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AB MOSFET UPDATE

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It has been a while since I created the mosfet build guide. So here is a useful kind of update.

 

They way I created the AB mosfets was half assed. Here is a better way,....

Step one...

Build your gearbox and lay out your wiring before you build the mosfet. This way will help the measuring process since all you have to do is find a suitable spot and clip the Negative wire. It should be the only wire that needs to be cut...

IMG_1713.jpg

 

Solder the two heatsinks together. A small amount of flux may help you do this along with chopping down the heatsinks. That way the iron can heat up the immidiate area sooner and avoid heatsoak which will cause you to leave the iron on the fet longer than needed and likely damaging it.

IMG_1702.jpg

 

Now you can remove the drain pins...

IMG_1707.jpg

 

I still bend the P-channel gate pin over to the N-channel gate pin...

IMG_1708.jpg

 

I use panasonic .25(1/4) watt carbon film resistors because they are cheap, good quality and SmaLL!!

IMG_1710.jpg

 

Now I use wire cutters to cut an angle into the P-channel heatsink. This is where the Negative wire will now connect and go to the motor...

IMG_1712.jpg

 

Here you can see I attached the motor side Negative wire...

IMG_1714.jpg

 

instead of cutting the Positive wire, I cut the insulation only, add some solder, and add the gate wire/P-channel mosfet connections...

IMG_1715.jpg

 

Don't shrink down any of the heat shrink tubing until you have tested the Fet.

IMG_1722.jpg

 

That's it!

 

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Guest Gcommando36

Nice guide. I'm currently thinking of making a MOSFET. Is it possible to add an integrated poly fuse underneath the heat shrink?

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Thanks for the update! I found your original guide really helpfull!!

 

I have a few question:

 

whats the main difference between both ways?

Does this one does not get as hot?

how exactly is the propper way to solder the mosfets together?

And how are the resistor put on, do I still us the 33k and 100 ohm ones?

How are the trigger contacts laid out now?

Could you make a paint diagram of the laid out??

 

 

 

Thanks!!

Edited by Mindcrime

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BTW, for a g36c, instead of soldering them on top of each other its easier to attach them long ways and sneak it under the hop up.

Just something from experience but great guide Golgo :)

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Heh, did you get the idea for such a compact lil :censored2: from my MP7's design? Just teasing, very nicely thought out and done! Keep up the great work mate!

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I find it best to shape mosfets to fit into many guns than to just use regular mosfet setups.

 

An easy way to get the flux to stick onto the heat sink is to rough it up a bit with some 320 grit sandpaper before applying the flux.

 

Here's a pic of the mosfet used in my PDW, still a WIP.

 

P1011089.jpg

 

Here's a picture of a semi-done PDW mosfet being made for a friend.

 

The heat sink and the P and N channel drain terminals are soldered together, I don't mind the redundancy as it gives less resistance though it's probably unnoticable.

 

P1011090.jpg

 

Awesome, thanks!

 

Is it nesesary to solder the back of the fets? Can I add termal paste and just solder the top Motor negative one on both?

 

It would be best to solder them together, thermnal paste isn't the ideal medium for electrical conductivity.

Edited by Suzaku

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While we're talkin' shop here, I might as well ask. For my MOSFET design I reinforced and insulated the exposed terminals (due to the very tight clearances I had with my particular MOSFET) with Hot Glue, it works so far. But I am worried that prolonged use will simply melt the glue again and defeat the purpose of sealing up the circuits. Guys, I would love to hear your input on this since you have built far more MOSFETs designs than the MP7 one I made.

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Guest OpSic66
While we're talkin' shop here, I might as well ask. For my MOSFET design I reinforced and insulated the exposed terminals (due to the very tight clearances I had with my particular MOSFET) with Hot Glue, it works so far. But I am worried that prolonged use will simply melt the glue again and defeat the purpose of sealing up the circuits. Guys, I would love to hear your input on this since you have built far more MOSFETs designs than the MP7 one I made.

 

Yeah Hot Glue is a BAD idea. Once you heat it enough to melt it, it WILL conduct electricity. I'd use Epoxy if you want to reinforce the build after your done.

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Yeah Hot Glue is a BAD idea. Once you heat it enough to melt it, it WILL conduct electricity. I'd use Epoxy if you want to reinforce the build after your done.

 

How does it conduct electricity? Interesting to know though.

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Guest OpSic66
How does it conduct electricity? Interesting to know though.

 

Most liquids can conduct electricity. Hot glue when solid won't be conductive (very high to infinite ohm rating), but when liquid has a low ohm rating to it, and will conduct.

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MOSFETs suck! I am trying to build one too but its soo confusing...WHat happened to that single N channel MOSFET you made in your original guide? I wanted to follow those steps cause it seemed easier but it seems like the N and P channel is the one everyone uses...Don't really understand the difference, aside from u saying earlier the latter one stops the motor differently or something and doesn't leave the spring compressed?

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the N channel only is a regular mosfet without auto breaking, this means that the mosfet is only use as a trigger switch, and when you let go the trigger the motor will not stop immediately thus pulling the piston back halfway cuz of the overspin. when you add a P channel mosfet to the N channel one you have auto breaking, this means that as soon as you let the trigger off it shoots a opposite current to the motor to stop it instantaneously preventing the overspin of the motor,

 

hey golgo, can you post off some paint schematic?

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Is it possible to wire the activation switch of an A&K Electric Box Mag to the wiring harness? I want to eliminate the need to press a switch to activate the reload and just have the A&K reload activated when the trigger is pulled. Planning to install a mosfet this weekend and was just wondering if I could splice the A&K switch into the existing wiring.

 

Thanks.

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Most liquids can conduct electricity. Hot glue when solid won't be conductive (very high to infinite ohm rating), but when liquid has a low ohm rating to it, and will conduct.

 

I've ran my own test on hot glue heated up to 800 degrees Fahrenheit

The hot glue didn't conduct any energy at less than a quarter of a millimeter of a distance in between the probes so unless you have proof otherwise hot glue doesn't conduct electricity.

Hot glue is widely used in PCB boards and waterproofing electronics for RC boats and Cars. I'm sure it does not conduct electricity when melted or solid.

 

Golgo, have you ran any tests on melted hot glue conducting electricity?

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Guest OpSic66
I've ran my own test on hot glue heated up to 800 degrees Fahrenheit

The hot glue didn't conduct any energy at less than a quarter of a millimeter of a distance in between the probes so unless you have proof otherwise hot glue doesn't conduct electricity.

Hot glue is widely used in PCB boards and waterproofing electronics for RC boats and Cars. I'm sure it does not conduct electricity when melted or solid.

 

Golgo, have you ran any tests on melted hot glue conducting electricity?

 

I'll see if I can track down the black hot glue I used that was supposedly for automotive use, that melted and conducted in the rig I built.

 

 

 

Is it possible to wire the activation switch of an A&K Electric Box Mag to the wiring harness? I want to eliminate the need to press a switch to activate the reload and just have the A&K reload activated when the trigger is pulled. Planning to install a mosfet this weekend and was just wondering if I could splice the A&K switch into the existing wiring.

 

Thanks.

 

Unless your planning on adding a relay or electrically isolated mosfet inside your box mag. No there is no "quick" way to wire into the mosfet to control you box mag.

 

You could however completely remove the switch assembly in the box mag and wire into the mosfet's lead going from the battery in the gun, to the motor in the gun. The box mag will then wind when ever you pull the trigger.

Edited by OpSic66

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I'll see if I can track down the black hot glue I used that was supposedly for automotive use, that melted and conducted in the rig I built.

 

 

 

 

 

Unless your planning on adding a relay or electrically isolated mosfet inside your box mag. No there is no "quick" way to wire into the mosfet to control you box mag.

 

You could however completely remove the switch assembly in the box mag and wire into the mosfet's lead going from the battery in the gun, to the motor in the gun. The box mag will then wind when ever you pull the trigger.

 

Thank you musch! Will just install the MOSFET wiring into the gun and leave the box activation switch alone. Thanks!

 

 

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In compare to P-N transistors design.

U a quit clever guys, BUT u forgot about easiest solving: DIODE. I use a powerful 3A 50V diode connected against usual +/- on the motor. U can also solder it to your MOSFET. Just remember that you need to solder it so, that it shorter motor from - to +. In that case u have "soft" AB. Self inducting voltage on motor will be dumped in diode and motor stops without producing a lot of "back-stroke" on gears.

And also don't forget about "low voltage" on motor start, in that case we(russians) adding a capacitor in GS wire and charging diode which hold voltage on capacitor. In that case you always have enough voltage to get your MOSFET into key-zone and prevent "half-opening" which leads to heat.

Have a nice day.

yeh, all these things get PSB or "wire-design" a little bit bigger, Harder to fing enough place. But you can solve it by putting components in-between wires without PCB.

Edited by Levande

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In compare to P-N transistors design.

U a quit clever guys, BUT u forgot about easiest solving: DIODE. I use a powerful 3A 50V diode connected against usual +/- on the motor. U can also solder it to your MOSFET. Just remember that you need to solder it so, that it shorter motor from - to +. In that case u have "soft" AB. Self inducting voltage on motor will be dumped in diode and motor stops without producing a lot of "back-stroke" on gears.

And also don't forget about "low voltage" on motor start, in that case we(russians) adding a capacitor in GS wire and charging diode which hold voltage on capacitor. In that case you always have enough voltage to get your MOSFET into key-zone and prevent "half-opening" which leads to heat.

Have a nice day.

yeh, all these things get PSB or "wire-design" a little bit bigger, Harder to fing enough place. But you can solve it by putting components in-between wires without PCB.

 

 

Could you post a diagram and a few more details about tihs Levande?

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Guest OpSic66

Placing a diode on the motor OR mosfet, may nearly eliminate the "active braking" depending upon the specs of the diode. As for the Capacitor, many of us are already doing that as well. If you read the entire thread you would have seen the link that I listed: http://www.airsoftforum.com/board/Wiring-G...l#entry17804505 The info is already there. This mosfet build on this page is merely an update.

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Even it does not work as break(as u sad) I have my MOSFET in "safe zone" without over-voltage at motor breakdown because of shortening diod at motor +/-. I have no wish to argue about all this stuff. It's wprking at my AEG.. and thats what I need.

 

Can u give a direct-link to ur layout with gate capacitor? I have finded just "battery capacitors"

 

 

I use a 330mF 50V 268517.jpg

Edited by Levande

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Such a crappy guide...

 

I presume the two black wires in the first pic are coming from the trigger. Do we connect those two to the both sides of the trigger?

Next question, to which pins do we connect the resistors?

You also fail to explain what the gate wires are and where do we connect them. The same goes for the other part of the negative lead.

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You also fail to explain what the gate wires are and where do we connect them. The same goes for the other part of the negative lead.

And you failed to do sufficient research. Had you done so, you would have realized that this guide is obsolete and that the back to back design for the AB MOSFET is dangerous.

 

Also, had you been a little more aware, you would have noticed that this thread is from 2010...you revived a dead thread for no good reason.

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