Best way to expand my 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 8 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?

[Sunking]

I would not do it unless your existing batteries are brand new. It is not a good idea to use parallel strings if it can be avoided, and it can always be avoided.

[Chris Miller]

I would not do it unless your existing batteries are brand new. It is not a good idea to use parallel strings if it can be avoided, and it can always be avoided.

Well they are brand new....

But how can it be avoided in this situation?

[Sunking]

Well they are brand new....

But how can it be avoided in this situation?

I was hoping they were a year or more older. You can parallel them up with another exact match set. The problem is they will not last as long as they were single sets. My poin tis to buy the capacity needed so only 1 single string is used. If you need 500 AH capacity then buy 500 AH capacity batteries.

One other thing is how much panel wattage are you running? Just to support what you have now requires a minimum of 1000 watts to generate a C/12 charge current. If you go to 2 strings you will need 2000 watt panel with 40 amp MPPT.

[Chris Miller]

I was hoping they were a year or more older. You can parallel them up with another exact match set. The problem is they will not last as long as they were single sets. My poin tis to buy the capacity needed so only 1 single string is used. If you need 500 AH capacity then buy 500 AH capacity batteries.

One other thing is how much panel wattage are you running? Just to support what you have now requires a minimum of 1000 watts to generate a C/12 charge current. If you go to 2 strings you will need 2000 watt panel with 40 amp MPPT.

Currently running 1000 watts of PV. Going to be adding a new string of 1000 though soon... and wanted to grow the bank then. I am running an 80 amp MPPT

[Sunking]

Currently running 1000 watts of PV. Going to be adding a new string of 1000 though soon... and wanted to grow the bank then. I am running an 80 amp MPPT

You are set to go then. When it is time to replace the batteries I suggest you buy 450 to 500 AH 6 volt cells like the Rolls S-600.

[RussN9ZP]

You are set to go then. When it is time to replace the batteries I suggest you buy 450 to 500 AH 6 volt cells like the Rolls S-600.

Yeah at only $460.00 x 8

[Sunking]

Yeah at only $460.00 x 8

Well whatever web site you are referring too is a bit too high. Rolls sell for $0.14/wh so the going price is around 2700 wh x $.14 = $378. It is a 7 year warranty. A Trojan T-105 RE is a 5 year battery @ $.13/wh. You get what you pay for.

[JNSMAR043]

I would not do it unless your existing batteries are brand new. It is not a good idea to use parallel strings if it can be avoided, and it can always be avoided.

Hi bit of a newbie why is it a bad idea to use parallel strings, i have been thinking about using up to 7 in the system I am building to increase the capacity (number of days the bank can supply the power for without charging).

[Mike90250]

This page

http://www.smartgauge.co.uk/batt_con.html

covers the math behind the reasons to not parallel batteries if you want long battery life.
Build the bank out of 6v, 200ah cells, or 4v, 400ah cells
you can, with careful matching, get 2 banks connected on the diagonal, to work fairly well