Disaster!!! Or, learning the expensive way...

[shaymcquaid]

Hello all,
Well, I really did it this time.

I SOMEHOW allowed my 24v big bank to discharge to 17.88v.
I’m not sure why at this point.
I thought my all in one Mpp 2424LV would shut off the inverter at 21v but that didn’t happen.
I only have one string of led lights on the DC side. Hooked up to the AC side is a mini split. (That was turned off).

My bank is sixteen 280Ah cells.

I had left the inverter on and didn’t check on it for 2 days.

When I did: The inverter was off and batteries are discharged to 17.88v!
Im really mad at myself and slightly embarrassed, but I need advice.

First: Could the inverter have that much power draw that it depleted to the very low voltage? I ASSUMED that the “low voltage cut off” would disconnect the battery from not only charging but discharging also. Seems this isn’t the case. (And by writing this out, it makes sense to me now why it would allow discharge.?)

Second: I want to try to charge the battery and conduct a discharge test to gauge the damage. However, the all in one unit won’t charge because voltage is too low.

Could someone please give me some advice? I’m really fretting over my dumb mistake.

Thanks in advance.
Shay

 

[MisterSandals]

However, the all in one unit won’t charge because voltage is too low.

I hate myself for suggesting this... seems critical to get these charged though.

Do you have a panel(s) that can output a charge current in the 20-30v range?
You could get your batteries up over the knees in a short CLOSELY WATCHED charge session. Just to where your SCC will recognize them.

I am assuming you would use an AC 24v charger if you had access to one or anything similar as a first choice.

 

[kernel]

The thing about inverters is they need to generally be disconnected in order to turn off the control circuit. It uses the standby power waiting to run even in lvd. Only power to the inverter ac section or forward power is removed from the line or otherwise rendered inoperative. Thats my observation amd not all electronics are designed so.

Some have very low standby even for large inverters. 6w for 7200W of outback inverter for instance. Some do not, like the outback radian which is gonna draw 30w no matter what you do to it..... not the best tiny home inverter and sometimes 3 of them cant make a dent in battery amd charging capacity.

 

[kernel]

You can morse code some s.o.s., Abba though...

 

[Mac6792]

Could you post more about your setup as well as the config settings your using? - Also what was the weather like for those two days - Sun or no sun

 

[SolarQueen]

I hate myself for suggesting this... seems critical to get these charged though.

Do you have a panel(s) that can output a charge current in the 20-30v range?
You could get your batteries up over the knees in a short CLOSELY WATCHED charge session. Just to where your SCC will recognize them.

I am assuming you would use an AC 24v charger if you had access to one or anything similar as a first choice.

I was about to suggest the same thing!

 

[John Frum]

Do you have a BMS?
If so both your chutes didn't open.
Poor yourself a stiff drink and swear enough to make a sailor blush.
Then pick up the pieces best you can.

 

[John Frum]

Oh and if possible check the individual cell's voltages.

 

[shaymcquaid]

Thanks for replies.
As stated above ,I had No power applied.
Not plugged in and no panels yet.
Had been charging with shore power.

Also. I had no BMS. It’s on the way.?

 

[shaymcquaid]

I suppose I will have to get some sort of manual charger. And try to get them to the charging threshold...

Also, I do have a battery tender. Could I try trickle charging it? I assume it’s for a 12v battery though.

 

[John Frum]

Thanks for replies.
As stated above ,I had No power applied.
Not plugged in and no panels yet.
Had been charging with shore power.

Also. I had no BMS. It’s on the way.?

Did you test the inverter low voltage cutoff?
I would set it comfortably high and test it.
>25 volts for the first test.

 

[MisterSandals]

Also, I do have a battery tender. Could I try trickle charging it? I assume it’s for a 12v battery though.

If its 12v only then you will need to split the 24v into 12v batteries. Get that going asap!

 

[shaymcquaid]

If its 12v only then you will need to split the 24v into 12v batteries. Get that going asap!

I just ordered a bench DC power supply.
But it will take a week.

Are you implying that time is critical?

Could there be a way to trick the battery charger portion of the all in one unit to charge the bank? ?‍

Thank you....

 

[MisterSandals]

Are you implying that time is critical?

I did not think i was implying. I thought I was stating.

And yes, every moment they stay in the danger zone, they deteriorate further. Heck, its not certain whether they are salvageable right now (you're doing the stress testing we all want to hear about).

 

[MisterSandals]

Could there be a way to trick the battery charger portion of the all in one unit to charge the bank? ?‍

Maybe. What do you have to make the batteries appear to have a higher voltage than they have right now?

I suggested using a solar panel earlier. Do you have any in the 20-30v range? Or even in the 12-16v range for doing half of your bank (12v) at a time.

 

[MisterSandals]

Do you have another 24v battery with a reasonable charge available?

 

[John Frum]

Maybe. What do you have to make the batteries appear to have a higher voltage than they have right now?

I suggested using a solar panel earlier. Do you have any in the 20-30v range? Or even in the 12-16v range for doing half of your bank (12v) at a time.

@shaymcquaid the dendrites are very likely growing. Did you check the individual cell voltages?

 

[shaymcquaid]

I did not think i was implying. I thought I was stating.

And yes, every moment they stay in the danger zone, they deteriorate further. Heck, its not certain whether they are salvageable right now (you're doing the stress testing we all want to hear about).

Aye Aye Cap’n!!
Got it!?

As far as a panel or a good 24v battery:
I have neither.

I have not tested individual cells.
I will ASAP

 

[KBWaldron]

While I'm not putting a BMS on my BYD's I will have a Victron Battery Protect between the batteries and everything else, because not only do you have to worry about the inverter, but any 24/12 draws as well. While I expect to be around my RV (I'll be living in it full time), you never know when you might unexpectedly find yourself away for an extended period of time.

 

[shaymcquaid]

I have a Victron battery protect.
In a box. On the kitchen counter.?