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Max amps on the GUI

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im.val
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Joined: 2017-09-24 16:54
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Max amps on the GUI

Hi guys,

I've been using a VESC 4.12 for my eBike since two years now and upgraded recently to the new firmware and the new gui.
I also swiched to a more powerfull motor, so I tried to ramp up the current step by step to see the capabilities.

The VESC 4.2 should be able to handle 240A continuous, from the IRFS7530 datasheet (with proper cooling, I know). Currently it's configured at 100A and is doing pretty good, not warming up too bad as I have a fan forcing fresh air in the case and temp monitoring.

I'd like to raise the motor amps limit to something like 150-180 amps to get a starting boost but the GUI is not allowing me to push the max motor current above 100A.
I understand the issue with sine waves and peak current, square root and stuff. So 169 amps should be the maximum for a 240 A peak max.

I can modify the code in the GUI and eventually the firmware but I thought that if the GUI is limiting it's for a good reason. Do you know why ?

Hoping you'll be able to provide an answer,

Best regards,
Valentin

TheFallen
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Last seen: 2 weeks 2 days ago
VESC FreeVESC Original
Joined: 2017-09-11 11:46
Posts: 222

MOSFETs typically cannot reach their rated current without liquid nitrogen and 2kg of solid copper heatsinks, and even then for short durations only. It is typical to de-rate the MOSFETs by 50% for normal use, in this instance the 240Amps of the IRFS7530 would be reduced to 120Amps. Of course this still requires thick copper tracks to deal with the high currents and good MOSFET cooling, neither of which the VESC v4.12 hardware has.

The other constraint to current limiting is the current sense. There are 0.001Ohm shunts, with a gain of 10  means that the VESC v4.12 can only measure ±165Amps. This would leave little room for monitoring & controlling the current above ±150Amps.