7 minutes ago, Skipbidipop said:

Thank you all for help.. I'm home now, and took the battery with me.. looks like I'll have to use lead-acid for few more weeks there .. good thinking for not taking those 200kg batteries out of the basement because my back would say "no" if I had to carry them down there again 🤣

They have been balancing (passive I guess, through the BMS) whole day today, while I was reconnecting my lead-acid back and traveling home.. and they are a bit closer to each other now.. when the BMS stops charging I will connect them in parallel again and top balance with my slow charger

I'm charging now with 20A.. Should I go higher?

So, should I go to 3.6 or 3.625, 3.65V ?

Less, if your using the bms  3.45 to start with. Then gradually increase as the current goes down.

Why less with the BMS?

You mean to 3.45 while in series(with BMS) and then to 3.6 when top balancing in paralel? 

Edited January 19, 20251 yr by Skipbidipop

I have increased the current to 30A

41 minutes ago, Skipbidipop said:

Why less with the BMS?

You mean to 3.45 while in series(with BMS) and then to 3.6 when top balancing in paralel? 

Less chance of the higher SOC cells going over voltage and gives the bms chance to do its balancing.

If you can get away without paralleling then you can still increase the voltage as the current goes down.

7 hours ago, Skipbidipop said:

So, should I go to 3.6 or 3.625, 3.65V ?

I would personally not exceed 3.6V, in fact 3.55V balanced is probably 99% full and maybe even a bit over... so, if you can provide 100A with all cells paralleled at 3.55V then you can probably just let it stand and when the current is down to less than 1A, I'd say the cells should be fairly well balanced... if you have time... wait for current to drop below 100mA

I got to around 3.45 for most of the cells except for that last 16th cell, which got to over-voltage protection and turned off the charging.. now I am slow balancing at around 8A again

so now this one cell got to more than 3.6V couple of times and sometimes even to 3.7 for few seconds.. did this damage this cell maybe ?

In the app there is this parameter called "overvoltage release delay" and I misinterpreted it and set it to 10sec.. and by default it is set to 2sec .. you can see a screenshot of my settings couple of posts ago

13 minutes ago, Skipbidipop said:

I got to around 3.45 for most of the cells except for that last 16th cell, which got to over-voltage protection and turned off the charging.. now I am slow balancing at around 8A again

so now this one cell got to more than 3.6V couple of times and sometimes even to 3.7 for few seconds.. did this damage this cell maybe ?

In the app there is this parameter called "overvoltage release delay" and I misinterpreted it and set it to 10sec.. and by default it is set to 2sec .. you can see a screenshot of my settings couple of posts ago

It should be ok. Keep dropping the current so it doesn't go over again. Don't rush the charging. Ther will still be big differences in SOC.

4 hours ago, Skipbidipop said:

so now this one cell got to more than 3.6V couple of times and sometimes even to 3.7 for few seconds.. did this damage this cell maybe ?

hopefully not, i still reckon if all the other cells are at around 3.45V and the one at 3.6V, I'd put a load on the high Voltage cell to bring its Voltage down, connect a 100W 12V Halogen lamp to it, that could draw maybe 25W, maybe, so 7 or 8A out of the cell and when it reaches 3.45V, disconnect the load/lamp and see what how things progress from there, rinse/repeat if required...

@Skipbidipop, thinking last night, my mental math was way off, I can only blame our daily peak temperatures of between 45 and 52degC in the shade, its turning my brain to mush...

To recap 100W, 12V Halogen, assume at 12V it is 100W, then P=VI, means 100/12=app 8A current, now V=IR, 12V/8A=1.5Ohm app. at 3.6V that would work out to a measly 2.4A or just less than 10W of draw out of the cell, which is fine, just it would take somewhat longer than the 7-8A I was thinking in my previous post... funny, no-one else picked up the screwup, maybe I'm not the only one having his brain fried this summer...

52°C ??? 🫠

I know this is South African forum.. are you from there also ? Actually I don't know how I ended up on this forum.. I guess while I was googling, this forum came up a lot, so I decided to join 😁

For me it's strange to think that south half of the world celebrates new year in the summer and have the longest day of the year in December ..and I am talking about how I'm afraid that my batteries will be damaged around 0°C while you have 52°C 😅

I know this is off-topic but it's interesting

btw, I also think in "12V math" all the time, so no problem 😆

45 minutes ago, Skipbidipop said:

I know this is off-topic but it's interesting

Here's a temperature graph and PV production graph for the last few days, you can clearly see when we had mostly (15th Jan.) and partial (18 & 19 Jan) cloud cover, but not really visible on the temperature graph, a BME280 sensor outdoor being handled by an ESP8266 module.

I have changed my wires for parallel/balance charging to copper strips and that has changed the current quite a lot.. finally my weak charger can give full current (10.2A) and go into constant current mode.. previously I had just wrapped and torqued regular electrical solid core wire around the posts ..and the resistance was too large so I was getting only around 8A .. so now I don't have to worry about voltage drop on the wires because it has almost none.. <0.001V on the wire to the charger and 0V on the copper strips

Yesterday it was charging at 3.47V, the whole day.. for a long time the voltage didn't change.. and during the evening, in just couple of hours the voltage raised from 3.47V to 3.58V .. and now(few hours later) its still in CC mode at 3.65V  and I expect to see transition to CV mode soon (voltmeter on the charger is showing a little bit more than it actually is)..

is this normal? Is this that flat part of the curve transitioning to vertical part ?

___

edit:

I just watched this video and I think this is my answer .. when I compensate for voltage drop in wires from the charger and the fact that my charger voltmeter is not precise

Edited January 23, 20251 yr by Skipbidipop

6 hours ago, Skipbidipop said:

its still in CC mode at 3.65V

Stop, don't go this high you should ideally if you want a longish life out of the cells, probably not go beyond 3.55V per cell, there is very little energy to be had at these extremes and you are just not doing your cells any favours hitting those Voltage levels...

the actual voltage was around 3.59.. because, as I said, the voltmeter on the charger is showing little bit more ... it's just not precise.. when I measue the voltage on the charger it's around 3.59 and there is couple of mV on the wires from charger to battery

I disconnected the charger and left the cells in parallel for over 8 hours now.. the voltage now is 3.500V - 3.501V, but the deviation of 0.001 volt is probably because of the instrument I'm using (poor battery in it and very bad test leads/wires - its UT61E btw)

Is this OK, expected ?

4 hours ago, Skipbidipop said:

Is this OK, expected ?

Yes, if they are all in parallel, then there can't be any deviation... the question would be, were the cells still squirelling away some current when the charger was running, which would imply they were still absorbing energy and may not be well balanced, even if they are now all at the same Voltage...
it is also normal for a fully charged battery sitting idle to have the cells drop down to even under 3.5V but be fully charged, the 3.55 to 3.6V charge Voltage/cell used to charge up the cells will allow the absorption to occur and then if you have a decent balancer additionally or as part of your BMS, to get the cells into a fair equilibrium over the whole battery

Edited January 24, 20251 yr by Kalahari Meerkat
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