Question on Inverter and battery connection

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scubasteve1

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Hi All
So I have a Rentech vm-3000 (3Kwh) inverter connected to my main supply. no panels.
then from there a breaker unit that connects to a lithium 2.5kwh lithium wall mounted 24V battery.
small setup purely just for wifi, tv and a few lights during outages.
so we had a power outage that lasted 2 days due to vandalism/sabotage on a substation in my area :-(.
anyways, the battery eventually ran down and the inverter switched off..
but since power back on.. inverter not coming back on. so not sure where the issue could be, the inverter or the battery. (been 'charging' for a few days now still no go)

waiting for the installers to come out to check.

however, i have done the following. if i disconnect the battery from the inverter.. my battery output is reading around 6v.. should read >24v - so yes its flat.
but.. the inverter has AC power coming in 220v all good. but my inverter DC output to the battery is fluctuating from between 6 and 22V constantly.. surely this is not normal?

is my inverter cooked perhaps? have the installers configured my inverter incorrectly perhaps to run the battery flat instead of shutdown at 20% perhaps?


Any ideas?
thanks in adv
 
I suspect the inverter has a system that detects the battery voltage and it is too low for it to start charging it. 6V is very low. 21 or something like that would have been expected.

The ones with lithium batteries can probably explain. I think it has something to do with the battery BMS rejecting the charge. It is unlikely the inverter.
 
scubasteve1 said:
Hi All
So I have a Rentech vm-3000 (3Kwh) inverter connected to my main supply. no panels.
then from there a breaker unit that connects to a lithium 2.5kwh lithium wall mounted 24V battery.
small setup purely just for wifi, tv and a few lights during outages.
so we had a power outage that lasted 2 days due to vandalism/sabotage on a substation in my area :-(.
anyways, the battery eventually ran down and the inverter switched off..
but since power back on.. inverter not coming back on. so not sure where the issue could be, the inverter or the battery. (been 'charging' for a few days now still no go)

waiting for the installers to come out to check.

however, i have done the following. if i disconnect the battery from the inverter.. my battery output is reading around 6v.. should read >24v - so yes its flat.
but.. the inverter has AC power coming in 220v all good. but my inverter DC output to the battery is fluctuating from between 6 and 22V constantly.. surely this
Click to expand...
I suspect battery bms has gone to sleep. Probably need external 24V powersource like a 24V garage battery or 24v battery charger to jump start battery.
 
The battery could have gone into deep sleep due to being discharged too much and isn't accepting charge.

You could get a 24V pack connected in parallel to try and wake it up, even those gate motor batteries would do.
 
TheChamp said:
The battery could have gone into deep sleep due to being discharged too much and isn't accepting charge.

You could get a 24V pack connected in parallel to try and wake it up, even those gate motor batteries would do.
Click to expand...
Just need jumper cables :D
 
Your battery needs to be "woken up".
Some inverters can do this by forcibly sucking the relay through the BMS and attempting to send charge to the battery, or you can put a 24v charger on it, as suggested by @TheChamp, and resetting the battery until it starts charging again.

Another option would be to open the battery up, disconnecting the busbars, and charging each cell to an equal voltage before rebuilding it.
 
LCBXX said:
Your battery needs to be "woken up".
Some inverters can do this by forcibly sucking the relay through the BMS and attempting to send charge to the battery, or you can put a 24v charger on it, as suggested by @TheChamp, and resetting the battery until it starts charging again.

Another option would be to open the battery up, disconnecting the busbars, and charging each cell to an equal voltage before rebuilding it.
Click to expand...
Need to be said that it must be a dumb charger, something hard to come by these days, unless you have one in the garage somewhere.
 
wingnut771 said:
Small garage battery cant push much current but should raise voltage enough to wake up bms then inverter can take over.
Click to expand...
Yes, i was thinking of the charging current from the inverter to the hungry battery that has just come out of hibernation, I forgot it will be flow through the installed cables the already installed cables.
 
It does sound like your battery BMS has shut down after the battery was discharged quite low, then the inverter can't charge the battery because the battery voltage isn't within limits it expected. I'm not familiar with your Rentech inverter, but Sunsynk inverters have a battery setting option called "Activate" which I understand is for this type of scenario, maybe see in your inverter manual if there's a similar setting?
 
Just get a boost converter to jump any12v dc powersuplly you have in the house for future jump start scenarios

Or use 2 alarm batteries in series to jump

The jump isn't like a car jump start

You don't leave the cables attached most likely just touch the terminals
Hence cable rhickness not that imortant as you just need a second for the jnverter and bms to kick into action

Expect an arc

Can set rhe shutdown voltage of the inverter to be higher than the shutdown voltage of the bms

Normally the bms is 20v

The problem though is this isn't set in stone as it actually works on cell voltage of 2.5v ie 8x2.5 =20v

If one cell is lower soc this voltage would be higher as some cells have higher voltage

The safe bet would be to set the inverter shutdown to 24v that would be a 3v per cell by that time you are down to a few % soc and basicalky totally flat (though with heavy load voltage drop can cause shutdowns sooner )

If you find the shutdowns is long before 3-5% soc lower voltage slightly

This way the jnverter wil stay away from bms protection mode and shutdown before ghat happens and then start charging when power returns with no jump starts needed
 
Hi All,
apologies for the late response.. had the guys take the battery away to test and and they charged it up.. and connected back this morning and all seems good again. so yes, does look like the battery ran down to below charging level.
need to check the settings on the inverter again to make sure it is set correctly.
thanks for the feedbacks.. appreciated.
 
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