Big Battery 24 volt battery

[LarryC]

I have been laid up and just got it installed after a year.

The video you said 23.5 volts be good for cutoff.

At 75 yrs I been in poor health and just could not get the work done installing it.

I changed program 5 to user and changed program 29 it to 23.5, but did not touch the other setting.
Should program 26 and 27 be change from default?

26 Bulk charging voltage (C.V voltage) default setting: 28.2V If self-defined is selected in program 5, this program can be set up. Setting range is from 24.0V to 29.2V. Increment of each click is 0.1V.
27 Floating charging voltage default setting: 27.0V If self-defined is selected in program 5, this program can be set up. Setting range is from 24.0V to 29.2V. Increment of each click is 0.1V.
29 Low DC cut-off voltage default setting: 21.0V If self-defined is selected in program 5, this program can be set up. Setting range is from 20.0V to 24.0V. Increment of each click is 0.1V. Low DC cut-off voltage will be fixed to setting value no matter what percentage of load is connected


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[Jim Burrow]

my cut-off is set at default of 21.0 volts and no problems

 

[LarryC]

my cut-off is set at default of 21.0 volts and no problems

William in his video says it should be around 23.5 to keep the BMS with in the battery pack from kicking in to shut it off.
I did that setting, but not sure about the other two setting.

 

[John Frum]

Is that a lifepo4 battery?
Glad to see you back.

 

[LarryC]

Is that a lifepo4 battery?
Glad to see you back.

Yes, the Used LiFePO4 Solar Battery w/BMS form (bigbattery.com)
We got snow and need to get it setup for our CPAP machines.

 

[John Frum]

Yes, the Used LiFePO4 Solar Battery w/BMS form (bigbattery.com)
We got snow and need to get it setup for our CPAP machines.

A good low voltage disconnect for you inverter should be a bit higher than the low voltage disconnect of the bms.
Do you know what the bms low battery and low cell disconnects are set to?

26 Bulk charging voltage (C.V voltage) default setting: 28.2V
This is fine

27 Floating charging voltage default setting: 27.0V
Set this to 26.8 or lower.
I have mine set to 25.6 volts so that I cycle my batteries

29 Low DC cut-off voltage default setting: 21.0V
I suggest 24.0 volts

Give those a whirl and we can tweak from their if necessary.

 

[Jim Burrow]

William in his video says it should be around 23.5 to keep the BMS with in the battery pack from kicking in to shut it off.
I did that setting, but not sure about the other two setting.

I've been testing with different settings for a couple of months as I don't have my system connected to the house power yet. That will be around April.

I'm using "2" 12v deep cycle Marine lead-acid (AGM) batteries from Walmart (cheep, cheep, cheep, I know) but they are working. I don't have any BMS as they are connected in series for 24-volts battery pack. I leave the system on 24/7 while testing. I have a 100-watt light bulb and my outside refrigerator connected as a load. The refrigerator adds 87-watts to the load when it kicks on.

I am set up to run the load on Solar first and battery for support. the Utility doesn't kick in until the battery reaches low cutoff voltage. I'm running just "2" 300-watt solar panels during testing and the Utility never kicks in even on rainy and overcast days that my area is experiencing as of late herein California. - That was a big surprise to me!

Here are my settings for my 2424lv-mds:
01 - 56u
02 - 20A
05 - user
11 - 10A
12 - 22v
13 - full
16 - cso
26 - 28.2v
27 - 27.0v
29 - "low cut off voltage" - 21.0v
31 - 56E "Solar power Balance"

Note: I'm always playing around with the settings as I want to make sure the Utility doesn't supply more than 10-amps as there are other circuits in the house connect to the outside out-lite that I'm using for Utility power for testing.

Second Note: with my batteries fully charge and resting at 24.5-volts, as soon as I apply a load, the battery voltage drops to 23.5-volts. If I had my low voltage cut off set at 23-volts, the Utility would be constantly kicking in and the battery would never run the load. Hence, the batteries would never supply power to the load at night time.

 

[LarryC]

A good low voltage disconnect for you inverter should be a bit higher than the low voltage disconnect of the bms.
Do you know what the bms low battery and low cell disconnects are set to?

26 Bulk charging voltage (C.V voltage) default setting: 28.2V
This is fine

27 Floating charging voltage default setting: 27.0V
Set this to 26.8 or lower.
I have mine set to 25.6 volts so that I cycle my batteries

29 Low DC cut-off voltage default setting: 21.0V
I suggest 24.0 volts

Give those a whirl and we can tweak from their if necessary.

27 Floating charging voltage default setting: 27.0V
Set this to 26.8 or lower.
I have mine set to 25.6 volts so that I cycle my batteries

So this will let the batteries drop to 25.8 before it charges again?
I just have this as a backup if the power goes out for the CPAPs.

 

[nwillitts]

Hello Larry.good to see you once more.
been a while.

 

[John Frum]

So this will let the batteries drop to 25.8 before it charges again?
I just have this as a backup if the power goes out for the CPAPs.

If there is no mains power and you don't have an alternative charge source float can't happen.
Actually since you are using this unit as a UPS=uninterruptible power supply you should set the #27 to 26.8 volts

There is another setting that determines if you prefer battery or to bypass mains power.
I suggest you set that to mains.
The let it charge up and give it a test by disconnecting mains power.
I choose 26.8 volts because that is the recommended setting for a UPS.

 

[GVSolar]

So this will let the batteries drop to 25.8 before it charges again?
I just have this as a backup if the power goes out for the CPAPs.

Hi Larry,
Hope you're feeling better.
I have 4 of those refurbished BigBattery BYD batteries. They run my whole house, with Schneider SW4024 and lots of solar PV. Very capable if gently used.
Here are the settings I use.
Bulk: 27.1
Absorption: 2 hours
Float: 26.8
Recharge/Re-bulk: 26.4
My low voltage disconnect is 23.8v with a 15 sec delay to allow for surge.
I rate them at 130ah each.They will almost always settle down to 26.4 after a full charge, and 26v after any appreciable discharge. My suggestion is not to push them too hard or individual cells will runaway and trigger a BMS disconnect. If you are only using them for a backup and keeping them fully charged with AC - I would drop the float charge down to 26.7 or 26.6.
I don't know anything at all about the MPP units.
Wishing you well and all the best.

 

[LarryC]

If there is no mains power and you don't have an alternative charge source float can't happen.
Actually since you are using this unit as a UPS=uninterruptible power supply you should set the #27 to 26.8 volts

There is another setting that determines if you prefer battery or to bypass mains power.
I suggest you set that to mains.
The let it charge up and give it a test by disconnecting mains power.
I choose 26.8 volts because that is the recommended setting for a UPS.

I have no solar panels yet and charge it only with line power.

 

[John Frum]

I have no solar panels yet and charge it only with line power.

Cool I like @GVSolar's settings.
Try those out and we can tweak from there if required.