The Mosfet Thread

[infected]

In all actuality you can run a 1K ohm resistor or even as low as a 220 ohm 1/2watt resistor and still be fine at 10v.

[chownsy]

In all actuality you can run a 1K ohm resistor or even as low as a 220 ohm 1/2watt resistor and still be fine at 10v.

 

 

in my AB circuit i run a 220R 1w resistor for the N channel Fet

[Docv400]

...The 27K ohm resistor is not a problem, but is way higher than it needs to be...

With a simple switching MOSFET set-up (non-AB), how low can you go on that resistor, and what's the advantage in doing so, if any?

Same question for the Gate pin resistor (100 Ohm nominally).

 

Try bending the resistor at the top so it's leads can't touch the tab on the mosfet and see what you get...

Good point.

Many people aren't aware (or forget) that the exposed metal mounting plate (of the TO-220 packaged MOSFETs, the type shown with the 3 'legs') is connected (electrically) to the 'Drain' pin.

I shrink-wrap that resistor and approx 4mm of the leads either side if I'm mounting it across the exposed plate like that.

Some of the MOSFETs I've used in the past don't have that, the plastic 'body' extends all the way up.

On those, I fitted the resistor across the top of the pins, no insulation needed.

[crackisbad]

i am planning on getting a Burst MOSFET. i want a Safe/Semi/Burst trigger group on my G&P M16A4. which brand Burst MOSFET is most highly recommended?

thank you!

-Joe

I would recommend this one: Click! because it comes with a sensor that is triped by the sector gear so I assume it would give you a more reliable burst. The sensor is also used to give you a complete cycle when you pull the trigger so you don't have to worry about a semi-compressed spring.

[masakarijoe]

thank you for the link... but i have a few questions:

-will this work with NIMH batteries? it specifically states in the options a lipoly cut off, and i dont use lipos.

-does this have "hold for full auto" capability? if not, which burst units do? i seem to remember the SW computer or something having that ability...

FYI, i dont know anything about MOSFETS!

my whole squad is looking to going the burst route, so hopefully we find something that fits the bill.

-Joe

EDIT: i found this: http://extreme-fire.com/SW-CHEETAH.html

which looks freaking awesome. any details on it? comments?

[evansy]

I'm new to mosfets so could someone help me out.

I'm thinking of getting a sentry from here for when I start using lipos but does anyone know if there would be any problems caused by the voltage cut off if I used my standard 9.6v minis?

[infected]

I'm new to mosfets so could someone help me out.

I'm thinking of getting a sentry from here for when I start using lipos but does anyone know if there would be any problems caused by the voltage cut off if I used my standard 9.6v minis?

 

Guys, you might find that you'll get more reliable answers from talking to the manufacturers of the respective parts.

[Disenabled]

I'm new to mosfet tweaking aswell, but I'm very interested in buying a SW-Panther of extreme-fire

http://extreme-fire.com/FeatureChart1.html

I want to put it on an AUG altough, with the special trigger. Anyone got any advice how to do that?

[jomarx]

@ masakarijoe -

-will this work with NIMH batteries? it specifically states in the options a lipoly cut off, and i dont use lipos.

Yes it will, its voltage cut off is based on percentage from the first mosfet reset (85%= warning, 80% cut-off). It also shutdowns when the battery is reduced to 7v.

 

-does this have "hold for full auto" capability? if not, which burst units do? i seem to remember the SW computer or something having that ability...

Yes it does, when it is configured to burst, it will roll over to full auto after a definite amount of time (0.4secs)

 

EDIT: i found this: http://extreme-fire.com/SW-CHEETAH.html

which looks freaking awesome. any details on it? comments?

 

Highly recommendable (works well even on 'extreme setups'), I use one myself.

 

@ Disenabled - Special trigger? Mosfet installation for the AUG is still the same with any other AEGs.

[Captainkickass]

Tried another mosfet...makes my gun shoot automatically, even on safe. This is driving me nuts. Is it possible that it could be the mosfet unit itself?

[infected]

Tried another mosfet...makes my gun shoot automatically, even on safe. This is driving me nuts. Is it possible that it could be the mosfet unit itself?

 

Sounds like an install problem. You're most likely either putting it together wrong, or overheating it during install. There is also the chance that you've created a short somewhere between the gate and the positive motor/battery wire.

[Noart]

Infected, have you built any for the Army R85 / GnG L85 Series ?

I don't know about Infected, but i have.

http://www.omegarpg.net/kadaver/index.php?...itstart=18#3305

 

(well, my friend made it but it's my rifle)

 

It runs fine with the wind-up and original 8.4 volt battery, response is PTW like on single.

[infected]

Infected, have you built any for the Army R85 / GnG L85 Series ?

 

Missed this post along the way. As long as it has 2 trigger contacts and 2 motor contacts, my system should work fine.

[Captainkickass]

Sounds like an install problem. You're most likely either putting it together wrong, or overheating it during install. There is also the chance that you've created a short somewhere between the gate and the positive motor/battery wire.

 

 

I dont think there is a short anywhere because I just installed brand new wiring on the gearbox.

I just tried 3 mosfets, all have the same problems. 2 out of the 3, i get one shot, and then it automatically shoots, and the MOSFET gets really hot.

 

I'm not sure what im doing wrong.

I have...

 

27K 1/4 watt

100 ohm 1/4 watt

 

 

I know im installing it right because I have mosfets from HHAirsoft from a year ago and I installed those and those work fine. So i'm not sure what the problem is.

[infected]

I dont think there is a short anywhere because I just installed brand new wiring on the gearbox.

I just tried 3 mosfets, all have the same problems. 2 out of the 3, i get one shot, and then it automatically shoots, and the MOSFET gets really hot.

 

I'm not sure what im doing wrong.

I have...

 

27K 1/4 watt

100 ohm 1/4 watt

 

 

I know im installing it right because I have mosfets from HHAirsoft from a year ago and I installed those and those work fine. So i'm not sure what the problem is.

 

Well, there are only a few things that can cause the problem.

 

1. A direct short between the gate and the positive wire.

2. A overheated and broken mosfet.

3. A incorrectly assembled mosfet circuit.

 

And that's it.

 

If the gate has been fried the gun will shoot full auto all the time. That can happen by overheating the mosfet during install, or using the wrong value resistor on the gate. The only other cause is a direct short.

 

Try this. Remove the mosfet from the gun. Hook your meter leads to the + and - motor wires. Plug your battery into the mosfet. Now tap the gate wire to the positive motor wire. You should get a reading on your meter that is the same as the voltage output of the battery. If you're getting a reading before taping that gate wire, you're mosfet is toast or incorrectly wired (most likely toast).

[Captainkickass]

Yeah i tried four of my mosfets, toasted, got one to work. For some reason though, when i remove the motor from the hand grip, and test the mosfet, it works. Then i put the motor back in, test it again, and it'll shoot fully automatic. Then i take out the motor put it to a volt meter, says its working fine, meaning no shot. then test it with a motor, works fine. then i put the motor back into the hand grip shoots fully auto.. So im trying to think what is making it shoot?

Should i just try a new hand grip? I got a few laying around.

[DFM56]

What mosfets should I use to build an AB circuit? I made one for my AK last year, but when I looked for the same 'fets I used then, I can't find them anywhere.

[Docv400]

Missed this post along the way. As long as it has 2 trigger contacts and 2 motor contacts, my system should work fine.

I think Apex may have been hinting at the Pre-cocking feature on the L85(s).

When I fitted a simple switching MOSFET set-up to one (ARMY L85), the extra speed caused it to over-run.

I had to tweak the passive braking contacts to stop it earlier.

With an AB MOSFET you wouldn't (shouldn't) have that problem.

[Kipper]

My mosfet burnt out at the weekend (was one from infected).

 

Not sure why though. I installed it a few months ago and its been absolutely fine until saturday when I pulled the trigger on semi and it fired a burst then smoke poured out of the handguard as the mosfet got so hot it melted the heatshrink and broke apart. The wires get very hot as did the battery. Checked the battery for damage and it appeared fine but I've binned it anyway and the motor was fine (not locked up or anything). The LiPo was on a voltage checker too so it was also fine, any ideas?

 

EDIT: Was a star LSW on stock gears and motor and running at 320 fps ish and there was no short in the circuit that I can see.

[infected]

My mosfet burnt out at the weekend (was one from infected).

 

Not sure why though. I installed it a few months ago and its been absolutely fine until saturday when I pulled the trigger on semi and it fired a burst then smoke poured out of the handguard as the mosfet got so hot it melted the heatshrink and broke apart. The wires get very hot as did the battery. Checked the battery for damage and it appeared fine but I've binned it anyway and the motor was fine (not locked up or anything). The LiPo was on a voltage checker too so it was also fine, any ideas?

 

EDIT: Was a star LSW on stock gears and motor and running at 320 fps ish and there was no short in the circuit that I can see.

 

Odd. PM me your Paypal Transaction number, and if you can, pm me a pic of the mosfet. Oh, and what voltage battery were you using?

[Kipper]

Will do in the next couple of days, gear is still in the van at a mates house.

[The Taurus]

My mosfet burnt out at the weekend (was one from infected).

 

Not sure why though. I installed it a few months ago and its been absolutely fine until saturday when I pulled the trigger on semi and it fired a burst then smoke poured out of the handguard as the mosfet got so hot it melted the heatshrink and broke apart. The wires get very hot as did the battery. Checked the battery for damage and it appeared fine but I've binned it anyway and the motor was fine (not locked up or anything). The LiPo was on a voltage checker too so it was also fine, any ideas?

 

EDIT: Was a star LSW on stock gears and motor and running at 320 fps ish and there was no short in the circuit that I can see.

 

Earlier on today exactly the same thing happened to me! However I have been using this mosfet (infected's) for just over a year now and it has performed flawlessly. It's been in a relatively high speed setup with a G&P M160 motor and a 9.6v mini battery shooting at around 330 fps. I would definitely recommend the unit to anyone looking to purchase one, however I am not quite sure why blew.

 

Just so you guys know when if it does blow it makes a terrible smell, think fish mixed with burnt rubber Also melted the heatshrink material it was covered letting of a bit of smoke.

 

Here are some pic's I took having disassembled the gun:

 

 

[Maekl]

Im making a mosfet switch to my new usp aep, and just asking, will it work fine with a irl1404 mosfet and 100ohm 30k resistors, or should I change the resistor values or something because its a aep? It will be a non-active breaking because I want shorter semiauto delay. With active breaking on the semi auto the piston always ends up on the rest position, and thus semi delay is longer, when the gears have to turn much longer way. I've never gotten the point of having a active breaking on aeg's anyway. I'm going to use a normal 7,2v nimh battery.

[gzus11]

i dont see why not, just as long as you can fit it inside usp body.

 

for resistors, they are flexible from my experiments, if you can figure out

what they are doing you can pick what you want.

[Maekl]

I could actually fit a extreme-fire sw-computer inside it, so space is not a problem. Having a active breaking is totally pointless in my opinion, unless the aeg is running really really tough springs...