Bypass / Blocking Diodes
Here is the situation: I have 2 roof top panels (95W GoPower, Imp 5.53, Vmp 17.2) mono and a 100W Windy City (Imp 5.75, Vmp 17.4) poly panel wired in parallel on the roof. No room for more. For l...
Forum Discussion
That doesn't bode well for the TriMetric battery monitor.
Here's the issue with pwm. Let's say the battery wants 2A in float mode. We have 4 panels, each produces 2A. So 4 panels produce 8A. But the battery only needs 2A. Here's where pwm comes into play. The controller shorts panels to battery and 8A charge the battery for a limited time period, which is defined by the duty cycle.
The duty cycle it the ratio of the time the battery sees 8A to the total time of the pwm cycle to produce average 2A.
For 4 panels, duty cycle = 2A / 8A = 25%
For 2 panels, duty cycle = 2A/4A = 50%
If we have only one panel then duty cycle is 100%
Without filtering or some very high speed measurements, it's impossible to measure average current of a 25% duty cycle. The smaller the duty cycle, the greater the error.
Here's the issue with pwm. Let's say the battery wants 2A in float mode. We have 4 panels, each produces 2A. So 4 panels produce 8A. But the battery only needs 2A. Here's where pwm comes into play. The controller shorts panels to battery and 8A charge the battery for a limited time period, which is defined by the duty cycle.
The duty cycle it the ratio of the time the battery sees 8A to the total time of the pwm cycle to produce average 2A.
For 4 panels, duty cycle = 2A / 8A = 25%
For 2 panels, duty cycle = 2A/4A = 50%
If we have only one panel then duty cycle is 100%
Without filtering or some very high speed measurements, it's impossible to measure average current of a 25% duty cycle. The smaller the duty cycle, the greater the error.
