It's an option I guess but would it not take a huge amount of time?
For example, assuming cell SoC is now 30%, charging at 3.6v @ 10A is 36W so it would take around 14hrs to add 50% (480Wh) charge. 14hrs x 32 cells = 19days.
Do I have to top balance if cells are all the same voltage?
- Thread starter Rob99
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For example, assuming cell SoC is now 30%, charging at 3.6v @ 10A is 36W so it would take around 14hrs to add 50% (480Wh) charge. 14hrs x 32 cells = 19days.
littleharbor2
Solar Addict
Can you explain how you can fully charge them overnight with the bench charger? Still takes me a week to charge 16 cells, 4 in series at a time. Maybe my power supply is lower output.
houseofancients
Solar Wizard
If you look at the steps, first charge them in series untill BMS cut off..
Then top off all individual cell to 3.6 v , shouldn't take more than 10/20 minutes after that
If you read earlier threads top balancing takes on the same excitement as watching paint dry, an Apple turning brown or watching the grass grow. A 10 amp bench tester will take a while.
One caution with top balancing in series is to closely watch your charge values towards the end. Do not trust the charger to turn itself off. The precision on these are typically average.
There was more than one thread asking for advice when the cells went above desired voltage. A good multimeter is your friend with solar.
One caution with top balancing in series is to closely watch your charge values towards the end. Do not trust the charger to turn itself off. The precision on these are typically average.
There was more than one thread asking for advice when the cells went above desired voltage. A good multimeter is your friend with solar.
So, if I read this right..........
1. hook up the built battery (inc BMS),
2. set the BMS to shut off at 3.6v,
3. charge battery (50A via inverter),
4. when BMS shuts off charging disconnect battery,
5. top up each individual cell using my bench supply.
littleharbor2
Solar Addict
Do you then want to put them all in parallel and let them balance out after that
TomC4306
Solar Obsessive
Correct.
Edit - when the cells go above 3.45 or so, you may want to dial back the 50 amp charge.
You'll get a little bit more into all of the cells if you ease up to 3.6 versus slamming up to 3.6.
Thanks.
I'll take the cells up to 3.45 first and then charge at 25A until it hits 3.6
No, because theyll be installed in the battery case and I wont be taking them out and reconfiguring them. Once top balanced I hope the BMS will manage it nicely from then on.
littleharbor2
Solar Addict
Let's see what houseofancients says as I asked him.
No need to disconnect the charger, but you may need to turn it off or really reduce the charge current while you boost the stragglers with a power supply. The bms will be cycling charge disconnect because the runners always run fast. When you use the power supply you will notice that a safe low voltage setting (3.65)on the power supply won’t deliver much current, so you will probably raise it. Now you are in the danger zone! You can NOT leave the power supply connected without monitoring it for a moment because things that hardly moved can suddenly run away in seconds and damage your cell. I used a roll of 500’ 10 awg as a resistor to bring the runners back. Regardless of whatever method you use to manually adjust the cells you must be aware that you must be looking at live data, working on the correct cells and never leave adjustment connections un monitored and connected.. not for a moment.
houseofancients
Solar Wizard
houseofancients
Solar Wizard
Why ?
Once the cells are close enough to eachother, let the BMS handle it.
This way the cells stay compressed an neatly in their enclosure and @Rob99 doesn't have to fiddle with busbars etc..
Agree that it would be good to dial the charging amp back, although this BMS will limit the charge amps to 10 once 3.5v is reached by any of the cells.
Furthermore, make very sure you set the voltage on your bench charger BEFORE connecting it, and DO NOT fiddle with the voltage, eventhough it may not do it max amps..
Just be patient untill amps drop to 1
MisterSandals
Participation Medalist
Does the BMS communicate with the charger to drop charging amps?
If not, I don’t think the BMS can do this other than cutting off charging (not reduce to 10A as stated).
houseofancients
Solar Wizard
Does both, limits through comm, but if no comms, "hard limits"
littleharbor2
Solar Addict
I hear you on that. I was trying to top balance my first LFP pack (all in parallel) and was shielding the whole thing with a large piece of cardboard due to being out in the sun. I must have nudged the voltage knob and on the last day they jumped to over 5 volts before I could catch it. Not pretty and I was sick with grief seeing my new and expensive cells sitting there all bloated up.
You lost me on this
houseofancients
Solar Wizard
Why?
This is a passive balancing BMS..
What does that do , besides shielding against over charging ?
It burns off power when get to a higher voltage than the others above 3.40..
If charging individual cells to 3.6, wouldn't that be rather counter productive ?
Of course when done charging the individual cells, they should be reconnected
Rednecktek
Solar Wizard
Let me grab a couple example photos of what I did with my nephew's battery box...
So the first step was to wire all the cells together as a pack WITH the BMS installed. I then threw a regular car battery charger on there at 25a and let it sit for a day. These were 304Ah cells that came pretty dead so it took about 9 hours until the battery charger said it was full. No real balancing was done, I just wanted to get them up on the knee as quick as I could to save time on the balance.
The next step was to pull the balance leads and BMS off and wire up a harness with enough leads to get to all the cells. All the cells are in parallel in the picture with just some 14awg and ring & butt connectors connected to my bench supply. I set the bench power to 3.58v because mine likes to drift a hair when the load is almost nothing and just let it go overnight. Since I did 95%+ of my charging with the big car charger it only took about 6 hours for the cells to get that laaaassttt little bit and since they were all in parallel the voltages would stop at 3.6v when everything was full.
After that the pack was re-assembled and installed and I know when we closed up the box the battery was 100% full and all the cells were perfectly balanced, Zero'd Out.
Does that help? Your process would be the same just with more cells involved.
You could do it that way, or temporarily disable the balance. I leave them on. I may boost a low cell a tad higher than the average, counting on it falling back immediately after, at rest. The passive balancer vs a power supply is like a fart in a gail storm.
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