Let me preface by saying I have a very limited understanding of how solar energy works. My question is why does the voltage in my battery bank (2 new deep cycle sealed 6v), as measured by my volt minder..... with the inverter turned off and no perceivable draw....... drop once the sun starts to go down? It was at 14.0 at 3:00 this afternoon and now at 7PM it is at 13.3. And this will continue all night. It does this every day. First thing in the morning it will be about 12.6. Is it a silly question to ask where did the volts go??? Sure there is the volt minder (which I unplug at night) and then there is the CO detector. But nothing else that I can think of. I have a 135W panel, a 800W inverter and a 35Amp controller on my 21' MH.

Simple. The battery will be from 12.7 full to less than that, so anytime it is being charged with solar or other charger it will be 13 or more. At night, the solar stops charging so the battery voltage falls to what it really is. The amount of charge above 12.x is called the "surface charge" and it takes time to wear off, so you could be 13.x for a while till it wears off to 12.X

But then in the evening when the sun goes down is when I want the most juice.....LED lights, fan for heater, 2 laptops. Plus have enough left over for heat in the morning. I have been told to never let the batteries go below 11.9 so get cautious around 12.5 and just turn everything off and go to bed.

With the lead-acid chemistry the battery can only hold about 12.7 volts max when fully charged. Anything above the 12.7 is created by the charging system. So as soon as the solar charging system provides no power the battery will drift down to 12.6/12.7 volts. All is normal.The volts are dissipated as heat unless power is drawn out of the battery.You have a long way to go from 12.5 to 11.9 volts. I exercise no caution until 12.2 volts.

solar is nothing more, than ANOTHER way to charge batteriesexample set a battery on the garage floorput a meter on it..12.xput charger on it..check with meter 13.xremove charger ..12.xsame thing with engine running, and the alternator charging the batteriesalso, the solar charges , then at night you USE power..lights, TV, water pump, heater..etc.. so voltage keeps going downnight is when you measure the REAL ACTUAL battery voltageday you are measuring the APPLIED CHARGING voltage

Stupid Solar Question | Good Sam Community

MrWizard
Moderator
Dec 31, 2014
solar is nothing more, than ANOTHER way to charge batteries

example set a battery on the garage floor
put a meter on it..12.x
put charger on it..check with meter 13.x
remove charger ..12.x

same thing with engine running, and the alternator charging the batteries

also, the solar charges , then at night you USE power..lights, TV, water pump, heater..etc.. so voltage keeps going down

night is when you measure the REAL ACTUAL battery voltage
day you are measuring the APPLIED CHARGING voltage
time2roll
Nomad
Dec 31, 2014
With the lead-acid chemistry the battery can only hold about 12.7 volts max when fully charged. Anything above the 12.7 is created by the charging system. So as soon as the solar charging system provides no power the battery will drift down to 12.6/12.7 volts. All is normal.

The volts are dissipated as heat unless power is drawn out of the battery.

You have a long way to go from 12.5 to 11.9 volts. I exercise no caution until 12.2 volts.
vtchris
Explorer
Dec 31, 2014
But then in the evening when the sun goes down is when I want the most juice.....LED lights, fan for heater, 2 laptops. Plus have enough left over for heat in the morning. I have been told to never let the batteries go below 11.9 so get cautious around 12.5 and just turn everything off and go to bed.
EMD_DRIVER
Explorer
Dec 31, 2014
BFL13
Explorer II
Dec 31, 2014
Simple. The battery will be from 12.7 full to less than that, so anytime it is being charged with solar or other charger it will be 13 or more. At night, the solar stops charging so the battery voltage falls to what it really is. The amount of charge above 12.x is called the "surface charge" and it takes time to wear off, so you could be 13.x for a while till it wears off to 12.X

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