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diy solar

How many hours to top balance cells?

Ampster said:
A short term solution is to set your Constant Voltage (Absorb) lower. Many here use 3.4 volts per cell and the runner cells stay with the pack at that setting. It is hard to tell how serious the imbalance is at resting voltages. Do we have data during end of charge cycle after this top balancing? Your earlier picture was helpful.
Click to expand...
How low? And I guess you mean on the inverter
 
smoothJoey said:
Lets keep it in the channel so others can help and/or learn.
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Yes, I agree. As I mentioned above it may not be a problem until we see the result of your next charge cycle. Others can benefit from that information.
I will repeat my suggestion that a solution just might be lowering your CV setting on your charger. Can you do that?
 
AlexanderKristiansen said:
How low? And I guess you mean on the inverter
Click to expand...
I mean on charger. If your inverter does both then yes on inverter. How low would depend on what it is now. Try 3.4 volts per cell. There is very little capacity above that.
EDIT:
I reread the initial post and assumed you charged 8 cells to 3.5 volts per cell (28 v for the pack). Try 3.45 per cell (27.5 for the pack) and see if you still have a runner. It does not look like a serious problem.
 
Last edited:
Ampster said:
Yes, I agree. As I mentioned above it may not be a problem until we see the result of your next charge cycle. Others can benefit from that information.
I will repeat my suggestion that a solution just might be lowering your CV setting on your charger. Can you do that?
Click to expand...
I guess this is "Bulk charging voltage (C.V voltage)" in the manual? Yes, I can lower it. How low?
 
How many days can you go without the battery in service?
You could try my suggestion from earlier and just enable balance during rest and let the pack sit for a day.
Report back tomorrow on the cell delta after 24hours.
 
AlexanderKristiansen said:
I cannot set CV for each cell, just for the pack.
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I am giving cell voltages for the benefit of other readers. The concepts are the same whether someone has a 4S pack or 16S pack. Cell voltage is the issue so it reduces most confusion if cell voltage is used. Since.that comment I reread your post and noted that you have an 8 cell pack. I will try to remember but science concepts and the laws of physics are easier for me than the details of every posters pack. Sometimes I can't remember why I went to the garage.
;)
 
smoothJoey said:
How many days can you go without the battery in service?
You could try my suggestion from earlier and just enable balance during rest and let the pack sit for a day.
Report back tomorrow on the cell delta after 24hours.
Click to expand...

I think I will just pack up my things and head home. I will bring the cell with me. Can you please explain to me in very simple terms how I can discharge just this one cell?
 
AlexanderKristiansen said:
I think I will just pack up my things and head home. I will bring the cell with me. Can you please explain to me in very simple terms how I can discharge just this one cell?
Click to expand...
buy a capacity tester and connect it to the cells terminals.

USB Adjustable Constant Current Electronic Load, LCD Screen, Configuration of CPU Fan, Battery Capacity Tester, Module 150W 200V 20A Over Voltage, Over Current, and Overpressure Alarm : Amazon.ca: Tools & Home Improvement

USB Adjustable Constant Current Electronic Load, LCD Screen, Configuration of CPU Fan, Battery Capacity Tester, Module 150W 200V 20A Over Voltage, Over Current, and Overpressure Alarm : Amazon.ca: Tools & Home Improvement
www.amazon.ca

discharge the cell until it is 100mv lower than the others.
Measure with a dvom at the cell terminals.
Let the cell rest for 2 hours and see how much it recovers.
Repeat of necessary.

This alone will not balance your pack though.
 
AlexanderKristiansen said:
I read somewhere that it's important to either connect the leads to the cells before or after you turn the power supply on. Dont remember which way is the right way. Do you know which way is correct?
Click to expand...

The recommendation is to have power supply disconnected from battery. Turn on supply and set desired voltage. Because there is no load, the voltage will be achieved and shown on display. Do NOT change supply voltage later. (I put tape over the knob of mine after adjusting.)
With supply set to correct voltage, connect it to cells. There might be a small spark, but limited current so not an issue.
(This is for lithium; if charging lead-acid batteries which give off explosive hydrogen gas we always either unplug supply or make the DC connection away from the battery terminals. Considering that a power supply unlike a battery charger has capacitors that could cause a spark, make connection away from battery.)
With cells connected to supply, current will show on display. Voltage may or may not drop below setting (depending on how much current is being drawn.) Do NOT adjust voltage. If you happen to bump the voltage knob, disconnect supply from battery so voltage setting is displayed and readjust.

The issue is, when charging individual or paralleled cells, BMS isn't able to monitor cell voltage and disconnect. So you must ensure power supply setting won't exceed allowed cell voltage. When using power supply to charge series-connected cells, you must use BMS with disconnect to protect the cells.
 
AlexanderKristiansen said:
I will bring the cell with me.
Click to expand...
The issue is the voltage of that cell when charging in the pack. Everything is relative. Taking the cell with you will not help you solve the problem. Leave it there. By your next visit it will probably settle close to the others. Have a nice drive home.
I think @smoothJoey and I are almost in complete agreement that the problem is not major.
;)
 
AlexanderKristiansen said:
Long story short, the top balancing did not go well. I charged the cells one by one, but it was difficult to get them to the same voltage. Now my battery pack is even more unbalanced. I need to discharge one 3,2V cell. I'm at my cabin, I cannot go to a shop and buy a resistor.

Is there an easy way to discharge this cell from 3,55 to 3,35 volts? (@Bob B @Gazoo @Supervstech )
Click to expand...
I don't know what you mean by it was difficult to get the cells to the same voltage?

You do realize the voltages of the cells will drop when disconnected from the charger? And the voltages will be different as the voltages settle?

If you charge each cell to 3.65 volts until the current shown on the power supply is 100ma's or less then you have fully charged the cell. The power supply should be in CV mode towards the end of the charge. If you do this for each cell it's the same as parallel top balancing.

You might have a dud cell. But I doubt it.
 
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