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Diodes to keep DC from going wrong way: specs and sourcing.


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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.


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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.

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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 by Stanley
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  • 2 weeks later...

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.


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  • 2 weeks later...

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