I've had this unit for about 8 months and it start at 199 amp hour and now it's down to 180 amp hour is this normal? There was quite a bit of difference of voltage on the cell so I ordered a 48 volt battery equalizer and now the voltage are pretty consistent on all the batteries but did nothing for increasing my amp hours that I lost. I hear that the lithium batteries will degrade just not sure how much? I'll post what pictures I can of the current voltage
I have a 48 volt 200 amp hour battery pack it seems to be degrading
- Thread starter Buick39
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400bird
Solar Wizard
How did you connect that battery equalizer? It looks like it is designed to connect to 4 series 12 volt batteries. But, you've got 16 cells in series inside a "sealed" battery, that should include a BMS with cell balancing.
To answer your question, that does seem like quite a lot of degradation. But it's more likely a software issue than an actual problem with the cells.
There are two options to calculate capacity:
1. Fully charge and discharge the battery, monitoring energy usage.
2. Guess based on energy moved in and out of the battery. Also known as an algorithm.
I'd recommend a full charge discharge cycle and see what happens.
To answer your question, that does seem like quite a lot of degradation. But it's more likely a software issue than an actual problem with the cells.
There are two options to calculate capacity:
1. Fully charge and discharge the battery, monitoring energy usage.
2. Guess based on energy moved in and out of the battery. Also known as an algorithm.
I'd recommend a full charge discharge cycle and see what happens.
Thanks for the reply I did hook to 4 battery's in each string and really did a good job in balancing all the voltages out. The BMS is lock by factory so cant do much there and prior to putting equalizer in I ran the battery way down to where I had to reset it to start charging. I used the unit for several days in this last cold snap and ran it below 50% several times and use my generator to charge backup and was very thankful to have battery backup which is why I built the system.
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400bird
Solar Wizard
Ok, that didn't really answer my question or address getting a full cycle into the pack.
After fully discharging to cut off, how full did you charge it?
All the way to cut off?
3.5-3.65 volts per cell would be ideal, closer to 3.65 volts per cell is more likely to trigger the reset, without knowing the BMS parameters.
The displayed imbalance isn't bad, 0.03 volts isn't much. But your right in the flat part of the voltage curve. When you charge the pack to high cell voltages again, get pictures of the cell voltages.
After fully discharging to cut off, how full did you charge it?
All the way to cut off?
3.5-3.65 volts per cell would be ideal, closer to 3.65 volts per cell is more likely to trigger the reset, without knowing the BMS parameters.
The displayed imbalance isn't bad, 0.03 volts isn't much. But your right in the flat part of the voltage curve. When you charge the pack to high cell voltages again, get pictures of the cell voltages.
When I discharged completely the internal BMS shut it down and measurement voltage was 8vdc I cant remember what the display showed thinking around 50vdc and had to reset to get my tp6048 6000watt Power solar mppt to start charging with utility power at 80amps and charged till it shuts off via BMS and the amp hours have slowly degraded every time I have charged and discharged. Hope I'm answer your questions kinda of a newbie here.
Ok so your cells are not top balanced, which can explain the "lost" amp hours. Not necessarily degraded. They probably need held at a float voltage high enough and long enough to let the BMS balance the cells. How long that will take will depend on how much balance current it can do, and if it is an active or passive balancer, and howbfar out of balance the cells are. Hopefully it isn't something pathetic like 20mA.
Don't think I tagged the right pictures I'm trying to do this on my phone as that's where all the pictures are at and very hard to see but you can see that the degradation of the amp hour as I took pictures several times
Attachments
the first photo's is was 99.9% charged just went out and gave it a little short charge and it shutdown and voltages about the same as posted in original post
400bird
Solar Wizard
Yeah, that one pic with cell 16 at 3.3 volts and cell 13 at 3.668 volts shows the pack is pretty far out of balance. Follow SparkyJJO's recommendation to balance the pack. If the cells have welded bus bars, you can't disassemble to top balance and will need to balance it in place.
There's plenty of options:
Can you get the pack back up into that range with a cell above 3.5 volts and charge it very slowly, probably an amp or less. It might take a few cycles where you discharge it down to 75%, charge back to 3.5 volts, then charge at an amp or two.
Or if you already have the pack opened up, you could individually charge the low cells or discharge the high cells manually (this would still need to be performed at high SOC, with cells above 3.5 volts). That would significantly cut down on the time compared to letting the BMS burn off the excess at 60-200 milliamps.
There's plenty of options:
Can you get the pack back up into that range with a cell above 3.5 volts and charge it very slowly, probably an amp or less. It might take a few cycles where you discharge it down to 75%, charge back to 3.5 volts, then charge at an amp or two.
Or if you already have the pack opened up, you could individually charge the low cells or discharge the high cells manually (this would still need to be performed at high SOC, with cells above 3.5 volts). That would significantly cut down on the time compared to letting the BMS burn off the excess at 60-200 milliamps.
Would you say the equalizer isn't doing the job should I remove and send back I will have to purchase a power supply to top balance.
400bird
Solar Wizard
That equalizer isn't meant for your type of battery and isn't going to help at all. You'd need one for 16 cells.
Would that be like a optimizer need for 16 cell? any recommendations? I had watched one of Will video's on the optimizer and he was very against them and I think it ended up burning up but have wondered if I was to buy a power supply and try to top balance unit if that would get my amp hours back?
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400bird
Solar Wizard
The thing you purchased has a valid purpose, it just isn't what you need.
If you want want to purchase something to speed up the process, you're looking for an "active balancer"
Please don't take this a recommendation for this specific one, but you're looking for something like this:
But again, you don't need to purchase anything. If the BMS in the battery does any balancing, it will do the job.
Also, your bus bars are bolted, not welded. You could disassemble and do a proper top balance, if you really wanted to.
If you want want to purchase something to speed up the process, you're looking for an "active balancer"
Please don't take this a recommendation for this specific one, but you're looking for something like this:
But again, you don't need to purchase anything. If the BMS in the battery does any balancing, it will do the job.
Also, your bus bars are bolted, not welded. You could disassemble and do a proper top balance, if you really wanted to.
WindWizard
Solar Enthusiast
It may be easier just to purchase a 12 volt automotive headlight and attach some alligator clips and then discharge the high cells. Just make sure you do not short out the individual cells.
Nobodybusiness
Collecting the leftovers of the Great Sky Reactor.
I have done that before. Most of time the IR or capacity of the cell is a little different and it just shoots back up to OVP.
Best way I have found it to bring all cells up to 3.65 individually or parallel.
Not sure when you say high cells but I have a load tester for 12vdc that would make quick work of draining a 12v set of battery's that I use on testing my golf cart battery's to test load . My original thought was that the BMS should balance the battery's my early voltage checks had 3.5 to some 3.6v battery levels I had found that if I discharge to low I had issues with my MPPT coming on to charge the battery backup
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