question

Doron Azulay avatar image

ADDING 2ND LIFEPO BATTERY TO EXISTING SYSTEM, WEIRD BEHAVIOUR

i have an existing system of
1 LIFEPO 200ah battery
1 MULTIPLUS 70/1600/12 INVERTER
1 cerbo gx
1 bmv monitor
ive added a second LIFEPO battery today, same type and has the same type of BMS as the first one.
what i did is simply parrallel everything to the first battery connections
how do i proceed now ?
i BT to my BMV monitor and changed the battery capacity there from 200ah to 400ah.
but the state of charge still shows 100%( the 1st battery is full, the second one wont be full as it was sitting idle for about 2-3 weeks now)
shouldnt it sense the SOC is less than 100% after adding it ?


reason i know the 2nd one isnt full is when i turned everything back on , it shows 100% SOC but the MP goes into BULK charging, so it senses it needs to charge more

Multiplus-IILithium Battery
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

You should charge the new battery individually to 100% before connecting it to the 'old' battery.

After adding a new battery and changing the capacity in the BMV you need to make a full charge cycle to synchronize the BMV.

- what i did is simply parrallel everything to the first battery connections

like this?

20201206-101305.jpg

if yes, you should change it to one of these:

screenshot-20201206-101210-drive.jpg

'diagonally' is the easiest.

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf


2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Paul B avatar image
Paul B answered ·

Matthias is correct

No the SOC will rest to the correct level only when the voltage increase to the setpoint set in the BMV its called the CHARGED voltage so once its fully charged all should be fine again.

and as Matthias say you should charge it fully first.

but as its in there now just get the voltage up to I presume 14.4 hold that for 1 hr and all should be fine

its maybe gone to 100% as you may have disconnected the batteries while putting the new one in without turning the system off thus the voltage went up and the SOC reset to 100%, JUST A GUESS not saying this is the real reason

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.