Best location for solar charge controller

[Swartkat]

I have a 20W solar panel which I bought to keep the cranking battery topped up during camping weekends as I have a lot of parasitic draw (switches with led lights, tracker system, persons plugging in phones, tablets etc ).

It came with some sort of controller but I could never see it really working when connected to the battery. (volts keep going lower)

Measuring at its battery terminal, I get 20V, at the usb port 5V and then there is another output cable that gives 9V

So the current ourput of the panel is 1,2Amp which I realize is very little. I just need it to slow down the discharge rate.

So just to experiment, I got this 3 amp PWM solar charge controller which I want use instead of the controller box that came with the panel.

My question… where would you position it for best results?

As close as possible to the panel itself? Or at the crocodile clamps for connection to the battery? The cable is about 4 meters but rather thin.

[plonkster]

I’d place it closer to the battery for a better voltage reading.

Because V=IR, it means that voltage pushes up on the side where the energy comes from, and the more R you have, the higher it pushes up of course. So what happens is that the charger is seeing 14.2V and has started throttling the power, but the battery is still at 13.8V because you have an 0.4V drop over that length of cable.

This is an exaggerated example, at 1.3A it is not going to be that bad. But that’s the principle.

The panel is at 20V and is being pulled down by the PWM controller anyway. No benefit to moving it closer to the panel.

Oh, and fuse the thing. Let that be your mantra. Always fuse for the wire size or smaller.

[Swartkat]

Thank you Plonkster. As always, much appreciated!