How to determine if Lifepo batteries are bad
- Thread starter Sonnyboy
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sunshine_eggo
Happy Breffast!
EDIT: nevermind.
So far this seem ok. I might not leave it unattended overnight in case something unexpected happens, but as long as you did not adjust the voltage on the power supply after connecting it should be fine. It is normal for it to take a very long time if the battery is not nearly full already
Watch the current. If current suddenly goes to 0.00 then the BMS has cut off charging. Let's assume that won't happen, but write back here if it does.
You will want to repeat this, first to get the batteries to 14.0v, and then again to get them to 14.2v. Both of those steps should go pretty quickly.
Also, the wires that come with power supplies are crappy. It will go much faster if you make new wires that you ring terminals you can bolt to the battery and PS instead of banana plugs and alligator clips.
sunshine_eggo
Happy Breffast!
Bump to 14.4V and continue charging. note how much is input after current drops to 0
sunshine_eggo
Happy Breffast!
So far it looks like your prior charger just wasn't up to the task of charging these batteries.
What is the total amount of Ah you've input into battery #2?
What is the total amount of Ah you've input into battery #2?
I’m not sure. Do you mean how long did I charge it for? This morning it was charged to 14.4. When I read after disconnecting, it dropped to 14.2
sunshine_eggo
Happy Breffast!
No. That was the purpose of the battery monitor - see how much you put into the battery.
Right. Figured that out after I disconnect the meter. Oops. Now reads 14.1 on DMM
Consumerbot3418
Fitting square pegs into round holes... for fun?
No worries--It'll still be useful for measuring the capacity of your batteries as you discharge them. Although it certainly would've been interesting to have known how much energy you were able to dump in.
I was using a Battleborn 100ah in my 5th wheel a few years ago, and never really could get it to charge well off the built-in WFCO "converter". If I put a good load on it, it'd drop the voltage down enough that the WFCO would put out max current for a while. But lead acid battery chargers don't want to destroy the battery by over-charging, and that means the the so-called "drop-in" LiFePos just don't get fully charged, and over time, become unbalanced. In my case, I had a Victron MPPT charging it according to the recommended settings, on sunny days at least.
With any luck, your issue is/was just unbalanced cells. Hoping to hear good news once you've completed the discharge test!
Thanks, me too! Can you you explain to me like I’m a two year old, how to do a discharge test? I read the earlier post three times but can’t follow it.
Consumerbot3418
Fitting square pegs into round holes... for fun?
Sure, should be dead simple, now that you have a shunt/meter!
If you apply a large load (up to the rated current, which I believe is 100 amps, circa 1200 watts, in your case), the test will go faster: it should take around an hour at that rate. If you apply a smaller load, like 120 watts, it should take around 10 hours. Smaller charge and discharge currents are more kind to the battery cells, and more efficient. So if you did the two tests I just described, you'd expect to see a higher energy count on the smaller load.
You could use any 12V/automotive device as a load, like a headlight bulb, for instance. I did my own capacity test on a similar spec battery recently, using a space heater plugged into an inverter, set to low, circa 800 watts. I ended the test when 100 minutes elapsed, and the energy counter was over 1300. I was satisfied with having all the capacity I paid for, and wanted to be kind to the battery. In retrospect, I probably should have let the BMS cut the test with low voltage disconnect, just to be sure that function works.
Good luck!
- Hook up the meter (make sure "energy counter" is reset to 0)
- Apply a load
- Wait for the BMS to cut off the output
- Look at the energy counter
If you apply a large load (up to the rated current, which I believe is 100 amps, circa 1200 watts, in your case), the test will go faster: it should take around an hour at that rate. If you apply a smaller load, like 120 watts, it should take around 10 hours. Smaller charge and discharge currents are more kind to the battery cells, and more efficient. So if you did the two tests I just described, you'd expect to see a higher energy count on the smaller load.
You could use any 12V/automotive device as a load, like a headlight bulb, for instance. I did my own capacity test on a similar spec battery recently, using a space heater plugged into an inverter, set to low, circa 800 watts. I ended the test when 100 minutes elapsed, and the energy counter was over 1300. I was satisfied with having all the capacity I paid for, and wanted to be kind to the battery. In retrospect, I probably should have let the BMS cut the test with low voltage disconnect, just to be sure that function works.
Good luck!
Does the charger ever get to zero? I’ve seen mine get to .017 current but not lower. This battery is at .054.
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RCinFLA
Solar Wizard
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- Jun 21, 2020
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Typical leakage current is 1 to 2% of cell capacity per month at mid SoC. For a 280 AH cell that would be equivalent to about 4 AH leakage bleed per month or about 6 mA of continuous leakage current. For 100 AH cell, about 2 mA.
When cell is held above 3.45v charging voltage there will be additional overcharge current that will increase minimum absorb current the greater the absorb voltage is above 3.45v.
If there is also a BMS involved, like for a self-contained 12v LFP battery, there may be balancing bleed current and power to run the BMS. The BMS processor has run and standby modes so its current consumption is variable depending on its mode of operation. When it is detecting charging current it may not idle cycle the processor as often and does more frequent checking of cell voltage and current.
When cell is held above 3.45v charging voltage there will be additional overcharge current that will increase minimum absorb current the greater the absorb voltage is above 3.45v.
If there is also a BMS involved, like for a self-contained 12v LFP battery, there may be balancing bleed current and power to run the BMS. The BMS processor has run and standby modes so its current consumption is variable depending on its mode of operation. When it is detecting charging current it may not idle cycle the processor as often and does more frequent checking of cell voltage and current.
No, it will never reach zero. It will get close, then stop going down.
Charging too long after this point can overcharge the battery, so when its close to zero and stops going down, consider it done.
I have two 4 amp batterytender with lithium settings … I used them back in 2020 to charge my 12v lithium batts while I bought other stuff to build a system..I had a voltmeter hooked to them while the charging occurred about every 3 month…
the readings went all over the place …bizzare readings..
I finally got some Victron equipment and it all settled down to normal readings…
it’s all fine now…
I don’t think they are made for what batts I owned at that time…don’t know but somthing wasn’t right.
I do not understand how so many newbies come on here , cop an attitude and want to argue their case with pros who know 100x what they know….
if you know this stuff , then why are you here…?
if you don’t know , then why are you arguing..?
I am impressed at the patience some of the forum guys have…
I would be going to get in a car and go beat these guys up after to listening to their nonsence..
this is why I would never offer tech advice to anyone…about anything..even if I were smart ….
