Mixed AH batteries?

[Mallison359]

HI Guys,

I set up my solar system in my shed at the end of the summer (I know timing kinda sucks). It's fulfilling my needs for now however I am planning on adding to it over the next few months so i can use all of my equipment.

I recently bought a second battery from a sellar on ebay that i got my first battery from. The trouble is, i was certain that my original battery was 95ah however this may actually be in fact a 110ah battery. Sorry for the newbie question but can i have a 110ah battery and a 95ah battery set up in series? or is this bad/dangerous?

Regards
Michael

[SunEagle]

HI Guys,

I set up my solar system in my shed at the end of the summer (I know timing kinda sucks). It's fulfilling my needs for now however I am planning on adding to it over the next few months so i can use all of my equipment.

I recently bought a second battery from a sellar on ebay that i got my first battery from. The trouble is, i was certain that my original battery was 95ah however this may actually be in fact a 110ah battery. Sorry for the newbie question but can i have a 110ah battery and a 95ah battery set up in series? or is this bad/dangerous?

Regards
Michael

Not only will two batteries with different Ah ratings be a charging/discharging issue but adding a new battery to an old one will cause the new one to shorten it's life closer to the old one.

Battery systems need to be installed all at the same time with all the components being the same. Any unbalance in wiring resistance (issue with parallel designs) or internal battery resistance causes unequal charging and discharging.

While not really dangerous, the worst issue is that when one of those batteries finally fail, replace them both at the same time with identical units.

[Mallison359]

Ah, thanks for the help.

So if I was to put these in parallel, would I put the small ah battery at the end or in the middle between the charge controller and the other batter?

[SunEagle]

Ah, thanks for the help.

So if I was to put these in parallel, would I put the small ah battery at the end or in the middle between the charge controller and the other batter?

The wire between the two batteries should be sized based on the amount of amps your inverter can draw from both and they also should be as short as possible to reduce circuit resistance.

The wire from the charge controller can be longer but you would have the positive one connected to the first battery + terminal and the negative wire on the second battery - terminal.

The positive and negative wires for the inverter would be wired to the same + and - terminals as the charge controller.

You should also use over-current protection (fuses) on the wires from the CC to the batteries and from the batteries to the inverter.

[Mallison359]

Sorry what I meant was

[charge controler]===[12 110ah]===[12v 95ah]

Poor drawing but what I'm getting at is do input the 110ah in the middle or end?

[SunEagle]

Sorry what I meant was

[charge controler]===[12 110ah]===[12v 95ah]

Poor drawing but what I'm getting at is do input the 110ah in the middle or end?

As long as the wire between the 110Ah and 95Ah is short as possible it doesn't matter which one is in the "middle"

The key is to make the two batteries appear as "one" to the CC so it sends the same amount of charging amps to each.

[inetdog]

Sorry what I meant was

[charge controler]===[12 110ah]===[12v 95ah]

Poor drawing but what I'm getting at is do input the 110ah in the middle or end?

The correct answer is neither way is correct!

Look at the information on wiring batteries in parallel at http://smartgauge.co.uk/batt_con.html.
What you would want is either what we call the diagonal connection or else the bus bar connection.

[Mallison359]

The correct answer is neither way is correct!

Look at the information on wiring batteries in parallel at http://smartgauge.co.uk/batt_con.html.
What you would want is either what we call the diagonal connection or else the bus bar connection.

The method I was imagining was akin to Method 1 in the link you sent. But thank you very much

[inetdog]

The method I was imagining was akin to Method 1 in the link you sent. But thank you very much

And Method 1 is there just as an illustrative example of how NOT to do it. It is not being recommended. Read the whole thing please.

[Mallison359]

And Method 1 is there just as an illustrative example of how NOT to do it. It is not being recommended. Read the whole thing please.

I did read it all, it clearly states that when using 2 batteries this cannot be improved on. I assumed as much as all examples had 4 batteries. I suppose method 3 could be used though.