Saturday, June 21, 2014

Analyzing the performance of my battery charging controller

After I installed my solar controller on my Prius, I wanted to study how much it affect the task of the default purpose of just reducing the internal temperature of the car by turning On the vent with the PV cell. One difficulty for a complete check is that the fan is not always turned On, it requires full sun and certain temperature to start spinning. Here on the Rio Grande Valley, normally there is always clouds passing by, so when there is a cloud there is not enough power on the PV cell to turn on the fan. So I was patient to wait for full sun to take the measurements.
   The first task was to monitor the currents and voltages of my setup.
Then turn On the vent
Then turned On the battery charge controller
Wow the solar is charging my Aux battery, there is almost 3 Amp flowing to it and the voltage increased to 13.2.. Unfortunately it seems there was not enough current to turn on the vent.
Now I took readings, I don't remember if every minute or every 30 seconds.  But what it is interesting is that the voltage at the battery is increasing until a point that I think is the max voltage allowed by the controller to charge a battery. I think this is the stage on the controller called PWM charging. And as the battery voltage is getting saturated, the current is being decreasing allowing the voltage on the PV cell to rise to the point that now it could have enough energy available to start spinning the vent.
Excellent! The cell controller is still charging the battery but also allowing the vent to work and take the heat out of the car.  Wait! I still don't have enough evidence that actually it is taking heat out of the car, I only know that the vent is getting outside air to get inside of the car, but that does not mean that it is dropping considerably the trapped heat. Well I will cover this later with a Design of Experiment.
Let's continue observing the behavior of my system:
It looks like if there is not a cloud passing-by reducing the power on the PV cell, it can continue the PWM charging and allowing the vent to work with power not used from the controller to charge the battery.
However if any cloud is blocking the sun enough time to let the battery reduce its voltage level again to normal which is 12.8 V, then we will not have a vent working until it "charges" again the battery to the top PWM voltage level.

I think this experiment illustrate how my arrangement to maintain the charge of my Aux battery can still let the vent to work. However, I don't know if the vent is spinning at a lower speed because it does not have the full PV Cell power for it, and as I commented early, I still don't know how good is this vent/PV cell system from Toyota to reduce the heat accumulation inside the car during the day.

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