Stupid Solar Question

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 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

You are barely scratching your batteries capacities, good thing too because your solar is matched up to your use rather than your batteries.

while you use a battery or charge it you will get a false reading. Just like there is a drop in surface charge after charging, there is a recovery from the voltage sag from putting a load on it. So the 12.5v that you see while you are using the battery is less than the true resting voltage. The 12.6v you see in the morning is the resting voltage after using it the night before and whatever parasitic loads there are.

Will they last over night? Well what do you want to run over night? I don't know how much load the solar is picking up in the day time but from your description, your night time use is very low. That's great for solar when you may need your batteries to carry you for days in bad weather. The thing is if you do actually get that bank down to 12.0v, that 135w panel is going to have a heck of a time getting it back up, especially if it has to cover your loads too.

So the best thing you can do is figure out how much power you want to use. Compare that too how much you can get out of your batteries and replace with your solar. It all should balance including time of year and situation. You are lucky with a MH because if you don't have a built in generator, you can always run the engine to bring the batteries back up if the solar falls short.

Solar only charges the batteries during the day. As you use current out of the batteries at night, the voltage will gradually drop.
Try to keep batteries at 50% or above for maximum battery life.
Plan on replacing batteries every 5 years or so just like your car.

To put this in simple terms, you have nothing to worry about.

As said above anything above 12.7V once the charger stops charging is surface voltage created by the charger. It will slowly dissipate to its rest voltage of 12.7V if the battery is fully charged.

Look at the chart EMD_DRIVER posted. This is state of charge voltage chart at resting voltage. Rest voltage is the battery voltage while not being charged or being used, drawing no current from it. The battery may have to sit unplugged for a few hours to measure its true resting voltage.

While you are using the battery at night to power your TV, laptop or whatever, the battery will measure below its resting voltage. Once you remove all of the loads the voltage will rise back up. Put a load back on it and the voltage will start going down.

As the above chart shows you can drain the battery down to 12.06V (50%) Rest Voltage and be fine. Measuring 12.5V while running your TV, laptop, lights etc is certainly fine. As stated above, you can go down to 12.2V and still be in good shape. Measuring 12.6V in the morning says your battery is still 90% charged or better. You have barely used its capability at all. Your doing good.

vtchris wrote:
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.

Yeah, then you need some lunar panels. :B

A dumb question deserves a dumb answer,....
Simple, you need "Nite Charging Solar"