Connecting panels directly to batteries

tonygcan · March 2011

A friend of mine who recently added pv panels and batteries to his RE system had his non mppt cc malfunction on him. He was advised by his integrator to attach his panels directly to his battery banks and just load his batteries so as not to overcharge the batteries.
From my understanding, you shouldn't connect PV panels directly to batteries because of the unmoderated higher charge voltage going into the batteries. If his pv strings of 4 panels for 48 volts output more or less 80 volts for charging will this not ruin his batteries?

BB. · March 2011

Re: Connecting panels directly to batteries

Not from "over voltage" during normal charging...

Solar panels are really Current Mode sources... I.e., under full sunlight, the PV panels/array will output 12 amps from 42 volts to 60 volts (assuming Vmp>60 volts)...

What happens, when the battery gets fully charged, the energy from the solar array has to go somewhere--and that is making hydrogen and oxygen--Basically equalizing the battery bank.

Equalization is hard on batteries (and can be death to sealed/AGM type batteries). So, you don't want to do too much of that.

Your friend can either put a switch in the array wiring going to the battery bank (make sure switch is well away from hydrogen gas fumes from battery) and simply switch the array off when he thinks the battery is charged.

Or, he could start using a microwave, or electric tea kettle, outdoor 500 watt flood light, etc. to "dump" the unneeded energy from the battery bank.

Basically, he becomes a simple battery charger controller.

-Bill

tonygcan · March 2011

Re: Connecting panels directly to batteries

Thanks Bill,

That's a relief to know.

Don't you sleep?

niel · March 2011

Re: Connecting panels directly to batteries

that's not exactly the best way to regulate the charge going into a battery. i've done it, but i can raise or lower the load to better suit and it's still somewhat tricky. if the battery(s) are low then a direct connection will work until it reaches the point it should go to absorb. at that point disconnect it and order another cc and preferably a better one this time. the battery(s) should be fine for the few weeks until the new cc arrives to give a proper charge.

and you are right as he is up at odd times and that gave me a chuckle. i too frequent the forum at any time, but you just don't always know it because i may not write to the forum right away.

mike95490 · March 2011

Re: Connecting panels directly to batteries

You also may have to disconnect the panels at night, or the battery may back feed, if the panels dont have anti-backfeed diodes in them.

BB. · March 2011

Re: Connecting panels directly to batteries

That is correct. A blocking diode is a good idea at 24 volts and mandatory on a 48v volt battery bank if panels are left connected over night.

-Bill

tonygcan · March 2011

Re: Connecting panels directly to batteries

Yes, as far as I know he has installed a diode between betteries and panels. Thanks for all the info.

Connecting panels directly to batteries

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