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crackisbad

The Mosfet Thread

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Just to add something about trigger switch corrosion with Lipos, here's my story:

 

After I bought my first Lipo and soldered my first MOSFET-unit, i thought it would be a good idea to use the Lipo (7.4 V 15C 2100mAh Thunder-Power) with my other, non-MOSFET gun. After around 1000 rounds, i opened the gearbox to change the current configuration and look what i found...

 

post-28723-1236618060_thumb.jpg

 

post-28723-1236618067_thumb.jpg

 

Looks good, doesn't it? So please, use MOSFETs if you're using Lipos.

 

 

PS: Finally made my first post, was about time... ;)

 

Cheers spoeni

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wow that sucks. great first post though! :P

 

in other mosfet news, talked to the guys over at AWS about ETA on their fets:

I am sorry but we have no ETA on our units. Our units will be back in stock within the month, but right now, we’re doing an overhaul on the website backend for functionality and ease of use. Our new units will be the market hog, so you can wait, you won’t be disappointed

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:) thanks guys

 

You can't see it very clearly in the pics, but some of the chrome-(or nickel?) plating of the metal part in the upper picture was destroyed and you can see the copper wich was underneath. Strangely a layer of the plating material has built up on the copper sheet in second picture.

 

I'm quite sure that's caused by sparks when the contacts are close to each other, got to ask the electronic/corrosion specialists at work what exactly happened...

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That's a nice animation, but I wouldn't say it *explained* anything, as such. More like the graphics you'd use on an advert, it tells you that mosfets with AB are good, but doesn't explain why they are good in any meaningful way.

 

Well you can take that or i can give you the real way MOSFET's work......but on the other hand its a college level electronics class topic for a reason...magik is involved

 

 

The amount of info Infected gives is plenty enough for 90% of people, for normal terms I could go a little more into why its significant for the special nature of the DC circuit used in airsoft guns but overall people just need to know it makes the magic fairies happy.

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Just finished my G&P M4A1 project running a LiPo and a infected mosfet, unfortunatly, I was able to make the mosfet burn after around 500 rounds.

 

The M4A1 is/was running around 130m/s, the battery is a Intellect 11.1V 1200mAh 20C.

Pretty bummed at the moment. :( ...

 

I was very impressed with first 500 rounds thou. ^_^ ...

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How in the world did you burn it up? I've run 400 fps gearboxes at 30 rps on 11.1v lipos (30C 2200mah). Did you just hold down the trigger forever? Mosfets can build up heat and have to dissipate it.

 

Not directed at you, but a lot of people think you can just hold down the trigger forever once you have a mosfet installed. The thing is, the mosfet can only dissipate so much heat. If you're building up more heat than it can dissipate, it'll eventually cook itself.

 

How did the mosfet "burn"? Did the heat shrink just burn up or did it smoke? The version you're using can handle 80A continuously @ 300 watts of dissipation. It's actually possible for the heat shrink to give way before the mosfet does.

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Actual fire was not present. I might have overexaggerated that event.

There was a cloud of smoke coming from the mosfet, but im not sure if it came from the heat shrink or from the acual mosfetparts, the heat shrink had melted thou.

I have noticed a small "crack" on top of the ST-P80PF55.

 

I was firing short bursts on fullauto when it happened. No M249:ish coveringfire.

 

 

Since i´ve changed all the cables on this mosfet to my own, im guessing one of my solderings might have come off by the immence heat resulting in a shortcircuit.

 

Anyway, I´ll be buying a new one asap if you have them in stock.

 

 

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Just going back to the resettable fuses (Polyfuses) for a moment if I may.

I recently got some, as I'm going to knock up some AB MOSFET units, just out of curiosity at the moment.

I got the ones recommended in a guide on AirsoftRetreat.

The specs say that the 'Max. Time to trip' is 16 seconds :huh: .

There's no minimum time mentioned in the specs.

That seems a long time to wait to me, or am I missing something?

Is it maybe the total time, for 'blow', cool and reset?

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I do believe that is the maximum time it would take to trip. so if the trip current is 20A, it could take as long as 16 seconds (or less) at that current rating to trip.

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Which is why i currently run all my guns without fuses. Regular fuses impede current too much and resettables kinda dont work when you have high output batteries and motors.

Just have to have faith in your mechbox work.

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Actually what happened to Hapter's I think is the connection on the PCB of the mosfet burnt up (and in turn burnt the shrinkwrap). That's happened to me twice. I've generally avoided mosfets with PCB unless the PCBs are well made or there's some other kinda protection in place.

 

The actual mosfets themselves were ok.

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Actually what happened to Hapter's I think is the connection on the PCB of the mosfet burnt up (and in turn burnt the shrinkwrap). That's happened to me twice. I've generally avoided mosfets with PCB unless the PCBs are well made or there's some other kinda protection in place.

 

The actual mosfets themselves were ok.

 

Hapter had one of mine (I believe), so that would be a NON PCB mosfet.

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I was firing short bursts on fullauto when it happened. No M249:ish coveringfire.

 

 

Since i´ve changed all the cables on this mosfet to my own, im guessing one of my solderings might have come off by the immence heat resulting in a shortcircuit.

 

Same happened to me on two of Infected's MOSFET's. The negative wire that curves around the MOSFET at a 90deg angle broke off from the MOSFET lead and contacted one of the other leads it's not supposed to. This led to rapid heat build up and the burning of the shrinkwrap (this happened to one MOSFET, the other just broke free and didn't contact anything). It was most likely a solder joint fail rather than any actual problem with the MOSFET.

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FaRKle I thought I fixed that one for you?

 

Anyway... Out of hundreds of mosfets sold, I've had 6 documented failures, and 2 of those were caught during testing before shipping.

 

IF any of you guys ever have a problem with a mosfet I've built for you, please tell me as soon as possible so I can either make it right or at least document it so make sure there isn't a problem with the product from the manufacturer or an issue with the guy who make them for me (um... that'd be me... :D).

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FaRKle I thought I fixed that one for you?

 

Yup! You sure did! Well the 1st one anyways. The 2nd one I just re-soldered myself since the chips weren't burnt out.

 

 

IF any of you guys ever have a problem with a mosfet I've built for you, please tell me as soon as possible so I can either make it right or at least document it so make sure there isn't a problem with the product from the manufacturer or an issue with the guy who make them for me (um... that'd be me... ).

 

Infected's very fast and helpful if you have any problems too!

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I had one mosfet that i got off infected burn out the other one has been running brillantly! Not sure what happened with the burnt out one.. i put it in my unicorn aksu and the 1st day i was using it smoke started coming out of it so i opened it up and the heat shrink had a large hole in it like it was melted :/ as i said i have one in my ca slr105 and its had no problems at all and its been used many times but hopefully i'm gonna get afew more from infected when i have the £!

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I'm hearing some stories of burned up heat shrink. I'm not liking that so I'm probably going to switch suppliers today on my heat shrink. Now to find a source of some quality heat shrink that isn't stupid expensive.

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Infected, I had one of your mosfets burn out on me. BUT it was my fault, I rewired my gearbox to be a bit cleaner with less wiring.

I think something was shorting out on the thinner trigger wire and something else. The gun jus went into full auto when a battery was connected, then smoke came pouring out of the mosfet.

 

I took it out, checked the gearbox, and found the possible cause. I think by that point it was too late for the mosfet. Everything was isolated, tho it kept on the full auto.

 

I replaced with one of my own mosfets ( without AB ) and still the same problem, somewhere around the trigger contacts, something was touching something.

It took that mosfet and my lipo battery with it.

 

Replaced all connections with clean wire, heatshrinked everything and checked. Normal wiring works again.

 

I shall be ordering two mosfets at the end of the month :)

 

Moral of the story: Always check your wiring, one wee touch is all it takes!

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This is my little contribution to the thread. I've trawled the internet looking for info about how to make an AB mosfet, then compared all the different bits of advice and made my own. I've made dozens now and fitted them into our site hire guns, all my own and quite a few others and they're all working fine. I've posted a guide on how to make them here. Your welcome to copy it and make your own, just don't send me the bill if it all goes wrong.

 

Just been asked this but I meant to put it in the post anyway. I get the Mosfets from Farnells in Leeds, they do mail order if you can't call in and the other bits and bobs come from Maplins.

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Good job there DoubleTap. That's a method I haven't seen people using (placing the fets above each other instead of back to back). It makes for a longer but thinner unit. I've been considering doing that myself for a while.

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