First Solar Install Voltage Drop

[Dobyx]

On my RV I have 2 x 100watt panels hooked up to my PWM controller in parallel with 10 gauge wire. Then from there off to the 2 x 6v deep cycle batteries hooked up in series. I have a battery disconnect on the negative line between my battery and the trailer chassis. I also have another disconnect on the negative line between my solar panels and controller.

After finishing the install everything seem to be working in order, the batteries were at 12.6 V when I left the trailer in the evening. I left it for one full day to charge, the weather was sunny with few clouds but smoky from a forest fire. While charging I am getting an average of 88 watt @ 5.1 amps. So the trailer batteries had a whole day and part of the next morning to charge. When I went back late the following morning the voltage read 13.2 V. I have the disconnect battery switch turned off so that there's no parasitic draws other than the solar controller. When I switch the disconnect switch off between the panels and the controller obviously the controller shows no more input to the batteries. However, the battery voltage starts to drop from 13.2 V down to 12.7 within 15 minutes.
I am assuming that I'm getting somewhat of a false reading of the batteries when they're being charged by the solar panels as that voltage is being read as well. But what I am not sure about is why the battery voltage is dropping or if that's normal with deep cycle batteries?

The other thing I would like to know is if there is a way of getting a reading on the controller that is reading just the batteries and not the power coming in from the solar panels? Or is this a feature of a better controller?

 

[acdoctor]

Battery voltage will settle. It will also sag under load and rebound after load is satisfied. So voltages is not a good representation of State Of Charge (SOC).
A battery monitor either a shunt type or current coil type that you can program your battery capacity into.

 

[pollenface]

Then from there off to the 2 x 6v deep cycle batteries hooked up in series

What condition/capacity?

I am assuming that I'm getting somewhat of a false reading of the batteries

You need to use a multimeter for reliable voltage readings.

But what I am not sure about is why the battery voltage is dropping or if that's normal with deep cycle batteries?

this is relative to loads connected to the battery, battery age/condition, state of charge, capacity etc. Lead acid batteries do sag a fair bit when loads are connected, it's nothing to be concerned about.

Can you describe your loads and power needs?

 

[Dobyx]

What condition/capacity?


You need to use a multimeter for reliable voltage readings.


this is relative to loads connected to the battery, battery age/condition, state of charge, capacity etc. Lead acid batteries do sag a fair bit when loads are connected, it's nothing to be concerned about.

Can you describe your loads and power needs?

Thanks for your reply pollenface. The batteries are brand new 220ah. Yeh I agree I need to use a multimeter, I use one tomorrow and see where they are at. At this point of time I have no loads on the batteries other than the controller, as I have the disconnect switch isolating the batteries. As for my needs moving forward; LED lights, furnace, oven fan and phone charging via 12v (no inverter) Thats why I only have two panels, we don't use a lot of power when we camp.

 

[Dobyx]

Battery voltage will settle. It will also sag under load and rebound after load is satisfied. So voltages is not a good representation of State Of Charge (SOC).
A battery monitor either a shunt type or current coil type that you can program your battery capacity into.

Thanks acdoctor, I thought that might be the issue but wanted to make sure. Thanks for the battery monitor idea too.

 

[foggysail]

You should understand your controller. Make sure that it has a high limit shut down or you might overcharge your batteries. A lead acid (flooded cell) will boil out. Not sure what gel cells will do although I read in the past where someone had one on a trickle charger in his basement and it exploded

 

[byteharmony]

You should understand your controller. Make sure that it has a high limit shut down or you might overcharge your batteries. A lead acid (flooded cell) will boil out. Not sure what gel cells will do although I read in the past where someone had one on a trickle charger in his basement and it exploded

I've read all Lead acid batteries should have distilled water added yearly.

I know that you should have a low voltage cut off on your batteries so that you don't drain them down to voltage that is so low that it damages the cells. That being said, in practice I haven't seen people use BMS systems on lead acid. Why?