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2 solar controller:




You cannot connect solar panels directly to a battery, you must use a solar controller. This will regulate
the power down to the proper charging voltage for the battery, as well as provide some protection against
things like deep discharge, overcharge, and backfeed into the panels. If you have 200 watts or less of panels,
you can use a pretty basic and inexpensive controller. Controllers have several ratings, including how many
amps they can handle, (usually a single rating that includes both battery charge and discharge) as well as
a voltage limit for the panels. If you're stringing together multiple panels, make sure your controller can
safely handle the MAXIMUM voltage the panel string can produce. If your panel Vmpp voltage is below 14
volts, it'd be a good idea to have a regulator capable of both bucking AND boosting panel voltage, to insure
you can continue to harvest power when less light is available. A controller with MPPT is preferred for the
best efficiency, but a simpler PWM controller will still get the job done. (PWM controllers cannot boost)

If you have more than one panel, you will have to decide whether you want to connect them in parallel or in
series. Parallel will double the current, but will increase power loss in your wire running to the panels,
and may exceed your controller's current limit. Series will double the voltage and improve efficiency, but
can present a high voltage hazard or damage your solar controller if its not rated to handle that voltage.
Always go by "Voc" when considering safety and controller max voltage. If your panel doesn't have an obvious
Voc (Voltage at Open Circuit) rating, LOOK HARDER. This is something you NEED to know.

Also, 16v panels have a lower Vmpp (13.0v) than 18v panels (14.6v), which makes it even more difficult (or
impossible) for a PWM controller (which cannot boost) to charge a 12v battery. So MPPT controllers aren't
just more efficient, sometimes they're the ONLY thing that will work, especially when its cloudy.

As an example, I have 2 strings of four 18v (22.5 Voc) panels in parallel, (getting near my controllers 100v
panel limit) which can produce 600 watts. My controller can handle 1000 watts, so I COULD add another
string of 4 panels and produce u to 900 watts. But my controller is limited to 40 amps on all ports, including
battery, and 600 watts will already hit that limit at 13.8 volts, so adding more panels won't improve my max
charge speed. HOWEVER, it WILL allow me to gather more power when less sun is available. So is it
worth it? Maybe?

A new issue I've been dealing with lately is electrical noise being generated by my controller. It's difficult
to predict what sort of noise problems you're going to have because so many different factors play into it.
If you find your controller is generating noise on your DC power line, you'll need to add an EMI filter.


CPY-2420 MPPT controller ($34 at eBay)

generic PWM controller ($15 at Amazon)

YWBL filter board ($16 at Amazon)



last updated 11/30/2023 at 20:12:36