My Mosfet/Wiring Upgrade

[Pointy]

Originally Posted by K3vX

Also, the two packs that you linked that have the same mAh rating, 1200mah, are the SAME pack, except one has the cells separate, and the other one has the cells wrapped together.

I didnt notice that

[Random Fire]

Hey pointy

I built that same circuit and have used it for 2 years in a g&g gr-15 and it works wonderfully. I then converted both my TAR-21 and m14 this year to the same circuit. The only different change I made to the wiring was I changed it out from the motor to mosfet with silicone test lead 18 gauge wire. I know the hobby guys use the same wire but in 12 gauge for building battery packs but it's too thick in some limited space guns. Very flexible down into the -40s and can handle more voltage and current than most of the OEM wire that come with most airsoft guns. And I did it for the same reason as you, it was cheap, it tested very well (I did test fire current draws, both with semi and full) and it was fun..
to finish the circuit up I shrink wrapped it and sealed the ends with liquid electrical tape but you could use a electrical safe silicone. I included a link (from their site) that shows the parts orientation, the only change I made was to the diode placement instead of on the side (rather fat circuit pack) I put it in line with the mosfet, the negative marked edge of the diode tucked under the bottom edge of the mosfet between the 2 leads. Also make sure you shrink wrap the 100 ohm res. so it doesn't short to the mosfet casing, and not that you have to but I did the leads of the diode as well just in case my packaging fails due to someone poking at it with something sharp.
http://unconventional-airsoft.com/20...mosfet-switch/

[Pointy]

Updated the schematic and parts list

[K3vX]

Thanks for this You're doing all the work, and I profit haha.

On a serious note, any reason you use Yageo Resistor over anything else?

I'll add a few notes on your design :P

- It is a TVS Diode, not a TSV
- People at AirsoftMechanics are saying that you should add the TVS diode (5KP18A) for maximum reliability, but that it should not fail if it isn't present. A couple of folks there are selling their own FET based on the exact design we are discussing, and they all use it for that reason.

Still, 10$! I'll probably order the stock to make more than one, so even less per unit.



Useful resources:

Making guide, some things are missing but it still helps to visualize the whole thing: http://ncairsoft.org/forum/showthrea...building-guide

On this image, you would add the TVS diode to the left, between the Source leg and the Drain



Wiring guide for dummies like me :

[Pointy]

Originally Posted by K3vX

On a serious note, any reason you use Yageo Resistor over anything else?

No specific reason for picking the Yageo brand resistors.

[K3vX]

I see.

I'm trying to make a part list myself. That includes ordering the screws and nuts from Digikey itself.

Any reason for using stainless steel over anything else? They are either triple the price or nonexistent.

Also, the motor connectors can be ordered there, too. Like part A27756CT-ND, at 17 cents each.

Thanks again.

[Pointy]

Originally Posted by K3vX

I see.

I'm trying to make a part list myself. That includes ordering the screws and nuts from Digikey itself.

Any reason for using stainless steel over anything else? They are either triple the price or nonexistent.

Also, the motor connectors can be ordered there, too. Like part A27756CT-ND, at 17 cents each.

Thanks again.

Only picked stainless as I really dislike rust etc. Feel it would holdup better. I am sure steel will be fine.

I saw those motor connectors, but the lonex ones I listed are gold plated. Should lower contact resistance.

[lurkingknight]

I got my hands on 4 of nukeduster's nutty fet units... the one that he pumped 2 7.4v 65-130C 2.25A lipos into in parallel and drove 6 gearboxes with.... 2 are going into client guns, a 3rd into a teammates' gun... the 4th... you know about the 4th gun. :P


I'm too lazy to build the units myself... plus I would need an actual solder station, not my crappy princess auto iron... and non shakey hands and better eyesight.

Originally Posted by K3vX

Thanks for this You're doing all the work, and I profit haha.

On a serious note, any reason you use Yageo Resistor over anything else?

I'll add a few notes on your design :P

- It is a TVS Diode, not a TSV
- People at AirsoftMechanics are saying that you should add the TVS diode (5KP18A) for maximum reliability, but that it should not fail if it isn't present. A couple of folks there are selling their own FET based on the exact design we are discussing, and they all use it for that reason.

Still, 10$! I'll probably order the stock to make more than one, so even less per unit.



Useful resources:

Making guide, some things are missing but it still helps to visualize the whole thing: http://ncairsoft.org/forum/showthrea...building-guide

On this image, you would add the TVS diode to the left, between the Source leg and the Drain



Wiring guide for dummies like me :

[ccyg8774]

I damaged 2 of the MOSFET when I was trying to solder them. It requires quick and nice soldering (if you trys to solder rather than bolt on), which is hard to do with my crappy soldering iron...

The sadder thing is, I destoried the 3rd one when I was heatguning the heat shrink...

[ccyg8774]

Originally Posted by K3vX

- People at AirsoftMechanics are saying that you should add the TVS diode (5KP18A) for maximum reliability, but that it should not fail if it isn't present. A couple of folks there are selling their own FET based on the exact design we are discussing, and they all use it for that reason.

I thought the diode is there to protect the MOSFET from the reverse voltage spikes as the powering stops.
We may not need something that big (or we may... I am not that sure), but I think a diode is required.

[K3vX]

Originally Posted by lurkingknight

I got my hands on 4 of nukeduster's nutty fet units... the one that he pumped 2 7.4v 65-130C 2.25A lipos into in parallel and drove 6 gearboxes with.... 2 are going into client guns, a 3rd into a teammates' gun... the 4th... you know about the 4th gun. :P

I'm too lazy to build the units myself... plus I would need an actual solder station, not my crappy princess auto iron... and non shakey hands and better eyesight.

Nuke's FET are awesome, and I planned on ordering some. I just love to DIY stuff, that's why I planned to make them myself.

Maybe I'll give up the DIY and order them, just for the sake of simplicity.

Originally Posted by ccyg8774

I thought the diode is there to protect the MOSFET from the reverse voltage spikes as the powering stops.
We may not need something that big (or we may... I am not that sure), but I think a diode is required.

Exactly, when the power stops, the motor turns into a generator and sends current back to the FET where it shouldn't, which means that the FET is damaged cumulatively each time you release the trigger. There is a small diode in the FET itself that prevent some damage, but the external diode is still require, especially for semi-auto spam.

That's why I said it was for extra reliability, because a FET *can* survive without it. Doesn't mean it *will*.

I would keep the one suggested, only because I don't know what else to choose, and being overkill never hurts.

[Pointy]

For the most protection I would suggest using both D1 and D2.

[K3vX]

So, have you got around to do it?

[Pointy]

Originally Posted by K3vX

So, have you got around to do it?

In my haste to build and get my gun back I completely forgot to take any pictures on the assembly!!!

Some items of note - I used a rivet instead of a bolt to attach the MOSFET to the heatsink.

Also, only used the Assmann WSW Components V7236A1 heatsink, the other one doesnt seem like it would work as well.

Installed D2 only.

Prior to heatsinking I covered all the exposed connectors with epoxy glue; to make sure nothing moves/shorts