I have a Cerbo GX managing 3x MP2 5kVA in a 3-phase setup.
I’d like to use excess solar to power a water immersion heater (probably around 1.5kW AC load).
The idea is to use the generator start/stop automation directly built into Venus OS - I’d like to avoid the complexities of Node Red or Home Assistant as neither are currently required for this particular installation. As I understand it, the relay operation would be inverted to that of a generator but I can use the NO side of a relay contactor to invert the operation.
The DIN mounted relay would be housed some distance from the Cerbo / Multiplus area and drawing a new dedicated 230V AC line isn’t really an option. I do have some spare low voltage signalling wires available though (pairs from a Cat6e cable) so my idea would be to use that simply to control the coil of a contact which is fairly low current and should be fine over the cable.
My question is which DIN mounted relay would people recommend? Most contactors I’ve found seem to operate on 24V DC or 120-230V AC. Wiring two contactors in series on the coil side seems wasteful and would use up two DIN slots which are precious.
Is there a 48V contactor I can run directly from the battery via a fused connection or a 12V I could use as I saw there’s a 12V 100mA power outlet available on the MultiPlus. The latter might be tough with voltage drop and a coil likely to take more than a 100mA current…
I don’t know the equipment you have and if I understood your questions correctly.
Why don’t you just use ac out 2 so that you can avoid an external relay and possibly a snubber?
I was using successfully an AC relay from Amazon but I dismantled that in favour of AC out 2. And if you have Node Red already set up , it is possibly the simplest, but it’s not necessary.
I can’t use AC Out 2: the MP2 are in an area a short distance away from the consumer unit with all the breakers and the water heater and I don’t have the ability to add a dedicated AC circuit from the MP2’s location back to the water heater.
That’s why I can only use signalling from the MP2 / Cerbo location back to the water heater where I have a spare Cat6 network cable where I can use a pair or two to control a relay.
The Cerbo relay outputs no voltage. Your relay may require input DC voltage to work. The relay I had required 3-32 v DC to switch big AC so I used a laptop charger to convert AC to about 12v DC to feed the external relay. Of course, I gave the external relay the AC to switch. So the Cerbo relay relayed the signal, my laptop charger injected the DC voltage required by my external relay, the external relay switched the big AC supplied by my quattro.
If you have only 48v batteries, you could use some device to step down the DC voltage.