Will regen braking damage a lifepo4?

[Glennsgarage]

I had a $700 Chinese lipo that fried a couple years ago after it had a full charge and the regen brake kicked in.

I want to buy another pack for Segway type robotics projects and they can generate quite a bit of regen.

I am strongly considering nimh, but would gladly switch to lifpo4 if I knew it could handle short bursts of high amps.

Thanks!!

Glenn

 

[neptronix]

Depends on the size of your pack and the C rating for the charge.

If you have a 10AH battery at 1C, then it can take 10A in, as long as your BMS can handle that power. So if you tune your regen to 10A, you'll be fine.

Regen is often tuned too high. This is why i like infineon controllers and their ability to be programmed. EBS level 0 should produce around a 10A current when the regen kicks in.

Nimh is awful, don't bother with it. Expensive, heavy, big, small capacity, and a pain in the ass to charge.

 

[biohazardman]

As mentioned it depends on what the batteries are able to handle for an input and what you are putting out in regen. Other weak spots are the BMS, if you have one onboard, and the controller which I fried several times using regen with no BMS. Toasted the same diodes in the controller several times before I replaced it and turned the regen off. My a123s and Infineon controller would probly do regen fine but I use a geared motor now so no joy there. Lots of things to balance out to do it right and have no problems.

 

[Glennsgarage]

The vehicles are only ebike size, and should only generate 20 amps tops, and just a few seconds.

I would like 10 amp hours and 36v. Can you recommend a BMs and pack that would accommodate 20 amp bursts of regen...

Thanks,

Glenn

 

[Kin]

Also, while you have killed a batch of LiPo, you might consider only charging lipo to 4.1v or 4.15v for longevity, that would give you some leeway if you happen to start down a small hill on full charge (you might still regen too much if you start at a huge hill, but I'm rather surprised that it actually happens in practice).

 

[cassschr1]

You DON'T do regen on a full battery. Some capacity has to be gone.

 

[Kin]

Well, you hopefully don't....But you might end up doing it, and then you're kind of screwed.

I'm not sure that LiFePo4 will help you. From what I understand, the controller input on a BMS does not always have a HVC. This was mentioned in another thread where someone was using 1 charger through the charger point and 1 charger through the controller port, to increase charging current. I don't actually have any experience with LiPO4

 

[amberwolf]

Perhaps you could setup the regen so that instead of sending the braking current to the battery, it uses plug braking instead, using a resistive load (coils of wire wrapped around the frame, perhaps, for heatsinking).

The problem with regen into a full battery is one thing that many ebike controllers do seem to have, assuming you use a battery that matches the controller's HVC or other cutoff values (or if it is programmable).

You can also use a BMS that prevents overcharging a full battery, and as long as the charge port is the same as the discharge port (or you setup diode paths that force that), it will protect the battery. The catch there is that the controller will still be outputting the voltage, and then suddenly without any load on it, the votlage may spike way up, beyond what the controller components can handle, and the controller coudl be toasted.