Conservation of energy… The energy needs to go somewhere. Either into heat, using a strong electric heater attached under your board, or you shift the energy towards your battery. It needs to go somewhere. If one value is lower than the other, the software uses the lower of both values to protect your system. You can’t evaporate energy into the universe. Conservation of energy…
It’s the same for acceleration. If you only allow 8amps from the battery, increasing your motor max to 100A will not increase the boards absolute performance. The lower value defines your max output power, since we can’t suck energy from the universe.
Sure would. This whole regenerative braking is always creating more questions than answers.
I actually thought the difference would be dissipated ‘somewhere’ in the VESC and not the motor. But who can tell for sure? Maybe it’s time to ask the questions about it on vesc-project.com forum?
The VESC converts the voltage of the battery to the right amount of voltage for the motor. This is the duty cycle.
So when the vesc works at 10% duty cycle then the motor runs at 10% of the batterys voltage. At the same time the battery only has to provide 10% of the motors current.
10% duty cycle
Battery 40V 4A
Motor 4V 40A
At 90% duty cycle the motor runs at 90% of the batterys voltage and the battery only has to provide 90% of the motor current.
90% duty cycle
Battery 40V 36A
Motor 36V 40A
Now braking works exactly the same. Only the power is going in the other direction but the duty cycle and ratios behave the same.
So when you do a full brake and the duty cycle is at 50% and the motor min is set to -70A and battery min to -10A then battery min sets the limit.
50% duty cycle
Battery 40V 35A
Motor 20V 70A
So in this case you would exceed the limit of -10A amps by far. So the VESC reduces the brake power to -10A at the battery which results at 50% duty cylce to -20A at the motor.
And when the speed goes down the duty cycle becomes lower and so the ratio changes and the VESC is allowed to use more and more amps at the motor side for braking.
So the maximum brake power is allowed at duty cycles below 14A (10A / 70A).
So the higher you set your battery min the stronger the brakes will be at high speeds.
Thanks for the explanation! So basically, if I got it correctly, Motor Min is like brake force parameter that will be adjusted according to the Battery Min and the duty cycle. There is no difference that should be dissipated.
Do you happen to be able to know or explain the voltage VESC puts back at the battery while braking (or how does that work)? It is not a set parameter as far as I can tell…
If your in FOC and hear ticking and are expecting a fault. Your running the motor at the wring Hz. Change to something else. (I think 20000hz is default) go higher.
Second calculating voltage for what comes in is easy. RPM/kv = V
However…amps will turn into volts if there’s no path for the current and can cause over voltage.
Just wanted to report in, my 6374, TB vesc, on 12sp4 battery is running good on FOC, however like others have said brakes are a bit weak, but not terrible. I also found that after climbing a pretty steep hill 25% grade thats decently long the brakes and throttle are fairly anemic for a short time, but return after about 30 seconds.
That is very likely. Your temp soft cuttoff is preventing that you overheat your system any further. Basically you surpassed the limits of your hardware and its time for an upgrade of components, or ride less steep hills. After 30 seconds the temp reaches acceptable values again and your brakes/power come back back to life. At this point you are close to reaching critical values again, so don’t attack a hill (riding downhill) because your brakes could fail again and you have no redundant brake system to compensate the loss of your motor brake. This is why I suggest to use disc brakes in addition (on MTBs it’s possible) when riding in hilly areas.
Okay good to know! I thought I had pretty good components already. TB 6374 Motor, TB VESC and TB 12s4p battery. Which components would you consider an upgrade? The board is street only, not a MTB, so disc brakes dont really seem to be an option or something I really want. My area definitely isn’t as hilly as say San Fransisco or anything like that. Thanks in advance!
I think for my next build I’ll go dual 6355 190kv. This motor is 190kv but I do beat on it pretty hard. In the interim I’ll try and add a heat sink or maybe even a small fan to the enclosure and see if that helps. Thanks for the replies!
So i guess the weather brakes issue has been addressed, but does anyone know why i get over current faults on high load? Mainly happens when i accelerate too quickly. Today one of my motors also cutout and was in perma brake mode, but resolved itself after a restart. Is this a sign of a burnt drv?
Okay so I switched back to FOC and also made some current changes to my setup and it seems to have helped somewhat with my vesc overheating issue when going up hills. I also played with the throttle/brake curve a bit and that also seems to have given me a little more brake at speed. Having adjusted the expo brake curve has made the brakes a bit more responsive when I’m at speed while decreasing the amount of brake I have while going slower. It’s still not great but it does feel better. Here are some screen shots for reference.
