adding more solar panels with same battery size

[Mosaab]

Hello DIY family,


I have a question about adding more solar panels to my system while keeping the battery size the same. For example, if I have an existing 400 watts solar panel and I have a single 1200Ah 12V SLA battery with max charge rate of 35amps. Now if I add solar panels, let us say we another 400 watt panel so now the total solar output is 800 watts (assuming no losses for calculation purposes), then the charge current would be 800/12=66.6amps. In this case people would say it would harm the battery to charge it at a faster pace than what it rated for! But I would argue that tfor this reason we have a charge controller attached to the system. Would my argument make sense? If not, then why?

 

[rmaddy]

You could put the two panels in parallel and point one more toward the east and the other more toward the west. Then you never get too much current at any one time and you get more total sun hours during the day. Just configure your charge controller to a max of 35A so you don't charge the battery too quickly.

 

[Mosaab]

Let’s say I have a 65 amp controller, then by default it will be configured at 65A, correct? Also, can I configure that charge controller to a lower current input, for example 35A?

 

[rmaddy]

I can't speak for all charge controllers but I know some charge controllers will let you specify the max output (not input) current. So you might be able to setup your 65A controller to only provide 35A output instead of its max of 65A.

 

[sunshine]

But I would argue that tfor this reason we have a charge controller attached to the system. Would my argument make sense? If not, then why?

You are right, partly.
If you look at your charge controller and compare it to a plug in mains charger then it doesn't matter what the amount of supply power is feeding them, The plug in mains charger has an unlimited number of power stations for supply yet only still puts out the same current. The same, theoretically, for the CC.
However CCs can only do so much and rely on the user to balance loads and inputs just as they do on the power grid but on a much smaller scale. Too much input will raise voltage. Too much load will lower voltages for both home and grid systems. To balance we either spend money or be more creative.