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The Mosfet Thread


crackisbad

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I have a quick question. I'm going to make myself an AB mosfet, and after reading this thread, and other ones, I think I understand how they work and more or less what specs are needed. My question involves the p-channel mosfet. Will a irf4905 work? I think it will, but since it hasn't been mentioned specifically in this thread I'd like to have someone who has done this before confirm that it will work.

Data sheet

http://www.irf.com/product-info/datasheets/data/irf4905.pdf

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  • 3 weeks later...

Personally I run a basic, big numbers Mosfet and a separate blade fuse. I would not use an electronic fuse and I would always use a traditional fuse.

Why do you not want to have a separate fuse? I can't imagine it is for space reasons as you must have loads internal space compared to us M4 users.

 

Tom.

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  • 2 weeks later...

OK.

A quick query for the more electronically-minded (more than me, not too difficult) among us.

 

I'm wiring up an A&K M60 with a simple switching MOSFET, with the Box-Mag running off the trigger circuit.

Without the Mag plugged in, everything's fine, as soon as I plug it in however, and activate the micro-switch, the gearbox runs constantly even with the switch released.

The MOSFET is then 'closed' permanently, i.e. 'ON' (read 'knackered').

This is the circuit I've made.

M60FET.jpg

It's obviously the way the mag is wired in that's causing the problem, but how do I rectify it?

I'm thinking maybe I need a Diode in the circuit somewhere, if so, where?

 

There are some connectors in the circuit, to make gearbox removal easier, I've omitted them for clarity as they don't affect the basic layout.

 

Thanks.

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I've got an ICS M4 that I'm planning on building a MOSFET for but if there's an issue with ICS's I'd sooner save my money! :P

Can anyone else confirm or deny whether or not this is the case with ICS rifles?

If it's all good then I have a project to keep me busy for a bit :D

This may be a bit late, not checked this thread for ages...

I've had a simple switching MOSFET in my ICS M4 for years, it works fine.

The gun is approx 6 years old.

Unless ICS have done something to their electrics in later/recent AEGs, I can't think why a MOSFET wouldn't work in them.

If they have the 'usual' trigger contact set-up, then a 'FET will work.

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Doc,

By micro switch are you refering to 'TS' or to a separate switch on the mag for the drive motor?

Also, by gearbox are you refering to the AEG gearbox or that of the mag?

By 'closed permanently' do you mean that even when you release the switch the gearbox keeps running as if the Mosfet has fused or something?

 

Is the motor of the mag not able to handle the full Voltage of battery? Could you not wire it in parallel with the motor?

 

Tom.

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Sorry...

TS = micro-switch (trigger switch). The mag switch is set to 'continuum' (their spelling). With the original wiring set-up, that selection means the mag runs only when the trigger switch is activated.

Gearbox is the AEG gearbox/motor.

The MOSFET is 'fused', the AEG gearbox cycles with the switch released.

The box-mag motor runs off the main battery as standard, I'm testing with a 7.2v pack, the owner was running with a 9.6v pack.

The box-mag motor is wired in parallel with the AEG motor ;)

 

I've not shown it in the schematic, but the 'FET has a 100ohm Gate-Source resistor.

 

Edit; Actually, I think I've just seen what you mean about the mag being in parallel with the motor.

You mean connect the -ve mag wire to the 'Drain' line, instead of the 'source' one?

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Doc,

As Darklite has said, by parallel, I mean as if the mag motor was directly attached the AEG motor.

 

Edit:

Edit; Actually, I think I've just seen what you mean about the mag being in parallel with the motor.

You mean connect the -ve mag wire to the 'Drain' line, instead of the 'source' one?

 

Yep, exactly that.

 

Tom.

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Cheers guys.

I think I was trying to look too 'deep' for the problem, when it was just a simple fix all along.

 

Having been awake for over 22 hours didn't really help either :nosleep:

 

Edit; Right! That's 'FET nr. 3 in the bin :headbutt:

Obviously not looking deep enough.

26 hours and counting...

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  • 4 weeks later...

Long story short - what are the most popular FET chips at the moment for a simple 1 chip mosfet withpout AB?

 

I havent built one for a while, last time there were the IRL1404, but I am sure that there is something better on the market by now?

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