question

rami-alaryan avatar image
rami-alaryan asked

using Victron's MPPT as individual 12V lithium charger before connecting in serial

Dear Victron Support community,

Warm greetings,

I would highly appreciate your technical advice on the following case:

Currently, I have two (12V/200AH) BlueCarbon lithium batteries connected in Parallel (400 AH-Capacity)....they are also parallel-connected to a 12V/1300VA inverter.

The batteries are exactly the same age/brand/capacity and each with its own individual BMS.

Now I am planning to update into a 24V/3000W inverter system, and thus I am planning on reconnecting the same two batteries in series instead of parallel.

Now, I have concerns regarding the requirement to do proper top-balancing for those two batteries before connecting them in series.

My question is: can I simply do it by using my Victron MPPT 150/60 solar charger to charge every battery individually using the Victron lithium charge profile (14.4 V Absorption, 13.6 Float) till they reach the float/full state ..... and then after having them fully charged connect them in series?

Or ..... is this method unacceptable and I have to use an external special CC/CV Lithium battery charger to charge each battery individually to full charge before connecting them in series?

are there any dangers involved in this battery arrangement change "from parallel to series"? noting that my batteries are relatively new out of the box and connected in Parallel for about 45 Days now.

Thank you in advance for your kind advice

MPPT Controllers
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1 Answer
snoobler avatar image
snoobler answered ·

Your method is acceptable. I would do it a little differently.


I would push the individual charges to 14.6V to get a little higher in the charge curve and cut charge when current drops to 5A (normal would be 10A). Then parallel them again for 2 hours at 14.6V or until current drops to 0A, then wire in series.


The above ensures that the two batteries are both truly at 100% SoC at the same time.


Moving forward, you will need to monitor them and confirm that they are both at the same peak voltage. Their internal balancing algorithms should take care of that for you, but cell quality varies and balance may go out of whack. The solution is to repeat the individual/parallel charges. Alternatively, there are balancers that connect to each 12V and transfer charge from the higher voltage to the lower voltage. Victron offers products along these lines. Personally, I prefer a cheaper solution that also transfers higher current like the Kilovault 24V battery balancer.


I use a similar device on my 48V bank to keep my 4S2P Trojan T-1275 all at the same voltage.









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