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LiFePO4 balancing.

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Siwastaja:

--- Quote from: shapirus on March 11, 2023, 10:58:13 am ---Whatever happens, it always tries its best to equalize the voltages.

--- End quote ---

Which is a wrong thing to do. You are assuming this is the right metric, but it's not, because voltage is not indicator of SoC under charging/discharging current, especially on LFP mid-curve. The balancer is doing needless work and wasting energy as a result. When on-grid, maybe the wasted energy doesn't matter, but if the "balancing" is going on while discharging, the wasted energy then reduces the usable pack capacity. This might be more serious than just the power consumed by the indicator LED.

It is impossible to say if the net effect is positive, neutral or negative by following the voltages alone. Much more sophisticated monitoring and analysis would be needed, involving accurate current measurements (for charge integration).

A proper algorithm would monitor a full cycle without any balancing to figure out the amount of active balancing needed during cycle, and then repeat just that pattern. All the small details need to go right.

This is clearly a cargo cult engineering product. As an expert, I would not recommend it.

paulca:
Some of the balancing boards I am looking at provide a whole set of parameters allowing things like, only enabling the balancer when certain conditions are reached.  Such as maybe only enabling the balancer while in "absorption" phase for an hour before cutting charge or maybe bring the balancer back in at the bottom when your pack starts on the descent again.  Many options.

The Victron "Smart shunt" thing sounds interesting, but it also sounds expensive and proprietary.  It's basically a learning fuel gauge type affair, with a coulombs counter maybe, you can get it to watch the pack for a full cycle, then pick what you consider 100% SoC and it goes from there. 

shapirus:

--- Quote from: Siwastaja on March 11, 2023, 12:44:41 pm ---Which is a wrong thing to do.

--- End quote ---
Depends on multiple factors. In my case, which is to keep well-matched cells equalized and not allow them to drift apart over time, and equalize them initially after they are assembled into a multi-cell battery, it's exactly the right thing to do.

I didn't care to add the circuitry to turn off the balancer during the discharge stage or only turn it on when the charger is on. Doesn't make any difference in my case: a few mA of the balancer's quiescent current or tens or even a few hundreds mA equivalent of energy wasted at charging and discharging the capacitors don't make any difference compared to the typical 10-30 A discharge current.

It may be a good idea to do it in the general case though.

Yes, these balancers may not work well (and, the rest of the variables being equal, neither will the resistive ones) with poor quality batteries made of cells that are unmatched in terms of capacity or internal resistance or both.

Those will obviously require more sophisticated logic to get the best performance of them and extend their life as much as possible, but it's a special case: normally it's preferred to pick matched cells of decent quality to build a battery.

Siwastaja:

--- Quote from: shapirus on March 11, 2023, 01:38:24 pm ---
--- Quote from: Siwastaja on March 11, 2023, 12:44:41 pm ---Which is a wrong thing to do.

--- End quote ---
Depends on multiple factors. In my case, which is to keep well-matched cells equalized and not allow them to drift apart over time, and equalize them initially after they are assembled into a multi-cell battery, it's exactly the right thing to do.

--- End quote ---

It's totally wrong thing to do, although as a side effect, if you equalize the voltages all the time, indeed the cells can't drift apart in SoC very far. However, this is very inefficient way to keep a pack balanced and reduces usable capacity, and the primary reason to balance a pack is to increase the usable capacity.

Especially if your cells are well-matched, then all you need is a small classic dissipative balancer.

You have absolutely no idea what you are talking about. You are a consumer buying some Chinese shit and based on that "experience" you come to teach experts who actually have researched and developed such systems. This is just getting ridiculous. I'm out of this bullshit discussion.

shapirus:
Yes it's difficult to admit that a dirt-cheap Chinese board can now in most situations solve the problem which previously required a skilled engineer and costed a fortune to solve. I understand.

However, there are still many cases where complex solutions are required, and skilled engineers are still in demand there. So there's no reason to get frustrated, not before AI replaces them in a few years, anyway.

(but balancing a damn battery pack is not one of them.)

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