Recommendation for a BMS for large 2V 1800 AH AGM battery.

[bryhan67]

Have a unique situation. My main goal is track and log battery voltage on my PC. My batteries are UPS 2V and weigh 300lbs each. I have a main bank of 24 cells I run the house with. I have a spare set of 12 Batteries. This spare set I would like to charge full then us a BMS like a Daly LiFePo4 12s 36v 250A or a 30A unit if I cant charge.

I am trying to keep a max 2.30v to 2.35v over several days to try and equalize the cells. I have a lot of different voltages. I am also trying to identify bad and good cells. Kinda tricky to spot them. I was thinking if I can view all 12 cells or 24 cells I can see voltage out of wack. I would put a inverter on them and run a heavy load to spot bad cells.

1# How low can a Daly BMS go on voltage per cell. I need 2.25 to 2.35

2# Which BMS unit is best to view remotely on my PC?

3# I see the tiny wires on these BPM and cant imagine if can put to much power in a single battery. Is it a waste of time to get a 250A or 500A bms? Of if its not possible to charge I can get cheapest 30A BMS just to monitor.

Thanks for the help.

 

[sunshine_eggo]

3.5V on AGM cells? Are you trying to destroy them?

0) BMS in the sense of lithium batteries is not a thing with AGM as they stay balanced on their own for the most part if properly installed and maintained.

1) DALY is not designed to work with lead-acid.

2) no idea

3) see #0

Using a BMS simply to monitor is possibly okay, but if your goal is logging, I have no idea which option would work for you.

 

[bryhan67]

3.5V on AGM cells? Are you trying to destroy them?

haha sorry typo not 3.5v

If cells are close to full and you set parameter of a voltage of 2.32 why would a BMS not work?

If I set each cell to 2.32 with a Daly BMS what happens ?

Not trying to charge from dead to full every day.

 

[sunshine_eggo]

haha sorry typo not 3.5v

Whew

If cells are close to full and you set parameter of a voltage of 2.32 why would a BMS not work?

The question isn't if it will work or not it's if you want it to actually do so, and if it actually will operate so far out of parameters for the design chemistry. 3.2V BMS may just not work with cells ALWAYS below the typical 2.5V cut-off.

If I set each cell to 2.32 with a Daly BMS what happens ?

See above.

Not trying to charge from dead to full every day.

Perhaps not, but you should be trying to charge to full every day.

If you plan to use the BMS as a cut-off for routine charging/discharging, that's not good. BMS will wear out if used that way.

If you're considering a BMS to help you balance the cells, that's pure folly. Their balance current is so low, they'll never make a difference.

Best to get all your cells balanced. Can you mix and match their voltages and charge them as parallel 12V rather than rag out the high cells stressing them while getting the low cells to catch up? Can you charge individual cells? The 30V/10A power supply folks use for top balancing might come in handy in your case allowing you to charge up the lowest cells one at a time by adding an extra 10A to it.

 

[bryhan67]

Whew



The question isn't if it will work or not it's if you want it to actually do so, and if it actually will operate so far out of parameters for the design chemistry. 3.2V BMS may just not work with cells ALWAYS below the typical 2.5V cut-off.



See above.



Perhaps not, but you should be trying to charge to full every day.

If you plan to use the BMS as a cut-off for routine charging/discharging, that's not good. BMS will wear out if used that way.

If you're considering a BMS to help you balance the cells, that's pure folly. Their balance current is so low, they'll never make a difference.

Best to get all your cells balanced. Can you mix and match their voltages and charge them as parallel 12V rather than rag out the high cells stressing them while getting the low cells to catch up? Can you charge individual cells? The 30V/10A power supply folks use for top balancing might come in handy in your case allowing you to charge up the lowest cells one at a time by adding an extra 10A to it.

Top goal is just monitor so I can load test 6 batteries at a time with 12v inverter . So I can move the best batteries to the main 48v system.

I have total 36 batteries 24 are using every day. The extra 12 trying to get nice and balance then put in the main bank. What I have been doing is hook 6 batteries together and put a 12v car charger 24/7 in float. I’m 100% off grid so yes my big bank is charging the small bank all night but does not take much power.

Bonus would be if all cells are charged keep each one perfect voltage for a week or two then put back in the big bank.

Hard to find a big amp charger to do 2.3v

 

[TorC]

You might take a look at something like the JK B2A24S20P. I haven't tried it, but per specs you can set it for as low as 1.2V/cell LVD. They don't specify the minimum number of FLA batteries in the string, but based on the LFP number, it requires 20-21.5V in order for the BMS to function, so probably about 12 cells to be reliable down to LVD.

I don't have mine up and running yet, so I can't confirm what logging ability it has. I know @upnorthandpersonal has direct experience with this BMS.

 

[bryhan67]

You might take a look at something like the JK B2A24S20P. I haven't tried it, but per specs

Yes looks interesting. I can put any 12 or 24 charger and perhaps they balance the voltage. So hard to check 12 or 24 cells at once to spot just how bad a cell is. also hard to laod test a singe 2v cell. I plan to put 6000 watt inverter and try pull 6000 watts at once and monitor all the cells same time see if any are way off. When I can get a constant full float on them they seem happier. I have 36 more 2V cells coming and I want to keep a good float on them and use as backup power vs a generator.

 

[bryhan67]

Can anyone tell me if a Daly Smart BMS voltage can be lowered from 2.25 to 2.35V ? Or can charging be turned off and just used to monitor each cell?

If I get a 24S that says 72v will it even turn on if I only put 48V to it ? Or should I get a 13S that uses 48V and turn the charge output down to 2.25V.