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Pete360

Mosfet on Army Armament R31 (Sa80)

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Hi, I’ve fitted a mosfet onto my AA R31 and it works great if I connect the battery directly into the mosfet itself but when I connect it to the extension wire that connects the top part of the gun to the bottom nothing happens? I’ve checked all the connections and wiring and it all seems ok? The trigger relay is standard and I don’t use Lipo batteries. Any ideas on how to sort this would be very appreciated.

 

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hi Pete the trigger contact on the M fet is just a loop circuit .check continuity between top & lower parts of the gun & both side's of the trigger .the trigger circuit should only be complete with the trigger is pulled.the noob mistake is to solder the wires to only one side of the trigger switch.we have all done it doh.hope you get it sorted.

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Hi Mr Gold, 

Thanks for your advice.  I’ve soldered the wires onto the two connections on the left hand side of the trigger connection.  The gun works on single and auto fire with the battery connected direct into the mosfet, I think this confirms correct wiring downstream of the mosfet itself.  I think it boils down to resistance on the wiring and mosfet itself.  I’m looking at trying a lipo battery! What are your thoughts on this? I don’t want to because it means spending money on something I don’t use. Your thoughts would be most appreciated. Thanks mate.

Pete

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I believe so mate, the gun cycles when I fit the battery directly onto the mosfet.  The problem only happens when I put the two parts of the gun back together by using the small length of wiring that enables this? I’ve checked all the wiring and connections with a multi meter and there fine? It’s got me baffled? I do think it’s down to resistance on the wire and mosfet. I’m yet to try a lipo yet.  Thanks for your interest, much appreciated.

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measure the rsistance on the link wire (in the top part) look at the resistance on the black wire, then see what it is on the red wire ( unplug the wire and probe each end of the wires), with the little fuse holder in, see if there's a difference. if your Mosfet has current protection built in at may be possible to run without the fuse (rewire with no fuse holder) if thats looking ok, try checking across the plug where the two wiring section join (connect the plug and probe into the back of both plugs) to see if ther'es a problem there if there is, rewire with deans connectors.

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I’ve fitted deans connectors and removed the fuze because there is protection on the mosfet. I’ve also fitted larger thickness wire to assist with current flow. I’ve tried different batteries apart from lipo and like I say mate it works if I connect the battery direct to the mosfet.  It’s a strange one! Thanks

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the mosfet must go direct on the battery so the mosfet sees full voltage or it will shut down make a foot long 2 wire extension from the mosfet to the gun so it works remove the upper loom and rout the wires and mosfet and battery to where you want to store them in the gun

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I’ve got the gun working by doing what you have suggested. I got there by trial and error in the end.  Thank you very much for your reply, it is much appreciated.

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