cool idea, hope that works for you. be sure to update
is this the switch circuit you have? https://endless-sphere.com/forums/viewtopic.php?f=3&t=40142&start=100
maybe @blasto might be able to answer the question about the diode for redirecting current around fets.
That was the main obstacle in my build but i think i found a way to protect the batteries and to maintain the board flexibility at the same time, i don’t now it yet if my solution will work but i’m confident it will
Something similiar, I used it in my boosted build and it works really well there, had not had any issues with it. Here is the scheme of the circuit I used. It pretty much works for any N-channel mosfet, and this part of it is the only limitation. The other advantage of this circuit is that once latched state is sustained even if the switch connectors are not latched, so this circuit may use 2 momentary switches, one for turning it on, one for turning it off, or one latching with NO/NC/C connectors.
I don’t have any better ideas for now how to solve this issue except this solution with diode as a shunt to bypass mosfet if the current goes the other way than normally, seems logical to me components should arrive today.
@squad The diode inside the body of your fet should be fine, it could handle up to 200A. Having an external one won’t hurt, but i’m not sure if it would be useful.
Do you have a zener diode on the gate of your fet? if you are putting the battery voltage exceeding 30V on the gate, this could blow the fet after some time.
@blasto Yup, there is zener diode in the circuit, as seen on the scheme 10V one. Then if the internal diode of the mosfet should handle current from the regen breaking, I’m starting to wonder, why would this fet blow up? I was testing driving direction change with nunchuck, and changing direction of motor rotation when the board was still rolling in the opposite one, in that exact moment it blew up… As You can see the terminals that blew up were both source, not the gate.
That fet only has around 500 watts of dissipation. Believe it or not, we use between 1000 to 1500 watts when accelerating hard.
@chaka Yup I know that, but the power it has to dissipate is the consequence of its internal resistance, which is 6 mili ohms, not so much, so this fet shouldn’t even get hot. Surface mounted fets usually have less power dissipation like 300-400W. I mean that if the mosfet would have to dissipate this 500W it would mean 500W power loss in the circuit.
Wonder if a overvoltage cause this failure, especially during a direction change. I know i blew a fair amount of vescs during a direction change, had to brake first then change the direction. Not sure if the vesc is emplemented this way (well i know it’s not when controlled by ppm)
The fet you got is obsolete (check the datasheet, not for new designs). Could opt for the 100v version http://www.digikey.com/product-detail/en/ixys/IXFN360N10T/IXFN360N10T-ND/2116933
@blasto Then I hope I did not blew the VESCs also, did not have a chance to check whether ther work or not yet… They do not seem to be damaged, at least nothing got burned on them.
Fu** One of the VESCs is down, one of traces between mosfets evaporated and one near the shunt also. Will have to order new one from @chaka.
Same thing happened to @siggs3000. I can probably fix it but you are welcome to purchase a fresh unit too I think a direct short is what caused this failure on siggs but I was able to bridge the burnt traces with some sheet copper and change out the drv chip and it was good as new.
@blasto It seems like the VESC failed due to direction change, and this failure caused mosfet to blow up. Dammit!
Man that sucks, mind posting pictures of the vesc damage?
I already packed it in the envelope to send it to chaka, maybe he’ll snap pic. Traces on board simply evaporated, first place is between mosfet source and shunt, near P4 pad. Second one between two mosfets drains, on the opposite side of the board. Ordered 2 new ones, and hope to get this one fixed, I’ll probably install it in my longboard.
that’s crazy… i don’t think i have heard of that before…
i never have reverse activated though…
Update: I’m still waiting for 2 new VESCs from chaka, (the one damaged will be repaired by him) in the meantime I decided to solve the problem of scratched support brace, I designed new one and milled it out of 12mm thick 7075 aluminium. It just needs to get anodized New one has 2 casters on bearings, it acts as wheelie-bar in drag racing
that is so cool! i love seeing new ideas.
IT’S ALLIIIIVEEEEEE! Received VESCs from @chaka yesterday. Today I made myself one of the best birthday gifts ever Trampa is up and running again!
that is awesome!!! i love the wheelie bar… can’t wait to get mine built…