12v LFP now at 5.8V. How screwed am I?

[Tomthumb62]

I screwed up. I left my battery at 40% SOC in October in an unheated location and without a charge source. I checked it today and no response via Bluetooth. Voltage reads 5.8v, or 1.45V per cell. This sucks.

From what I’ve read, this is into severe damage territory and perhaps it’s toast.

Any advice or comments?

It’s currently heating up indoors with a heated blanket and heated floor. I plan to wait at least 24 hours before trying to apply a charge. It does have low temp protection but I wasn’t sure if it’s designed to work at such a compromised voltage.

 

[sunshine_eggo]

DIY or off-the-shelf battery?

Either way, get it warmed up and apply a 0.01C current to it until all cells are above 3.0V.

 

[Tomthumb62]

DIY or off-the-shelf battery?

Either way, get it warmed up and apply a 0.01C current to it until all cells are above 3.0V.

Thanks. It’s off the shelf. 200Ah PowerUrus.

None of my LFP chargers can do 2A, but I do have an automotive “automatic” charger that will do 2A. Will that work? Or do I actually need a bench power supply?

Edit: I used my clamp meter on the automatic car charger set for 2A, hooked to my car’s battery for testing. Meter said 1.89A but over about a minute it went down to about 1.39A. Doesn’t seem like a good fit.

 

[time2roll]

Do you have a 12v lamp to put in series for charging? This will limit the amps.

 

[Tomthumb62]

Do you have a 12v lamp to put in series for charging? This will limit the amps.

You mean like a 12v taillight bulb? How does this work? Would I put multiple in series, as many as necessary, to reduce amps?

I have a Victron ip22 charger that has a power supply mode but the lowest amperage I can set it for is 7.5A. How do I calculate how many 12v lamps would be required to get to 2A?

 

[sunshine_eggo]

Since it's an off the shelf battery, I believe you're reading a protection voltage and not the actual battery voltage.

I would simply set it to power supply mode @ 12.4V. Once the battery will hold this voltage with the charger removed, charge normally.

 

[Tomthumb62]

Since it's an off the shelf battery, I believe you're reading a protection voltage and not the actual battery voltage.

I would simply set it to power supply mode @ 12.4V. Once the battery will hold this voltage with the charger removed, charge normally.

Thanks again, sunshine_eggo. Powerurus support confirmed the protection mode status.

I’ll do what you suggested to revive it.

 

[Tomthumb62]

I would simply set it to power supply mode @ 12.4V. Once the battery will hold this voltage with the charger removed, charge normally.

Good news. After two days of warming it up I woke the battery up with by applying 14.4V. The BMS woke up and reports 44% SOC. Voltage read 11.32V. Whew. It has risen to 11.76 in about 15 minutes with the below charging parameters.

I’m assuming this means I don’t need to baby the battery in terms of charging, but I’m following your advice best I can nonetheless. My Victron IP22 charger on power supply goes as low as 12.8V and 7.5A. I’ll leave it this way for however long it takes to reach that voltage, then charge normally to 14.0V.

Below is a screenshot of the charger. It reads “output voltage is kept constant” (set at 12.8V), but the display shows 11.33V? What does this mean as I would expect it to instead read 12.8V?

 

[sunshine_eggo]

Good news. After two days of warming it up I woke the battery up with by applying 14.4V. The BMS woke up and reports 44% SOC. Voltage read 11.32V. Whew. It has risen to 11.76 in about 15 minutes with the below charging parameters.

I’m assuming this means I don’t need to baby the battery in terms of charging, but I’m following your advice best I can nonetheless. My Victron IP22 charger on power supply goes as low as 12.8V and 7.5A. I’ll leave it this way for however long it takes to reach that voltage, then charge normally to 14.0V.

Below is a screenshot of the charger. It reads “output voltage is kept constant” (set at 12.8V), but the display shows 11.33V? What does this mean as I would expect it to instead read 12.8V?

View attachment 188080

charge with wild abandon!

 

[time2roll]

Below is a screenshot of the charger. It reads “output voltage is kept constant” (set at 12.8V), but the display shows 11.33V? What does this mean as I would expect it to instead read 12.8V?

Normal voltage sag when charging in bulk mode. Charger will provide 7.5 amps until the voltage rises, then amps will taper off in absorption mode.

The process will start over when voltage is then increased to 14.0

 

[Tomthumb62]

Update:

The 200Ah battery charged 193Ah in bulk and 7Ah in absorption, so it was apparently quite empty. So I’m not sure just how long it’s been at 0% in the cold, but my guess is it’s been a month or two. I’ll see over time if it seems to be able to hold its charge or starts to slip a bit. Fortunately it’s not been all that cold here this winter, around freezing more or less.

 

[sunshine_eggo]

Were you able to charge to peak voltage without over-volt protection?

 

[Tomthumb62]

Were you able to charge to peak voltage without over-volt protection?

That I don’t know. If it did, I wasn’t there to see it and the BMS records no history.

However, prior to this winter, I had followed your instructions how to eek the cells back into balance. I had to start at 13.8V, then slowly up to 14.0 or maybe up to 14.1 (don’t remember).

Edit: …and after doing so, the battery was able to be charged to 14.0V without triggering BMS protection.

 

[sunshine_eggo]

That I don’t know. If it did, I wasn’t there to see it and the BMS records no history.

However, prior to this winter, I had followed your instructions how to eek the cells back into balance. I had to start at 13.8V, then slowly up to 14.0 or maybe up to 14.1 (don’t remember).

If it retained its balance after this, that's a good sign.

 

[Tomthumb62]

If it retained its balance after this, that's a good sign.

My limited understanding is that balance at rest is a useless number. At rest, it’s usually about 0.008V difference, cell 3 being the highest one. I always forget to see what it is under load. What is considered reasonable under load?

 

[MisterSandals]

My limited understanding is that balance at rest is a useless number.

Voltage measurements at rest are usually (always?) the meaningful measurements.
Measurements in the flat part of the curve, where a voltage of about 3.2V could be anywhere from 25% to 75% SoC, are the "less useful" numbers.

At rest, it’s usually about 0.008V difference,

This is a good sign! ...especially if near fully charged (3.35V and higher, at rest)

What is considered reasonable under load?

Its always desirable for cells to have similar voltages under all conditions (load, rest, charge). The most meaningful at rest.

Do you have any screenshots of cell voltages (smart BMS)?

 

[Tomthumb62]

Voltage measurements at rest are usually (always?) the meaningful measurements.
Measurements in the flat part of the curve, where a voltage of about 3.2V could be anywhere from 25% to 75% SoC, are the "less useful" numbers.

Ah okay! I guess I got the meaningful part flipped backwards.

This is a good sign! ...especially if near fully charged (3.35V and higher, at rest)

That’s good to hear. FYI, battery got fully charged two days ago to 14.0V. I removed it completely from the system and it’s been sitting indoors where it’s warmer. Voltage sat at 13.5V for over 24 hours, now it’s settled at 13.4V. I believe that’s a very good sign.

Its always desirable for cells to have similar voltages under all conditions (load, rest, charge). The most meaningful at rest.

Do you have any screenshots of cell voltages (smart BMS)?

Screenshot taken just this morning:

 

[sunshine_eggo]

My limited understanding is that balance at rest is a useless number. At rest, it’s usually about 0.008V difference, cell 3 being the highest one. I always forget to see what it is under load. What is considered reasonable under load?

Correct.

Under load, it should be pretty darn close, but this is true even if the battery is imbalanced.

You want to check the cell voltage at peak charge current voltage to see if it's top balanced.

 

[MisterSandals]

You want to check the cell voltage at peak charge current to see if it's top balanced.

Hmm, we're contradicting each other. I think i'd agree if you wrote "peak charge" rather than "peak charge current" (at an unspecified SoC).

 

[Tomthumb62]

I think i'd agree if you wrote "peak charge"

By this do you mean to check cell voltage differences when charging is at or almost at the set absorption voltage? It’s set at 14.0V in my case.