JackTerminus wrote: ↑Tue Feb 27, 2024 1:42 amwait... is there a video of damien using the dc board??
Bench test, not vehicle test. But yes.
also nick's website appears to be offline now sad.......
Oh what a shame.
Archive.org has it, but no pics. I'll repost text. Has some character/translation issues from the spanish keyboard settings but it's readable:
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"I thought it was unkillable. Â It's got builtin overcurrent protection, It survived all the “R&D” that created derpbike, and it was pressed into duty as a welder without ever quitting.
but I seem to have found a weakness. Â I was driving around the yard and lost all power while accelerating. Â A reboot didn't help. Â I figured a phase was shot, so I swapped the motor wire from V to W, updated the firmware, and limped back to the base.
I measured all of the resistances and flyback diode drops of the six IGBTs in the motor side inverter. Â Here's what I found:
DSC_9930
The multimeter revealed that the low side switch on the V leg failed short. Â Unfortunately, that reduced the functionality of that leg to either doing nothing, or shorting the bus.
well 2 should be better than 1, right?  In a gruesome surgery, I amputated the dead leg and spliced the remaining two together.
IMG_1761
but wait a minute. Â why did that leg die without tripping overcurrent protection, and how will I not do the same thing again?
here's what I think is going on:
2 states
The half bridge has two states. Â In state 1, the motor is connected across B+ and B- through the top switch. Â Current flow through the motor is increasing. Â di/dt is positive. Â In state 2, the motor is disconnected from B+ and current flow decreases, recirculating through the flyback diode of the low side switch. Â di/dt is negative.
At 50% duty cycle, motor current over time probably looks something like this:
motorcurrent50
At 20% duty cycle, it may look more like this:
motorcurrent20
Because the old brushed motor in this truck never really wants more than about 120VDC, the duty cycle never goes higher than about 30%.  The half bridge always spends more time in state 2 than it does in state 1.  Given a duty cycle of 20%, the low side switch will be conducting 4x longer than the high side switch over a single switching cycle.  Operating at such a low duty cycle puts disproportionate thermal stress on the low side switch.
The half bridges of the Prius inverter were not designed for prolonged operation at constant extreme duty cycle.  The electric motor/generators in a Prius are three phase permanent magnet synchronous machines (PMSM).  The only time you have this killer condition is when the motor is stalled.  Any time it is rotating, the six switches share the load evenly.  Even when the brushed DC motor in DerpTruck is rotating, the majority of the thermal load is still on that low side flyback diode.
with these findings, I reconfigured the remaining two legs as an H-bridge.
IMG_1846
Now, both PWMs are centered at 50%. Â To make the motor spin, the duty cycles are drawn apart to put a voltage across the motor. Â This spreads load more evenly between the upper and lower switches. Â The code looks like this:"
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I don't know for sure what Damien's design had, but someone pointed me to Nick's page when discussing why Damien's might not work. Maybe it was earlier in this thread, I'm not sure.
