Battery Protect dis- and reconnect voltage with new LifePo4-battery

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ernstsl asked Oct 7, '23

Battery Protect dis- and reconnect voltage with new LifePo4-battery

Goodday to all of you,

I just installed a brandnew Lithium 200Ah battery, and as you probably can imagine, I would like to treat it as good as possible ;-)

Attached two photos: the charcing/discharging settings that came with the battery, and a menu item of my BP 12/24v 65A.

Do the discharging-settings really mean I can enter this voltage in the BP? So disconnect at 10V, reconnect at 12.6v?

Especially this 10V seems so low…. Is it better to stay at the safe side and enter a slightly higher voltage? It will decrease the output of course, but the last thing I will is damaging this expensive battery.

Thanks for your advice!

Ernst

Battery Protect

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Alexandra answered · Oct 07, 2023 at 06:05 PM

@Ernstsl

You can't charge through the battery protect. Just making sure you know that.

10v is what your battery manufacturer system the BMS will shut down at. So that is what they call safe.

You can go a bit higher if you would rather have the loads off before the battery shuts down.

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Answer 1 · 2023-10-07T19:12:10Z

ernstsl answered · Oct 07, 2023 at 07:12 PM

@Alexandra

Thanks for your quick and clear response! I do not charge trough the BP.

So it is safe to set the disconnect voltage to 10V, as the manufacturer states.

I’m new to batteries with build-in BMS, learning every day ;-) I understand now the battery will shutdown by itself at 10v as well. So too deep discharging is not possible thanks to a build-in BMS? Does such a BMS make to use of a BP-device less usefull? Apart from better two protections then one, possible.

And if I decide to put the disconnect voltage on the BP a bit higher as you suggest? What would you recommend? 0,5v higher, or less?

Thanks again!

Ernst

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Alexandra ♦ commented · Oct 08, 2023 at 04:51 AM

0.5v is ok. It will allow for cell imbalances as well.

Some batteries shut down earlier than 10v if one or two cells run too low as a protection.

Are you batteries actively or passively balanced?

If they are passive balanced them make sure they get 100% every few days and stay in absorption to allow cell balancing.

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ernstsl Alexandra ♦ commented · Oct 09, 2023 at 05:34 PM

Hi @Alexandra , thanks again!

Your writing batteries in plural, I’ve only one battery. I’ve read some about balancing but it seems to deal with more then one battery in the system.

If you refer to some proces in the internal of the (one) battery, I honestly couldn’t tell you if there are actively of passively balanced.

Regards,

Ernst

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Alexandra ♦ ernstsl commented · Oct 09, 2023 at 05:47 PM

@Ernstsl

Sorry referring to batteries in plural from the previous statement. I guess I could have changed tense and referred to it in singular or as a battery pack. Either way the information does not change. You're going to need to know how the pack balances internally.

You only have to worry about balancing between battery packs when you use 2/4 X 12v in a 24v/48v system. They naturally balance when in 12v parallel. But you don't even need to worry since you only have one.

The battery will have to internally balance it's cells. One of the reasons it asks you to fully charge it before it's initial use in the manual is the cell balancing. It is most likely passive balancing since it refers to energy loss during charging due to the balance process. I had hoped they stated explicitly somewhere in your manual.

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ernstsl Alexandra ♦ commented · Oct 09, 2023 at 08:02 PM

Hi again, I’m learning every day on this subject, but must say I am reaching the point as to where I want to learn. After all, I just want a reasonably good battery in our new (second-hand) camper as where the old lead-acid household battery did not produce much any more.

The battery I bought is a Renogy Deep Cycle Lithium Posphate Battery, 12.8v/200Ah. For me quite costly, however I see lithium batteries of other brands with same capacity up till 5 times the amount I paid…. Do not directly understand such a big difference.

Back on topic, I found some information about the balancing, so I copied it in the picture FYI.

Greetings,

Ernst

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Answer 2 · 2023-10-07T19:31:40Z

Nev answered · Oct 07, 2023 at 07:31 PM

300Ah 4 cell Sinopoly LiFePO4 battery with no internal BMS.

9 years of full-time travel. The battery also starts our motorhome 3.9l turbo diesel engine.

These are our now at least 7 year old BP65 settings:

Apart from the occasional test it has never triggered.

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Answer 3 · 2023-10-09T19:07:54Z

grahamwood answered · Oct 09, 2023 at 07:07 PM

I wouldn't allow the battery BMS to shut down the battery coz you will have no DC power to the charge controllers which might still be getting some panel voltage. They don't like that.

I would use the BP to shut down at 12.5 volts to cut off the loads but connect the charge controllers from the battery side of the BP.

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Answer 4 · 2023-10-09T20:09:51Z

ernstsl answered · Oct 09, 2023 at 08:09 PM

@Grahamwood Thanks! As a matter of fact I read in the manual about the estimated SOC and voltage a very gradual decrease of voltage; from 100% 13.6v to 9 % still at 12.6v. From 9 to 0% is goes down to 10v.

So this makes sense referring your opnion. After all, if I put the disconnect-value of the BP at 12,5, I only “miss” the last 10%. Which would be better anyway not to let the battery drain that deep.

Greetings,

Ernst

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