# Is regenerative breaking bad for battery?

Hi i have a 18650 pack made from 50x LG HE4 cells. Each cell has a max charge current of “fast charge” 4A.

My question is what is my max regenerative charging power in the BLDC tool.

is it

4A * 10 = 40A

or is it

4.2V * 4A = 16.8W * 50 = 840W / 42V = 20A ?

I think on paper it would be 20a with 5 cells in parallel with each of them stated as good for 4 amp charge rate, but is that charge rate similar to discharge and we could consider a peak or continuous? I bet, and think it’s probably all related to how much heat is produced in the cells. I think a graphing of regen current at different amounts and time periods would show a similar curve as the discharge graph

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10s5p?

10char

Yes 10S5p battery

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I talked to Hobbyking support and they said that 40A should be fine for charging. Im going to ask them about the formula since im a bit confused .

What is the mAh capacity of each cell?

2500 mah pr cell. and 12.500mah when packed

surprised they would give out info so casually that could be so dangerous. I bet for short periods it would be fine at 40amps regen. how bout you get a temp sensor and hook it up to the vesc and your batteries and tell us what happens!!

Open up the specs sheet of your battery and see whats the max charge current and add like 5 10amps more since you will not be breaking full power all the time

The max charge current is 4A pr cell. But as i write in the top its a homemade 10S5P battery of 50Cells

So 5x4=20a I have set mine to 20a and im pretty sure never reached that much amperes if 20is low for you increase it id say to around 30

Yup, momentarily exceeding max charging current is fine.

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I would not set it to 40 amps regen… If max charge current is 4 amps, I would suggest not exceeding 20 amps regen.

If you are running dual motors it should be even lower, at 10 amps per vesc.

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Hope this isn’t off topic but how exactly does the VESC figure out what voltage to regenerate? Is there a step-up converter managing the recharging battery? Does the VESC turn excess power into heat since there is a battery regen limit?

It regens to whatever the voltage of the battery is.

No.

Up to a certain point yes, then to protect itself, decrease the brake power.

the bldc tool has two variables for the brakes and I hear theyre similar to the amp output and have a “motor max” and “battery max”…I’m guessing the motor regen can be adjusted with the same limits as the motor max and depending on the vesc model it will likely have a 120 amp override limiting it, but you can adjust this to your heart’s content and its the battery regen which is the what is actually true regen and going back to the battery?

I got this formula for calculating max current charge from Hobbyking.

each parrallel packs of 5 cells can charge the current of 1cell but at higher voltage. So its 4A pr pack.

So with 10 packs its 4*10 = 40A max. Doesnt that seem right

To me this sounds funny…

Charging current will be distributed between parallel cells, so that a charger providing 5a to your pack will roughly give each cell 1a charging current

(exact current draw somewhat depending on how parallels are connected).