How does VESC braking work?

It also depends what limits it to 5A. A typical 18650 can charge at 4A per cell. 6p means six parallel cells so you can push up to 24A and each cell still gets only 4A. If the 5A limit is from the BMS and u use it for discharge as well, you can’t put battery min to more than -5A. If the limit is your charging port then you can still push up to 24A back (assuming the BMS allows it, if it’s used for discharge as well).

I run -12A per vesc (so -24A per total) on a 10s4p. Rated value is 4*4 so 16A but taking duty cycle into account I will generate 24A only if I apply full brakes from 100% duty cycle. Since I never do a full brake from top speed, I never actually push 24A back into the pack. And if I do, it’s for a good reason (emergency braking) and it will be a short spike so damage is minimal.

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That makes perfect sense if the voltage in the motor is varied, is that only in duty cycle mode? In current control mode is the motor voltage constant and the current controlled directly.

I did a little testing today and it seems even with max regen locked to 10a, increasing negative max motor current does increase braking. It started raining, Ill have to double check tomorrow, maybe im imaging it.

No, you’re not imagining it. Increasing the minimum motor current improves braking especially at low speed. This is true in all control modes.

Both valid reasons for bypassing the bms for charge only!

I discharge through a bms and ride my brakes downhill on a full battery and get no reset. Watching my voltage while doing so, it appears evident that my bms monitors the regen charge and prevents charging when the battery reaches the overcharge detection voltage which is set at 4.28v I have reached that voltage and continued riding the brakes downhill. My battery voltage would not exceed that limit but held there until I reached the bottom and let off the brakes. At that time the bms proceeded to trim the battery back down to 42v while I was coasting. During this test there was no reset and no overheating. This test was with the Bestech HCX-D223V1 I can’t say if this is the same for other bms’s.

Here is an old thread with info on brake settings.

are there resistors in that bms that are capable of burning off as much energy as youre using going downhill? wondering where the energy is going if not the battery.

It’s my understanding that the vesc can “recirculate” the regenerated power through the windings of the motor and the mosfets of the vesc to allow braking without generating any net power to the battery. The heat is spread between the motor and the fets.

if the battery isn’t connected and you brake its a quick doom, how would it be any different in this situation? How exactly would it “recirculate” if you know? sounds like it would have to be shorting the leads to brake

Pretty much. Controlled shorting of the leads using the fets.

The bms I mentioned has some decent heat sinks on the fets it also has a heat sensor and would shut down if over heated. I wouldn’t recommend braking a mile downhill with a full battery. My test was on a fairy short hill.

Yep confirmed, is seems maximum braking power is independent of maximum battery charging current limit. The excess energy must be wasted as heat like any other form of braking. Higher charge rate batteries are still the best way to go though, for better efficiency and to keep the motors cooler.

Let’s say your settings are -50 A Motor min and -10 A Battery min.

When you do a full brake the VESC will try to achieve 50A brake power because with the remotes trigger you control the motor min value. Which means at half trigger the VESC will try to reach 25A brake power, at 3/4 trigger 32.5 A and at full trigger 50 A.

When you go full speed and brake full immediately then the duty cycle goes down. Because of back EMF which goes in the other direction but that’s to much details. So in reality the duty cycle drops to around 60% in this case.

At 60% 50A at the motor would be 30A (60% of 50A) at the battery. But battery min only allows -10. So the brakes wouldn’t be as strong as the trigger tells the VESC. It will only brake with 16.6A (10 A / 0.6) at the motor.

While you continue braking the wheels becomes slower and the duty cycle quickly drops. So at 40% duty cycle the VESC still want’s to reach 50 A brake power but that would mean 20A at the battery. But 10 A are the maximum so it will only brake with 25A at the motor.

At 20% duty cycle it is possible for the VESC to brake with 50A at the motor.

So it is good to have a high battery min value. I for example set the settings about 50% higher than the max charge of the battery would allow. With 4A max each cell in a 4P setup that would be 16A. But i set it to 24A because i think it doesn’t hurt the cell when you brake hard from time to time. And you reach these high amps only for like 2 or 3 seconds. And i try to brake gently at high speeds during my normal rides but want full brake power if i need it in a emergency scenario.

I think that charging the cells with a power supply at high amps damages the cells much more because it is a constant charge instead of a short pulse. But maybe i am wrong with my theory.

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Hi everyone, do you know how to setup the force of brake via vesc-tool, to make skateboard can stop complete when i push the throttle to maximum? thanks

Increase “motor min regen” its usually at -40 some have it at -60 at most play with those values vesc has a smooth throttle you generally don’t want to stop completely at full break instantly asking for trouble that’s what ESC’s are for if your into that stuff.

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So I have Racerstar motors that has max current is 46A. I have a 10s4p battery made of samsung 30q which has a discharge current of 15A and for a BMS i have a Bestech190 that has a max charge current of 10A. I’m running dual setup So for motor max and min it should be 46 and -46 and for battery min it should be -5?

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Are you bypassing the bms for discharge?

If so… 4p* 20a = 80a/2 ESC… or 60 if you wanna use the 15a rating.

40a bat max per esc

3ah*4p = (12ah * 2c charge)/2esc = -12 bat min.

For simplicity for the motor… Motor max 46 Motor min -46

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Just correcting my comment from a few months ago. I was wrong. All braking is by regen.

The reason for a separate regen current setting and negative battery current settings is to do with braking efficiency at difference speeds. So low c rated batteries will break more poorly at higher speeds, but catch up with high rated batteries at lower braking speeds. The vesc designer guy explained it on his forum a few days ago.

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I guess I would be bypassing the bms for discharging because it is a 10a charging with no discharging. It was from the group buy the TGH did in novemebr

http://www.bestechpower.com/37v10spcmbmspcbforli-ionli-polymerbatterypack/PCM-D190.html

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Thank you very much all of your help, I am trying it. thanks so much.