Regenerative Braking - How does it work?

I am fairly new to the ESK8 community and I am working on building my first board. I have heard many things about regenerative breaking but I can’t figure out how it works or how to incorporate it into a board.

Can anyone help me better understand how regenerative breaking works? I would really love to have it on my board.

Thanks for reading this. I could really use some help.

You set it in the BLDC tool. There is a “battery min (regen)” that is a setting in Amps and you set the maximum Amps that you want your board to charge the battery when you break. You can set it to 0 and pretty much disable it I think but I have never try it so dont take my word for it.

Depends if the ESC supports it. The VESC and all its iterations do. If BEMF voltage generated overcomes battery voltage, current will flow into the pack as you brake. The amount of current is controlled by the Battery Min value on BLDC tool.

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So the voltage created while breaking has to be greater than the present voltage of the battery or it will not regenerate the battery? If there was a way to control the BEMF voltage, then you could prevent regen braking from trying to overcharge the battery. Especially at lower pack voltages like 8s and 6s

I think this would be achievable with a more advanced bms, but I’m no EE. if you could apply bemf voltage toward a lower S count you could theoretically regen at slower speeds as well.

hmm I always wonder this. Let’s say you got two lipo batteries in series with NO BMS and 80% charged. You started from the top of a mountain let’s say. Does going down hill BALANCE charges your battery to 100%? I’m scared to go downhill because I don’t have an bms and I don’t know if it will mess up my battery voltage.

If you’re discharging through BMS it should balance charge if you’re hitting the balance voltage (upper 4.1x volts), but honestly I don’t see it drifting much at all during a single cycle. If it is drifting much, you probably have high resistance in one of the cell groups which indicates an issue with the cell and it should probably be replaced.

If you’re bypassing discharging you won’t be balance charging at all.

So anyone without a BMS trying to go down a long hill should be careful because it doesn’t balance charged is what you’re saying?

As far as I understand the only advantage of discharging through a BMS is the max current safety it provides. If you bypass the discharging, and current runs back to charge the battery pack (regen), the BMS will balance out everything, as long as the charge connection is connected. Am I wrong?

Not at all, I’m saying cells don’t really drift much during a single charge cycle, with or without BMS. You should be fine with the balance, unless something is wrong with a cell/cell group.

@solidgeek BMS’s don’t actively balance the pack as you go, meaning if you hooked up a 2s BMS to two cells, one at 3.8v and one at 4.0v it won’t do anything. Each cell will stay at their respective voltage until you do a full charge on the 2s pack.

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Couple of thins are still unclear to me regarding this.

BMS has a separate charge and discharge port. When VESC pushes back during braking you’re basically using discharge port to “charge”. Not sure how the BMS copes with this? Does it even charge the battery?

Where is the VESC setting that prevents overcharge? Is that Maximum input voltage? Because I’ve heard that it is not good to touch that setting. On the other hand, blasting 57V to 6S pack would not do much good…

The best reason to use a BMS for discharge is it can shut your board down before dropping the voltage too low. Some builders are bypassing and using a simple in rush/controller switch but this can be dangerous for the battery if you get absent minded and continue to ride or forget to turn your board off.

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Does’nt the vesc do the same at the V we set ?

No, it only disables the throttle/limp mode. The power will still be on and the system will continue to draw a small amount of power from the battery.

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What happens if you hit the bat max, during braking down a Hill ? Then the brakes stop working right ?

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Battery and motor min are the attributes for braking, and it depends on your BMS and whether or not your discharging through it. Most BMS’s backoff strategy is simply cut the load which will kill power to your VESC. If you’re bypassing, the VESC doesn’t know what “battery full” means and will simply keep dumping excess current into your battery if it’s full and if your BEMF voltage is higher than the pack voltage.

Let me put my question this way. I plan to use my bestech bms (80a) for both charging and load. Then if i have a fully charged battery , and starting on top of a Hill, and braking the entire time down the Hill, i would under normal circumstances with bypassd bms and voltage max at default 57v (i’m running 10s) going to overcharge my batteries right ? But because i use my bestech as the ‘load’ All so, the BMS would cut of and protect my batteries while i’m still being able to brake right ?

I asked similar questions above but no one answered. First, it is questionable if BMS will even charge because you’re essentially charging through discharge port. BesTech BMS’ have separate charging port.

Will charge but not balance charge.