by admin | Jan 18, 2014 | Tech Updates
The sun hasn’t been out for almost two weeks now and my batteries are still not fully charged even if it has been charging for a week after I drained it last week. I now must find out why it is taking so long to recharge in cloudy conditions. In theory, my 100W, 24V solar panel should produce 4.1A of charging current during sunny conditions. 4.1A should fully charge my 100AH, 24V battery setup in 24 hours of sunshine which should be just 2 to 3 days. But because of the the low pressure area (and now a tropical depression), the weather has been cloudy for almost two weeks now. So how much charging is being done in cloudy conditions? Because I don’t have a battery monitor yet, I just created a make-shift shunt resistor. It is basically a resistor with very low resistance and high current capacity. The smallest resistor I could find was a 0.22ohm, 5W resistor. To measure current, I simply need to get the voltage through a known resistor value and use the equation: I = V/R. I also don’t want to introduce a large voltage drop between the batteries and the charge controller and inverter because it would affect charging. I expect to measure about 5A of current and the voltage drop would be V = IR or 5 * 0.22 = 1.1V. This is actually too large. The solution is to connect several resistors in parallel which reduces the resistance. I soldered together eight 0.22 resistors in parallel to get a combined resistance of 27.5mOhm. The voltage drop of 5A across it would...
