[jake556]

I have been wanting to purchase a MOSFET chip but am still confused as to how they work. I don't want to install some "wonder part" until I really know what's going on in this heat-shrinked chip.

I see the benefits like a quicker trigger response, the lack of need for an anti reversal latch, and stopping the firing cycle with a compressed spring (please confirm last).

I'm wondering how this thing works and how a MOSFET can be sold as a universal unit if there is a different tooth count on gearing in AEGs? Wouldn't the amount a motor has to spin vary based on the tooth count? This sounds like it really should need programming based on the application.

Anyway, can you guys chime in?

 

[sanguinor]

Personally, I run normal MOSFET's rather than active braking ones. Mostly because when I did run a Active Braking MOSFET with no anti-reversal latch I had all sorts of problems with it firing twice on semi. If I remember correctly, you have to have your system balanced correctly because the AB MOSFET reverses the polarity on your motor (stopping it) when the circuit is broken (by letting go of the trigger).

A basic MOSFET increases trigger response in a very simple way. Your charge goes directly to the motor from the battery rather than via the trigger mech, saving your trigger mech the displeasure of have 9.6v go through it and completing the circuit considerably quicker!

For it to stop the firing cycle with a compressed spring it'd have to be a computer not just a MOSFET. These more advanced MOSFETs have sensors built into them which sit inside the gearbox and tell the motor when to stop turning.

I know it's not a perfect answer, but I hope that helps!

 

[goldentrigun]

Every time a gearbox cycles on semi the cutoff lever breaks the connection between the battery and the motor causing the motor to stop. An AB mosfet will reverse the polarity of a motor and quickly stop it.

Always always always run a AB mosfet with a anti reversal latch no matter what your setup. At least on higher spring or lower ratio setups the motor will not be able to hold the position and it will unwind slightly (not all mosfets will stop at the beginning of every cycle consistently) which generates heat on the mosfet. Do this a bunch of times and the mosfet will fail prematurely.

Low ratio setups/ high voltage setups still generate some degree of over spin.

There are three styles of mosfet: a basic, active breaking (some times full featured), and mosfets which replace the trigger contacts on your aeg.

Basic mosfets simply bypass the trigger switch and run directly to the motor. They do this using a transistor and having the gate wired on your trigger contacts.

Active braking mosfets do the same as basic mosfets but they brake when the cut off lever signals the end of cycle.
^just reiterating what Sanguinor said.

The final style completely replaces your V.2(there are only v2 models of this at the moment) trigger contacts with something similar to a micro switch. This counts each cycle your aeg makes via the cutoff lever and is able to precisely apply burst fire and more will allow for a better stop at the end of the cycle. These however are the most involved when installing them into your gearbox. Due to different tolerances you can have problems with the trigger not contacting the switch enough, same with the cutoff lever, the selector plate can also not contact the switch enough to let it know what mode it is in, and the switch may need to have its edges trimmed slightly to fit the gearbox shell.

All that aside you may be wondering about the prices of these mosfets.
Generally a standard mosfet will run you 20USD or less.

A basic AB mosfet will run you about 20USD.

A full featured mosfet will cost anywhere from 40USD to 100USD.

Mosfet trigger systems are about 100USD.

I currently run a mosfet trigger system in my m4 based system and it has been absolutely the best purchase I have ever made in airsoft. After overcoming the initial hurdles to get it to work I really would not ask for more. The main thing that I like about it over everything I stated earlier is the fact the trigger pull is minuscule compared to a standard setup. This allows me to have a run semi as quickly as a polarstar and systema.

 

[the3rdeye88]

I have the Cheetah mosfet that you can program for semi, burst, or full auto. I don't know if its AB or not though.

 

[goldentrigun]

^It's a full featured mosfet, but instead of counting gear cycles it uses a timer to apply burst fire. It'll work but depending on how your battery is your 3round burst will end up being a 6 round burst or something similar.

 

[chiba]

I think no one has told you that you DO have to do some tinkering with the wires in your gun if you plan to install a MOSFET (unless its computerized trigger system, which replaces the wiring anyways). If you're not technically inclined, you will need to go to a tech for installation.

BTW, mosfets are a much needed item for AEGs running on Lipos. It prevents the wearing of the trigger contacts (the plating starts to wear out using Lipos)

 

[jake556]

Thanks for all of the replies everyone and I think from this site and a few others I have gathered what I need to know.

I am confident in wiring/soldering and have also watched quite a few videos installing a MOSFET into a V2 gearbox. Seems to be easy and since I am rewiring the replica anyway, I shouldn't have any trouble with the installation.

I was mainly trying to figure out what it is actually doing so I have an understanding of WHY I'm installing this part instead of just throwing parts at my GR25.

Another note, I do run lipo batteries.

 

[Libelle]

Also, something not mentioned is the mosfet lowers the resistance of the circuit, basically meaning more efficient use of the battery and a stronger motor turning.

Also, it will keep things from heating up so much, and allow for higher voltages without cooking the gun.

 

[jorn84]

Mosfet

MOSFET is a transistor used for amplifying and switching electronic signals. It has an infinite impedance and also well suited to high-speed switching applications and can act as a variable resistor.

 

[the3rdeye88]

^It's a full featured mosfet, but instead of counting gear cycles it uses a timer to apply burst fire. It'll work but depending on how your battery is your 3round burst will end up being a 6 round burst or something similar.

Actually it fires 1 shot 2 shots on the trigger pulls when you have the selector in full auto. Don't know why, but it does in burst mode.