PWM CC efficiency operating near maximum input rating?

PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
Are pwm charge controllers operating more efficiently when the panel or array's output current is just underneath the charge controller's max input current rating?

In my situation, my smallest 15watt panel works fine with a Morningstar 4.5a pwm controller. But I also have a 10a pwm morningstar, and the 15w panel works fine with it - but I always wondered if there was any meaningful increase in pwm charging efficiency when the panel's current output is more closely matched to the controllers maximum input rating.

Comments

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM CC efficiency operating near maximum input rating?

    There wouldn't really be any noticeable difference, other than at max current, there would be slightly more losses due to normal resistance losses in the various circuits, both internal to the controller, and external in the connecting cables. Push the controller and/or wiring hard enough and they get warm/hot, and heat = loss of efficiency.
    Of course there is always a slight consumption of power by the controller just to keep it "fired up and operating", so it would often be inefficient to use a huge controller for a wee tiny panel. For instance a big controller might self consume 2 or 3 watts to run it's internal electronics, so what would you have left over from a 5 watt panel?
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: PWM CC efficiency operating near maximum input rating?

    Thanks! That's what I thought. What kicked this off for me was when I was trying to size up an inverters load to be somewhat close to it's rated capacity to be more efficient, and wondered if the same might apply to charge controllers. You got me to look at some prospective CC specs, and they draw very little current comparitively, so I was off base, unless one went to the total extreme. Appreciate the feedback..
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: PWM CC efficiency operating near maximum input rating?
    PNjunction wrote: »
    I was trying to size up an inverters load to be somewhat close to it's rated capacity to be more efficient.

    You might want to have another look at that idea as well. Many inverters are most efficient at roughly 1/3 their rated capacity and their efficiency drops off as you approach their max rating. IMHO it stresses an inverter to drive it to the max for more than a few minutes at a time, as it can cause the internal components to heat.
    Think of it as a car engine that is just capable of powering the car to a max of 180 MPH. A short run at 180 will prove that yes, it will do the job, but maintain that speed for 15 minutes and you'll be stressing the engine big time.
    On the other hand, using a 2000 watt inverter to run a 15 watt load on a regular bases would be very inefficient, as generally the larger the inverter, the greater it's self consumption to run it's internal electronics. That's why many of us run more than one inverter. A small one for regular small loads that require power 24/7, then a large one for intermittent use on large loads like a water pump, microwave etc.
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