So is 93.7 my max capacity now?
- Thread starter Ennis437
- Start date
Lt.Dan
Solar Wizard
Do a full cycle from HVD to LVD and I bet it will update with the true value.
I also would take these capacity with a grain of salt because the shunts built into the BMS's are not always the most accurate thing.
I also would take these capacity with a grain of salt because the shunts built into the BMS's are not always the most accurate thing.
Brucey
Emperor Of Solar
There's a problem with at least one of the cells being high, the BMS probably stopped taking charge earlier than ideal. But as mentioned soc may be a way out guess especially with very low loads.
Lt.Dan
Solar Wizard
True, but based on the other cells being really closed to 3.5v, I would bet they are just a few mA behind cell 5. Nothing to be concerned of. They are all still at 100%
I would consider that a well balanced pack.
Ennis437
New Member
Well, I did that last night. The BMs actually cut it off reported 0 Ah and it fully charged only to 937. Also, it says the state of health is only 93.7. I’ll isolate the pack and try again and see..
What were your results?
Quattrohead
Emperor Of Solar
That is a badly balanced pack. Try to lower your charge voltage enough so that cell #5 doesn't hit the over voltage protection and see if you can drag cell 15 up to the others too.
shadowmaker
Solar Wizard
Cell #13 is 3346mV while #5 is 3610mV. That's delta 264mV @56,2V which is too much. You need to balance that pack better (within 50-100mV @~56V is usually good enough, although there are always people who say delta needs to be less than 2mV @58,4V...). If you have only some crappy 50mA passive balancer in your BMS it's not going to work and you need to drive up low cell(s) with external power or insert aftermarket active balancer to your pack like I have done (Neey 4A). Even 1A active balancer can balance your pack fairly fast.
At least for me it usually is enough to only once top balance with active balancer (<10mV @56,4V) and then I can disconnect it for good as crappy original balancer is then beefy enough to keep it balanced. I just leave wiring loom (~15e) there if ever needed again.
At least for me it usually is enough to only once top balance with active balancer (<10mV @56,4V) and then I can disconnect it for good as crappy original balancer is then beefy enough to keep it balanced. I just leave wiring loom (~15e) there if ever needed again.
Ennis437
New Member
I tried all the suggestions on this thread charged at 5 amps @56 v land it would never balance. Should I lower voltage and try again?
DIYrich
Solar Wizard
Charge until the bms cuts off charging. Back off 0.1v from that cutoff voltage, and hold that voltage while the cells balance and bms doesnt cut off charging. Once balanced, increase voltage by 0.1v. Rinse and repeat.
shadowmaker
Solar Wizard
Balancer specs? If passive and 50-100mA it will take weeks to balance even with your small 5kWh pack. The problem with passive balancer is that it can only burn energy from highest cell. It works fine if you have only few high cells on your pack and the rest are fairly even, but it seems you have super low cell(s?) so it needs to burn that extra energy from 15 cells to get that last one on par with the others.
I am not sure.
Ennis437
New Member
I have no idea on the balancer the battery is a sungold rack battery 100 AH sg48100 p
Suijkerbuijk
I cannot be held responsible for this information.
0.1volt behind .
No not good Balance and the reason he do not have its max battery pack.
If its 0.02 volt different than its a good balance cells.
3.5v vs 3.6v
Lt.Dan
Solar Wizard
Yeah that's not true. You can have a 200mV imbalance and still have 100% charge.
Don't forget 3.4v at rest is 100% charge. So if all cells are over 3.4v at rest, the pack is fully charged. It doesn't matter.
If the pack is low on capacity, but all cells are over 3.4v at full charge, then it's not an imbalance problem causing the low capacity, it's a cell with low capacity.
shadowmaker
Solar Wizard
Balancer not mentioned at all on their web page, so I'm pretty sure it's some tiny passive balancer which is very common. Active balancers are usually advertised with cat size letters as it is a new thing.
You need to open up your batt and either install active balancer or charge up low cell(s) with other means. Passive balancer is going to be extremely slow in your case.
My friend opens BMS connector and charges low cell using existing leads with 5V phone charger. You just need to monitor cell voltage as you can overdo it easily. After ~3,38V voltage starts to rise fast.
Ennis437
New Member
I have a desktop power supply that I used to balance before, is it worth even messing with I really don’t want to open up the pack and if i left it charging at say 56 or 55.5 volts would it ever balance out? The software reports 93.7 ah and that was almost exactly what I got on a capacity test. So the low voltage cell could it just be it won’t hold anymore? Thanks in advance
shadowmaker
Solar Wizard
It will eventually balance your pack, but my guess is it'll take closer to month than week to do it. Passive balancer is really crappy when you have low cell(s).
Here's video where your battery is opened. Would be really easy to use your power supply to charge low cell(s) up. Just get your other cells close to 3,50V and charge low cell(s) with constant 3,50V. Doing so you don't need to babysit it.
Suijkerbuijk
I cannot be held responsible for this information.
I agree.
Same with bms with a Active old balancer that only do 0.5a .
I'm a week and its still not balance correct.
You have to wait 2days for that the balance have drop the cells and than charge up again.
Special with close box and you can not open it.
Ennis437
New Member
Ok guys I am charging cell 13 at 3.6 volts 5 amps and it seems to be rising. Do you guys have recommendations for doing capacity test on my server rack battery? I have a victron shunt and a Chargeverter if those would be useful
Can you post the Voltages for all cells when fully charged? Your data is from May, so I would think it is a bit better now if bms was allowed to do its job. However, BMS balancing is a bit confusing for a lot of folks on this forum.
There are a few criteria that one should know to understand the balancing function. If you can adjust 1,2,3 you can really optimize the BMS function just for balancing.
1: At what V will the BMS start its balancing function?
2: At what V differential between cells will it start and stop?
3: At what V does BMS cutoff for high cell V protection?
3: At what current is the balancing taking place
Here's a table of just an example of what your cell V is when BMS cuts off.
Based on this, you should set your charger to <56.07V, but keep in mind there will be a slight Voltage drop (dependent on current) from what the inverter reports to what the battery terminals > the cells actually sees. As time goes by, you can adjust cahrger V higher by .05V-.10V.
The idea is to keep the BMS working continuously as long as possible.
Example, just a 1% cell capacity differential between highest and lowest =1Ah. If BMS is 100mA capable = 10hrs BMS needs to continously work to get it to balance. Now factor in what happens and the time spent when BMS is in protection mode.
The 93.7Ah you observed is the useable energy between the highest cell V cutoff during charge and the lowest cell V cutoff during discharge = not correct if cells are not balanced.
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Ennis437
New Member
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Ennis437
New Member
The numbers from May are pretty much unchanged cell 13 is low and cell 5 is still high with every other cell reporting near identical readings. Cell 13 and cell 5 only begin to drift at the very end of a discharge or the very end of a charge. My inverter voltage is set to 56v but anything higher always trips the battery BMS high voltage shutoff when cell 5 hits the 3.65 volts. every other pack is almost flawless. My hope is (by bringing up cell 13 by charging it directly with bench power supply). will allow the pack to discharge fully and bring cell 5 back in to check because previously when I got to 93 amps of discharge the BMS would cut off for low voltage from cell 13 so if I can get those 2 cells to behave I should have all 5 packs at 100ah or more.
sunshine_eggo
Victron's little biatch
All cells 3.5-3.6 isn't an issue. That's a very slight imbalance. The outlier at 3.3X is a big deal. Bringing that one up to at least 3.5V should restore a good chunk of your lost capacity.
In addition to the shunt and charger, you simply need a load.
shadowmaker
Solar Wizard
That is only true if only one cell is high and rest 15 are 1% lower. Then passive balancer burns that one cell down in about 10h. But OP has at least one cell substantially lower than 15 others. Your example with one cell 1% lower than others would mean that actually passive balancer needs to burn that 1Ah times 15. So balancing time is ~150 hours...
With active balancer things change as it transfers energy from the highest to lowest so deltaV comes down quite fast.
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