BMS Shuts Battery Down During Charge

Super Dave · May 9, 2023

Good day all

I’ve recently purchased a 400ah lifepo4 battery and and when I put a standard 10amp charger on it the BMS shuts down the battery for a minute or so and then opens up to accept the charge for about 5minutes. It kept cycling like that before I went to a 4amp charger and the battery has been just fine with no shutdowns. The battery temperature never went above 22c and the battery is rated to be able to receive up to 100amps of charge. The battery was drained during a capacity test as soon as it arrived so there was no question as to whether or not the battery was fully charged.

Any thoughts?

Thanks, Dave

LakeHouse · May 9, 2023

This isn't really enough info for us to help you...
What brand of battery? Are you able to get any information from the BMS, like error or warning codes, cell voltages, state of charge, etc.?
What is a 'standard 10A charger'? Specifically for LFP batteries, or for Lead-Acid car batteries?
What's the voltage at the battery terminals without the charger connected?

sunshine_eggo · May 9, 2023

Super Dave said:
Good day all

I’ve recently purchased a 400ah lifepo4 battery and and when I put a standard 10amp charger on it the BMS shuts down the battery for a minute or so and then opens up to accept the charge for about 5minutes. It kept cycling like that before I went to a 4amp charger and the battery has been just fine with no shutdowns. The battery temperature never went above 22c and the battery is rated to be able to receive up to 100amps of charge. The battery was drained during a capacity test as soon as it arrived so there was no question as to whether or not the battery was fully charged.

Any thoughts?

Thanks, Dave

Very common for new batteries to have some cell imbalance. The lower current charger also likely charged to a lower voltage.

Would help to know what the charge voltages of the two chargers are.

Berseker · May 9, 2023

Super Dave said:
Good day all

I’ve recently purchased a 400ah lifepo4 battery and and when I put a standard 10amp charger on it the BMS shuts down the battery for a minute or so and then opens up to accept the charge for about 5minutes. It kept cycling like that before I went to a 4amp charger and the battery has been just fine with no shutdowns. The battery temperature never went above 22c and the battery is rated to be able to receive up to 100amps of charge. The battery was drained during a capacity test as soon as it arrived so there was no question as to whether or not the battery was fully charged.

Any thoughts?

Thanks, Dave

What do you mean by standard charger?. lifepo4 requires specific chargers and voltages....a standard charger as you label it, may be outputting 14.7v, which is way higher than a lifepo4 battery wants.

confirm the voltage of the charger and post a screenshot of the bms settings page

Super Dave · May 9, 2023

Hello LH. Good questions.
Standard charger was referring to a standard regular battery charger without a LI option.
I've been charging the battery for the last couple of days with a standard 4a charger.
There aren't any error or warning codes on either of the 2 BMS apps I am using to monitor the battery. I have attached a screen shot from the BMS/Battery status app.
State of charge is currently 89%.
The voltage at the battery terminals without the charger connected is 13.44

I have attached 3 screenshots of the information the one app provides.

Thanks for having a look.

Super Dave · May 9, 2023

Berseker said:
What do you mean by standard charger?. lifepo4 requires specific chargers and voltages....a standard charger as you label it, may be outputting 14.7v, which is way higher than a lifepo4 battery wants.

confirm the voltage of the charger and post a screenshot of the bms settings page

Super Dave said:
Hello LH. Good questions.
Standard charger was referring to a standard regular battery charger without a LI option.
I've been charging the battery for the last couple of days with a standard 4a charger.
There aren't any error or warning codes on either of the 2 BMS apps I am using to monitor the battery. I have attached a screen shot from the BMS/Battery status app.
State of charge is currently 89%.
The voltage at the battery terminals without the charger connected is 13.44

I have attached 3 screenshots of the information the one app provides.

Thanks for having a look.

I forgot to mention that this is a chinese purchased battery, so no brand name.

Super Dave · May 9, 2023

Super Dave said:
I forgot to mention that this is a chinese purchased battery, so no brand name.

And the charger is putting out 9.76v

sunshine_eggo · May 9, 2023

Super Dave said:
Hello LH. Good questions.
Standard charger was referring to a standard regular battery charger without a LI option.

With the charger that caused the BMS to trigger protection, did you observe it happening on the app?

if so, what were the cell voltages.

if you did not observe it in the app, I recommend you connect the other charger and observe the behavior during the disconnects.

Super Dave said:
I've been charging the battery for the last couple of days with a standard 4a charger.

Have you confirmed that the charger is actually sending current to the battery?

Super Dave said:
There aren't any error or warning codes on either of the 2 BMS apps I am using to monitor the battery. I have attached a screen shot from the BMS/Battery status app.
State of charge is currently 89%.
The voltage at the battery terminals without the charger connected is 13.44

It sounds like the 4A charger may not be charging at all. Some chargers might see 13.44V as "full" and not bother.

Super Dave said:
I have attached 3 screenshots of the information the one app provides.

Oof... hate the font...

Super Dave said:
And the charger is putting out 9.76v

This implies the charger is looking for a battery voltage and is not diagnostically useful. Consult the manual for the charger. It should publish the charge voltages.

LakeHouse · May 9, 2023

Ok, good info. There are some things you might want to change in your BMS to prolong battery life. Specifically, your overvoltage is to high (decrease to ~3.5V), undervoltage is too low (maybe ~2.7 to 3.0 V), and low temp charge should be no lower than 0C. The first two will very slightly decrease usable capacity (by maybe 1%), and the last one will keep you from destroying the thing the first time you try to charge it in winter...
Back to your original question: With the 10A charger, are you sure the BMS shuts off charging and not the charger? If the charger is expecting a lead-acid battery and what it gets is LFP, it may not like it and turn off charging.
If it was the BMS, it shouldn't turn off charging without throwing some sort of error or warning.

sunshine_eggo · May 9, 2023

LakeHouse said:
Ok, good info. There are some things you might want to change in your BMS to prolong battery life. Specifically, your overvoltage is to high (decrease to ~3.5V), undervoltage is too low (maybe ~2.7 to 3.0 V), and low temp charge should be no lower than 0C. The first two will very slightly decrease usable capacity (by maybe 1%), and the last one will keep you from destroying the thing the first time you try to charge it in winter...

Disagree. while 3.75V is on the high side, it's a very very common "canned" setting, i.e., most "dumb" BMS are set at this level. most cell specs specify a 3.65V voltage. There is ZERO reason to set below this value and doing so will be more likely to trigger charge cut-off, which actually causes unnecessary wear and tear on the BMS FETS. they've been known to fail in situations where repeated protection has been engaged.

It buys you nothing but additional risk.

LakeHouse said:
Back to your original question: With the 10A charger, are you sure the BMS shuts off charging and not the charger?

While this is a good question, the next...

LakeHouse said:
If the charger is expecting a lead-acid battery and what it gets is LFP, it may not like it and turn off charging.

...is very speculative and something of a red herring. LFP both encourages and discourages charging depending on the charger.

Discourage:

If the resting voltage of the LFP is very high - 13.6V or higher, the charger may just assume the battery is fully charged and drop to float; however, this would require a relatively smart charger. The vast majority of chargers will charge to absorption voltage, hold for a charger-determined period of time and then drop to float or shut off. Victron inverter/chargers hav an undocumented feature where they will not go into bulk charge unless the voltage is X below the float voltage. A Victron inverter/charger might see a LFP sitting at 13.2V and decide it doesn't need to be charged.

However, most dumb chargers just need a valid battery voltage to progress through the bulk, absorption and float phases.

Encourage:

Lead acid requires significant input above 13.8V. LFP takes on a much larger portion of its charge below 13.8V, particularly at low current compared to lead acid. Logic-wise the charger is encouraged to charge longer because the LFP voltage will be lower for longer.

LakeHouse said:
If it was the BMS, it shouldn't turn off charging without throwing some sort of error or warning.

Only if you're watching in the app. There is no visible or audible indicator on a JBD BMS.

LakeHouse · May 9, 2023

sunshine_eggo said:
Disagree. while 3.75V is on the high side, it's a very very common "canned" setting, i.e., most "dumb" BMS are set at this level. most cell specs specify a 3.65V voltage. There is ZERO reason to set below this value and doing so will be more likely to trigger charge cut-off, which actually causes unnecessary wear and tear on the BMS FETS. they've been known to fail in situations where repeated protection has been engaged.

It buys you nothing but additional risk.

I'm not sure I buy your argument on this one, but it's not unreasonable. I don't think a lot of people on the forum are happy with their cells going above 3.65V or below 2.5V. I know I'm not.

sunshine_eggo said:
...is very speculative and something of a red herring.

Of course it's speculative. But hardly a red herring. If the charge shut-off is caused by the charger, then either the charger is malfunctioning or it's incompatible with LFP. Or is there some other option I'm missing?

Super Dave · May 9, 2023

Thanks for those tips LH. I will implement them for sure.
To answer your question, (now the possibly embarrassing part), the charger is an old lead acid type charger as I mentioned. I had the charger at the low setting which I assumed would be 2a. Once I initiated the charging process, I saw the app's reading to be at 4a +/-, and constantly fluctuating by around .3 or .4a. I left that for a day as the battery was doing just fine. Then the next day, as things seemed to be going well, I thought I'd up it to the 30a setting and speed things up a bit as it says right on the battery 100a max charge/discharge rate. I flipped the switch and the app shot up to about 40a and fluctuated for a couple of minutes, similar to the lower setting. I then heard the charger go tick tick 3 or more times with varying degrees of strength, saw a brief spark, tiny flame and a puff of smoke. I immediately went to the charger and switched it back to low where the amps settled back down to the previous numbers from before. Talking to an electrical engineer friend, said that I fried the units ability to put out the higher amps. I also took notice of the battery's internal temperature and it was only raised a single degree c during that time.
With the 10a charger, I had the battery at my friends house. The charging seemed to be doing just fine when we heard a very audible "click". We checked the connection with an clamp meter and no power going to the battery. About a minute or so later, the power flowed again with a normal reading on the clamp meter. This cycling happened a couple of times and the loud click certainly seemed to come from the battery itself. I'll double check with my friend later and see if there's any chance the click came from charger, but I doubt it.

I've attached a pic of the charger itself for your reference.

Super Dave · May 9, 2023

Super Dave said:
Thanks for those tips LH. I will implement them for sure.
To answer your question, (now the possibly embarrassing part), the charger is an old lead acid type charger as I mentioned. I had the charger at the low setting which I assumed would be 2a. Once I initiated the charging process, I saw the app's reading to be at 4a +/-, and constantly fluctuating by around .3 or .4a. I left that for a day as the battery was doing just fine. Then the next day, as things seemed to be going well, I thought I'd up it to the 30a setting and speed things up a bit as it says right on the battery 100a max charge/discharge rate. I flipped the switch and the app shot up to about 40a and fluctuated for a couple of minutes, similar to the lower setting. I then heard the charger go tick tick 3 or more times with varying degrees of strength, saw a brief spark, tiny flame and a puff of smoke. I immediately went to the charger and switched it back to low where the amps settled back down to the previous numbers from before. Talking to an electrical engineer friend, said that I fried the units ability to put out the higher amps. I also took notice of the battery's internal temperature and it was only raised a single degree c during that time.
With the 10a charger, I had the battery at my friends house. The charging seemed to be doing just fine when we heard a very audible "click". We checked the connection with an clamp meter and no power going to the battery. About a minute or so later, the power flowed again with a normal reading on the clamp meter. This cycling happened a couple of times and the loud click certainly seemed to come from the battery itself. I'll double check with my friend later and see if there's any chance the click came from charger, but I doubt it.

I've attached a pic of the charger itself for your reference.

and for the record, the charge status of my battery when things shut down with the 10a charger was about 40%ish.

sunshine_eggo · May 9, 2023

Super Dave said:
and for the record, the charge status of my battery when things shut down with the 10a charger was about 40%ish.

Were you monitoring the individual cell voltages?

With the 4A charger, have you confirmed it's actually charging?

BMS Shuts Battery Down During Charge

Super Dave

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