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Colin Wright avatar image
Colin Wright asked

Help with mppt relay switching for external load

Hi, thanks for everyone's help to date with my mppt (100/50) external load switching.


I have now sourced and installed the mppt digital tx cable, which I should be able to control my relay from.

Unfortunately the DC/DC solid state relay (SSR) I have used is supposed to switch on between 3v and 50v. However the voltage on the digital tx cable from the mppt gets pulled down to 2.8volts by the relay, so it doesn't trigger. I'm guessing that the relay is taking too many milliamps to trigger, or the mppt cannot supply enough milliamps for the relay.

Can anyone help me with the specs of a Solid State Relay that will work?

It should be DC/DC with an output side of say 12volt and 1amp.

The input side of this relay should be able to trigger from the digital tx cable on the mppt. I know it is a 5volt output, but cannot find spec of milliamps on the digital tx out that would be available to trigger the load relay.

My plan is then use the output of this smaller relay to trigger the larger load relay. This is the easiest work around I can come up with.

I'd be grateful for a part no. and manufacturer of a suitable DC/DC solid state relay, or an Amazon link or similar.

I'm looking for a DC/DC solid state relay that the tx digital out cable on a 100/50 smart solar mppt will trigger.

Kind Regards and many thanks for your time and help.

Best wishes

Colin and Nichola Wright

Yacht Emerald

Cartegena Spain

In virus lockdown, stay safe everyone.


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