# PC-DC-PS Conversion Guide



## modamag (Oct 9, 2005)

*Section #1 - Introduction*
The purpose of this document is to provide a step by step guide in order to convert your PC power supply into a high current DC power source.

Most PC power supply within the last 10 years will provide at least 100W of power. This will supply more than enough power to operate +3.3V, +5V and +12V DC components such as the Triton battery charger.


*Section #2 - Warning & Disclaimer*
Power supplies contain electrical hazards which may cause bodily harm or serious injuries. You’re performing this modification at your own risk.

Opening a power supply cover will voids any remaining manufacturer or resale warranty.

Never perform work inside the power supply when the power cord is connected to electricity. 


*Section #3 - Pre-Requisite*
This mod is rated at a 2/5 for difficulty. If you can solder and/or cut & strip wires you can do this.

Required Tools:
•	1x	Soldering station
•	1x	Wire stripper
•	1x	Shrink tubing or electrical tape
•	1x	Philips screwdriver
•	1x	AT/ATX power supply
•	2x	10? 10W power resistor

Optional but Recommended Parts:
•	1x	Volt meter
•	1x	Power drill
•	1x	Crimper / Pliers
•	1x	Toggle/pushbutton (SPST) switch
•	4x	Banana jack
•	4x	16-14 AWG (blue) ring lug terminal 


*Section #4 - Functionality Verification (5 minutes)*
When selecting a power supply, you want to select one with the highest power rating at the lowest cost possible. Sometime the total power rating is not quite accurate (marketing gimmick). Pay special attention to the “Max Amperage” rating per output voltage. For my power supply its rated 235W but only provide 8A @ +12V, which is more than enough for most application.






Figure 4-1

Since more than likely this unit is a used/old power supply you want to verify that it’s still functional.

_Precaution: Not all power supply manufacturers follow the industry pin out or color standard._

As a safety feature switching power supply require a load on the +5V line to power up. So to trick out the power supply connect the power resistor from +5V to COM to create a dummy load as shown in Figure 4-2.





Figure 4-2

*** ATX Power Supply Only ***
Connect PS_ON (pin14 / green) with COM (pin13 / black) as shown in Figure 4-4.





Figure 4-3





Figure 4-4

Connect the AC power cord, the fan should start spinning. If you have a Volt meter you can now check the output voltage +3.3V (pin1 / orange wire), +5V (pin20 / red wire), and +12V (pin10 / yellow wire). If the fan is not spinning or the voltage is not coming up then the power supply might be bad.


*Sectiom #5 - Create Dummy Load (15 minutes)*
Using the Philips screwdriver remove the four screws holding the case together.

Get the two power resistor and twist them together so they connect in parallel.

Cut off a +5V (red) wire and solder it to one end of the power resistors. Cut a COM (black) wire and solder it to the other end of the resistors.

Insulate the exposed wires with shrink tubing or electrical tape.

_Tip: Cut the wires to 8” length so it’s easy to relocate inside the power supply._

_Logic: The dummy load (resistor) will experience approximately 5-6W of power. This power is fixed regardless of the resistor size. However, varying the dummy load will result in a change in the output voltage level. P=V2/R

A 10? resistor will carry a load of ~0.6A and provide 11.8V output

Some devices require the voltage to be greater than +12V. In those cases you can just connect two 10? resistors in parallel so the effective resistance is 5? which will change the output voltage to +12.3V._

Mount the resistor to the to the vent holes of the supply casing for heat sinking.

_Tip: Do not use wire tie or any plastic tie. These resistors will dissipate enough heat to melt the plastic. Use bare copper wire to tie them to the chassis._

_Tip: Mount the resistors as far apart as possible for maximum heat spread._

*** ATX Power Supply Only ***
We need to connect the PS_ON (green) and the COM (black) to the switch.

_Logic: Although some power supply may have a rocker switch already installed but we will still need a separate switch for the PS_ON.

The majority of PC power consumption is established at power up. Only a small amount load change will be due to floppy drive, hard drive, and USB/Firewire. So when we turn on our charger there will be a large current draw which could trigger the overload circuitry. So we need to toggle the PS_ON to reset the power supply to apply when this happens._

At this point, the power supply is good to go, providing +3.3V, +5V, and +12V. 

But are you satisfied leaving it looking stock like that!? …


*Section #6 - External Banana Jacks (45 minutes)*
Now we’re going provide some cool external banana jacks for ease of use.

Drill four equally spaced 5/16” hole into the power supply casing.

*** ATX Power Supply Only ***
You should also drill the hole to mount your PW_ON switch at this time. The hole size will be dependent on the switch you have.

_Tip: You do not need a drill press for this operation. You can use a cord/cordless hand drill and up size the bit until the desired size have been achieved._

Mount the standoff banana jack at the location of the previously drilled holes.





Figure 6-1 

_Tip: Use a 7/16” socket for the panel mount nut. Use a 5/32” or 6mm socket for the rear locking nut._

Group all the +3.3V (orange), +5V (red) +12V (yellow) and COM/GND (black) wires together.

_Tip: Cut the wire as close to the connector as you can at first, you can shorten them later._

_Precaution: Do not attempt to desolder the spare wires from the PC board. You could potentially loosen one of the components and cause your power supply to no longer function properly. _

_Precaution: For power supply produced after June 2004, you must also connect the remote sense wire (brown) to the +3.3V (orange) wire. Otherwise the power supply will not latch to PWR_ON state._

If your standoff jack provides a solder pad then solder the grouped color wires to the corresponding voltage jack.

_Tip: Twist the grouped color wire and tint them. This will make it easier to solder._

If your standoff jack provides a locking nut then grouped the identical color wires together and crimped them to the ring terminal.





Figure 6-2 

Mount the ring terminal to the corresponding voltage jack.

_Tip: Use at max three wires per connector otherwise you might not be able to properly crimp the connector._

_Tip: Use at max two ring terminal per jack otherwise you won’t have enough threads to lock them in place._


*Section #7 - Reverse Fan Flow*
Flip the fan around so that the air is going into the power supply.

_Logic: Most power supply fans are designed to draw the hot air from inside the case to the outside. However, for our case the power supply is pretty much the only heat source.

It is much more beneficial to create turbulent flow inside the power supply than laminar flow. This will reduce the localize hot spot. _


*Section #8 - “Electrify Me!”*

*** ATX Power Supply Only ***
Now you will have 4 remaining wires -5V (white), -12V (blue), PWR_OK (gray) and VSB (purple). Since we have no need for these just bend them 180o and insulate them with shrink tubing or electrical tape.





Figure 8-1

Put the power supply back together and tighten the four screws.

Congratulation! You have just modded yourself a high power DC Power Supply.





Figure 8-2 

If you have the time, it’s also a good idea to make some accessories for your new power supply with the excess connectors.





Figure 8-3


Download offline/printable copy here.


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## Icarus (Oct 9, 2005)

Great post Jonathan! :twothumbs


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## Icarus (Oct 9, 2005)

Hmm... seems like the link for the download doesn't work... :thinking:


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## modamag (Oct 9, 2005)

Thanx Icarus for the catch.
Darn Yahoo for not allowing direct link to briefcase item.
I changed the link to my folder instead for now till I can find a place to host files.


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## Grox (Oct 12, 2005)

Great guide!


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## jtice (Oct 12, 2005)

Excellent giude !!!
I have been thinking about doing this, even though I have a nice PS 

You have a few tips etc that I wasnt thinking of, thanks alot !!

~John


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## .308 (Oct 12, 2005)

Thanks for posting this modamag. 

I recently purchased a triton charger and went this route for the power supply. After doing so here are a few thoughts/lessons learned.

1) All pc power supplies aren't created equal. You may me better off buying a lower watt ps from a known company (i.e. Antec 350 watt)

2) You can get a +7v connection by using the +12v (+) as the 7v(+) and the +5v(+) as the +7v (-).

3) If you are purchasing a new pc ps and your budget and workspace will allow do not open the ps or cut any wires. Purchase a project box like this one RS project box  and purchase a cable extender from a compnay like Xoxide. They sell lots of neat stuff plus pin extraction tools. Make a hole near the top in the project box and run all the pc cables into the hole. Mount any bananna jacks on the new project box. This may add $15-$20 to the cost of the project but I think it is money well spent. This will keep your warranty intact and make it very easy to switch power supplies if you ever needed to.






4) If you will be using a triton charger cut the power input cord and attach bananna plugs (male) to that side of the cable. With the cable that has the alligator clips attach bannana jacks. Now if you need to take the triton on the road you can easily attach the alligator clips to the triton and use it with a 12v car battery.






Just my 2 cents worth. Thanks again to modamag :goodjob: 

Chris
.308


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## kstump98 (Oct 27, 2005)

Could a modular power supply be used for this type of application? Something similar to this:
http://www.xoxide.com/ocz-modstream-450w-modular-psu.html

Thanks


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## cy (Mar 10, 2006)

bump


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## Aircraft800 (Aug 1, 2007)

*Great Guide modamag!*

I liked the idea so much, I had to build one out of my 200W Dell PS to power my SuperNova 250S. I cut off the charging clamps and added the banana connectors, but then I made my clamps removable, an idea I got from the Triton 2. I wish I could boost the voltage above 12V, I only get 11.67V, but the SuperNova can handle 10-15V fine. I tried 2 resistors in parallel, but the voltage only came up 10 11.83V. Oh Well.


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## bombelman (Aug 4, 2007)

Thanks for posting this !!


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## cat (Nov 10, 2007)

bombelman said:


> Thanks for posting this !!



Yes. Excellent. I've been reading about charging for weeks but I only got to this thread now after asking about using a PC power supply in the DN/Tenergy thread. 

Question: Why do we need those 5V and 3.3V connections when we're only powering 12V battery chargers?


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## Aircraft800 (Nov 10, 2007)

cat said:


> Yes. Excellent. I've been reading about charging for weeks but I only got to this thread now after asking about using a PC power supply in the DN/Tenergy thread.
> 
> Question: Why do we need those 5V and 3.3V connections when we're only powering 12V battery chargers?


 
You don't _need _them, but they come in handy. Example: to test a Shark Driver you need a 3V supply (I used 3.3V). You can also use combinations of jacks like the +12v and -5V = +17v (for LED series), or +12v and -12v = +24v etc... I just couldn't stow them inside the case, might as well use them.

If I had room, I was also going to ad a Cigarette Lighter Adapter for when I need to plug in any of my car accessories..


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## cat (Nov 10, 2007)

ok. Thanks. 
I know this big one of mine has a _huge_ bunch of wires and connectors coming out of it. It's about 20-30% bigger than your standard size Dell PSU. 

I've just been re-reading Silverfox's charger comparison. The Triton doesn't seem worthwhile to me for the C cells.


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## Aircraft800 (Nov 10, 2007)

I recomend a FMA Direct Cell Pro or any of the *Hyperion* (make sure it has the Data Port for balancing)

I don't own either, but they are the highest rated Li-Ion chargers in the RC Forums. I wish I did purchase one, I got a RC Power 601BC and had to send it back for a noisy fan, after all of the shipping charges and time involved, I wish I would have sprung for the FMA Direct. I do have another FMA Direct product, the Supernova and it has never failed me, but it doesn't charge my Li-Ions.


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## cat (Nov 12, 2007)

Thanks. I'll check that out today. 

Re shipping returns, etc.,_well__,_doing it internationally is..._no_. :sick2:

I checked out that PSU. It's much smaller than I'd thought - smaller than your Dell one. When I said it was big, I must have been thinking about the one I had before. :thinking:

AOpen FSB400-something 400W 
DC OUT: +12V 15A -12V 0.8A 
FUSE RATING: 10A, 250V~ (+3.3V & +5V = 235 W Max)

Looks like 15A at +12V, vs modamag's 8A at +12V.


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## cat (Nov 12, 2007)

Aircraft800 said:


> FMA Direct Cell Pro



Looking at their manual...



> Manual charge rates of 0.25A to 4A (in 0.25A increments) allow for special situations.



ok...good. Does that mean we can get the recommended 0.7C for the AW C cells instead of the 0.6C with the Tenergy? 

One thing that doesn't seem as good or convenient as the Tenergy is the output connectors. From what I can see here, just the jumper cables with crocodile clamps, and something about connecting to the FMA LiPo pack node connectors. The Tenergy has that simple green screw terminal block.


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## Aircraft800 (Nov 12, 2007)

cat said:


> Looking at their manual...
> 
> 
> 
> ...


Sorry I don't own one of these Celpros, but I did a lot of research on them a few months back because I own another FMA Charger I really like.

I was planning on using the screw-type terminal block adapter to the Voltcraft seeh here:
http://www.fmadirect.com/detail.htm?item=2200&section=45

Now you can hook it up the same way and select the number of cells and charge rate right on the charger :thumbsup:

Hey Cat, I think we need to move this over to the *Day to Day - DN/Tenergy4P, FMA-Cellpro/HD6S and Voltcraft Balanced Sys. Charging* thread.


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## cat (Nov 13, 2007)

modamag's original post lists 2 x 10 ohm 10A power resistors. One is used initially to check that the power supply works - the photo shows a big ceramic resistor. So are these the two that are connected in parallel and used as a dummy load between +5V red wire and COM black wire, mounted on the case housing?

Then what is this one?


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## Aircraft800 (Nov 13, 2007)

Cat,

No, that one is the PS On Signal wire, I just connected it to ground and didn't use a resistor. 

"*Connect PS_ON (pin14 / green) with COM (pin13 / black) as shown in Figure 4-4."*

I used One 10 Ohm 10W Ceramic Resistor I found at Radio Shack from one of the 5V to a ground just to give it a load and keep it powered up. I tried 2 in parallel, but it didn't boost the voltage much. It barely gets worm and it gets airflow from the fan. In this pic you can see where I mounted it.


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## cat (Nov 13, 2007)

ok, So you changed to only one because it wasn't worthwhile having two.
But what's the little one used to jumper the connector (on the ATX PSU only - which applies to all except very old ones)?


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## Aircraft800 (Nov 13, 2007)

I read that wrong, he is connecting the green wire PS_ON (pin14 / green) with COM (pin13 / black) as shown in Figure 4-4. That was JUST for testing purposes, that is where you connect your power on switch. You will not need a resistor here, just connect it to your switch, and the other side of the switch to a ground wire.

Here is another guide just in case your color coding is a little different.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply


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## cat (Nov 14, 2007)

ohh, right. Thanks. I'd read it wrong, I didn't see that that was still part of the verifying/testing section. 
ok, shopping list sorted, I'll go at lunchtime. 1 or 2 10 ohm 10W ceramic resistors, 3 red and 3 black jack plug/sockets. I'll see if they have good enough screw-type banana jacks.


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## cat (Nov 15, 2007)

Is your on/off switch also connected to the the PS_ON (green) and the COM (black), as in modamag's instructions? 

I got 2 little incan indicator lights yesterday, along with the resistors and jacks, thinking I'd use one to show DC on and the other to show that the AC rocker switch was on, but maybe it makes more sense to have just the one light.


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## Aircraft800 (Nov 15, 2007)

cat said:


> Is your on/off switch also connected to the the PS_ON (green) and the COM (black), as in modamag's instructions?
> 
> I got 2 little incan indicator lights yesterday, along with the resistors and jacks, thinking I'd use one to show DC on and the other to show that the AC rocker switch was on, but maybe it makes more sense to have just the one light.


Yes it is.


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## SafetyBob (Nov 16, 2007)

Since you guys have bought good chargers, let me ask a question or two. 

I have been looking at the Triton2 and the Triton Jr. Would any of you make a hard recommendation for any one of those? They looked essentially the same except the Jr. has less capacity due to no cooling fan. 

Are most of these R/C chargers about the same? The Great Planes Triton series really seems easy and simple to work with. 

So if I make or purchase a 2 C cell [email protected] with 3 cree's in it and use 2 of AW's protected Li-ions with it and have a charging jack on the bottom, does the charger know what voltage to charge to, or do I set that up first? Sorry I am so ignorant on this, all I have ever used are the 4xAA plug in the wall chargers. 

Appreciate any words of help or advice.

Bob E.


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## cat (Nov 16, 2007)

aircraft800: This may be how to get more voltage out of your PSU: 
http://www.rc-monster.com/forum/showpost.php?p=61531&postcount=26
Adjusting trim potentiometers and adding resistor to 5V line. 
Some useful information for this thread. Thread starts here: 
http://www.rc-monster.com/forum/showthread.php?t=3962


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## Aircraft800 (Nov 16, 2007)

SafetyBob said:


> Since you guys have bought good chargers, let me ask a question or two.
> 
> I have been looking at the Triton2 and the Triton Jr. Would any of you make a hard recommendation for any one of those? They looked essentially the same except the Jr. has less capacity due to no cooling fan.
> 
> ...


 
Bob,

I didn't get the Triton JR because of the timer shut off can not be disabled, and when I wanted to slow charge my NiMH, it would shut off via timer. The Triton 2 looks excellent, but without an additional external balancer, you can't balance charge Li-Ion packs, although you can still charge them. The best thing to do would be to charge them one at a time every few cycles to make sure they stay balanced. The battery nearest the light, the one that gets subject to the most heat, will discharge a little faster from my own experience.

The charger must be set to how many Li-Ion cells you are charging, very easy on a Triton.

Cat,

Thanks for the tip, I'll pop it open and check, I'm not to low anyway, Like 11.8v and my charger is stable down to 10v, so If I can't get it boosted, I'm not too worried.


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## cat (Nov 16, 2007)

@SafetyBob, if you haven't been there yet, check the links aircraft800 posted above in post #15, and these: 
https://www.candlepowerforums.com/threads/161694
https://www.candlepowerforums.com/threads/158121


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## vacuum3d (Nov 16, 2007)

Great write up. Now I have a reason to get a Triton.


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## aljsk8 (Dec 13, 2007)

Just been directed to this thread - i tried this out before i read the thread
i thought that if i took the psu out of the pc then plugged it in and switched it on that it would work - when it didn't i binned the psu!

are there any psu's that dont need the resistors etc?
as im a bit scared!

Alex


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## cat (Dec 13, 2007)

No, unless you have one that is about 20 years old. So the instructions for ATX PSU apply: You have to jumper the PS_ON (green) to one of the COM (black) wires. The photo showing it jumpered with a resistor at the motherboard connector - that's just for verifying that the PSU does work before you go any further. So all you have to do (after cutting off the big motherboard connector) is join the PS_ON green wire to one of the black wires. Then it should start when powered on - unless it has a black rocker switch for power on/off, in which case that switch will have to be ON. (this is so that when you use MS Windows to "shut down", the PSU i s powered off without you having to operate a switch.)


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## aljsk8 (Dec 13, 2007)

man i wish i understood all this :thinking:

i need to print it off and re-read it

how do i know if i have the old or new type?


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## Mash (Dec 13, 2007)

Done this kind of thing with a couple PSUs. For quick and dirty checks, and playing around, I would just take an old hard disk, and connect it up and use that as the load. Also noticed, that with some PSUs which have an "auto fan speed" or similar control, the current supplied varied with the load placed. Keep this in mind when using the PSU in current sensitive applications, and make sure you dont initially setup and adjust your system in a low load situation, since you might get a surprise when the PSU decides to suddenly UP the current! 
This is one situation where the cheap PSUs (without any gizmos) are probably better for our purposes!


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## cat (Dec 13, 2007)

aljsk8 said:


> i need to print it off and re-read it
> 
> how do i know if i have the old or new type?



Re-read it. I've read it _many_ times. Print it and go through it when you've got the PSU in front of you. 

There's also a link to an RTC forums thread which describes it differently. 

It's very unlikely it's not an ATX type PSU. It should have a sticker on the side that explains what each colour wire is. Go through that comparing to what it says here - in the first post.


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## Aircraft800 (Dec 13, 2007)

If you are in doubt, than maybe you should pick up an unexpensive *AC to DC 12V 5 Amp Power Adapter *from eBay or HERE for $18.00.

Also there is the *AC-DC 12V, 5A Switching Power Adapter (110/220V).* It is made for a mini PC.

Sorry to Hijack this thread.


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