Mix and Match

[RogerSun]

Hi,

We did not quite anticipate how much power a satellite modem would need and ended up expanding the solar system and batteries until the system remained online 24/7.

Consequently the system grew from 2 x 100w panels with one 12v 90AH deep cycle battery. To 4 panels and 4 batteries in series.

From what I understand its not good to have many batteries in paralel. And should have bought two large 6V batteries.


What to do?

1. Add more batteries (same type and all bought within the past 6 months)?
2. Add similar 12V deep cycle batterie's but with larger capacity (105Ah)
3. Add 2x6V in series to the paralel string

Currently the solar panels are capable to get a full charge by 3PM on a partial cloudy day with winter sun.
Budget permitting will add some more panels later. If running low due to heavy use or no sun we can supplement with a generator.

Looking forward to your advice!

Rogier

[Mike90250]

Well, it looks like you got the problem solved. If you are getting full charges in winter by 3pm, you got enough panels. And don't be afraid to run the generator if they are low, a tank of gas costs a lot less then replacing a ruined set of batteries.

[RogerSun]

Yes but for various reasons we need more storage. What about my question ?-)

[SunEagle]

Yes but for various reasons we need more storage. What about my question ?-)

If you need to enlarge your battery system you need to almost start from scratch because adding new batteries to old one will usually make the new ones age very quickly and end up costing more then you wanted to.

Unfortunately a solar / battery system needs to be planned and sized in the beginning and not along the way. Yes you might be able to add panels but that can change the charging ratio for your batteries and in most cases overload your charge controller.

A bigger battery system should be comprised of low voltage / high Ah cells wired in series. So if you need a 12volt 400Ah battery then the best way to get it would be to get 2 x 6v 400Ah or 3 x 4v 400Ah or 6 x 2v 400Ah cells. Try to stay away from any parallel wiring if at all possible.

[RogerSun]

So 6 month old batteries will be to far out of spec?

[John Galt 1]

First understand that when adding new batteries to an older battery bank the new batteries will rapidly degrade to match the old batteries, takes a few months but I've done it and seen the SGs slowly settle to match the older batteries. A basic rule if thumb is to NEVER use batteries more than a year older than your oldest battery in the bank.... so 6 month old batteries should be ok if you are willing to accept that they will age within few months to match the older batteries condition.

[SunEagle]

So 6 month old batteries will be to far out of spec?

As John Galt has stated adding new batteries to an old set (even only 6 months old) will affect the new ones and age them quicker than using a totally new set of batteries.

Also when adding a set requires wiring them in parallel you will introduce an uneven charging and discharging actions that will usually hurt the weakest battery in the group.