Using a solar regulator with a laptop power supply

[PNjunction]

I have a 20W panel, and that works fine with the 2A battery.

Note that most small ups-style agm like your 2 or 7ah battery has a maximum current inrush of only about .25 to .3C. (C being the 20-hour ah rating, ie 2ah or 7ah for your batteries) If it isn't listed on the case, then use this value. That means that for your 2ah battery, the maximum current you should be supplying is about .6A, or 600ma. Your 20 watt panel is capable of more than this, about 1amp under the very best conditions, but with some inefficiencies of the controller and lower light levels, you may be just getting away with it. Your 7ah battery should only be able to handle about 2.1a inrush current max.

It's when I swap the 20W solar panel with a 19V laptop power supply that the battery starts to cook. Is the regulator supposed to limit the amount of current that reaches the battery?

Nope - it regulates the *voltage*, and the the battery (or maximum current that your source provides) is doing the current regulating. The CMP12 regulates the voltage you set and merely passes all the current that you provide. In your case, the laptop charger is providing WAY more than 600 milliamps, and the 2ah battery is cooking. Note that solar charge controllers are really meant to be used with solar panels, and not with other power supplies as inputs.

One thing you want to be sure of is connecting the battery *first* and then attach the panel. Otherwise, some controllers can get confused without knowing the battery as a reference first. Also, you cannot determine if a controller is working without having a battery attached. Merely using a voltmeter on the CC output terminals without a battery does not work.

I would now doublecheck that the controller isn't fried. Attach the 7ah battery, then your 20 watt panel, and follow it with a voltmeter during the charge procedure to make sure. It should not rise beyond 12.7v or so during absorb. Also, toss your 2ah battery - being cooked, it is no longer trustworthy for any project.

[pete_melb]

Hi again,

Thanks for the info. Makes sense.

I've decided to ditch the idea of using a laptop power supply.

Instead, I'm now using standard SLA battery charger (that does float charging). So, I now have the option of either using a solar panel (connected to a DC input socket), or a the SLA battery charger (connected to the 12V cigarette socket) which I can use indoors.