diy solar

diy solar

150Ah 4s BLS initial balance / test questions

JohanB

New Member
Joined
Nov 10, 2019
Messages
44
I am just about to put together my first lifepo4 battery ever for a van build. I bought these cells and a daly 200a bms back in dec 2019, but the project got delayed and the cells have just been stored in the boxes. It is the same higee cells as keith among others have mentioned here in previous posts. I am a newbie on this, but I have generel technical understanding (even a masters degree in vehicle engineering, but it doesnt really help me here).

I've watched a bunch of youtube videos and read some posts here and came to the conclution that i should test ans top balance my cells. I just assumed that the BMS would take care of the balancing after charging but i realise bow it might not be that simple.

This is what I've done so far:
Measured each cell when they arrived and after 9 months stored. All 3.290-3.292 as marked, same now as 9 months ago. Built a box, connected the BMS and charged with 20A 14.6V charger. My idea was to try a couple of cycles hoping the cells would stay the same. This did not happen though. I ended up with one cell at 3.65 where the BMS shut off charging, and three cells at 3.33. I waited for a couple of hours and nothing changed and then i staryed doung some research and ended up here.

So what to do now? I have a battgo bg-8s balancer, a shunt battery monitor, a 20A 14.6V AC charger and a 2500w pure sine inverter to play around with. Ive seen some recommendations of charging and discharging individual cells to see how closely they are capacity wise, but i do not have a suitable charger.

My idea is to top balance with the balancer, fully discharge and measure capacity and individual cell voltage, charge again and see how they follow and if needed repeat. How doess that sound? Any other suggestions?

The cells are slightly bulged when I check closely (1-3mm) but they look new, have serial numbers and BLS claims they are new grade A.

I would really appreciate any support on how to proceed. I would ideally spend as little time and work as possible and get the pack ready.

Btw, does anyone now the balancing algorithm in the Daly 200A BMS from 2019? I read somewhere that it just puts a 1A load on tye cell that are above the other. There is no measurable current in any of the BMS balance leads now when one cell is 3.65 and the other 3.33. I will now leave it overnight and see if anything changes.
 
Ok I found the Daly bms balancing data. 30 mA bleed above 3.5V. Thats kind of less than i can measure with my clip on (or whatever they are called) amp meter. So I guess I could also just leave the charger plugged in and eventually get all the cells up to 3.65, even if it would take a few days. Is that a good option?

I also wonder if these values are a concern or if it's kind of normal?
 
Ok I did some more research. I realize the ideal way would be to get a bench top psu, connect the cells in parallell and charge them all to 3.60 or 3.65. I also realise my AC charger only does constant current 20A to 14.6. Is there any downside worh using that? What if i hook up the battgo balancer and balance with that and then charge again until any cell reaches 3.65? And if there is still a difference, repeat until i get them all to 3.65? Or should I to get a sutiitable power supply for charging in parallell?
 
I bought the HiGee 150 Ah cells from BLS in about the same time frame.

I did full capacity tests on each individual cell using a programmable PSU and an electronic load. That is in no way needed, but it did give me a lot of information.

Most valuable to you would be that while all the 33 cells shipped at basically the same voltage (within a few mV), and their tested capacity were all within a few Ah, their shipped state of charge differed quite a lot. In the initial charge cycle, the largest difference I found was above 8Ah.

Your BMS could take care of that imbalance, but with a balance current of only 50mA it would need to stay in balancing mode for 160 hours.

In order for your BMS to be able to balance for that long, you would need to charge with a current as low as the balancing current. It would also mean that you would keep your cells at 3.65V for extended periods of time while doing this balancing, causing them harm.

Get a suitable power supply and charge the cells individually or in parallel, before reassembling the pack.
 
I bought the HiGee 150 Ah cells from BLS in about the same time frame.

I did full capacity tests on each individual cell using a programmable PSU and an electronic load. That is in no way needed, but it did give me a lot of information.

Most valuable to you would be that while all the 33 cells shipped at basically the same voltage (within a few mV), and their tested capacity were all within a few Ah, their shipped state of charge differed quite a lot. In the initial charge cycle, the largest difference I found was above 8Ah.

Your BMS could take care of that imbalance, but with a balance current of only 50mA it would need to stay in balancing mode for 160 hours.

In order for your BMS to be able to balance for that long, you would need to charge with a current as low as the balancing current. It would also mean that you would keep your cells at 3.65V for extended periods of time while doing this balancing, causing them harm.

Get a suitable power supply and charge the cells individually or in parallel, before reassembling the pack.
Thank you so much for the reply, exactly what I wanted to hear! I just ordered a power supply that shouös be here in a couple of days.

After 24 hours the bms took the 3.46. I am now testing to balance with the battery go but it is really slow. So I'll wait for the power supply to show up!

This is pretty fun when a start to understand how it works!

May I ask what capacity you got from the cells? And if you noticed any degradation over time?
 
For my capacity tests, I charged with 30A until 3.65V, no CV stage. Rest for 10 minutes, then discharge at 30A to 2.7V. Results varied between 145.5 and 150.7Ah.

I've not done any further capacity tests since installing. In my application, a full cycle from full to empty will basically never happen. I will thus not "naturally" get any real capacity tests. Might do some capacity test at some point, if I find something off. For now I haven't.
 
Back
Top