Best way to expand 48v battery bank?

Chris Miller

So I am currently running 8 6v Trojan T-105-RE's in series to create a 48v system. I had thought about expanding this to 16 batteries to have additional storage, but I am unsure on the implications of doing this.

Obviously I would series the new 18 together, and then wire the 2 series banks in parallel with each other. I have read some things on here though that wiring in parallel will shorten the life of the batteries?

Can I run 2 banks of batteries like this with one Outback FM 80 charge controller and 1 Magnum Energy 4448PAE Inverter?

Any thoughts?

niel

Re: Best way to expand 48v battery bank?

a1- it will if done improperly. good sized wire or busbars need to keep the interconnections low resistance and what is done to one bank has to be duplicated exactly with the other bank or inequalities will arise and cause one side to charge/discharge more than the other and will lead to its downfall eventually.

a2- imho yes, if you are careful to make both banks have identical resistances before being combined and combining them properly. i am not on my desktop right now so if someone will please give him the smart gauge link that explains a bit of combining batteries properly.

Cariboocoot

Re: Best way to expand 48v battery bank?

Two parallel strings of eight is fine, providing the batteries aren't too different in age/condition.
It won't shorten the life, but the more strings you have in parallel the more difficult it becomes to keep the current flow through all the batteries even. You can easily get in to a situation where some batteries are doing all the work and the others just sit there, which is bad for all.

You want to do the "diagonal wiring method" outline on the Smart Gauge site, Method #2: http://www.smartgauge.co.uk/batt_con.html
Just imagine each of the individual batteries depicted is instead a string of 48 Volts and there are only two strings.

inetdog

Re: Best way to expand 48v battery bank?

niel wrote: »

i am not on my desktop right now so if someone will please give him the smart gauge link that explains a bit of combining batteries properly.

Check out the advice for paralleling batteries (applies equally well to strings) at http://www.smartgauge.co.uk/batt_con.html. Then when you have time look at all the rest of the pages on that site. Lots of good stuff there about batteries, etc. Especially handy if you are looking at renewable energy for a boat.

Chris Miller

Re: Best way to expand 48v battery bank?

Thanks for the posts guys.

I have seen that link before and to be honest, I get confused as to how it applies with a series string. Or does it only apply when I put two strings in parallel?

More importantly, is there a better way to do what I have done here? How would the second string come into play?

The batteries here are not facing the same direction. The top row is upside down.

Attachment not found.

Thanks again

Cariboocoot

Re: Best way to expand 48v battery bank?

What you have there is a single string of batteries "wrapping back on itself". It makes no difference to the electrical configuration, but might be a consideration in the mechanical application.

With two strings you'll have a duplicate of your drawing right beside it. You need equal length cables to connect the two (+) and two (-) of the two strings. Then the load attaches like this: positive connection to one of the battery strings, negative connection to the other.

niel

Re: Best way to expand 48v battery bank?

you are correct, that it is for paralleling batteries or strings of batteries. that is exactly what you indicated you wanted to do is parallel another battery string with your first string. just be sure all wires are to be the same on the new string as was in the older string. ie, they have the same gauge and wire length. if the older string is tied with 1ft lengths of #2/0 for example then this will be the case for the new string too. when combining the strings together you should have equal sizes and lengths of wire there too to keep it electrically equal.