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diy solar

Top balance with out charger?

Wycowboy

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Dec 30, 2020
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Getting ready to get into building my bank.
I’ve got some time , I’ve heard you can top balance by hooking up the cells and waiting quite a while.

Does anyone have experience and a method for this?
How long does this take?
Down sides?

Is top balancing routine maintenance so I should just get the charger any way?

If so any recommendations?

Thanks so much!
 
Getting ready to get into building my bank.
I’ve got some time , I’ve heard you can top balance by hooking up the cells and waiting quite a while.
That doesn't work.
Does anyone have experience and a method for this?
Its a frequent topic on this forum
Is top balancing routine maintenance so I should just get the charger any way?
Top balancing should only have to be performed once during commissioning if the cells are reasonably matched the BMS should be able to maintain the top balance going forward.
If so any recommendations?
 
Does anyone have experience and a method for this?
How long does this take?
Down sides?
Yes, I have tried it in the past. It is hard to tell how long it takes because if the cells are not in the upper knee of the charge curve you have no way of knowing whether the cells are actually at the same SOC because the charge curve is very flat at lower voltages.
The down side is that you won't accomplish much for your effort is putting all the cells in parallel.

I have gone through too many benchtop power supplies so now I use Meanwell or equivalent power supplies which are typically fixed but have some adjustment. I can buy them used on Ebay with higher Amperage for a lot less than a bench top power supply. There are many with a range of 3.5-4.0 volts. I also use an inexpensive current meter so I can tell when I am nearing the end as the current tapers off. The built in current measurement is the only advantage of a bench top power supply.
 
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OK thanks that seems like great information! Next question is I was just watching a video but I will prowes Building a 16 S battery almost identical to what I will be building and he said that he was not going to top balance connect given time the BMS will handle this.
What is the downside of letting it be an ass down for batteries is it just because they will not be at maximum performance from the geckoBuilding a 16 S battery almost identical to what I will be building and he said that he was not going to top balance connect given time the BMS will handle this.
What is the downside of letting it be an ass down for batteries is it just because they will not be at maximum performance from the get go? Or if the risk of damaging the cells? If I can avoid buying an $80 bench top power supply for the One time operation I’d prefer to avoid it.
Also if I do buy a power supply I heard that for my 48 V system it would need to be 60vpower supply is that correct?
Thank you so very much!
 
I hooked some cells in parallel for months and they still weren't fully balanced. It may work better with somewhat voltage matched cells at a high state of charge, but generally speaking, it won't work well reliably.

You can always buy a power supply and resell it on eBay. You can even buy a used PS on eBay and resell it for around the same price. I call it e-Bay tool rental.
 
he was not going to top balance connect given time the BMS will handle this.
What is the downside of letting it be an ass down for batteries
The downside is what you stated that you will not have optimum capacity until the pack gets balanced. You may experience nuisance disconnects if one cell is a runner. To reduce that likelihood and to give your BMS more time to do that balancing you may want to reduce your Constant Voltage (Absorb) setting.
 
I built my batteries without a top balance. Assembled with the BMS and go. The first I manually bled off some power from individual cells as it charged to get all in the 3.60 - 3.65 range. Found no real need to go to 14.5 - 14.6 battery volts so the next batteries I assembled and put in service charging to 13.8 volts and added an active balancer. Took some time to get settled but all has worked fine.
 
Thanks for the info :) seem like I should just go for the top balance and be done

Yes! I thought my power supply was going to sit on the shelf for eternity after I completed the top balance. But I've found it to be useful for a few other projects since then. Having a variable voltage power supply does come in handy. My nephew's hot wheels track with the old school battery powered launcher works better when you can crank up the voltage a little bit.
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Hey can I connect 4 banks of four 280ah cells in parallel to a car battery charger to bring up the SOC up then fine tune with bench top power supply at 3.65v.
Do I need bms in the circuit or will battery charger stop when banks are at 14.2?
 
Hey can I connect 4 banks of four 280ah cells in parallel to a car battery charger to bring up the SOC up then fine tune with bench top power supply at 3.65v.
Do I need bms in the circuit or will battery charger stop when banks are at 14.2?

I would charge each battery, one at a time with the BMS in place with conservative parameter settings, say 14.2 volts for high voltage disconnect.

Some car battery chargers don't put out many amps, so it depends on what you're going to use.
 
Hey can I connect 4 banks of four 280ah cells in parallel to a car battery charger to bring up the SOC up then fine tune with bench top power supply at 3.65v.
Do I need bms in the circuit or will battery charger stop when banks are at 14.2?
You can but be prepared to either sit there and baby sit them or be prepared to accept the risk of possibility of destroying them.
 
I've bought them to build a 48v system, and from what I've read, connecting them in parallel will take a long time to top balance. I've also bought the jk bms 24s so didn't think it would be suitable for only four cells on car charger?
 
If charging any number of cell combinations you can dream up that requires greater than 3.65 volts total without a BMS is risky and the closers you get to the top the greater. BMS job is to monitor each cell voltage and stop charging when the first cell exceeds 3.65 volts. DIYing anything requires a curtain set of tools and knowledge. If you want to do the job correctly you need the tools and knowledge.
 
Hey can I connect 4 banks of four 280ah cells in parallel to a car battery charger to bring up the SOC up then fine tune with bench top power supply at 3.65v.
Do I need bms in the circuit or will battery charger stop when banks are at 14.2?
Not sure what 4 banks of 4 cells means exactly. If any cells are in series they need to be protected with a BMS.

The battery charger will stop at 14.2 only if that is the battery charger specification.
 
Do I need bms in the circuit or will battery charger stop when banks are at 14.2?

You don't need a BMS as long as you are OK with buying a new set of cells to replace the ones you just ruined.

That is my way of saying you ALWAYS need a BMS.
 
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