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Top Balancing "How to"

In 8S, the cells would alternate on connections. + to - on each cell to the adjoining cell. This would require using a BMS as the voltage would be nominal 24V. Do you have a 24V BMS? My guess is you are building a 48V pack and have a 48V BMS but not sure if you have a 24V BMS.

Are you using a power supply or charger? With the power supply you can turn the voltage down to 3.65V and charge using C.V. (constant voltage) with cells in parallel.

Would be best to let us know what you have for charging and what you have for any BMS's. Photos or links to what you have.


What do you for a BMS? The idea behind using the BMS is to charge cells up quickly until one cell causes the disconnect, then finish balancing cells in parallel. It doesn't take long to finish balance on 8 or 16 cells in parallel after charging using the BMS A few hours and it will be done.

Is my BMS.

I wasn't going to charge them either BMS just a DC charger but all I have is this Jesverty DC Power Supply Variable, 0-30V 0-10A Adjustable Switching DC Regulated Bench Power Supply with High Precision 4-Digit LED Display, 5V/2A USB Port, Coarse and Fine Adjustment SPS-3010 https://a.co/d/5vuiH5g


But I was thinking I get a second one of those and then could charge 2x 24 volts at 10 amps? Maybe I can wire the chargers in series to achieve that.
 

Is my BMS.

I wasn't going to charge them either BMS just a DC charger but all I have is this Jesverty DC Power Supply Variable, 0-30V 0-10A Adjustable Switching DC Regulated Bench Power Supply with High Precision 4-Digit LED Display, 5V/2A USB Port, Coarse and Fine Adjustment SPS-3010 https://a.co/d/5vuiH5g


But I was thinking I get a second one of those and then could charge 2x 24 volts at 10 amps? Maybe I can wire the chargers in series to achieve that.
No need for a second power supply. Use the BMS for initial charging in series using 8 cells with your power supply set to 29.0V, set the BMS to high cell volt disconnect at 3.65V. When the BMS disconnects, break down the pack and put cells in parallel. Set power supply to 3.65V and when amperage drops to almost 0A, you are done. Then do the other 8 in series using the BMS the same way.

This will shorten the time considerably.

The other way to let the BMS balance cells is to charge to around 28V or less. When the 8 cell pack pack hits 28V, the BMS should have started balance. You can limit the amps on the power supply so the BMS can passive balance the cells. Once cells are balanced at that level, the voltage is increased by 0.5V, amps kept low and let the BMS balance cells again to that voltage level. You can balance all the way up to 29.2V but it isn't really necessary. If you plan on charging to 3.5V per cell as an example, (which is 28V) when you are using the battery, then just balance cells to that point. I run my 48V pack to 56V bulk and 55.5V float. This allows balancing to occur and cells are about 99%+ SOC.
 
The other way to let the BMS balance cells is to charge to around 28V or less. When the 8 cell pack pack hits 28V, the BMS should have started balance. You can limit the amps on the power supply so the BMS can passive balance the cells. Once cells are balanced at that level, the voltage is increased by 0.5V, amps kept low and let the BMS balance cells again to that voltage level. You can balance all the way up to 29.2V but it isn't really necessary. If you plan on charging to 3.5V per cell as an example, (which is 28V) when you are using the battery, then just balance cells to that point. I run my 48V pack to 56V bulk and 55.5V float. This allows balancing to occur and cells are about 99%+ SOC.
This method works best with active balancers that have a reasonably high balance current. Ideally, the charge current during this balancing process would be less than the balance current. Otherwise one of the cells will hit the cell voltage limit too soon.
 
No need for a second power supply. Use the BMS for initial charging in series using 8 cells with your power supply set to 29.0V, set the BMS to high cell volt disconnect at 3.65V. When the BMS disconnects, break down the pack and put cells in parallel. Set power supply to 3.65V and when amperage drops to almost 0A, you are done. Then do the other 8 in series using the BMS the same way.

This will shorten the time considerably.

The other way to let the BMS balance cells is to charge to around 28V or less. When the 8 cell pack pack hits 28V, the BMS should have started balance. You can limit the amps on the power supply so the BMS can passive balance the cells. Once cells are balanced at that level, the voltage is increased by 0.5V, amps kept low and let the BMS balance cells again to that voltage level. You can balance all the way up to 29.2V but it isn't really necessary. If you plan on charging to 3.5V per cell as an example, (which is 28V) when you are using the battery, then just balance cells to that point. I run my 48V pack to 56V bulk and 55.5V float. This allows balancing to occur and cells are about 99%+ SOC.
So the BMS's 0.6 amp balancing isn't to low to depend on? You say passive balance but I think the BMS does active? Or is passive just something that occurs anyways?

Also you say ~28Volts but 16s would be for 48V system?
 
This method works best with active balancers that have a reasonably high balance current. Ideally, the charge current during this balancing process would be less than the balance current. Otherwise one of the cells will hit the cell voltage limit too soon.
One can turn the amperage down with the power supply. My Batrium uses 0.75A for balancing bypass and it has to end the load as the heat sink builds up heat. I've seen 120A heading into a 64 cell bank and it handles it fine. I have one major runner that will be heading for use in the golf cart but the Batrium still handles it well in bypass.
 
So the BMS's 0.6 amp balancing isn't to low to depend on?

Also you say ~28Volts but 16s would be for 48V system?
Your are limited to charging under 30V with the power supply. So you have to use 8S to charge using the 30V power supply.

Yes, the 0.6A will work but you have to set overall pack voltage low enough plus limit amps as you approach higher cell voltages. That is why you move up in steps. 28V would be 3.5V per cell and balance should begin at 3.4V. Once you see any cells over 3.4V, then turn the amps down lower. This gives the passive balancer time.
 
What is the easiest way to bleed off one cell? Only resistor I have is a 10w 250 golf cart pre charge…lol…
 
Anyone know a good balancer ? i bought one from alliexpress 10A but that thing wil take weeks/months to balance 8x 314Ah cells.

i see a lot of people taling about the EBC-A40L but i havent found clear instructions/settings on how i could balance 8x 314ah cells with it
 
Anyone know a good balancer ? i bought one from alliexpress 10A but that thing wil take weeks/months to balance 8x 314Ah cells.

i see a lot of people taling about the EBC-A40L but i havent found clear instructions/settings on how i could balance 8x 314ah cells with it
A balancer ( when cells are fully charged) will balance in 2 hours

EBc is a cell tester/charger/discharger, NOT a balancer
 
Anyone know a good balancer ? i bought one from alliexpress 10A but that thing wil take weeks/months to balance 8x 314Ah cells.

i see a lot of people taling about the EBC-A40L but i havent found clear instructions/settings on how i could balance 8x 314ah cells with it
as below its a tester, but you can use it to top balance by simply using it to charge all cells to the value you want, and then assembling the pack. now if you want/need continuous balancing then you might want to buy better cells that do not drift as bad.

A balancer ( when cells are fully charged) will balance in 2 hours

EBc is a cell tester/charger/discharger, NOT a balancer
but you could use it to top balance which is the subject of this thread.
 
Anyone know a good balancer ? i bought one from alliexpress 10A but that thing wil take weeks/months to balance 8x 314Ah cells.

i see a lot of people taling about the EBC-A40L but i havent found clear instructions/settings on how i could balance 8x 314ah cells with it
and
A balancer ( when cells are fully charged) will balance in 2 hours

EBc is a cell tester/charger/discharger, NOT a balancer
Indeed, but I do use it to topup individual cells.

The way I do it is (for topping up individual cells):
- The battery is configured as for normal operation, If there is a cell that needs topping up I disable the BMS balancer
- I connect the EBC-A40L leads to the cell using the crocodile clamps (the cell is still in the battery).
- I set EBC-A40L to charging with constant current (40A for example) and cutoff voltage 3.65 and I charge it briefly.
- Check voltage, leave for 15min and repeat if necessary
To charge multiple cells:
-Charge them one after another. If the cells have unknown state of charge best to discharge fully and charge to full stopping at 0.05C current.
 
and

Indeed, but I do use it to topup individual cells.

The way I do it is (for topping up individual cells):
- The battery is configured as for normal operation, If there is a cell that needs topping up I disable the BMS balancer
- I connect the EBC-A40L leads to the cell using the crocodile clamps (the cell is still in the battery).
- I set EBC-A40L to charging with constant current (40A for example) and cutoff voltage 3.65 and I charge it briefly.
- Check voltage, leave for 15min and repeat if necessary
To charge multiple cells:
-Charge them one after another. If the cells have unknown state of charge best to discharge fully and charge to full stopping at 0.05C current.
True, but that in not balancing, that is charging to the top ;)
 
Thanks for the info, i want to use it to top balance, so i cant charge them all at once to top balance them ?
You can, but then you need to parallel them while charging, which could take a long time, unless you first charge them in series ( USE A BMS !! )
 
Ok clear, wil order the EBC-A40L then.
As @houseofancients intimated, use your BMS to bring them up to BMS shutdown. that way you can fast charge them.
once the BMS shuts down, re-configure them into parallel and then use the EBC-A40L to top balance them. that would be the fastest way to top balance them.
After that choose a BMS that has built in balancing to keep them there, that or buy cells of high enough quality to avoid the need to constantly balance them. full disclosure, I have two different brands of cells in my packs, Winstons, and CALB's. the Winstons were new form the factory direct, they hold a balance and I have not had to re balance them since commissioning last year. the CALB's were 3 separate orders and were either pull offs, or old stock that had sat around, of the CALB's they were several packs that did not hold a balance nearly as well. I had to re top balance them roughly once every 3-4 months at first. after 18 months of fighting them I reconfigured them into a 3p16s pack that I had capacity tested and IR tested then I matched them myself. by the looks of things it helped immensely but I will probably still need to re-balance them eventually.
 
Anyone know a good balancer ? i bought one from alliexpress 10A but that thing wil take weeks/months to balance 8x 314Ah cells.

No it won't.

i see a lot of people taling about the EBC-A40L but i havent found clear instructions/settings on how i could balance 8x 314ah cells with it

You see people testing cells with them.

Have you considered reading the top balancing guide?
 
I had it running for a few days and it did nothing, the A from the 10A alliexpress charger stayed the same.

Testing and charging what i saw right ?

i am building lots of battery packs (20x 24v 314Ah cases in parallel, so the total per 2 cases wil be 628Ah,) so i thought a good tester/charger could be useful, and from what i understood from the above posts is that i can charge the cells with a BMS connected to max with a 24v lifepo4 charger, and then put the cells back in parallel and top balance them with the EBC-A40L.

Or did i miss something ?
 
I had it running for a few days and it did nothing, the A from the 10A alliexpress charger stayed the same.

It put 3 * 24h * 10A = 720Ah into it. If you have a bunch of cells in parallel, charging at only 34W may take "forever." Voltage often won't budge for days due to the flatness of the voltage curve and the very low C rate. There's a couple places in the curve where voltage might dip 0.01V-ish.

Testing and charging what i saw right ?

i am building lots of battery packs (20x 24v 314Ah cases in parallel, so the total per 2 cases wil be 628Ah,) so i thought a good tester/charger could be useful, and from what i understood from the above posts is that i can charge the cells with a BMS connected to max with a 24v lifepo4 charger, and then put the cells back in parallel and top balance them with the EBC-A40L.

Or did i miss something ?

The guide instructs you to build the battery with the BMS installed and charge until the BMS activates charge protection @ 3.65V/cell. This allows you to charge at nearly 300W cutting your charge time by 90%. If the battery is imbalanced, then you put them in parallel to top off/balance.

With an active balancer or a BMS with active balancing installed, the balancing may only take 24 hours simply holding the battery at a voltage sufficient to engage balancing and paralleling may be completely unnecessary.

Did you follow the guide?
 
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It put 3 * 24h * 10A = 720Ah into it. If you have a bunch of cells in parallel, charging at only 34W may take "forever." Voltage often won't budge for days due to the flatness of the voltage curve and the very low C rate. There's a couple places in the curve where voltage might dip 0.01V-ish.
I don’t think either of you understand how active balancers work.

If one cell has a voltage difference of 100mV or more from ALL other cells, you’ll get a full 10A of balance current for that ONE cell.

When multiple cells are out of balance, that 10A gets shared between them (ie: 2 cells at 100mV delta from all other cells will get 5A of balance current each).

If you are attempting to balance multiple cells in the ‘flats’,, a 10A active balancer is going to be driving far less than 10A of balance current to the most out-of-balance cell…
The guide instructs you to build the battery with the BMS installed and charge until the BMS activates charge protection @ 3.65V/cell. This allows you to charge at nearly 300W cutting your charge time by 90%. If the battery is imbalanced, then you put them in parallel.

With an active balancer or a BMS with active balancing installed, the balancing may only take 24 hours simply holding the battery at a voltage sufficient to engage balancing.

Did you follow the guide?
The guide has the correct advice - charging up well into the knee and holding there using BMS protection is the most effective way to take advantage of an active balancer.

The most out-of balance cell will likely get close to a full 10A of balance current in that scenario (single runner).
 
If one cell has a voltage difference of 100mV or more from ALL other cells, you’ll get a full 10A of balance current for that ONE cell.

When multiple cells are out of balance, that 10A gets shared between them (ie: 2 cells at 100mV delta from all other cells will get 5A of balance current each).

Are you sure?

In one case 10A for 1 hour into one cell.

In the other case, 5A for 1 hour into each of two cells?

Or 10A for 1/2 hour into one cell, followed by 10A for 1/2 hour into another cell?

I've got a JK BMS 2A active balancer that I haven't installed yet, and I see a single toroid inductor (transformer?) about 1 1/4" diameter.
My guess is it has a single isolated DC/DC converter and multiplexer with 16 different 2-wire inputs. Sucks juice from one high 3.6V cell and delivers it to 48V pack.
 
My JK BMS 2A active balancer worked great after 2 cycles batteries are within .008. went from the box right into service. I didn't want to invest in a power supply I would use one time I have enough one time use tools.
 

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