Active energy transfer balancing

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Inwo   10 kW

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Active energy transfer balancing

Post by Inwo » Jun 11 2019 11:36am

There are many new active balance boards showing up from China. I have tested most of them, if anyone needs an opinion before ordering.

It was requested that I do a more thorough test of the potted 4s board by a boat owner using 4s 60ah LiFePo4 for starting battery.

Getting to the end of test. I won't bother to list all the data points. Most important is how it finishes.

Test started by discharging #2 till dead <2v and charging #3 till near full.
.15 shunts to measure average current in and out.

Less than 2ma drain with switch off. Does not appear to be zero when using shunts.
The most current measured is less that 1.5 amps. However 5 amps has been seen by a user with an overcharged cell. Not me!

This is where it's at after about 3 days:
Cells 1-4

3.278 -142ma
3.239 +124ma
3.323 -68ma
3.292 -1.3ma

Differences between + & – may be test errors or losses. Ie. discharging more than charging.
Also expect high cell #3 to be discharging more than #1.
Who knows. Going the right direction in any case!

I have the same ones in 16s and 20s if someone wants to test and not wait for China.
potted 4s.gif
potted 4s.gif (58.85 KiB) Viewed 795 times
MVC-011F.JPG
MVC-011F.JPG (96.33 KiB) Viewed 795 times
MVC-010F.JPG
MVC-010F.JPG (94.57 KiB) Viewed 795 times
Shows current and waveform on balance leads only.
4s waveform.png
4s waveform.png (235.51 KiB) Viewed 794 times

Grantmac   10 kW

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Re: Active energy transfer balancing

Post by Grantmac » Jun 11 2019 12:22pm

Are they available for Li-ion? Programmable? Can the 20s run a lower cell count?

Thanks,
Grant

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Inwo   10 kW

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Re: Active energy transfer balancing

Post by Inwo » Jun 11 2019 10:57pm

Yes, as they are energy transfer only, they are not chemistry dependant.
Works with lto up to 4.2v cells or supercaps.
Many versions available, such as 8s and 12s.
All work with fewer cells and can be overlapped for more. I'm building a harness for 36s. 3 volt modules in series connected 4p.
Using 2 pcs 20s balancers.
First thought was that volt leads would not handle the high current. Test shows <2amps average current..

Grantmac   10 kW

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Re: Active energy transfer balancing

Post by Grantmac » Jun 12 2019 10:11am

That's a very interesting and hooefully robust way to balance cells.
Could they be used during a charge cycle or only after? Link?

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Inwo   10 kW

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Re: Active energy transfer balancing

Post by Inwo » Jul 31 2019 8:51pm

Yes, they work 24-7. Anytime there is over 30mv difference. Unless you turn it off.

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amberwolf   100 GW

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Re: Active energy transfer balancing

Post by amberwolf » Aug 01 2019 1:41am

So if there was a leaky cell (group) that kept dropping in voltage, this balancer would drain the rest of the cells attempting to keep that group alive?

I suppose that's good that it would "save" the bad group (really, the good cells in that group) from being pulled below "death" level, but bad that it could drain the pack to whatever LVC the balancer has, and then the leaky group would still die.... and potentially the power drain from the BMS as a whole on the rest of the pack could kill the rest of the now-drained cells. :/

I'd guess it would take a long time, but on a small pack, left unattended after a ride already low in voltage....

Something to make sure people monitor their packs, I guess.

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fechter   100 GW

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Re: Active energy transfer balancing

Post by fechter » Aug 01 2019 8:24am

That's pretty impressive. Thanks for posting the test results. Those will be ideal for those "Frankenpacks" made from mismatched recycled cells. Also cool that it's chemistry independent.

So when all the cells are within range and no longer actively balancing the current was about 2mA?
"One test is worth a thousand opinions"

fourbanger   100 W

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Re: Active energy transfer balancing

Post by fourbanger » Oct 05 2019 12:12am

Inwo, thank you for offering your expertise on this matter.

Before this thread grows too old, I'd like to ask your opinion of the super cheap active balance boards such as this.
HTB1EwRgTq6qK1RjSZFmq6x0PFXas.jpg_220x220q90.jpg
El Cheapo.
HTB1EwRgTq6qK1RjSZFmq6x0PFXas.jpg_220x220q90.jpg (12.82 KiB) Viewed 203 times
Are they any good at all or not even worth the fiberglass they're printed on? They claim to only start balancing when one cell is out by 0.1V which is.. not very accurate. Still, I'm curious as to how they perform If they do at all.

Many thanks!

Punx0r   100 GW

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Re: Active energy transfer balancing

Post by Punx0r » Oct 05 2019 4:35am

If they are chemistry agnostic does that mean there is now LVC?

fourbanger   100 W

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Re: Active energy transfer balancing

Post by fourbanger » Oct 05 2019 1:18pm

If by now you mean no then I think yes.

Wow. That was a weird sentence.

Punx0r   100 GW

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Re: Active energy transfer balancing

Post by Punx0r » Oct 05 2019 4:56pm

Yep, typo, was suposed to say "no LVC".

That's a bit of a shame as it does mean it's fully capable of killing your battery rather than protecting it. DIP switches to select LVC in 0.5V increments would be a good addition.

It's great to finally see active balancing hitting the hobbyist end of the market.

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Alan B   100 GW

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Re: Active energy transfer balancing

Post by Alan B » Oct 05 2019 5:03pm

One problem with these balancers is if the cells are at unequal temperatures the balancer will unbalance the pack according to the cell voltages which are a function of the cell group temperature. So if a pack has sun shining on one side it may make the balance worse. State of charge isn't represented precisely by voltage alone. Also in mixed packs the variations in SOC vs voltage may cause the same effect. So energy gets shuffled around (and some of it lost) for no useful purpose. For these to work well the cells need to be well matched and at the same temperature.

America   1 µW

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Re: Active energy transfer balancing

Post by America » Oct 10 2019 3:57am

That's amazing and a robust way to balance cells.

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Re: Active energy transfer balancing

Post by melanieconroy » Oct 14 2019 5:57am

thanks for this assistance.. and thanks for posting the test results.

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spinningmagnets   100 GW

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Re: Active energy transfer balancing

Post by spinningmagnets » Oct 15 2019 10:38am

Bump, to mark this thread. I like this idea. Tesla, Chevy Volt, and Nissan Leaf charge to 4.05V per cell. Doing that helps the cells last longer, and also provides a safety margin.

That leaves a need for some way to balance the cells. Equalizing seems like a reliable way that has no failure mode where the pack dies, like a janky BMS...

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