MorningStar TS45

CT_WANDERER wrote:

ewarnerusa wrote:
I'd say it is duty cycle. Essentially the inverse of how much clipping the solar controller is doing to prevent the battery from exceeding the charging setpoints. During bulk charging, the duty cycle is 100% because the controller is allowing all of the solar current input to reach the battery. Once your absorption charging setpoint is reached, the controller begins to taper the current by decreasing the duty cycle (increasing the off time of the on/off PWM cycle) so that the absorption setpoint voltage is maintained. This is why you see that number fluctuating. As sun comes and goes and as battery SOC increases, the controller will do what is necessary with the duty cycle to allow the battery voltage to remain at the absorption setpoint. The Trister PWM will transition from absorption to float based on time at or below a preset duty cycle percentage.

This seem to help. I know my battery voltage was at 14.8 volts. As I am not in full sun, I have a tree that is over my panels. So it could be trying to clip the power but with the low output from the panels it could be having a hard time regulating the charging system. I will try to keep an eye on the meter when in full sun and see how it react. Maybe it will smooth out the meter reading. Will update when I have more information. Thanks again everyone for all your help. Gary

14.8V sounds like your absorption voltage setpoint. So the PWM% duty cycle is analogous to the amount of solar input current being passed through the controller to the batteries in order for them to not exceed 14.8V. If there was no solar input, the battery voltage would begin to drop. If the controller allowed all solar input current to reach the battery, the battery voltage would continue to climb. The controller is actively controlling the PWM duty cycle so that the voltage remains constant at the absorption setpoint. As your battery's SOC increases, it requires less and less current to maintain that voltage. Eventually the SOC is such that the controller determines it to be full and then transitions into float charging.

I believe that the default absorption to float trigger is 5 minutes at or below 30% PWM duty cycle. You can change these parameters to whatever you want when setting up a customized charging profile.

MPPT controllers all use PWM in all stages of charging. The difference is how the power is provided in different stages. In bulk the controller controls the output, in absorb and float the voltage of the battery and its acceptance rate control it. Unlike what we call PWM controllers, the battery is never directly connected to the panel. The power always comes into the buck converter no matter what stage it is in.

ewarnerusa wrote:
I'd say it is duty cycle. Essentially the inverse of how much clipping the solar controller is doing to prevent the battery from exceeding the charging setpoints. During bulk charging, the duty cycle is 100% because the controller is allowing all of the solar current input to reach the battery. Once your absorption charging setpoint is reached, the controller begins to taper the current by decreasing the duty cycle (increasing the off time of the on/off PWM cycle) so that the absorption setpoint voltage is maintained. This is why you see that number fluctuating. As sun comes and goes and as battery SOC increases, the controller will do what is necessary with the duty cycle to allow the battery voltage to remain at the absorption setpoint. The Trister PWM will transition from absorption to float based on time at or below a preset duty cycle percentage.

This seem to help. I know my battery voltage was at 14.8 volts. As I am not in full sun, I have a tree that is over my panels. So it could be trying to clip the power but with the low output from the panels it could be having a hard time regulating the charging system. I will try to keep an eye on the meter when in full sun and see how it react. Maybe it will smooth out the meter reading. Will update when I have more information. Thanks again everyone for all your help. Gary

I ask, because my Tracer3215BN does a very similar thing, in boost/abs. But it says % soc, not pwm %. And it goes up and down with the available wattage. I would think that as wattage goes down, duty cycle would increase, to compensate for the drop in available voltage, and vice versa? So, I'm thinking it's two separate issues, mine vs. CT-W's?

MPPT does switch to PWM in absorption. Drop to float method will depend on the controller.

ewarnerusa wrote:
I'd say it is duty cycle. Essentially the inverse of how much clipping the solar controller is doing to prevent the battery from exceeding the charging setpoints. During bulk charging, the duty cycle is 100% because the controller is allowing all of the solar current input to reach the battery. Once your absorption charging setpoint is reached, the controller begins to taper the current by decreasing the duty cycle (increasing the off time of the on/off PWM cycle) so that the absorption setpoint voltage is maintained. This is why you see that number fluctuating. As sun comes and goes and as battery SOC increases, the controller will do what is necessary with the duty cycle to allow the battery voltage to remain at the absorption setpoint. The Trister PWM will transition from absorption to float based on time at or below a preset duty cycle percentage.

Would this also apply to an mppt controller, in abs?

I'd say it is duty cycle. Essentially the inverse of how much clipping the solar controller is doing to prevent the battery from exceeding the charging setpoints. During bulk charging, the duty cycle is 100% because the controller is allowing all of the solar current input to reach the battery. Once your absorption charging setpoint is reached, the controller begins to taper the current by decreasing the duty cycle (increasing the off time of the on/off PWM cycle) so that the absorption setpoint voltage is maintained. This is why you see that number fluctuating. As sun comes and goes and as battery SOC increases, the controller will do what is necessary with the duty cycle to allow the battery voltage to remain at the absorption setpoint. The Trister PWM will transition from absorption to float based on time at or below a preset duty cycle percentage.

SMK...awesome link, thanxx!

The OP said it bounces around quite a bit, though. Should this be considered "normal" for pwm in a solar application?

https://en.wikipedia.org/?title=Pulse-width_modulation

PWM is how the controller regulates battery voltage.
Percent relates to the On vs. Off ratio.

"the PWM time slice"

Please elaborate, thanks!