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48v battery reading 322mV?

developmental

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Oct 30, 2021
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I’m running into an issue and am assuming it is related to a low voltage disconnect. The battery is a 1 year old BigBattery 48v HSKY. The display and power button are not lit which I assume is a result of the disconnect being triggered.

I checked the voltage with my multimeter and was getting 322mV.

I’ve had the battery on 15a charger going on 5 hours and the multimeter is still reading 322mV.

The multimeter was checked on a 12v lifepo4 battery and it’s reading correctly ~12.84v. So I’m at a loss for why the multimeter is reading so oddly on the 48v battery, I would assume a weird contact might read funny once or twice but 10+ consistent 322mV readings seems wrong.

Any ideas on what’s going on, or what I’m doing wrong?


Battery specs:
Operating voltage: 43 – 58.8V
Capacity: 5.3kWh / 103Ah
 
If the BMS is in protect mode, BMS may read very low.

Charger may require a certain minimum voltage before it will charge.

This is typically resolved by "jump starting" the battery either by placing the battery in parallel with another 48V battery, or using a power supply that will deliver a voltage regardless of the battery level.

If your charger reads >48V when the charge leads are not attached, you might try energizing the charger first with one lead disconnected and then touching the other lead to the battery terminal direct (i.e., making your battery connections AFTER the charger is energized) or through something like a #2 pencil lead to provide a little resistance.
 
Thanks for the help!

Since the battery and charger have Powerpole connections touching the terminals like that isn't particularly easy.

I was able to get a cheap 60v variable charger pretty fast, which helped jump start the battery and energize the charger. I find it odd that the dedicated charger needs outside help to energize itself, seems to defeat the purpose. Is this typical of lifePo4 chargers?

Also once the battery and charger were awake the voltage of the battery was reading 53.4v. So if it wasn't a low voltage discount, what other protection mode could cause the battery to not power up?
 
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53.4V = 3.337vpc Average.
But that does not mean it is what's going on inside the pack. You need to check the voltage on each cell, any cell that reaches below the Low Volt Cutoff of the BMS will cause the BMS to shut off. I always recommend not allowing the cells to get below 2.700 (2.800 is better though) because a large surge demand can drop the voltage with the sag and be long enough to trigger an LVD. Also to have the BMS shut down @ 2.600 to leave restart room.

Once you put the external charger on, it probably pushed the cell that was too low just above the recovery point.
 
Thanks for the help!

Since the battery and charger have Powerpole connections touching the terminals like that isn't particular easy.

I was able to get a cheap 60v variable charger pretty fast, which helped jump start the battery and energize the charger. I find it odd that the dedicated charger needs outside help to energize itself, seems to defeat the purpose. Is this typical of lifePo4 chargers?
This isn't unique to lifepo4 battery chargers. It's a built in safety feature for many battery chargers. It helps prevent accidental shorts on the charger output among other things.

Also once the battery and charger were awake the voltage of the battery was reading 53.4v. So if it wasn't a low voltage discount, what other protection mode could cause the battery to not power up?
You assumed low voltage disconnect. But, it could be a single cell over or under voltage (due to imbalance) an over current trip, or even temperature related depending on the built in BMS.

Do you have a way to read the cell voltages or communicate with the BMS?
 
Many chargers and inverter/chargers will not attempt to charge if they measure attached battery voltage out of range.

When BMS has a protection shutdown for over-discharge undervoltage this can create a 'catch22' situation requiring a separate power supply or charger that does not require a legit battery voltage to recharge battery enough to reset BMS.

If your inverter has low voltage cutout setting you should set it so the inverter shuts down before BMS trips undervoltage cell shutdown.

This also requires you keep the cells balanced properly and your battery cables are sized properly so a heavy inverter load does not create too much cable voltage drop tripping inverter low voltage shutdown.
 
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