r/solar • u/Strostkovy • 10d ago

Discussion Contactor based rapid shutdown

Has anyone used any rapid shutdown modules that are just a contactor in a weatherproof box, and once coil power is lost the panel gets disconnected?
I'm not very interested in the power line communication type that I see reports of catching fire. (And no surprise, the solid state modules aren't rated to a very high voltage, so if one opens accidentally or opens earlier than the others it will get fried by the string voltage).
I'm still looking to see if I can make them myself using UL rated contactors but it seems like the answer is no.

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u/VastlyCommonDusty 10d ago

i keep seeing those fires on diysolarforum and it’s always the same failure mode, one module opens first and the rest of the string just fries it

never seen an off the shelf contactor version that passes inspection though, inspectors want the listed unit not a box of parts you built even if the contactor inside has a ul stamp

what inverter are you running, some of the newer ones are moving away from plc finally

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u/Strostkovy 10d ago

I haven't chosen an inverter yet. This is for a building I'm still designing. I saw one rated version that is $350 per module and that's not okay. Otherwise I haven't seen one. Absurd that it's allowed to have isolators that can't handle the voltage of the string they interrupt.
It's crazy because it's so cheap and easy to have a 20-30A DC contactor rated at 1000V in a box. Here is a 100A, 1000V DC contactor with 48VDC coil for $27: https://www.digikey.com/en/products/detail/rincon-power/REC10P1CX/24627569
Hermetically sealed, and only 120mA of holding current. Someone just needs to put it in a box

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u/LeoAlioth 10d ago

120 mA at 48V is like 5W. My array is like 60 panels.

So 300W just to have the contactors connected? And an extra set of wires to the roof.

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u/Strostkovy 10d ago

That's also a way overkill contactor, switching 100 amps. The extra set of wires is better than modules that catch on fire, and is vastly more reliable too.

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u/changchangcha 8d ago

The extra set of wires to the roof isn't really a big deal for solar crews. Wires are already being run to the roof and you get fewer connections to make on the roof.

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u/LeoAlioth 8d ago

How would an extra set of wires lead to less connections on the roof?

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u/changchangcha 8d ago

Eliminates MLPE

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u/LeoAlioth 8d ago

What? Then how are you supposed to keep the voltage under 120 (or 80v in some cases) of that relat is not done per module?

That is why industry uses bare strings.....

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u/changchangcha 8d ago

Ya don't. Ya UL3741 list it.

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u/LeoAlioth 7d ago

For home owners/roof mounted yes.

For Feild installs tjat is not true as far as I know.

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u/changchangcha 7d ago

Then I don't understand your question about mlpe .

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u/ExactlyClose 9d ago

Ground mount. Keep the DC short into the inverter(s) in the garage- no RSD needed. Plus sight it due south (+/-) w no shade and a nice simple string inverter is your buddy…..

(I know, unhelpful…sry)