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I currently have a PWM 12/24v (auto commute) with ~18V as input and a 12V battery in the output.

I wanted to switch to 24V battery and I thought about going ~36v solar panel. (18V * 2)

Then I saw online some examples of putting more in series for a higher voltage, like this one:

enter image description here

These solar panels are 100W and can go up to ~22V. So if I'm correct this schematic will send about 66V to the PWM/MPPT to charge a 24V battery. (two 12V in series.)

Can a charge controller handle whatever amount of voltage? And is there on this aspect a difference between MPPT and PWM?

And is there a difference in efficiency between sending 66V or 33V?

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    \$\begingroup\$ That's up to the charge controller. Its datasheet will tell you. \$\endgroup\$
    – user16324
    Commented Jan 23, 2020 at 20:49
  • \$\begingroup\$ @BrianDrummond Yeah i'm looking into that. What about efficiency ? Is getting closer to the 24v is "better" ? \$\endgroup\$
    – bob dylan
    Commented Jan 23, 2020 at 21:38
  • \$\begingroup\$ Essentially no difference, if the MPPT is competent. \$\endgroup\$
    – user16324
    Commented Jan 23, 2020 at 22:38

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At the risk of stating the obvious, the MPPT is always going to do a better job. It is "gaming the panel", making experimental adjustments upward or downward in current draw to see if that improves or worsens voltage enough to produce a net increase in V*A.

In theory, both of them, MPPT or PWM, should buck the input voltage down to an appropriate battery charge voltage given the stage of battery charging, while preserving W as much as possible through the bucking (i.e. if they buck down from 48V@4A to 24V, that should be about 8A).

However, I have been told by solar tech supports that PWM converters do not buck, and that it is impossible for output current to exceed input current: So if the panel is outputting 48V @ 4A, then the battery charge will be 24V @ 4A. And if I want the current-multiplication of bucking, I need to go with an MPPT controller. I'm not 100% sure I believe that, but I haven't been able to put meters on my setup.

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  • \$\begingroup\$ Without buck (and/or boost) you cannot have MPPT, but you can have buck/boost without MPPT. | ie A controller COULD be inductive buck and not MPPT, but, once you have bucking adding MPPT is just a control issue. | SO essentially all PWM controllers are essentially cheap and just a mark-space controlled switch and not MPPT. \$\endgroup\$
    – Russell McMahon ♦
    Commented Jan 24, 2020 at 1:41

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