question

@MrHappy

If it is a 48 volts system a minimum of three, with 24 volt then you can use one, it will take longer to balance though so you can add more balancers to each string. 1A/0.7A per balancer balancing ability, once the threshold is triggered.

http://bb-demo.victronenergy.com/

Going by the manual, it is one balancer per string, so if you ave 16 strings, it is 16 balancers.

What voltage is your system though? Maybe some clarification with a battery connection diagram would help clear up how many you need.

As the manual suggests though, if you use a bmv and you get the midpoint from that then you can use less balancers in the system, I reiterate it can take longer to balance a system that way, especially if you did not start by charging and setting up the bank correctly in the first place.

Hi Alexandra.

If you read the part furthest down on Victrons own wiring manual, which I put in my initial post, it says the following:

"Once the midpoint of the battery bank is connected one battery balancer can be used, instead of using 3 battery balancers (one for each string)."

With an example of a 24V battery bank with three strings of two batteries in each. This is the information which made me ask the question. In the example there are three strings balanced by one single balancer, but there is no information about how many would be the limit.

(even the demo page you link to shows three strings with one balancer)

Thank you for your involvement, @Alexandra. I kind of get it now. My question is a bit like asking "how long is a rope" or "how fast is a boat". One balancer can handle a specific amount of balancing current and how much current is needed to keep up with balancing depends on the time frame needed, the amount of imbalance, the size of the batteries connected, how high charging current connected chargers are pushing into the system and how high current is drawn from the batteries by loads. My question is a simple one but with no simple answer.

My batteries are 75Ah AGM 12V batteries connected as pairs with equal length cables to two busbars. Now 30 batteries, so in my mind 15 "strings", each with a "midpoint" usable by a balancer. I would not want to connect any midpoints at all, so I suppose I would have to go with 15 balancers. I really want this pack to last as long as possible. At this point, the highest difference between any two batteries in the same pair is 0.089 volt or 89 millivolts. Most of them are between 40 and 60 millivolts, some as low as 9. Not sure that needs balancing, but maybe it would be a good preventative measure to install balancers...