Can I charge a bank of batteries from two different sources?

Question

I live completely off grid, and I love it. Currently, I have 1000 watts from my solar panels delivering about 58 amps with a 60 amp charge controller. I would like to add more solar power to charge my 8 deep cell 12 volt battery bank. My question is, can I add another set of panels with a 60 amp CC to the same bank of batteries? The CC will be the same brand and kind set to the same settings. If so, should I connect the controllers in parallel first or connect the leads from each CC directly to the batteries? I have done a lot of research on this subject, and the consensus is that I can do it either way, but I am wondering if I hook it up the latter way, and the bank is receiving about 17 volts from two sources, will it be too much voltage for the battery bank? Each CC would be receiving about 46 amps each.

Answer 1

You need a charge controller that is rated to operate two in parallel.



In theory you can hook up two CCs with diodes for isolation (although they may have diodes internally) but that may result in overcharging. Talk to the CC manufacturer.



What you want is a CC that handles two imputes and combines them. Those you can find.

Answer 2

The latter way is best. The 17 volts happens only when the charge controller thinks the battery is fully charged. Possibly the charge controller is turning off the charging too soon, because the current is not distributing evenly between your 8 deep CYCLE batteries. You should not connect the charge controlers in parallel, as one will shut down and the one still on will try to pass 92 amps which will destroy the second charge controller. The new charge controller should be in series with the new panels and another set of batteries. 92 amps of charging current will shorten the life of one set of batteries. You can probably connect the batteries all in parallel even if they are different brands, sizes and shapes. You can reduce the amp hours going to one set of batteries by adding a 100 amp silicon diode in series with the battery getting too much charge, if adjusting the charge controller voltage does not work well. Are you checking your cells specific gravity with a hydrometer? Possibly that is not practical with your set up. I'm confused about how most battery banks are checked for equal distribution of the charging current, especialy parallel batteries. My friend's parallel bank had lots of troubles. The battery in a parallel bank that the charge controller is connected to usually gets the most charge and even a milliohm of contact and wire resistance reduces the charging current to individual batteries in a parallel bank. Cleaning the connecting surfaces of the battery terminals is very important in a parallel connected battery bank.

It would really be better to go to 24 (or more) cells in series = about 50 volts (or even more) but that will require replacing your 12 volt inverter with one that can tolerate up to about 60 volts dc input = likely more expensive. Series makes it much easier to trouble shoot your battery bank, and reduces the amount of expensive copper needed. The charge controller you have possibly is not rated 60 volts. It is likely to fail if used at more than the rated voltage, but will likely work good at 12 amps or even less. Your charge controllers likely will not shut down until you go more than 24 hours drawing little or no current from your batteries, so you may not have the optimum setting of your charge controller. If your batteries are not fully charging you can try it without a charge controller. Possibly you have already damaged your batteries, by excessive discharge.

Answer 3

I think you better not,dangerour