Electrics

For a decade and more, aboard a 45ft vessel with 4 x 45w panels, the control was manual. I had a moving coil voltmeter connected permanently and would turn the panels towards or away from the sun to keep the voltage where I deemed appropriate given the previous day's usage and projected use of the current day.

When I was residing alone on the land and often absent for a day or more I wanted an automatic charging system and when I renewed the batteries and new panels I bought a few controllers.

I bought two makes of MPPT type for the new panels and a PWM for the old set-up.

PWM (Pulse Width Modulation)

The one I have is a is a Stecca Pro 10|10. This means it can have a maximum input of 10A and a maximum output of 10A. This was fine for the old '12v' panels.

PWM's are not as efficient as MPPTs but have their place when using '12' volt panels. The quotes around the 12 is to note that that is the nominal voltage, as in 12v battery. A 12v battery under charge can reach 16v plus for short periods, as long as the battery doesn't get too warm and the electrolyte level is monitored . . . 12v solar panels usually have a maximum output voltage of 19v.

Solar panels have a maximum efficiency at a specific voltage, which may be 19v. If charging at 14.25v then some 25% of the energy is not being generated by the panels. This is fine on a sunny day if you don't need much charge. This loss is the same whether you manually turn the panels as I first indicated or you use the PWM. The PWM just allows you to go away and not bother. The Stecca also has an LCD screen with loads of info as well as the voltage etc. so is very useful and it is made in Germany.

MPPT (Multi Power Point Tracking)

These types check the voltage from the panels every second or more and adjust the output to maximise the overall power. This does this as it is a converter, which the PWRs are not the PWR will stop the extra voltage from overcharging the battery but the power is just not used. The MTTP converts a wider range of input voltages to that set for the battery. Hence the MPPT model number will include the maximum voltage i.e. Model 75|15 meaning a maximum input voltage of 75v and a maximum current, in or out, of 15A.

A solar array of 75v giving 8 amps through an MPPT would provide 15v to a flat battery at 40amps (75 x 8 = 15 x 40)

So where solar panels are of the household type generally producing 37v then an MPPT is all but essential. With 12v panels, albeit they may produce 19v you can connect them straight to the battery and manually control it, but connecting a 37v panel will need a worrying amount of control and I haven't wanted to try it.

As for makes of MTTP I have bought they are:
1. Victron designed in Holland and produced in India and
2. Morning Star designed in USA and produced in Taiwan.

The morning star is the more professionally looking and more informatively usable straight out of the box: both can be connected to a computer for more elaborate control.