Regenerative braking + fully charged battery

I've seen many cases with broken e-bikes+electrical scooters when using regenerative braking on a fully charged battery.
What is most likely to break in such a combination, fully engage regenerative breaking + fully charged battery, the controller, battery cells or BMS?

There are multiple factors. If your controller can't handle the higher voltage produced by the regen you could blow things in the controller such as capacitors. If the BMS does not have a way to cut power when it senses cell over voltages then you will damage/destroy your battery cells as they will go over voltage. I don't know if it would damage the BMS but if it didn't cut power when it sensed over voltage I would assume it would also be damaged as they can only handle up to a certain voltage as well depending on what it was designed for.

People mostly don't need to worry about this. My solution is to charge to something conservative like 4.05 / cell and you can run plenty of regen right off the start as long as you don't go down a mountain.

The Phaserunner controller has programmable regen parameters. You can set current and voltage limits and it will taper and terminate regen after reaching your numbers. Maybe other controllers have this, too?

This is of great interest to me.

Heavy cargo / tandem, long sometimes pretty steep hills

need drag braking for long descents, separate from stopping brakes

need to continue getting the drag braking effect even if the bank is full

Do not want to allow voltage to go higher than my usual charging stop point.

Willing to put in big heat dissipation elements.

Using big (1000+W) aluminum wire-wound and hollow ceramic power resistors for load testing storage banks, regularly getting up over 500°F.

Can those or something similar be used to help burn off the regen energy from drag braking on say 20-30min descents?

Links to relevant threads or howto resources would be appreciated.

eikido said:

What is most likely to break in such a combination, fully engage regenerative breaking + fully charged battery, the controller, battery cells or BMS?

Click to expand...

That depends on what parts each one has, and what it's settings / limits are.

Unless you ahve a long downhill at the start of your trip after you've charged the battery, and use regen the whole way down, you're unlikely to be able to overcharge the cells.

If the BMS has separate charge and discharge ports you can damage the battery (probably not the BMS) by overcharging in that kind of situation, because the BMS cannot shut off charge current from regen.

If it's only one port, it'll just shut off the port and shutdown charge current, protecting the battery.

If the controller has no regen voltage limit (or it's higher than your battery's BMS limit) then when that happens the voltage spike that will occur *could* damage the FETs in the controller.

If the Controller has a regen voltage limit, then set that to below teh point your BMS will shut off for overcharge, so that you don't overcharge the battery *and* you don't damage the controller.

I read of a scooter manufacturer that solved this by providing chargers that would not fully charge the batteries.
A problem was later discovered that this voltage was below the BMS balancing voltage.

In this case, the user fully charged the scooter (actually not an ebike but a scooter) and straight away started driving it in slope and engaged the regen brakes.

No settings can be made to the BMS as it is a mass produced scooter. Ninebot ES2
I'm leaning towards a damaged controller.

Be sure to know the capabilities of the controller regarding regen. Some have "plug braking" in combination with regen, where electric braking will continue at low rpm and/or max charge voltage is reached. These along with controllers where regen works down to zero have issues with heat dissipation. With all of the controllers I've used, mountain descents have cause heat issues with regen, because they weren't nearly as efficient during braking as under load. Heavy loads and long steep hills with continuous regen requires some significant real world testing to understand your controller's limitations before considering it reliable.

Be sure you have adequate mechanical brakes as backup. I had to walk a bike down 2km of continuous 20% grade that was no walk in the park. When the controller popped and then quickly blew through the shorted mosfets I was lucky to have just enough mechanical brakes to get stopped. Another 50m and the pads would have overheated leaving my only bailout a deep concrete ditch on the uphill side of the road.

Yes exactly my concern.

Heavy loads and long descents demand as much attention be paid to stopping & drag braking as propulsion,

with mission-critical reliability required, including redundancy.

I am hoping collective wisdom here can reduce the trial and error aspect.

Couldn't you just use a dummy load that engages across the battery when the voltage reaches a certain threshold and releases when it drops? Basically a big ass bleed resistor circuit. You'd need so pretty hefty switching gear but it's totally doable.

You could even have multiple loads that engage sequentially if one isn't able to keep up.

john61ct said:

Yes exactly my concern.

Heavy loads and long descents demand as much attention be paid to stopping & drag braking as propulsion,

with mission-critical reliability required, including redundancy.

I am hoping collective wisdom here can reduce the trial and error aspect.

Click to expand...

I'd look at Nucular controllers and specifically discuss efficiency during braking with Vasili. If it's modest power then Ebikes CA and discuss your concerns with Justin's crew.

John in CR said:

I'd look at Nucular controllers and specifically discuss efficiency during braking with Vasili. If it's modest power then Ebikes CA and discuss your concerns with Justin's crew.

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Thanks. Power needs are "sorta modest" long as I'm in flattish country, not looking for speed.

But heavy cargo loads in mountain country will mean at least some occasions very high power is required.

Also considering looking at multiple motors for redundancy.

I take it Ebikes CA is Grin?

Are they a sponsor here?

dustNbone said:

Couldn't you just use a dummy load that engages across the battery when the voltage reaches a certain threshold and releases when it drops? Basically a big ass bleed resistor circuit. You'd need so pretty hefty switching gear but it's totally doable.

You could even have multiple loads that engage sequentially if one isn't able to keep up.

Click to expand...

Exactly what I'm referring to here

john61ct said:

Willing to put in big heat dissipation elements.

Using big (1000+W) aluminum wire-wound and hollow ceramic power resistors for load testing storage banks, regularly getting up over 500°F.

Can those or something similar be used to help burn off the regen energy from drag braking on say 20-30min descents?

Links to relevant threads or howto resources would be appreciated.

Click to expand...

Just don't know what sort of gear is required to actually do it, I know batteries, but not component-level DIY electrickery, yet anyway.