phil99 said  

Yes, as long as the switching 'on' time is short enough to prevent excessive burning and the 'off' time long enough to extinguish the arc.

Well, maybe. All thermostats are not created equal. If the contacts are slow to open or/and the opening distance is insufficient, it will create a DC arc when the contacts *open*.

Once the arc is established, 'off' time no longer plays any role as long as there is solar power and a load to feed it.

Hello Davo99,
             Yes, It was the Arduino board and the caps that I was referring to. I just wanted to get as close to what you  used and any other unit you used.

                                                             JS.

  Quote  

phil99 said  

Yes, as long as the switching 'on' time is short enough to prevent excessive burning and the 'off' time long enough to extinguish the arc.


Well, maybe. All thermostats are not created equal. If the contacts are slow to open or/and the opening distance is insufficient, it will create a DC arc when the contacts *open*.

I worded that poorly. I should have said the 'on' and 'off' times of the MOSFET. The MOSFET 'on' time needs to be short so that if the thermostat opens while it is on you want the MOSFET to switch off before the arc damages the contacts. The MOSFET 'off' time needs to be long enough to ensure the arc has extinguished and prevent the arc re-striking.

Having the thermostat switch the gate or gate power supply is the safer option.

  phil99 said  

Having the thermostat switch the gate or gate power supply is the safer option.

Understood, that is exactly what my system does.

Davo99,
        With what the lads are saying and what you say in your long post. In there
any modifications you'd make.  Any chance of a simple diagram.
                                  J.S