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Old 23-10-2018, 14:10   #136
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

I don't think so. If I am wrong and you are right, why do you think unmanaged LFP batteries have an almost 10 times lower life expectancy?
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Old 23-10-2018, 14:30   #137
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

Perhaps they were being charged to voltages over 3.45Vpc, and/or held to too low an Absorb taper.

I have yet to see a House bank treated as I (and many others) outline go out of balance, some with years of service.

In that context active balancing is completely unnecessary.

And risky, several reports of poor per-cell BMSs being **the cause** of damaged banks.
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Old 23-10-2018, 14:33   #138
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

> It is essential for a healthy and long lasting battery to keep the cells balanced.

I actually agree with this, but see no need for the process to be automated.

Checking cell voltages at first weekly, scale back to quarterly, is sufficient.

Then if needed, re-balance manually. NBD
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Old 23-10-2018, 17:07   #139
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

Thanks, Johnct your statement below answers a question I had for you about how frequently you manually balance.

Next question is it top balancing that you do and at what cell voltage?

As I see it these two approachs being taken by some brave DIYERs are pushing our understanding and will result in improvements for everyone.

Neither approach should be considered wrong, they are different, and in time we will know more. With the low key manual approach, the cost for the bms is used to build a bigger bank to try to avoid balancing issues. Who knows, it may work over time, although apparently there have been some unknown types failures reported.
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Old 23-10-2018, 17:25   #140
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

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Originally Posted by CatNewBee View Post
I don't think so. If I am wrong and you are right, why do you think unmanaged LFP batteries have an almost 10 times lower life expectancy?
Because you said "essential." The evidence shows that it is not "essential."

Separately, I'd be interested in seeing where you gleaned your data ("10 times lower life expectancy").
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Old 23-10-2018, 19:02   #141
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

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Originally Posted by CatNewBee View Post
Most LFP installation do not fail because of charging to high SOC, but because of unbalanced cells that run away.

That's why I put a cheapie (although I calibrated every one of them to a Fluke meter) digital voltmeter from eBay on each cell in addition to a BMS after the initial top balance.
The voltmeters were only $1.77 each, but it's nice to look at my home's bank box and see 3.33 volts on all eight 700 aH cells (or 3.2 or whatever).


The boat has four of those meters mounted under the companionway stairs so I can read them (if I want to) from the V berth in the middle of the night.
They also act as a nightlight for the stairs. Gotta make everything work double duty!
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Old 23-10-2018, 19:03   #142
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Re: Good thesis on preserving the life of LiFePo4 lithium batteries

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Next question is it top balancing that you do and at what cell voltage?
LFP/LiFePO4 Top vs bottom balancing on sailboats

Remember so far just once per bank, so not like I do it often, I've gone both ways.

But since I get closer to the top than to the bottom shoulder, I now just do top.

Parallel the cells, up to 3.6V, endAmps right to zero. Let rest 24 hrs, separate and check. So far that's been enough, within .01V is fine.

If I had a bit less balanced set (not yet knock on wood) get them equal and repeat a bit higher, maybe go up to 3.65V if needed.

But remember this is a special protocol, like equalizing with lead. In normal usage I stay well under 3.5V, and usually "to" 3.45V and stop, zero Absorb.

For precise calibration endAmps = .04C, used to push to .03C, prolly not a significant difference
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