I searched the forum but could not find a discussion of diodes in DC circuits. 

If this is not the place to ask for help, please point me to where I could find info on this?

In short, I have a PV array supplying 200VDC which heats a geyser. When the thermostat switches off the current should charge up a power wall battery supplying an inverter.

A diode is thus needed to keep the  batteries from heating the geyser after dark. Any help with specification and sourcing such will be much appreciated.

 

Maybe you should draw a little diagram of what exactly you would like to do.

Diodes could work (if I understand what you want correctly although a diagram may help) but you would need 2 diodes.

From the PV positive, you would have 1 diode to the geyser element and 1 diode to the battery.

The diodes should be rated for more than the short-circuit current of the PV array.

You will get about a 1V drop across the diode which should be ok at 200V. (Theoretically ~0.7V for a silicon diode, but will be temperature and current dependant)

Also, I assume you are using a DC rated thermostat? Otherwise you could cause a fire if your AC thermostat tries to break 200Vdc and starts arcing internally.

Actually, you could do it with just 1 diode to the battery. The Geyser element would just need to get it's power from the PV side of the diode.

If you give some specs of the PV array I can probably find you a suitable diode at RS components.

Also, how are you charging the battery? I assume the PV is not connected directly to the battery. You should have some sort of charge controller.

Edited October 19, 20205 yr by Stanley

Hi Stanley, and thank you very much for your considered replies.

ACDC did not have a suitable diode in stock, but got me a 16F120 the next day. (16A 1200V DIODE - CATHODE to STUD)

I simply screwed it in the PV breaker output on the way to the batteries. It causes at most a 1 V drop. 

I installed a 6mF capacitor over the geyser thermostat to keep it from arcing. 

All working well, when thermostat opens, volts go up and batteries charge.

 

I what to do this in my combiner box. so every string will have a Diode on.