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solardude avatar image
solardude asked

250/100 Smart Solar Relay Wiring Question

Just installed 2 of the 250/100 Smart Solar MPPTs. I would like to use the streetlight function to turn some lights on/off automatically. I have the relay working as expected in the settings, but really have no idea how to wire it. Not much info in the manual.

System details:

MPPT is charging 48V batteries

48V-24V dc-dc converter

Relay is Gigavac P115BDA, 12V coil, (takes 170mA to power coil)

Lights use 5A @24V.

I have a small 12V house bank for DC lights I can pull power from to power the coil.

My questions: Do I run 12V- to the relay coil from the battery? Then run 12V+ from battery to MPPT “Common” terminal? Then from “N.O.” terminal of MPPT back to 12V+ side of relay coil?

Any help is very appreciated!

MPPT Controllers
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2 Answers
Mark avatar image
Mark answered ·

Use the relay in the MPPT to close or open the circuit leading to the coil of the larger relay/contactor that switches on/off the load. Just think of it as a switch that links the common terminal between NC (normally closed) & NO (normally open).

It is possible for the relay in the MPPT to switch either positive or negative but do NOT run both to the relay. Also ensure that the all wiring is appropriately fused.

You seem to be running 48v, 24v & 12v - this is not really ideal and unnecessarily complicates things a bit. I would try to commonise voltage where possible. You can easily buy relays that can be energised with 24v or even 48v.

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solardude avatar image
solardude answered ·

Thanks, this makes sense. I have it working perfectly now.


It’s definitely a bit more complicated that most systems, but really not too bad. I run some pretty specific outdoor lighting that requires 24V, but the radio and a few house lights run on 12V. I also run air conditioning all summer, so I went with 48V inverters to reduce amp loads, and to be able to utilize all 10kw of solar array.


I appreciate your help.

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Mark avatar image Mark ♦♦ commented ·

No problem, I'm glad it's working well.

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