How many hours to top balance cells?

[Ampster]

Another option would be to use a resistor to pull down those two high cells. That process can be time consuming because it has to be done in little steps and charge cycles have to be repeated until all the cells get near 3.6 - 3.65.

 

[AlexanderKristiansen]

Another option would be to use a resistor to pull down those two high cells. That process can be time consuming because it has to be done in little steps and charge cycles have to be repeated until all the cells get near 3.6 - 3.65.

@Ampster how?

 

[time2roll]

A 3.5 Ohm resistor will pull 1 amp. and dissipate 3.5 watts
A .7 ohm resistor will pull 5 amps and dissipate 18 watts.
A 110' #18 wire is .7 ohms.
Some have used an automotive incandescent lamp but might be slow.
Just be careful, lots of energy in each cell.

 

[Ampster]

@Ampster how?

@time2roll roll described the math above. Finding that exact value is tricky.

 

[Gazoo]

@Ampster how?

If it was me I would charge them individually. You don't need to disconnect anything. You will be surprised how quickly it will be done.

 

[Gazoo]

@Gazoo can I leave them in their current position, disconnect the wires and charge the cells one by one to 3,6V?

Yes. You do not need to disconnect the wires.

 

[time2roll]

Ohmite 825FR70E on amazon

 

[Ampster]

Ohmite 825FR70E on amazon

I used some like that. I attached them to a heat sink. It started adding up until the cost was getting close to to the cost of a variable discharger like Will has recommended.

 

[Bob B]

My 2 cents ..... there are multiple opinions about how to proceed ... and from what I see, all methods will probably work.

I would suggest to the OP that he choose that method that seems right for him and work with the person who recommended that method.

 

[Ampster]

If it was me I would charge them individually.

My experience suggests that process could be more expedient. Even though that means charging 6 cells instead reducing two cells with resistors. The time to drop capacity with a resistor can take longer than the more automated process of charging a few cells. And of course that is easier with a 4S or a 8S pack. My pack is 16S and therein lies the dilemna.

 

[John Frum]

My experience suggests that process could be more expedient. Even though that means charging 6 cells instead reducing two cells with resistors. The time to drop capacity with a resistor can take longer than the more automated process of charging a few cells. And of course that is easier with a 4S or a 8S pack. My pack is 16S and therein lies the dilemna.

It would mean topping off all 8 cells.
Its what I did.
The longest took ~1 hour and the shortest <15 minutes.
Did it all in an afternoon while I watch the boob tube and had a drink or 2.
Don't forget the safety glasses.
I prefer the yellow ones because I don't forget I'm wearing them.

 

[Ampster]

Did it all in an afternoon while I watch the boob tube and had a drink or 2.

Haha. My resistor process took days. I even overshot the discharge on one cell and had to then charge it back up.

 

[John Frum]

Haha. My resistor process took days. I even overshot the discharge on one cell and had to then charge it back up.

This is the buck converter I used.

Adjustable Voltage Regulator, DROK DC to DC 5.3V-32V to 1.2V-32V 12V Power Supply Module, 12A LCD Step Down Volt Transformer 160W CC CV Buck Converter Reducer : Amazon.ca: Tools & Home Improvement

Adjustable Voltage Regulator, DROK DC to DC 5.3V-32V to 1.2V-32V 12V Power Supply Module, 12A LCD Step Down Volt Transformer 160W CC CV Buck Converter Reducer : Amazon.ca: Tools & Home Improvement

www.amazon.ca

This is the capacity tester.

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

 

[Ampster]

This is the buck converter I used.
......
This is the capacity tester.
....

I have since added those tools to my toolbox. I also installed an active balancer on a test pack and am going to use it on my larger pack when I reconfigure the pack. I tried several active balancers and will try to find the link.

 

[AlexanderKristiansen]

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 )

 

[John Frum]

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 )

Before you do anything what is the cell voltage of each cell?

 

[AlexanderKristiansen]

Before you do anything what is the cell voltage of each cell?

Cell 1-7 is 3,34-3,35, the 8th cell is now 3,53

 

[John Frum]

Cell 1-7 is 3,34-3,35, the 8th cell is now 3,53

Do you have a 100 watt incandescant bulb per chance?

 

[Ampster]

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.

 

[John Frum]

Do you have a 100 watt incandescant bulb per chance?

Or a a very long run of wire?