The wiring of A&K Mk43 MOSFET?

[ccyg8774]

Originally Posted by ThunderCactus

it's not good for any piece of electronics to have high frequency voltage spikes going through it

But the MOSFET (barebone MOSFET, no computerized chip) are fine with PWM control...

[ThunderCactus]

it'll work as long as it doesn't have active braking, I'm just saying it's not a good idea.
Think of it like this;
You're flicking your light switch on and off so fast it essentially dimming the bulb a little. Do you think that's good for the bulb or the switch? Or the power source for that matter? lol

[ccyg8774]

Originally Posted by ThunderCactus

it'll work as long as it doesn't have active braking, I'm just saying it's not a good idea.
Think of it like this;
You're flicking your light switch on and off so fast it essentially dimming the bulb a little. Do you think that's good for the bulb or the switch? Or the power source for that matter? lol

Based on my poor knowledge on microcontroller and PWM control, that should be fine, MOSFET is made to handle that. That should also be fine to the motor as PWM seems to be the way they control the ROF in computerized MOSFET unit with a ROF control.
If that causes problem, I will just change to a OMRON V7-1S17D8-022 microswitch which have almost no bouncing.

[ThunderCactus]

it would be best to get the good switch right away lol

[horto]

I have an A&K M60 mk43...

The mosfet that comes with the gun is more like a basic rheostat, used to control the variable rate of fire. Based on my own research it does not perform voltage regulation to the trigger switch like other typical airsoft mosfets do. In general I think it's pretty useless.

m102404 rewired mine to bypass the original variable fire control mosfet and put in one of Stealth's original Gate basic FETs to protect the trigger switch - he tucked the mosfet in just behind the gearbox. The pig runs like a champ now - we've put tens of thousands of plastic bb's downrange from it without a single hiccup. The PicoSSR would be a pretty sweet set up too.

These diagrams may help http://www.red-alliance.net/forum/in...?topic=19544.0

edit: the stock hopup was also pretty useless... I modded it with a small piece of 16 AWG speaker wire insulation, to form a better cylindrical "nub". I think you could also replace it with a CA hopup if you wanted to throw money at it.

[Kos-Mos]

Originally Posted by ThunderCactus

it'll work as long as it doesn't have active braking, I'm just saying it's not a good idea.
Think of it like this;
You're flicking your light switch on and off so fast it essentially dimming the bulb a little. Do you think that's good for the bulb or the switch? Or the power source for that matter? lol

Not applicable.

A MOSFET typically has a switch rate under 10 nanosec, with high quality MOSFETs going as low as 0.4 nanosec. (the ones I use are that fast).
Meaning that the switch would have to bounce over 10kHz to cause the FET to enter triode and start heating/degrading.

The only thing that it does is everytime the switch bounces, it sends a back EMF to the drain pin. If there is no diode to protect the FET, or if the diode is not fast enough (thing regular N-type diode vs.Stocky), the high voltage spike might scramble the doped semiconductor in the FET and screw thing over.

The other side-effect is that when the switch bounces, it does not cut instantly. The resistance increases a lot while the air is still ionized enough to arc across the contacts. That in turn means that there is a current spike going through the MOSFET, and depending on the unit used, it might exceed the rated max instantaneous current. That same current spike also "boosts" the resulting back EMF (the larger a current is in a given load, the higher the voltage will be when you cut the circuit).

[ccyg8774]

Originally Posted by Kos-Mos

The other side-effect is that when the switch bounces, it does not cut instantly. The resistance increases a lot while the air is still ionized enough to arc across the contacts. That in turn means that there is a current spike going through the MOSFET, and depending on the unit used, it might exceed the rated max instantaneous current. That same current spike also "boosts" the resulting back EMF (the larger a current is in a given load, the higher the voltage will be when you cut the circuit).

Thanks for the detailed explanation.
Guess it is worth to get a no bouncing swtich on first try.

Also thanks to horto and ThunderCactus again.