I have 4 strings of 4x65AH battery's can i ad a string of 4x100AH battery's to increase the total capacity for my ESS system MultiPlus II 48v 3000VA
The battery's a SUN Battery SB12-65 (12V65AH) and SB12-100 (12V100AH)
asked
Parallel 65AH and 100AH battery in 48v ESS system
If my maths is correct, you have 16 x 65Ah batteries? Stringed up as 4p x 4s ??
I do not see why not.
You have to make sure that they are at the same SOC when connecting them in parallel.
Edit:
The discharge current of such parallel system should be adjusted to the smaller battery in this parallel setup.
I would agree with @MarekP, this would work and Pylontech actually allows this config but I would be hesitant to do it without a BMS. I would do it if you maybe install a Victron Battery Balancer to make sure the 2 strings stay balanced but that means you would need 6 balancers.
Hi @shaneyake
Author has a AGM batteries and they do not need BMS.They would benefit from battery balancers.
He would need 15 battery balancers for his 12V AGM batteries. (12 for 65Ah sets and 3 for new 100Ah set)
Hi Jens-Due, in my opinion, this is a very bad idea. The batteries not being of the same capacity, it will create an unbalance between the batteries, and creating also issues with the cabling and charging. You will toast the smaller batteries as the mppt will continue to charge (unable to get the real picture of the SOC).
Michel
Can you explain how MPPT would toast the smaller battery?
SOC of those batteries is judged by its voltage.
Two batteries, regardless of their size, connected in parallel have the same voltage.
Hello Marekp, circulating current will result from the slightest difference of cell voltages. Cell resistance is the only restraint against a dead short circuit for the difference voltage. Batteries go to hell without even being connected to a load per se.
For short-term tests , yes you can, but you you will be disappointed with this arrangement if you install it permanently - there will be a quite high self-discharge going on unless you separate the batteries (e.g. with a relay) when they are not in use or being charged.
Both batteries will lend in the extension of usable power time with the lower ampere battery dieing out first which thereafter will speed the end of usable power remaining battery.
So, definetely a no way to go ! Unless you want to change your smaller capacity battery bank soon.
Have fun. Michel
PS, forgot to mention : However a parallel circuit is also a loop, so what's actually going to happen is that the battery with the higher voltage is going to push current backwards through the weaker one, charging it in an uncontrolled and probably destructive way.
Why the lower capacity would die out first?
Battery when discharging is lowering its voltage, but when connected in parallel to the other battery, it will not lower its voltage until the other battery does it.
The other battery will provide the missing power until it is empty.
As a result both batteries will be empty at the same time.
@MarekP I did such kind of experience, and the SmartProtect did trigger, so a no go.
Two batteries of different types, if connected in parallel is not recommended. Because of these reasons:
They may have different terminal resistances and will deliver different currents to the load.
They will take different charging currents and both will not be charged to the same level. Also they will not be discharged to same level while on load.
Their terminal voltages may not be same and one having the higher voltage will deliver charging current to the other and a circulating current will arise and heat up both.
