7 replies to this topic

[SirBrass]

I have rewired my rs.

Edit: See below for full write up & detailed information of the problem.

Edited by SirBrass, 27 February 2017 - 08:57 PM.

[Rivenwolf]

What seems to be the problem?

[SirBrass]

Sorry for the post screw up. Phone b0rked while posting.

So, 3 blade 180 motors with 16 awg wire, 2s lipo, mosfet on the flywheel circuit. Wired according to the bsuk circuit diagram & using the bsuk kit. Artifact red cage, worker flywheels. Rectifier diode correctly placed.

I tested the circuit with c-cell alkalines first & everything was fine, and fine with the lipo too until a few seconds into shooting bursts from a mag of darts. Motors go out of control, but only the flywheel motors. Pusher is fully in control.

I think it's the mosfet but I have no idea why.

Help?

EDIT!

Okay, more info, the mech switch & negative from pusher are on the mosfet source line that runs from battery negative. When I test just flywheels with alkalines & lipo, everything is fine. When I tested trigger & flywheels (pusher won't go without flywheels going) on alkalines, everything is fine.

BUT, AS SOON as I test pusher with lipo, that's when the mosfet fails (no outward sign of failure on the mosfet, ie no smoke or device getting hot) & the flywheel motors go nuts.

I think somehow back emf from the pusher is somehow leaking into the mosfet. Looked at my wiring & the circuit diagram and I'm stumped as to how though.

Edited by SirBrass, 24 February 2017 - 02:05 PM.

[Rivenwolf]

Welp! At the sight of "mosfet" I scree and shrink back into the shadows. Not familiar with those.

[NerfGeek416]

Why use MOSFET? A single stage build, even with 180s, is perfectly acceptable to run on standard microswitches.

I have a triple hellcat build that's been running great for like 7 months on 15A switches with no issue. You could go to 21A switches, and still not have to deal with MOSFETs.

[SirBrass]

Why mosfet is due to "best practices" concept especially with 10A microswitches. It's just a good idea when 3 motors in parallel will each pull 22A at stall if on hellcats. The acceleration switch will take the most, handling the current from parallel wired motors, so 44A at stall. The pusher switch is better off and will be just fine without a mosfet, but it's just good sense not to abuse the acceleration switch like that even if using a bulky 21A switch.

[NerfGeek416]

Those are burst currents, and are only seen for a 1/10s max. The switches can easily handle that.

[SirBrass]

That's why I said "best practices". It's a design safety reinforcement. Also, easier to replace a blown mosfet than to pull out a cemented down blown switch.