Airsoft Canada - m249 fuse by-pass

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m249 fuse by-pass

Hey, so I just got my hands on an A&K M249. Before I begin rewiring it to Deans I was wondering if it is advised to leave the fuse in or bypass it. It's mostly going to be shooting bursts but if I ever want to drop the rain of fire I'm wondering what your opinions are. Thanks!

Go ahead and bypass it. As long as you dont hold the trigger down if you get a gearbox jam, there's no harm in it.

Thanks for the quick response.

If you are going to switcht to Deans, I suggest rewiring with low resistence wire as well. Seems to be one of the main upgrades everyone suggests for the A&K.

Quote:

Originally Posted by Chotto (Post 1850879)

If you are going to switcht to Deans, I suggest rewiring with low resistence wire as well. Seems to be one of the main upgrades everyone suggests for the A&K.

The wire is not the "low resistance" part, it's the trigger.

And it's not even worth the difference in resistance. You mostly get a thicker trigger contact, so the material does not overheat as fast and burn a hole through as fast.

The only permanent upgrade to the trigger system is a MOSFET.

^ what he said
Upgrading the wiring harness without a mosfet on the PGC mechbox just puts more current through the microswitch making it more prone to melting.

Using MOSFET is a little tricky on guns using micro-switch. (But those guns need MOSFET the most as the micro-switch don't play well with high current.)
The micro switch will bouncing due to viberation, which will cause a lot of problems if using a MOSFET with active breaking (obviously by causing unnecessary active breaking), and some problem if using a MOSFET without active breaking. (not so obvious)

Quote:

Originally Posted by Kos-Mos (Post 1844526)

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).

The solution I used was replacing to the no bouncing microswitch in this study: http://extreme-fire.com/Micro-Switch-Bounce.pdf
Haven't do that on my Mk43 yet, but did that on an Ares G36C (also using microswitch) and it now works like a dream.

The solution I used was buy a GOOD M249 that uses a V2 mechbox lol

Quote:

Originally Posted by ThunderCactus (Post 1850996)

The solution I used was buy a GOOD M249 that uses a V2 mechbox lol

Well, some times you got to go with what you have LOL

Thinking about it, maybe a simple 0.1uF capacitor on the trigger would be enough to remove all bad effects of the switch bounce. Maybe even smaller cap if it delays the cut too much...

Remove gearbox, install polarstar, problem solved!