Voltage below threshold. Battery 51.2V Value 8.2V

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TreccaLab65

TreccaLab65

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Jan 1, 2025
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[EN]
"They brought me this battery pack, and upon exit, the value is just 8.2 V. The battery pack, along with 8 others, have been without a charge for 4 years, so they have dropped below the minimum threshold. Since there are 16 cells in series, it is assumed that each one is at about 0.5 V. I told the customer that it is dangerous because chemical causes can cause short circuits. Do you think it could be the BMS that interrupted the operation? I haven't opened the chassis yet."

[IT] Original Message
Mi hanno portato qst pacco batterie all'uscita il valore è di appena 8,2 V. Il pacco batterie insieme ad altri 8 sono stati senza carica 4 anni quindi sono scese sotto la soglia minima essendo 16 celle in serie si presume che ogniuna è a circa 0,5v. Ho detto al cliente che è pericoloso per i motivi che avvengono cause chimiche che possono causare corto circuiti. Secondo voi potrebbe essere il BMS che ha interrotto? Non ho ancora aperto lo chassis.
 
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Ciao TreccaLab, in english please! [io ti capisco ma il forum no! Usa Google Translate e copia / incolla, ti ho messo la risposta in italiano sotto, però fai un tentativo con Google Translate]

That's a nice battery: Energy / Capacity: 1.2kWh / 24Ah, Nominal Voltage: 51.2V, Maximum Discharge Current / Power: 50A / 2.5kW, Standard Charge Conditions: 57.6V / 24A.

Going down from 51.2V+ to 8.2V may indicate a permanent damage to the battery. It could have been caused by the BMS circuit which is a load for the battery. There's also a natural discharge of the cells, plus the current used by any other circuit connected to the battery. And if the storage place was exposed to extreme heat or cold that could also cause extra damage.

They should be carefully examined by a professional (using all safety measures YES), cell by cell, and maybe a low-current recharge could be performed. I wouldn't use them for any critical application. But, personally, if I could recover them, after extensive testing I would use them for my stuff. The recovery would start by a careful visual inspection of the packs and the connections for damage / leaks / rust; a voltage/IR measurement of all packs; a low current (for e.g. 0.1C) and low voltage recovery attempt (I'd start from 10-12V and slowly increase the voltage if the pack seems to respond without overheating).

Italian translation for you below, but don't get used to it! English only in the forum!

[IT]
Si tratta di una bella batteria: Capacità: 1,2 kWh / 24 Ah, Tensione nominale: 51,2 V, Corrente di scarica massima/Potenza: 50 A / 2,5 kW, Carica standard: 57,6 V / 24 A.

Un calo di tensione da oltre 51,2 V a 8,2 V potrebbe indicare un danno permanente alla batteria. La causa potrebbe essere da attribuire al circuito BMS, che rappresenta comunque un carico fisso per la batteria (a meno della presenza di circuiti di disconnessione automatica, da capire). Bisogna inoltre considerare la naturale scarica delle celle e la corrente assorbita da qualsiasi altro circuito collegato alla batteria. Anche temperature estreme, sia calde che fredde, potrebbero aver causato ulteriori danni.

Le batterie dovrebbero essere esaminate attentamente da un professionista (ovviamente con tutte le precauzioni di sicurezza), cella per cella, e potrebbe essere possibile effettuare una ricarica a bassa corrente. Personalmente, non le userei per applicazioni critiche. Tuttavia, se riuscissi a recuperarle dopo averle testate a fondo, le utilizzerei per i miei dispositivi. Il ripristino inizierebbe con un'attenta ispezione visiva dei pacchi e dei collegamenti per individuare eventuali danni, perdite o ruggine; una misurazione della tensione/IR di tutti i pacchi; un tentativo di ripristino a bassa corrente (ad esempio 0,1C) e bassa tensione (inizierei da 10-12 V e aumenterei lentamente la tensione se il pacco sembra rispondere senza surriscaldarsi).
 
Sorry for the distraction, I forgot I had to write in English. Thank you for your quick response. I'm familiar with lithium batteries like 18650s, but not with LiFePO4s. I'll open the package and examine it cell by cell; I'll check the BMS and see how it goes.
 
It's also possible that some cells have reverse voltaged. That could also account for the overall low voltage. Without having coms with the built in BMS can't really tell for sure what's going on.
And unless you can find some unlock procedure, you may have a bricked BMS on your hands and would need to be replaced if you are able to recover the cells.

Found a pretty decent tear down of the battery pack. A weeeee bit bigger than I thought it was :LOL:
View: https://www.youtube.com/watch?v=P9SjB393RD0
 
I've processed many individual 18650 cells at 0.5v and they can recover but it's a toss up. A key piece of info can be determined by charge / discharge-test / charge (looking for self-discharge) of the batteries. If they have reasonable (say 90% original) capacity and charge up to the full voltage (that's will uncover negative volt cells) and don't self-discharge (over a few weeks) then you may have some useful batteries.
 
Also LFP's have a little better bounce back from low voltage than NMC's So there is that added possibility in your favor

The other good thing is that the cells are standard LFP cells. So you can always replace the busted ones and have a whole system back up and operational.
BatteryHookup (tho in the US) sells this size cell a lot. I'm sure there are EU places you can get them from as well
 
Thanks everyone for the advice, I opened the battery pack and as per theory 8.2 volts output 16 cells in series about 0.5 volts instead of 3.2 for a total of 51 volts. So the pack should be thrown away.
 
Did you check each group of cells, or just the overall voltage past the BMS? Or are you just checking for warranty reasons and replacement?
 
Ciao, sì, ho controllato la tensione prima del BMS ed è di circa 8,10 volt. Poi ho testato tutte le singole celle, che misuravano tra 0,46 e 0,52 volt. Faccio riparazioni e mi hanno portato questo pacco batterie, che fa parte di un impianto fotovoltaico fuori servizio da 4 anni. Ne ha altri 7.

Hi, yes, I checked the voltage before the BMS and it's around 8.10 volts. Then I tested all the individual cells, which measured between 0.46 and 0.52 volts. I do repairs and they brought me this battery pack, which is part of a photovoltaic system that's been out of service for 4 years. It has 7 more.
 
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Yeah, if the packs are all close to the same undervolt condition, I'd say the BMS pulled them down that far. With that said, it is possible to do a slow charge bypassing the BMS/circuitry of about 5A and you might be able to bring the packs back online.

I would charge each pack individually to a 2.5V, and then see if the BMS will re-initialize. If it does, then you could finish charging through the BMS so it can continue to monitor each cell in series and keep things balanced.
 
If nothing else it's a good learning experience 😃
 
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