# D.I.Y -- Simple FET Switch KIU-D Mod -- How To Guide . PIC Heavy



## petrev (Dec 9, 2007)

Hi

An FET Switch for reduced resistance and higher current use without damage to switch parts.

Did this once before but didn't take any guide pics ! so here is a Simple-FET-Switch How To . . .

*Circuit by JimmyM* [opens in New Window]





First Cut a 30mm Disc from 2 Sided Copper PCB - I used 32mm hole saw 





Mark it up + These are most of the tools and parts I used 
(little DPAK is for reference - Used the bigger D2PAK F2804L for upto 40V)
4.7K Resistor only for Voltages ~>20+V

(JimmyM suggests a switch to 2.2k and 5k for the IRF2804 MOSFET - it will switch faster and thus reduce the heat generated during turn on and off)

Alternative MOSFETs are the 24V 1324 (?24V Ref) or if voltage won't exceed 30V the IRLR7843 (Ref.JimmyM)
or >40V with IRF3206





Dremel off the rough edges of the disk to fit and chamfer the edges so that there are no unwanted contacts.





Use the KIU-Base as a guide to drill through the mounting holes





Dremel off the rough edges round all the holes and make the hole for the Batt-Neg wire to go to the back side.





Cut the grooves to form a rudimentary circuit . . . I used the small engraving tool in the Dremel.





Prepare the surface with some Emery Paper/Wet and Dry Sandpaper/Or Similar





Mark the Through Hole position for the Source FET leg





Drilled and then cleared a non contact area on the circuit side using the engraving tool






Solder all the parts in place . . .
1. First tin the contact area for the Drain HeatSink. Then place FET in position with the Source Leg folded back through the hole and solder Drain HS. 
2. Then the Gate leg is soldered down.
3. Then solder the G-S resistor in place on the Source leg
4. Then solder the G-S resistor to the Gate Pad/Area
5. Then solder the (+20Vonly) Switch-Gate resistor to the Gate Pad/Area
6. Then solder Sw-G resistor to the SW Pad/Area



 

Attach the Red Switch Wire (Front)
and the Brown/Black Batt-Neg Wire (Rear) and solder Source leg to back.



 . 



Stuff it into your KIU-Base and feed the KIU-Socket wires through the central hole





I attached some temporary pins to the Batt Neg and KIU-Pos wires, then temp. soldered the Drain-KIU wire and tested using a 3x C-Lion Mag-KIU.
I always wire my KIU-Sockets with the NEG to the Pin-Socket near the Logo and then fill the Logo in Black to remind me !





Plug together then touch the SW-Wire to the POS and :thumbsup: all OK.

That's it ! ! !

All you have to do then is fit it into a KIU modified D-Switch as before.









Assemble into D-Mag . . .
Done

Pete


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## LuxLuthor (Dec 11, 2007)

I nominate you for the "Mr. Wizard of 2007" award. You make it look so easy. :thumbsup:


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## saeckereier (Dec 11, 2007)

Very nicely done, indeed!
Nice pictures and well written, won't be of any interest for myself, but I'm sure it'll be for others, thanks for the effort!


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## petrev (Dec 11, 2007)

Lux you slay me 

Thanks Guys


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## JimmyM (Dec 11, 2007)

I should be taking more step-by-step pictures of the stuff I do.


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## lctorana (Dec 11, 2007)

That's superb. Well done, and thanks for taking the trouble!


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## cat (Dec 11, 2007)

Thanks, Pete. :thumbsup:

So,... if >= 10A, then do this with KIU socket.


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## petrev (Dec 11, 2007)

cat said:


> Thanks, Pete. :thumbsup:
> 
> So,... if >= 10A, then do this with KIU socket.


 
Hi Cat

Will save wear and tear at any current but definitely required over about 10A in my opinion. 
Might be useful from about 8A or lower depending on state of switch !

*Caution:* As JimmyM has just pointed out over in Most Powerful Thread 



JimmyM said:


> This won't soft-start the bulb though. It is a super low resistance switch. Damn sturdy by the look of it. But since it switches on really fast AND has low resistance, it will give the bulb a larger current spike than standard modded mag switch. It's a great idea for high current bulbs that aren't going to instaflash. Like the 64623 on 13 cells. Or the 64458 on 16-17 cells.


 
No SoftStart so beware of lowered resistance 

Pete


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## JimmyM (Dec 11, 2007)

cat, That's right. I actually did this to my 2C ROP-Hi.


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## petrev (Dec 11, 2007)

JimmyM said:


> cat, That's right. I actually did this to my 2C ROP-Hi.


 
Need photos of that mod - Must have used smaller components ? and where did you fit them in a standard PR C-Switch ?

Cheers Pete


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## cat (Dec 11, 2007)

ok, so...
if >= 10A [and no instaflashing with existing resistance-reducing mods], 
then do this with KIU socket. 
...and if the quicker start pushes it into instaflashing, then...I don't know, individual choice. I'd prefer not to rely on the standard switch resistance, and the switch getting hot. 

Re the ROP Hi application of this switch... I was also about to ask where you put it.


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## petrev (Dec 11, 2007)

cat said:


> ok, so...
> if >= 10A [and no instaflashing with existing resistance-reducing mods],
> then do this with KIU socket.
> ...and if the quicker start pushes it into instaflashing, then...I don't know, individual choice. I'd prefer not to rely on the standard switch resistance, and the switch getting hot.
> ...


 

Maybe +NTC for slower start high current apps ? 

. . . or probably the best thing is going to be the JM-SST ! Second half of batch probably won't be too far down the line - I think JM is just waiting on a few parts ?

Pete


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## JimmyM (Dec 11, 2007)

petrev said:


> Second half of batch probably won't be too far down the line - I think JM is just waiting on a few parts ?
> 
> Pete


How right you are.

That C switch mod used an Internation Rectifier IRLR7843 (smaller) and only one resistor since the voltage would never exceed 18V at the gate. It's a little tricky since the MOSFET has to be in the negative leg of the bulb. I had to put a washer under the focusing roller/screw to lock down the bulb slide. Otherwise contact with the metal reflector would turn the light on. So I adjusted the height of the bulb until the reflector wouldn't touch it even when screwed down all the way. Now I get just a mV or 2 drop through the whole switch. On fresh AW C Li-Ions, it's quite nice.


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## JimmyM (Dec 11, 2007)

More JM-SSTs are ready to go here...
https://www.candlepowerforums.com/posts/2249552#post2249552


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## cat (Dec 11, 2007)

petrev said:


> Maybe +NTC for slower start high current apps ?
> 
> . . . or probably the best thing is going to be the JM-SST



This for applications where the current is higher than the AW driver can handle?




JimmyM said:


> More JM-SSTs are ready to go here...
> http://www.candlepowerforums.com/vb/...52#post2249552



I need to get my parts list together before these are gone. For one of the top 5 or 6 on * LuxLuthor's Most Powerful Maglite Mods List*
...I'm trying to sort out which is the smallest with a runtime of 20 minutes at least.


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## JimmyM (Dec 11, 2007)

It's just a simpler cheaper alternative. It has just one mode and you can adjust the maximum duty cycle. It doesn't regulate.
AWs existing PWM softstarter has low-medium-high plus flashing ans is about 3 times as much.
My unit can handle up to 40 volts as it is right now. If you have needs that exceed that, let me know. Ultimately, it can handle 80V.



cat said:


> This for applications where the current is higher than the AW driver can handle?


I'm not sure how much current AWs can take, but this one handled 16V at 20+ amps. It's the amps that cause heat. If you have a 24V bulb running at 28V and 10-11 amps, this will run cooler and still drive a ~300W bulb. SO if we say that 20A is it's limit and it can handle 40V, I suppose that an 800W bulb is not out of the question. Not reasonable, but it shouldn't exceedc the capabilities of the driver. I welcome someone to give it a try.


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## matrixshaman (Dec 11, 2007)

Nice work and How-to details! Thanks for all the work you put into this DIY.


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## JimmyM (Dec 11, 2007)

I've got some single sided board laying around, I could just etch a batch of MOSFET switch boards that you guys can mount your own components on. I could make it suitable for both surface mount and thru-hole resistors. You would only have to supply 1 or 2 resistors and the MOSFET.
Pretty sure they'd be cheap.
I could even just send you guys a PDF file you can print on photo paper with a laser printer, iron them onto the board and etch them yourselves.


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## petrev (Dec 11, 2007)

cat said:


> This for applications where the current is higher than the AW driver can handle?
> . . .
> I need to get my parts list together before these are gone. For one of the top 5 or 6 on * LuxLuthor's Most Powerful Maglite Mods List*
> ...I'm trying to sort out which is the smallest with a runtime of 20 minutes at least.


 
Yes Cat - Get one of the JM-SSTs quick before this run goes and then sort out how to use it ( well that would be my route !)

:twothumbs

Have fun
Pete


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## cat (Dec 13, 2007)

JimmyM said:


> I'm not sure how much current AWs can take, but this one handled 16V at 20+ amps. It's the amps that cause heat. If you have a 24V bulb running at 28V and 10-11 amps, this will run cooler and still drive a ~300W bulb. SO if we say that 20A is it's limit and it can handle 40V, I suppose that an 800W bulb is not out of the question. Not reasonable, but it shouldn't exceed the capabilities of the driver.



ok, AW D driver :
 - Input voltage from 6V - 30V Max. open voltage ( Vin = Vout );
- Drive bi-pin hotwire bulbs up to 150W ( 200W intermittent use ); 

How does that compare? 28V, 30V, that's ok, but some of the top 5 or 6 setups in LuxLuthor's list exceed 150W. You estimate about 20A, but amps is not specified for the AW - can it be estimated from the V and the 150W limit? 

[edit:] I'd guess that this setup would be able to handle more than the AW switch. I don't know what those extreme top 5/6 use - there doesn't seem to be that much detail given. I'd probably use the AW switch if I could, to avoid having to try to do the soldering. (I have a 5761 setup just waiting for the reflector to arrive from the PO, so I want to do something substantially more powerful next.)


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## rizky_p (Dec 13, 2007)

guys i am still in the dark. What is this use for? Care to explain?


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## cat (Dec 13, 2007)

I'm not qualified to explain, but you could check this: 
PWM Soft-starter design discussion


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## petrev (Dec 13, 2007)

rizky_p said:


> guys i am still in the dark. What is this use for? Care to explain?


 
Hi

? The idea of using an FET switch ?

An FET switch is used where the current would melt a standard switch so for the Mag Switch it's max rated about 8-10A (actually probably rated 5A but seems to work OK upto about 8A). It is also lower resistance so no losses in switch resistance - but that can mean InstaFlash so the upgrade from a simple FET switch is a SoftStarter like AW's or JM's.

The FET carries all the lamp current and the existing switch just supplies the logic level current/voltage.

OK ?

Cheers 
Pete

ps Cat

P=IV so for AW's SS at 28V 150W the current would be I=P/V = 150/28 =5.4A

My 64458 readings with 6xfresh A123 cells
19.5VBulb @ 11.6A (226W)

Hope that helps
Pete


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## JimmyM (Dec 13, 2007)

Just a plain MOSFET switch using something like the IRF1324 (works up to 24V) can handle 100+ amps (spikes exceeding 1000 Amps). So that's not a problem. Any light up to 24V can use the straight IRF1324 MOSFET switch. If you substitute the IRF2408, you have slightly higher resistance, but you can use it in 40V lights. If you have a Larry14K and just want a MOSFET switch, the 2804 is the MOSFET for you.

The JM-SST (PWM Soft starter) can easily handle any of the lights on Lux's list and more. If you have a light that exceeds those specs, let me know. I've got a Larry14K driver in the works. Good up to 60V and 50+ amps continuous.


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## cat (Dec 13, 2007)

petrev said:


> P=IV so for AW's SS at 28V 150W the current would be I=P/V = 150/28 =5.4A
> 
> My 64458 readings with 6xfresh A123 cells
> 19.5VBulb @ 11.6A (226W)



Thanks, it helps, but I'm puzzling over it. If the AW switch specified an amps rating, I'd understand (I think.) I can see that more voltage reduces the amps through the switch/driver (and I see LuxLuthor's running the 64458 on 22V), but 226W...overdriven 90W bulb...makes me think the AW driver can't handle that. But then what Jimmy is saying re the MOSFETs (and I guess the AW setup is basically the same) suggests to me that the AW driver could handle it. 

What body are you using for the 6 x A123 ? 

Looking at the LuxLuthor list and the NiMH pack threads again, I realised that the biggest problem I've got is getting a bored body. ...Unless I use a really long one.


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## JimmyM (Dec 13, 2007)

Not all MOSFETs are created equal. The ones I'm using are D2PAK packages and rated for 70+ amps continuous. He's using a logic level MOSFET, probably a DPAK package (smaller). His also switches faster (I believe, which can cause more heat depending on the slope of the voltage curve at the gate of the MOSFET. There are too many variables involved to make blanket assumptions.
I can tell you that my JM-SST can handle 20 amps continuously at any voltage between 10 and 40. You'll have to ask AW about his starter.


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## petrev (Dec 13, 2007)

cat said:


> Thanks, it helps, but I'm puzzling over it. If the AW switch specified an amps rating, I'd understand (I think.) I can see that more voltage reduces the amps through the switch/driver (and I see LuxLuthor's running the 64458 on 22V), but 226W...overdriven 90W bulb...makes me think the AW driver can't handle that. But then what Jimmy is saying re the MOSFETs (and I guess the AW setup is basically the same) suggests to me that the AW driver could handle it.
> 
> What body are you using for the 6 x A123 ?
> 
> Looking at the LuxLuthor list and the NiMH pack threads again, I realised that the biggest problem I've got is getting a bored body. ...Unless I use a really long one.



Hi

Agree - Personally an amp rating would help me too - I don't know but it is probably the chosen MOSFET that limits the power - you may have to ask AW But I think the 64458 may be beyond the AW SS !

My 6x A123 is an extended Mag 6D - short FM works nicely. I have been working on a new solution for longer E-Moli torches but it is proving problematic and I am just not sure all that many people want longer E-Moli/C-Type Mags ?

Cheers
Pete


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## rizky_p (Dec 13, 2007)

thanks for the infos guys, i never build such high amp light that is why i didnt know what are you guys talking


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## cat (Dec 16, 2007)

petrev said:


> My 6x A123 is an extended Mag 6D - short FM works nicely. I have been working on a new solution for longer E-Moli torches but it is proving problematic and I am just not sure all that many people want longer E-Moli/C-Type Mags ?



Did you use the 6D (rather than a 3D like LuxLuthor's Deathblaster) to avoid needing a bored body or because you wanted to use the A123 rather than a NiMH pack?


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## petrev (Dec 16, 2007)

cat said:


> Did you use the 6D (rather than a 3D like LuxLuthor's Deathblaster) to avoid needing a bored body or because you wanted to use the A123 rather than a NiMH pack?



Hi Cat,

I had the A123s and the 6D so I just put them (and this FET switch) together with the FM short mag-charger extension - also get a bit of useful runtime (~13min total) as long as you don't mind the length.

Cheers
Pete


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## AW (Dec 16, 2007)

My Mag D driver is using a D2pak ( big ) MOSFET which can handle 100+ Amp continuous / 55V. The rating of 150W is being conservative considering the KIU socket is only rated @200W. I always leave big room for tolerance in all my designs because the spec. data from manufacturers are only quoted under ideal conditions.


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## cat (Dec 16, 2007)

Is that more than you'd get with the 16 x 1700mAH ? :duh2: 

As far as I know, boring the whole diameter would make it too thin. So I must decide - long or lonnnng.  I'm telling myself that 3D's are long anyway, so......... - no, it doesn't work - the thought of a 6D freaks me out.


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## cat (Dec 16, 2007)

:wave: Thanks, AW ! :thumbsup:


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## JimmyM (Dec 16, 2007)

AW said:


> My Mag D driver is using a D2pak ( big ) MOSFET which can handle 100+ Amp continuous / 55V. The rating of 150W is being conservative considering the KIU socket is only rated @200W. I always leave big room for tolerance in all my designs because the spec. data from manufacturers are only quoted under ideal conditions.


 
What kind of rise/fall times are you getting?
I would think that you're using some sort of gate driver since the PIC has an operating voltage of 5V and the big D2PAK MOSFETs have a pretty high gate capacitance, >6 nF.
My PWM soft starter is using a comparator and pullup resistor to get ~20 uS rise and 12 uS fall times on a 6.2nF gate.


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## JimmyM (Dec 17, 2007)

I'll pose my question again.
I have a design for a simple PCB than can be used to build a straight forward MOSFET switch. You can use D2PAK or TO-220 MOSFETs and SMD resistors or thru-hole.
I figure $5 a pop including 1st class postage.
Interest? If there's interest I'll whip up a batch.


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## JimmyM (Dec 19, 2007)

Ahhh. What the heck. I'll etch an few and populate them with some IRF1324 MOSFETs and see who wants them. Nice part is... I did some math. From 10-15V keep a little trace in place. From 15V to 24V, cut the trace.
0.8 mOhm. That's right. 0.0008 Ohms.
I'm buying a laser printer tomorrow. PCB etching HERE I COME!


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## bpelham (Dec 16, 2008)

Jimmy, this thread still open? Do you have some built-up 1324's ? I've been rummaging on a UPS board and found a couple IRL7843's on it. Huge capacity, 6.4mOhm nominal, don't need to go that big. Would consider your pre built assembly.


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## bpelham (Dec 16, 2008)

Oops, correct that last note to IRL 3713PBF mosfet. Sorry


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## bpelham (Dec 16, 2008)

Losing my mind with scrap notes. I'm looking at HRF3205. Both the above are from different concepts.


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## ellum68 (Jun 23, 2010)

Would the IRF2408 cross with Fairchild's FDP8441 http://www.fairchildsemi.com/ds/FD/FDP8441.pdf . Mouser doesn't carry IRF, so I'm trying to figure a substitute. I take I would run the 2.2k and 5K resistor with this unit? Also, is there any minimum wattage rating on the resistors. Thanks


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## petrev (Jun 24, 2010)

Hi 

Best to PM JimmyM as I am not technically qualified ! 

Cheers
Pete


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## ellum68 (Jun 24, 2010)

He got back to me ASAP . That number is fine. I have a better understanding of what a MOSFET is doing in this circuit now. You need to look at the voltage rating, resistance, and gate voltage. The voltage and current ratings need to meet or exceed the demans of the bulb. When you close the stock switch, it sends voltage to the gate of the MOSFET and that triggers the MOSFET to flow current. You also have to pay attention to make sure the gate voltage is rated low enough to trigger things. It seems the ones I've been looking at are in the 3 voltage range which is plenty low enough for our needs. Also look for units that have a low reistance to make sure you're letting maximum current pass. I'm pretty darn excited about this build. The biggest thing I've built to date is only a 3x18650 WA1185 leef based light.


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