precision supplies*

Works good for my "tinkering around"... /ubbthreads/images/graemlins/naughty.gif

Have to get it at a surplus store (just by luck), otherwise they are too expensive.


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## gadget_lover (Feb 18, 2004)

*Re: Review of a neat bench power supply from MPJA.*

Many thanks for posting this. I've wanted a good bench supply for most of my adult life, but could not justify the expense.

I picked up model 5003. It hits 3 amps and 0-50 volts, so I can use it with UPSes that use a 4 battery string.

The 5003 features dual meters and indicators for current and voltage regulation. It was not much more than the 30 volt supply.

Daniel


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## milkyspit (Feb 18, 2004)

*Re: Review of a neat bench power supply from MPJA.*

*Daniel*, glad to be of assistance. /ubbthreads/images/graemlins/grin.gif Also very pleased to hear you made a good purchase and satisfied a longtime need. That 5003 model looks nice.

*Drs2000*, I've come up with one other mod you ought to try on your PSU. Install a nice aluminum or stainless steel handle on top, for easy carrying. /ubbthreads/images/graemlins/thumbsup.gif

Also, what's that you said a while back, that the heatsink-mounted transistor exposed on the back uses no thermal pad or compound between itself and the heatsink? Or am I imagining that comment? Seems to me some Arctic Silver compound would work wonders for the thermal properties back there, as might a small PC case fan... but maybe that's overkill. /ubbthreads/images/graemlins/crazy.gif


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## drs2000 (Feb 18, 2004)

*Re: Hacking neat bench power supply/RS232 DMM*

Just another teaser. I've pretty much finished all the mods I'm interested in. The final results are:
(All listed results at 117VAC in. If your line is substantially lower, your top voltage out should be reduced. Say if youve got 110VAC, set for 26V top.) 

Max current setting 2.5A. Unit can hold for 15 minutes at least at this current. (Tested 1/2 hr at 2.8A, 24V out)

Max voltage setting 28V. continuous, at 2.5A

Old setpoint for transformer voltage tap change was 9.2V. Changed to 14.9V. (If low line, use 14.0V) This allows the P/S to stay on the lower tap up thru normal 12V testing and SLA charging levels, reducing the wasted power and 50watts worth of heat that it used to burn. Regulation and output quality still solid.

Added indicator that shows when supply is in current regulation (RED) or voltage regulation (GRN) mode. Very handy.

Added 1.999A full scale ammeter range and switch. (Yes the meters are full 3-1/2 digit. Don't know why they were wasting the capability..) Also minor mod to zero out sample current.

Added the 10 turn pots mentioned above. 10K full range.

Added another 4700 mfd to main cap.

Tested the snot out of it.. Poked holes in it. Lit up Luxeons. Light bulbs. Batteries..

Almost thru with the upgrade/mods documents. Plan to pix stuff and scan docs and upload, hopefully this weekend.. For giggles, here's the cost of parts for each mod:

2.5A output. Free with 10K 10 turn pot. Added 4700mfd cap to stiffen things a bit. about $7.00 for the pot, $1.00 for the cap. The cap also helps for the voltage uprange.
28V output, see above. Free with 10 turn 10K pot. ($7.00)
(Might drop setting to 26v if low line or really paranoid. Worked flawlessly for me.)

Current limit/voltage limit indicator: 2 transistors, 1 zener, 5 resistors and either two LEDS or 1 bi-color common ANODE unit. Cost. Ratshack $4.00- $5.00. Surplus $1.50ish or ask me to mail you some bits. limited quantity.

1.999A ammeter range: Little tricky here. Requires a bit of patience to do, and a few bits. My solution ended up using 3 .5ohm 2W resistors and 1 2.2ohm 1/4w resistor, as well as a trimpot, toggle switch and another 1/4w resistor. All surplus bits. Probably $1.00 to $4.00 depending on how you achieve this. The decimal point stays fixed. Too lazy to rip into the unit. So it shows 19.99. divide by 10. /ubbthreads/images/graemlins/grin.gif

Tweaking the transformer tap setpoint. 1 20K trimpot. $.50.


So, if you do the 10 turn pots, you'll be out $14 for those, plus pretty much worst case, another $10 for the other mods, and if you go surplus or hit me up or have parts rattling around, close to nothing..

If you've already done the 5K 10 turns, you lose the higher range stuff. I'll look at other minor changes that would allow the 5K folks to get that back..

The poor thing was pretty nice when I started. I like it better now, and it's more my kinda use. Most of those changes are stock in pricier supplys, except the low range ammeter. But this one's tiny and useful and easy to mod. And the meters are some of the most accurate I've seen on any bench supply. (This includes $450 B&K, $130 lobos, $$$ sorensen, my own custom beast..)

Keep on moddin'..

Yours, drs the slobber slinger..


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## drs2000 (Feb 18, 2004)

*Re: Review of a neat bench power supply from MPJA.*

[ QUOTE ]
*milkyspit said:*

*Drs2000*, I've come up with one other mod you ought to try on your PSU. Install a nice aluminum or stainless steel handle on top, for easy carrying. /ubbthreads/images/graemlins/thumbsup.gif

Also, what's that you said a while back, that the heatsink-mounted transistor exposed on the back uses no thermal pad or compound between itself and the heatsink? Or am I imagining that comment? Seems to me some Arctic Silver compound would work wonders for the thermal properties back there, as might a small PC case fan... but maybe that's overkill. /ubbthreads/images/graemlins/crazy.gif 

[/ QUOTE ]

It has a top?? I've been hauling it around without it's top since the day it got here.. /ubbthreads/images/graemlins/blush.gif
An excellent idea. Especially as it's small enuff to want to schlep it around. Handles are good. Think i've got some old Osbourne I computer handles still here..

I was wrong about the thermal pad. It does have one. Thinnest one I've seen, tho. Wasn't working very well. Removed and added Dow heat sink compound to both sides and clamped 'er back down. (Expensive stuff, but ya buy one tube, it lasts about three lifetimes..) Much better. Arctic Silver, as long as it's not electrically conductive, should work nicely.

The transformer tap voltage setpoint change also cuts way down on heat. The transformer's pretty much the limiting current factor. Tho if you set this for 2.5A at 15V out, you will be blowing off about 40 watts in the transistor. Set it for 14.8V at 2.5A and you're tossing about 10 watts. Before the setpoint mod, 10V at 2A would be wasting 50watts. at 2.5A, 62 watts. You can see why I re-arranged things. (Rectifier voltage under load is 19.5 or so at low tap, 31V or so, high tap.) Great for topping off my SLAs. Stays cool..

By the way, I didn't find any part that seemed to be close to the edge, rating-wise, except the 4700mfd cap. It's a bit small, value-wise, and it's 35V rated. At no load, and the output set above (10V stock)15V, it has 36V on it. I plan to replace it with a 50V part, but it holds OK. They do have a decent safety margin.
Everything else seems quite adequate for 2A and 2.5A in short hops is fine. The transformer'll get too hot if you really push it past 2A for more than 20 mins or so..

Of course, you could put a small case fan in it, and run it off the reference's 12V regulator, and you'd be able to pull 2.5 or even 2.8 amps all day. /ubbthreads/images/graemlins/grin.gif Hang a 3.3-4.7V Zener on the fan to slow it down some for noise..

Keep on moddin'!

Yours, drs the crazed.


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## milkyspit (Feb 18, 2004)

*Re: Review of a neat bench power supply from MPJA.*

*Drs2000*, Arctic Silver has the potential to be mildly conductive, but Arctic Ceramique also offers great thermal performance in a nonconductive compound. There's another technique you can do to guard against conductivity... "Doug S" makes tiny standoffs out of thin strips of Mylar film, positions them toward the edges of the component, and puts a layer of thermal compound in the space between them. The standoffs hold the component just off the heatsink's surface, while the nonconductive thermal compound fills the gap for improved heat transfer. I've never done it, but sounds like a good plan.

As far as Arctic Ceramique, take a look over here. These folks specialize in thermal compounds for the CPU overclocking crowd, so their products are designed to handle extreme heat transfer. Arctic Silver is 99% micronized silver particles, and Arctic Ceramique is tiny ceramic particles of some sort. I've read several third party comparisons of these products vs. generic thermal compound, and the Arctic products typically blow the doors off the competition. Very nice! /ubbthreads/images/graemlins/grin.gif

Regarding the fan, if you look carefully at the surplus electronic houses you can sometimes find the Panaflo "L1A" 8cm fan, which has become a classic in silent computing circles. The exact model number is FBA08A12L1A. These use fluid bearings of some sort and are extremely quiet, plus they undervolt extremely well, remaining startable at 5V and even a bit less. They're quite expensive retail, but the surplus houses typically get them in the $2-4 range. If you find any, my advice to would be to buy a whole tray of 'em! Seriously. I'll take some off your hands if you don't want them all. I love these things! /ubbthreads/images/graemlins/blush.gif

I can even recite the key specs from memory, which is a bit scary: 24cfm, 21dBA. Proportionally less as they're undervolted.

Take a look over here for a nice discussion of quiet fans, with the Panaflo not surprisingly winning top honors. Incidentally, I really like the SilentPcReview.com site, with which I've been associated even longer than I've been at CPF. /ubbthreads/images/graemlins/grin.gif

Sadly, I thought I was making a cash-saving move in transitioning from building custom PCs to building flashlights. /ubbthreads/images/graemlins/ooo.gif


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