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The Mosfet Thread


crackisbad

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  • 3 weeks later...
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I think I'm going to build a basic, non AB, Mosfet circuit but could someone give me some advice on the componentry I've chosen.

There are two Mosfets that I'm considering, and I'm unsure about the resistors. Here are the specs:

 

Mosfet Hexfet IRL2203N: http://www.irf.com/product-info/datasheets/data/irl2203n.pdf

 

Vds = 30V

Id = 116A(25C) / 82A(100C)

Pd = 180W(25C)

Rds(on) = 7.0mΩ

 

 

Mosfet Hexfet IRF3205N: http://www.irf.com/product-info/datasheets/data/irf3205z.pdf

 

Vds = 55V

Id = 110A(25C) Silicone Limited / 78A(100C) / 75A(25C) Package Limited

Pd = 170W(25C)

Rds(on) = 6.5mΩ

 

Resistors:

30K Ohm 0.25W Carbon

100 Ohm 0.25W Carbon

 

or

 

the same in 1W, 2W or 5W Metal.

 

 

 

So, which Mosfet would I be better off with, I presume the the first one with the highest Pd? Also, could someone clarify that extra info for the Id of the second Mosfet i.e. 3x ratings and descriptions?

 

I'm guessing that I can go with the low wattage carbon resistors, correct?

 

Cheers,

Tom.

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Thanks.

Am I ok with the low wattage carbon resistors?

 

I read somewhere that it is not recommended to use a mosfet with anything less than 8.4V or 9.6V, I can't recall exactly.

Is this true, as I want to use it in conjunction with a 7.4V Lipo?

 

Tom.

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I am looking to place the Mosfet circuit up front, inside of the RAS, while my battery will be in the buffer tube.

Have I drawn my circuit correctly? I presume it does not matter where the Mosfet sits in the circuit just as long as the positive connects to the Drain and the negative to the Source?

 

MosfetDiagram2.jpg

 

Tom.

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  • 2 weeks later...

Hi guys I'm having a big issue. I have made an AB mosfet system using Doubletaps guide here: http://www.cerberusairsoft.co.uk/Mosfet/

 

I built the mosfet a while ago but never got it running and assumed I had some knackered batteries. I finally received my new battery (a flightpower evo-pro 30c (30c continuous, 60c burst) 4200mah 7.4v) the other day, charged it (with an Eclipse LX61b) and connected it up only for nothing to happen. The only thing I could think to try was to swap the thin wires I was using to connect to the trigger switch around (although I couldn't see how that could make a difference what with it just being a mechanical switch).

 

I wired up my battery to the open gearbox (V2) via the mosfet system with the motor (golden eagle super high power) electrical taped to the table. I pulled the trigger and the motor activated. However upon rebuilding the gearbox and pistol grip assembly with the motor inside I reconnected the battery, selected full auto and pulled the trigger. The motor felt like it was trying to move but was jamming on something and so I removed the bottom of the grip and pushed on the bottom of the motor until it was in the gearbox and pulled the trigger again. This time the same thing happened but I could see some smoke coming from the motor. I thought I may have wired the motor backwards as the terminals are not clearly marked (both sides have some red paint on them so I assume the one with more red paint than the other is positive), so I tried the other way round and nothing happened at all.

 

I am beginning to think I imagined it working yesterday as I am sat here now just looking at it and poking it with no real idea how to troubleshoot. If you understood any of the above (I certainly don't) then whatever suggestions you have will be appreciated!

 

Cheers,

 

Mike

 

EDIT: Update: I just had the same thing happen again. I had the gearbox open and all the wiring connected up. Pulled the trigger and the motor spins. Put it back together (pistol grip back on with motor in it), selected full auto and pulled the trigger. There was a click noise as if the motor was trying to spin and I felt a jerk which would indicate the same. After this I let go of the trigger for a second or two before pulling it and holding it on (I believe stress is getting the better of me). This time nothing in terms of movement however the mosfet began to smoke and sizzle. I immediately disconnected the battery. Again this problem is well beyond my expertise. Could it be the mosfet itself is a bad design/badly made? This doesn't seem so due to the fact that the motor spins very well when the gearbox is apart. Could the gearbox itself be jammed causing the circuitry to overload? I simply don't know.

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Got my Mosfet today and immediately went to work on it. Not the usual installation as I have the battery in the buffer tube and the mosfet up front.

It worked out very nicely without any bother or fitment issues. Plenty of heat shrink and then superglue to hold all the components together.

Lastly, one large piece of tubing will cover the whole ensemble.

 

Still yet to test the circuit under load but without a load it works a treat.

 

Tom.

 

P107062740cutjpeg.jpg

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  • 2 months later...

I was referred to this thread by Hedganian, p'raps you gents can help.

 

I'm looking for a one or two-wire MOSFET diagram of a finished AUG with CLEAR pictures. It seems the rest of the internet is terminally retarded when it comes to taking any kinds of pictures of a finished product.

 

Hed said that it's not too different than any other mosfet installation, but the pictures I've seen online seem to have the mosfet wires attached to the full auto circuit contacts on the outside of the gearbox.

 

I'd really prefer to do this the right way the first time, and a clear picture of a wiring diagram (not something someone drew on MS Paint) would be immensely helpful.

 

Thanks in advance.

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Currently I have the IRL2203N fitted to my 1J M4 and I'm looking to buy some more Mosfets for other similarly rated guns.

From looking at the specs below will I get any perceivable advantages from paying extra for the alternative mosfet.

 

Current Mosfet (IRL2203N).

Vds: 30V

Id: 116A

Pd: 180W

Rds(on): 7.0mOhm

 

Prospective Mosfet (IRL1404ZPBF).

Vds: 40V

Id: 75A

Pd: 230W

Rds(on): 3.1mOhm

 

So, will there be any great advantage to getting 50Watts more and a lower resistance rating? Will the Id Amperage be a negative or since an AEG never tops 40Amps then the value of 75A is a perfectly acceptable headroom?

 

Should I stick with my current mosfet type or pay the extra?

 

Cheers,

Tom.

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