How does a PWM charge controller work?

Johann
Johann Solar Expert Posts: 245 ✭✭✭
in General Solar Power Topics #1
How does a PWM charge controller work?
I know that it will charge batteries and that it is keeping the batteries from over charging and under charging.
What I like to know is....If a PWM controller is charging the battery is the panel voltage kept high or is the panel voltage dropping down close to the battery voltage for example.
What happen to the battery voltage while the controller is in use? Will it go up and down?


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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited July 2016 #2
    I'd say that both are jumping around when the device switches on and off.   But it doesn't have to be this way - with the right filtering and fast enough PWM, the voltages can be almost constant.  It could even hold the panel voltage at MPP (potentially useful for some loads other than battery charging).

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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    edited August 2016 #3
    PWM turns the output off and on very rapidly. Thousands of time per second. It also varies how long the power is turned on; varies the on time and off time in each time division. 

    Here's a wiki on pwm
    https://en.wikipedia.org/wiki/Pulse-width_modulation
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #4
    I think you will find that solar charge controllers are typically in the 30 to 300 hz range.

    I am available for custom hardware/firmware development

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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    The actual frequency depends on the design of the controller, but PWM is basically a switch, that connects the panels to the battery for a moment, then as the battery voltage rises to the desired voltage, reduces the time ratio of connected (charging) to disconnected (idle).  When the battery is low, the panels are connected, when full, they are disconnected.  When measuring, your meter will read an average of the voltage, you may read Vbatt at the PV terminals , or Voc, depending where in the charge cycle you are.
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  • Johann
    Johann Solar Expert Posts: 245 ✭✭✭
    edited August 2016 #6
    Thank you very much for all of your answers and link.
    So, a PWM is still basically a '' soft '' switch that will connect/disconnect batteries to the solar panel,  that may still drag your panel voltage down close to the battery voltage and with it will lower your panel out put.
    For some reason, I thought that the PWM function would keep the panel voltage up so more power could be harvested from the panel.

    Am I missing something here?



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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
    Johann said:
    For some reason, I thought that the PWM function would keep the panel voltage up so more power could be harvested from the panel.
    That's what an MPPT controller does.   --vtMaps
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