Saturday, March 4, 2017

More Solar Graphs

Thursday and Friday were mostly clear and sunny days. And it appears that the solar charge controller had not finished with the equalization charge that I had manually started a couple of weeks ago. I'm guessing that since the array voltage wasn't above the equalization voltage as there just hasn't been a whole lot of sun for the last couple of weeks.

This is the output from the log file from Thursday showing the battery voltage (blue), array voltage (grey) and charge current (orange). Once the array voltage got high enough for equalization to occur, current was "pushed" into the battery until the battery voltage was high enough for equalization. Most of the morning and afternoon, the charge state was either at bulk charge or absorption. The log file shows that at a battery temperature of 7°C, the target voltage for equalization was 15.83 volts and the absorption voltage was 15.30 volts.

This is the output for Friday. It looks similar at first but since the charge controller is no longer in equalization mode, the current doesn't increase beyond about 2 amps after the charger drops into absorption mode. The array voltage is just allowed to rise up to it's maximum.

What have I learned from this? I never realized how much impact temperature has on battery charging. The upper limit of the input voltage for most 12 VDC devices is 15.5 VDC. An example being the Xantrex 2000 watt inverter that I am using. I ran into a lot of comments about the Xantrex inverters when they dropped their maximum input voltage from over 16 volts to 15.5 volts. At the time I didn't know why folks were complaining. When using flooded lead acid batteries like I am, the lower battery temperature limit would be a bit above 0°F. The temperature compensated absorption charge voltage at 0°F is 14.8 + 0.75 = 15.55 volts. The equalization voltage at 0°C is 16.05 volts, well above the upper limit for many DC devices.

In other words, be sure to disconnect all DC loads when doing a manual equalization if the temperature is near freezing. Also, don't start a manual equalization unless there is enough sun for it to complete. It just means a little more thought on my part.

It's still too cold (-32°F on Friday) to do much of anything. I did drive the Ural but it was just out of the garage. The truck is in the garage so I can get some stuff taken care of.


  1. All good to know stuff...thanks. I've tried equalization/recondition on my RV battery using house current to power the charger so no real issues having to compensate for temperatures.

    1. The charger still needs to compensate for the temperature of the batteries or the ambient temperature of the charger. The TS-45 PWM charge controller I'm using doesn't have a built in temperature sensor so unless an external sensor is installed, it doesn't do temperature compensation. The log file indicates that it has a sensor on the heat sink.

      The temperature compensation doesn't have anything to do with the solar panels but the temperature and type of battery.