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Silent_Assassin

How to build an AEG MOSFET

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With lots of Airsofters switching to LiPo batterys the requirement of a MOSFET is ever increasing. This guide will help you build your own MOSFET for around £5.

 

 

Parts.jpg

 

Parts.

  • 30K Ohm resistor
  • 100 Ohm resistor
  • MOSFET IRF2804
  • 2x 25cm of black 16AWG Silicone wire
  • 25cm of blue 22AGW PVC wire
  • Heatshrink in assorted sizes

 

Tools.jpg

 

Tools.

  • Wire cutters
  • Soldering Iron
  • Solder
  • Scissors (for cutting heatshrink to length)
  • Heat source to shrink the heatshrink (I used a gas torch but a ciggy lighter is fine)
  • 3rd hand for holding components in place (optional but recommended)

 

Step 1.

 

Step1.jpg

 

Put a small length of heatshrink on the 30K to insulate and solder it between the Gate and Source pins.

 

 

Step 2.

 

Step2.jpg

 

Insulate the 100 Ohm resistor and solder it to the Gate pin.

 

 

Step 3.

 

Step3.jpg

 

Solder the Blue wire onto the end of the 100 Ohm resistor and cover with heatshrink.

 

 

Step 4.

 

Step4.jpg

 

Solder a length of Black wire onto the Drain pin and cover with heatshrink.

 

 

Step 5.

 

Step5.jpg

 

Solder the remaining length of Black wire onto the Source pin and cover with heatshrink.

 

 

Well done, you have just built a MOSFET solid state switch.

 

 

Fitting.

 

You will need a 2x lengths of Red 16AWG Silicone wire for this part

 

  1. Solder the Blue wire from the Gate pin to the upper tab on the switch.
  2. Solder the Black wire from the Drain pin to the motors negative tab.
  3. Solder the Black wire from the Source pin onto the negative battery connector.
  4. Solder a short length of Red wire to the lower swith tab and solder the other end to the motors positive tab.
  5. Solder the remaining length of Red wire to the same lower tab of the switch and solder the other end to the positive battery connector.

 

MOSFETCircuit.jpg

 

Congratulations, with your new MOSFET your AEG will benefit from increased ROF and faster trigger responce due to reduced resistance, and you can now run higher voltage and bigger capacity batteries without having to worry about spark erosion corroding you switch contacts.

 

 

Notes.

 

I used Red Silicone wire in the above MOSFET build purely because I ran out of Black wire. I recomend using Black Silicone wire to prevent mixing up the battery polarity and damaging the AEG's components.

 

It's also recomended that, when completed, you cover the entire MOSFET switch in heatshrink. I haven't doe it in my guide because I didn't have any big enough.

 

Credit to the Airsoft International team as it was their magazine that I learnt how to build this MOSFET circuit.

 

Feel free to link/copy this guide to other websites, media, etc. However out of respect to myself and the time, effort and resources I put into making it, please credit me for the work and don't try and pass it off as yourown. You WILL be found out!

 

Disclaimer - This guide is for referance only. I cannot, nor will not, take responsibility for any damage caused to persons or property while using this guide.

 

Thanks for reading,

 

Josh (Silent_Assassin)

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Simply awesome, I shall be using this in the near future :)

 

I take it Maplin is a good source for the above parts? Either that or the lab in uni :P

 

Actually Maplins don't stock the MOSFET and they charge £6 a meter for the wire!

 

Resource list...

 

Mosfet IRF2804LPBF - RS Components

30K Ohm Resistor - RS Components

100 Ohm Resistor - RS Components

16AWG Silicone wire - Ebay

22AWG PCV wire - Ebay

Heatshrink - Halfords

 

Josh

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I've just fitted the above MOSFET into my G36c and the ROF increase just from fitting a fet and heavier wiring (I used 14AWG in this gun) is phenomenal. I can't believe that people spend all this money on high speed gears, motors and lage batteries when and simple £5 component can do almost the same job.

 

Josh

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Congratulations, troll. Way to compare an AEG mechanism to RS and next time, use proper sentence construction and grammar to make uneducated, derogatory comments. I fail to see how your post was in any way related or enlightening to the discussion, perhaps it could have been if you knew anything about how a MOSFET works, in that by replacing a mechanical switch a MOSFET will increase the reliabilty and longevity of your gun.

 

Now with that out of the way, I actually found this guide very informative. I have been considering building myself a MOSFET for a while and this guide really breaks things down well. Keep up the good work. One thing though: how did you fit 14AWG wire inside a G36? I'm having issues with 16 in my M249.

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Hey,

 

Excellent guide.

 

I am still a little tentative about installing mosfets or using lipo's, I guess this is purely based on me still trying to get my head around everything else (gearbox, shimming etc). I will endeavor to begin experimenting in the next few months. At least now I have your guide to being with as it makes it seem so simple and with the added bonus of the parts all being relatively cheap really helps too.

 

Keep up the good work....

 

J.

 

Ps ignore people who make comments of others work and yet are unable to positively contribute.

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Now with that out of the way, I actually found this guide very informative. I have been considering building myself a MOSFET for a while and this guide really breaks things down well. Keep up the good work. One thing though: how did you fit 14AWG wire inside a G36? I'm having issues with 16 in my M249.

 

It was fitted with great difficulty and I'll just leave it at that ;) . I recomend that you use 16AWG as my fire selector is a little stiffer then before as one of the wires is pressing against it. It doesn't hinder the changing of safety/semi/auto, it just takes a little for force to change it.

 

I am still a little tentative about installing mosfets or using lipo's.

 

Thanks for the kind words. MOSFET's and LiPo's are not things to be feared, they're just the next evolution for powering AEG's. You can pick up a LiPo for between £10-£25 depending on the Voltage and capacity, mine cost £13 for a 7.4v 1300mah 25C (check the LiPo thread in the stickys for more info). The charger I bought cost less than £40, has a built in balencer and will charge my NiMh batteries too. How much does a ProPeak charger cost? £30? And that only charges NiMh.

 

As long as you can solder then you should have no problem fitting a MOSFET, and as I've said before it costs about £5.

 

If you want more info then just drop me a PM, I'm happy to help.

 

Josh

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Thanks for the guide. I plan on ordering my bits tomorrow :) I had a couple of resistors lying around but no wire oddly enough and I need my mosfet too.

 

Any chance of a pic of it attached to a gearbox so I can get a better idea of what it should look like when I'm done? Preferably a V3. Thanks

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What about us American friends. Where are our parts? :(

 

Just Google the part code and I'm sure you'll find a US site. Or try Radio Shack ;)

 

Any chance of a pic of it attached to a gearbox so I can get a better idea of what it should look like when I'm done? Preferably a V3. Thanks

 

No chance, sorry. It's taken me a good hour to pusuade the gearbox to fit into the body and I'm not taking it apart again unless it stops working.

 

Don't use 14AWG as its too thick and unless you want to spend ages trying to get everything to fit I suggest you go with 16AWG. The wiring its self is exacly the same except you splice the positive wire from the motor onto the positive battery wire going to the top switch tab (for ver3 GB).

 

Josh

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This looks remarkably similar to the 'Project Ares' fet published in Airsoft International, Pg 40/41, Vol 4, Issue 6.

 

I can only assume you both used the same source, especially as you list the same RS parts & have the same wiring diagram. :D

 

It is a good fet, I've knocked up a few myself.

 

It is not an Active Breaking fet but a pretty good vfm starter fet, if you have the soldering kit & are up for it.

 

One question: Why the heavy guage wire on the gate pin?

 

It's only a signal carrier. A thinner guage will do the trick, cost less & be easier to thread through the bodywork/gearbox, to the switch.

 

Unless you are running sustained (over 3 mins) fire at 12v+, you will be ok with a good quality 18swg on the power carrying wires, making threading a lot easier than your 14swg. ;)

 

Good work on the photos & how to, you may want to get it merged into the Mosfet stickie, so it is easier to find.

 

 

Greg.

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Nice guide SA.

When I do mine, I cut the pins of the MOSFET down to approx half their length, and do the same to the 100ohm resistor pins, and also fold the pins of the other resistor tight around the MOSFET housing.

I then shrink-wrap the whole thing (as well as each pin and resistor seperately), it keeps the whole assembly nice and compact, and also less prone to damage due to bending.

MOSFET1a.jpg

 

...One thing though: how did you fit 14AWG wire inside a G36? I'm having issues with 16 in my M249.

It's a squeeze, you need to Dremel out the inside of the grip a little to get the wires down the back.

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This looks remarkably similar to the 'Project Ares' fet published in Airsoft International, Pg 40/41, Vol 4, Issue 6.

I can only assume you both used the same source, especially as you list the same RS parts & have the same wiring diagram. :D

 

Yes thats where I learnt how to build it. And RS components are one of the only companies to stock the perticular MOSFET.

 

It is not an Active Breaking fet but a pretty good vfm starter fet, if you have the soldering kit & are up for it.

 

Well it's a nice and cheap FET to get people started. I've got them fitted to my both my JG 416 & G36c but the 416 is getting treated to one of Infected's AB FET's in the next few months as part of my high ROF project.

 

One question: Why the heavy guage wire on the gate pin? It's only a signal carrier. A thinner guage will do the trick, cost less & be easier to thread through the bodywork/gearbox, to the switch.

 

The Blue signal wire is 22AWG (0.644mm) compared to the 16AWG (1.291mm) so it's about half the width. It only cost about £3 for 3 meters which I'm happy paying.

 

Unless you are running sustained (over 3 mins) fire at 12v+, you will be ok with a good quality 18swg on the power carrying wires, making threading a lot easier than your 14swg. ;)

 

I only used 14AWG on my G36c because I had just enough space to fit it in. For all other airsoft guns I recommend 16AWG if it will fit or 18AWG, both with high strand counts.

 

Oh and Docv400, thanks for the tip. I'll do that next time ;)

 

And again thanks for the kind words and support.

 

Josh

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What is the math to determine ohms (resistance) for both resistor?

 

They're the same resistors that a guide in the Airsoft International magazine used. I'm not going to argue with them as it works ;)

 

Josh

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This looks remarkably similar to the 'Project Ares' fet published in Airsoft International, Pg 40/41, Vol 4, Issue 6.

 

I can only assume you both used the same source, especially as you list the same RS parts & have the same wiring diagram. :D

 

Funny to see this, it feels like a lifetime since I wrote the original article. Glad to see its being put to good use :)

 

As to the design of this system, I have a lot to thank a colleague of mine for when it comes to the maths - i'm mechanically inclined, he's electrical. As to the MOSFET used, it was chosen because it has the ability to dissipate a truly silly amount of Watts, and my colleague (who shall remain nameless, as requested) knows that I'm the king of doing stupid things (AEG + 14.4V Bench power supply being the recent "incident")

 

Silent_Assassin - you're soldering is far better than mine!

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good guide you have put together,

though the diagram seems a little complicated, but i cant see why.

i would suggest having a fuse installed in the positive battery lead,

especially if lipo batteries are to be uesed due to high discharge current.

 

i hope you dont mind me uploading some pics i took into your thread.

i took info from the sticky thread and some other resources on dc motor

controll.

 

from what i have been looking at, the risistor values do not nee dto be specific

i use 1k and 10k as they are acting as a voltage divider providing 10v at fet gate

(max20v) and the larger resistor drains any gate source capacitance, which

prevents the fet from conducting when gate signal is cut. (small resistor may

not be required for some fets, but i have not yet tested this)

 

for an active brake circuit, i also try to insulate the heat sink tabs of the

fets as some are connected to the source lead so +v and -v and

can cause a short circuit.

 

inspiration from doubletap-tag link to cerberus airsoft

so an active break unit i have built with n and p channel fets insulated

using a 11Amp polyswitch (pc motherboard resettable fuse)

post-40305-1245704310_thumb.jpg

 

solder gate and drain of both fets, i install the larger resistor behind

the n channel fet.

post-40305-1245704319_thumb.jpg

post-40305-1245704327_thumb.jpg

 

positive comes from battery through thr fuse, connected to the p channel

fet then to the motor, i install the small resistor here.

post-40305-1245704371_thumb.jpg

post-40305-1245704387_thumb.jpg

 

then attach wires for the switch to the gate and small resistor,

motor negative to nchan fet drain and battery -ve to source.

 

i did not take any more pictures before installation in mp5k

post-40305-1245706230_thumb.jpg

post-40305-1245704300_thumb.jpg

post-40305-1245704401_thumb.jpg

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What is the math to determine ohms (resistance) for both resistor?

 

They're the same value that the magazine used (Airsoft International) where I learnt how to build the MOSFET. It works so I'm not going to argue with them ;)

 

Silent_Assassin - you're soldering is far better than mine!

 

Thats from 3 years of college studing BTEC Electronic Engineering, all I did was spend all day making bloody circuits :P . I still managed to give myself a nasty 1 inch burn on my wrist from the soldering iron :(

 

Josh

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Funny to see this, it feels like a lifetime since I wrote the original article. Glad to see its being put to good use :)

 

As to the design of this system, I have a lot to thank a colleague of mine for when it comes to the maths - i'm mechanically inclined, he's electrical. As to the MOSFET used, it was chosen because it has the ability to dissipate a truly silly amount of Watts, and my colleague (who shall remain nameless, as requested) knows that I'm the king of doing stupid things (AEG + 14.4V Bench power supply being the recent "incident")

Ah, so I've finally found the man to thank!

 

I really appreciated that article & have used this fet quite a bit. I have also seen the pattern in various forms (including this one), so on behalf of all who have benefited, many many thanks for making the fet thing so accessible.

 

I have been using 'Infected's' AB fets for some time & continually sing their praises, but with the weak pound & current climate, it's nice to have a cheap alternative.

 

Where the active breaking is required or if you don't do soldering, I would always point people at 'Infected's' product, it is excellent. In the past few years I've fitted about 20 of them with no failure rate. I usually receive delivery within 10 days of placing the order.

 

 

Greg.

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good article!

 

like greg says above, i need AB so i'll be sticking with infected's ones unless some one knows how to add that feature to the original guide.

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read double taps link from post 99 in the mosfet thread, i linked it above

before the pictures. again here

 

active break is just as easy to build as a standard switch just a few more steps.

if you can build the first one, you can build an active break circuit.

 

some info here from edn.com last page of the article

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