Mosfet Amperage issue

[Triss]

Hi all, I have just converted to 11v LiPo but I have an issue with the Mosfet installed on the gun I bought, it has a mini blade fuse 30A (that's the max the come in), ummm the LiPo kicks out 32A continuous/48A Burst.

I am not sure of the Mosfet Build although I would assume the components are pretty much the same with all Mosfets (resistances etc).

not sure what to do. Any suggestions welcome.

Thanks,
Triss

[Clot]

Re: Mosfet Amperage issue

The battery doesnt kick that out.. thats what it CAN kick out.
The motor will only draw what it needs. So unless you are pulling a really big spring and big motor, its unlikely you should draw more than 30A.

Perhaps you are though, in which case, you are protected by a fuse

[Triss]

Re: Mosfet Amperage issue

Thanks, I will get another fuse and see if if blows, the rifle does have some high moded systema kit in it but we see what happens.. I will update when I try it

[richardy]

Re: Mosfet Amperage issue

as above the gun will only draw more than about 20 if something goes tits up hence the fuse. Obviously too much draw and wire starts too melt.

[dope_on_a_rope]

Re: Mosfet Amperage issue

I've had a perfectly good high cycle gun drawing closer to 60 amps than 20. It was a systema turbo motor, and so very current hungry, especially on startup. You'll find the current peaks on startup, to more than it's regular draw. So unless you've got some fancy ameter that can tell you the most current drawn through an area of time, you'll never be sure what the draw is, while the gun is still operating well within it's safe ampage.

If it's a self protecting mosfet, you don't need a fuse. If not, you should be able to find out some spec about the fet unit you have installed. They come in all different shapes and sizes, some can only take 2 amps, some can take over 80 continual. It's worth finding out more about the mosfet before you do anything else. You could well go through another couple of fuses, before you find out that there's nothing wrong with the gun, it's just operating at a higher draw than most.

Also, make sure the shim job is good. Could just be that causing extra resistence.


To add to what the guys have said about the gun drawing as much current as it needs, how are we to know how much it needs? If previously the current we've been giving the motor is limited by the battery, a battery upgrade can increase the current, and blow the fuse quite happily. Alot of motors will run faster if given more amps. Sure there will be a point where they just don't use the current avaliable, but who's to say that's been achieved with your old 8.4v 20 amp battery pack?

I hope some of this makes sense. If it doens't, I don't think you should be playing around with lipols.

[Triss]

Re: Mosfet Amperage issue

Thanks Dope,

yeah, this had a 30 amp fuse in it, did try a couple new 30 amp fuses but they blew as soon as I plugged the battery in. I have seen some hi cont fets advertised somewhere, will have to find them. the gun does have a systema 170% complete mech box and systema magnum motor, it's for a PSG,

Any suggestions as to where/which Fet to get?

Thanks,
Triss

[richardy]

Re: Mosfet Amperage issue

no need to fuel the lipos are only for bomb disposal teams debate, anyone can use them dude.

Id love to see your proof that your gun draws 60amps even on initial draw. If it is as you say, you need to take your own advice and remove the lead weights from your gear box. I mean for a start a high rof setup should be effortless, a lighter spring and lightened internals, regardless of having a crap systema motor it should be peaking that high surely youd pop even fuses sat near it. The amp graphs over on airsoftmechanics where of a standard aeg nothing special. 18 amp normal draw i think it peaked at 25, The more work the motor has to do the more it will try and draw. Its why they heat up the more load they get. All i know is if my gun was drawing that much as a pro i wouldnt be happy if it was high rof. Maybe a bit higher on a single only setup a 425, rapid singles with a magmum id invisision being more but still not 60.

You never stop learning in airsoft you show me the results of testing on yours and ill hold my hands up.

[dope_on_a_rope]

Re: Mosfet Amperage issue

Believe it or not, electronics is not my strongpoint. I'd say you'd need around 80amp capacity though, and I know RS electronics sell them. You need resisters and things as well, not just the fet. There's wiring diagrams for fets in airsoft use around the internet. Check them out.

If you want to keep a fuse of sorts, you could get a resetable one, much like a trip switch for your household lights, but smaller. I believe they also come in a variety of sizes.

[richardy]

Re: Mosfet Amperage issue

Thanks Dope,

yeah, this had a 30 amp fuse in it, did try a couple new 30 amp fuses but they blew as soon as I plugged the battery in. I have seen some hi cont fets advertised somewhere, will have to find them. the gun does have a systema 170% complete mech box and systema magnum motor, it's for a PSG,

Any suggestions as to where/which Fet to get?

Thanks,
Triss

what that as soon as you fired it? or as soon as you plugged the battery in.

the systema comes as standard with a 35 amp fuse, and a mosfet built in

Fit a purple 35 amp fuse and if your still poping them like m&ms something is wrong..

Honestly custom fet, reisitors ? theres seriously no need to reinvent the wheel here..

you need to test try a standard battery, low voltage if it doesnt pop its safe to say the new bat is allowing it to draw more than 35 amps.

You can fit a 40 amp fuse.. its an option.

You can wire in a mosfet rated for high voltages.. Thats if your running the standard systema fet..

its pritty poo

AWS if you can get them do great ones for the magnums as they have much more allowance for the systema motor voltage drop issues... which is why i never use them.

Evolution mosfets do some heavy duty ones as well.

3 options... just a little testing to help you decide

[dope_on_a_rope]

Re: Mosfet Amperage issue

In reply to richardy, there is no testing, no evidence. The gun has long since moved on. It was an extreeme set up for sure.
The only evidence I could ever have provided would be the fact I continually burnt out a 50 amp self protecting fet unit. Afterwards it was replaced with an 80 amp fet unit, and I had no issues after that. The problem with the 50 amp unit wasn't imediate. It would take about 3 quick shots on single and fail on the 4th. It would fire on auto all day. So the startup current must have been rather high. May I add, I was useing 14awg wire throughout the hgih current parts of this unit, and a low voltage set up as my 8.4v battery would take longer to get the motor to top speed, and so use more current initially. A bigger voltage battery would have made it easier on the fet.

You don't have to believe me if you don't want to. I don't give a shit either way. I didn't collect evidence, because I didn't think this was out of the ordinary. I just fixed it, and moved on.

Edit: Ok, the above post is much more sensible than the last one.

Also, when I said you'd need 80 amps, I'm being cautious here. Better safe than sorry.

[richardy]

Re: Mosfet Amperage issue

The problem back in the day with older fets, was the like you say the unusually large draw on the systema motors.

http://forums.airsoftmechanics.com/i...p?topic=1194.0

I think eventually it was found to be the distance between the bellhousing and it being metal or something and the rest of the motor, it cuased voltage spikes higher than what they should be. Its been a while since i read it.

later i think they worked it out as an initial draw going down first before it went up and peaked which was cuasing fets to "shut off" or even compltetely die.

Which may explain your fire fire fire stop issue on the magnum.

I had issues with any gun that used lot of singles and the magnum. but only with a mosfet.

Not so bad on new fets but its gutting when you shell out on fets and then a new one comes out every other week. well it did back then.

[Triss]

Re: Mosfet Amperage issue

cheers, for the help, I am not much of electrician either but if it comes to it I may give that a try,

I have just spoken to the previous owner of the gun and he has pointed out that the mosfet comes with the systema 170 kit, to see it you can go to wgcshop . com and search systema 170, there is a picture there but no details,

the previous owner has had a LiPo running in the gun before and had no issues, which leads me to believe that maybe I have done something wrong. All I have done though it a) bought the new batt, b) soldered DIN cnnectors to gun and bat, (correctly I believe) c) plugged the battery in.

I am a little lost but I'll probably end up cutting it out and putting a higher spec one if necessary.

[dope_on_a_rope]

Re: Mosfet Amperage issue

Maby you just got a better lipol than he had. It's entirely possible. If this is the case, your lipol may be capable of giving more power than his, and that's what's blowing the fuse. If he had no problems, bypassing the fuse might not be a bad idea, but you might still kill the fet if you do this.

If the fets provided with the Systema PSG-1 FTK are anything to go by, I'd replace it.

But lets not discount the posibility something has actually gone wrong inside the gearbox. It's unlikely from what you've described, but may still have happened. If you do bypass the fuse, and then run without it and there's a problem in the GB, it'll make a horrible sound and possibly overheat the fet curcuit or the motor, or even the battery, which could be bad. It would normally take a while to cause any lasting damage though. So bypass the fuse, see if the gun works, and if it don't, don't hold the trigger down or try too many times.

[richardy]

Re: Mosfet Amperage issue

cheers, for the help, I am not much of electrician either but if it comes to it I may give that a try,

I have just spoken to the previous owner of the gun and he has pointed out that the mosfet comes with the systema 170 kit, to see it you can go to wgcshop . com and search systema 170, there is a picture there but no details,

the previous owner has had a LiPo running in the gun before and had no issues, which leads me to believe that maybe I have done something wrong. All I have done though it a) bought the new batt, b) soldered DIN cnnectors to gun and bat, (correctly I believe) c) plugged the battery in.

I am a little lost but I'll probably end up cutting it out and putting a higher spec one if necessary.

like i said systema special, just fit a TM eg1000 and see if that sorts the problem out, easy if you have one just lieing around in another gun.

If the fuse pops before you pull the trigger then you solder it on wrong. somehow.

[Triss]

Re: Mosfet Amperage issue

well, put a cable in place of the fuse and attached the battery (against my sane judgement), anyway, the motor initialized so it seems that the fet still works, however, the cable, fet and heatsink got really hot. after literally only connecting the batt for 1/2 second.

what do you think?