# diy dc motor controller



## Isaac97 (Jun 3, 2019)

Looks good! Wisdom says isolation good, high voltage leaks bad.
Is current limiting the next step?


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## arklan (Dec 10, 2012)

current limiting is the next step.
i want to have it current limited to eg; 300amps by reducing the duty cycle on the mosfets.
if it goes above 300amps for a few seconds then it cuts the contactor off.
it will also sound a buzzer when its above the 300amp limit so u know and u can back off a little.
this should make the fuse redundant and i dont know of any controllers that have anything like this.
it should throttle back with the temperature of the mosfets too.

after current control it will be stuff to do with turning the key on while ur foot is on the accel pedal and driving off with the charger plugged in.


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## remy_martian (Feb 4, 2019)

So only one of the MOSFETs is blocked by the contactor? Seems reckless.


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## arklan (Dec 10, 2012)

not sure where you got the idea about 1 mosfet being blocked by contactor D:
i got a metre of 8mm x 20mm copper bar and measured where i wanted the mosfets and caps to be soldered to it.
unfortunately i snapped a drill bit for every 3 holes drilled.
then i tried to put some solder in to the little holes that were drilled by unfortunately the soldering iron wasn't up to the job to make the solder stick to the copper.
so i then heated the copper with the butane torch from underneath and put solder on top to tin the holes and surrounding areas.
then i thought the soldering iron would be enough to attach the mosfets to the copper and nope, the copper once again absorbed and dissipated all the heat away.
i didnt want to kill the mosfets with the torch so i attached the mosfet to the heatsink i have for this with a screw, then used a mosfet that i dont care about to test.
i tinned the mosfet pin first with the soldering iron, then went to the shed and torched the copper so that solder would turn to liquid, then pressed the mosfet on and added a bit more solder. i was holding my thumb over the mosfet while pressing it on with the heatsink and it actually never got hot enough that i had to take my thumb away.
after that i brought the whole thing back inside and connected it all up to the scope to check that the mosfet is still working and as you can see from the picture, it does.
so i can safely torch all the mosfets on to the copper without killing anything.

the problem is going to be how do i do this with the caps? they dont have a heatsink and their pins are half as long, ill have to come up with something.
still trying to figure out how im going to read the current.


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## arklan (Dec 10, 2012)

i have the source and drain pins bent up pointing forwards and backwards so the source pin folds up under the heatsink. first i attached all the mosfets backwards on to the heatsink so that they dont get cooked when i heat the pins with the torch to solder. then i connected them one at a time to make sure none died during the soldering process and they were all good.
then i took the heat sink off and put it on the other side (correct side) so now the heatsink sits on top of that first copper bar. then i soldered the other copper bar on to the other pins, leaving a gap between the copper bars of about 6mm for the gate pins to fit through.

i also learned how to measure dc current with a linear hall sensor and a toroid, so ill be using that to limit the current.
now i have to think what to do if 1 mosfet blows without taking out the rest, its too late to put a fuse on each one now.


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