No bench charger, 'First charge' with SCC instead?

[kaizday]

so, i am building a 24v 100ah pack with a 8S overkill bms and raw cell but just realize that i dont have a dedicated 24v charger. so question is, can i charge it via the mppt? i understand that it will take longer than an ac charger and probably take multiple days, but beside that, any reason that i should order and wait for a real charger? i read the Top Balancing guide and it says something like a quality bms will balance the cells over the time anyways, right?

thanks

 

[Bubba1]

Yes you can and it will speed up the balancing time. If you don't balance it will trip BMS with one or more cells going over voltage or under voltage. This will effect the usable power your battery can supply. A bench top power supply ($50ish) can balance one cell at a time. Set voltage to 3.65 and wait for current to drop to half amp or so. Move on to next cell. You can leave the battery assembled to do this. Someone correct me if I have anything wrong.

 

[kaizday]

Yes you can and it will speed up the balancing time. If you don't balance it will trip BMS with one or more cells going over voltage or under voltage. This will effect the usable power your battery can supply. A bench top power supply ($50ish) can balance one cell at a time. Set voltage to 3.65 and wait for current to drop to half amp or so. Move on to next cell. You can leave the battery assembled to do this. Someone correct me if I have anything wrong.

in your first sentence, do you mean that i must get a bench top power supply?

thanks

 

[Bob B]

It depends on how well matched the cells are .... and how much balance current the BMS has.
Many of the BMS have very low balance current and may have a hard time getting things balanced. There are also options for manually bleeding off high cells and some will get an active balancer.

The least expensive method will be to use a resistor or light bulb to bleed off the highest cell ... but that will also be labor intensive.

If you do a search for manual balancing or resistor balance you should get some hits.

 

[kaizday]

I'm rewatching Will's videos, in this one, his pinned comment said:

"Nowadays, you just slap a bms on the cells and it's good to go. It will top balance your pack and you don't need to think about anything. So don't worry about top or bottom balancing. Use a BMS and you are set."

 

[John Frum]

I'm rewatching Will's videos, in this one, his pinned comment said:

"Nowadays, you just slap a bms on the cells and it's good to go. It will top balance your pack and you don't need to think about anything. So don't worry about top or bottom balancing. Use a BMS and you are set."

Are your batteries new commodity grade cells?
What is the current voltage of each cell?

 

[time2roll]

Yes there is no issue with building the battery including the BMS and charging with solar or anything else.

If the cells turn out to be way out of balance you can:
1) Lower the solar charge voltage to avoid high cell cut off and wait many cycles for the BMS to balance.
2) Get an active balancer to speed up the process.
3) Bleed off power from the high cells manually.
4) Get an adjustable bench charger to boost the low cells.
5) Use the adjustable bench charger to top charge all in parallel.

Post the cell voltages as you hit high cell cut off and talk about which way to proceed.

 

[Pierre]

I am going to be controversial here. Check the voltages of all the cells - if they are all within about 50mV of each other , charge with the SCC and monitor on the BMS BT app for runaway cells. When the sun is gone the cells will settle down again and the balancer will try to pull the high cells down - slow process as the balancing current is about 30mA. Adjust the BMS settings as you go along - you will soon identify the wayward ones.

 

[John Frum]

I am going to be controversial here. Check the voltages of all the cells - if they are all within about 50mV of each other , charge with the SCC and monitor on the BMS BT app for runaway cells. When the sun is gone the cells will settle down again and the balancer will try to pull the high cells down - slow process as the balancing current is about 30mA. Adjust the BMS settings as you go along - you will soon identify the wayward ones.

Best outcome is all the cells are top balanced and converge on 0 delta right at the top
2nd best outcome is 1 high cell for the bms to knock down.
Worst scenario is 1 low cell, in that case the bms has to knock down 7 cells to balance the pack.
If your scenario looks more like the last 1 then the first 2, suggest you buy a bench psu to top off the low cell.

 

[Pierre]

Best outcome is all the cells are top balanced and converge on 0 delta right at the top
2nd best outcome is 1 high cell for the bms to knock down.
Worst scenario is 1 low cell, in that case the bms has to knock down 7 cells to balance the pack.
If you scenario looks more like the last 1 then the first 2, suggest you buy a bench psu to top off the low cell.

Agree Joey , my comments were more for tinkerers who know when to stop, upcharge or downcharge single cells , monitor performance etc and not for the newbies. Had fun and games balancing / conditioning 8 cells in a batch of 28
that arrived from China with voltages varying between 0,425 and 1,513 volts. All recovered and working in my 48v pack
but hey , I digress. Sorry OP ?

 

[kaizday]

out of 8, one lowest at 3.226 and two highest at 3.231. should I put them in certain order? does it make any difference?

thanks

 

[time2roll]

Since it is a single series string I don't think it matters. The numbers are too close at this point to indicate anything.

 

[kaizday]

Since it is a single series string I don't think it matters. The numbers are too close at this point to indicate anything.

thanks so much again time2roll. so much to learn still lol