lazyterrier avatar image
lazyterrier asked

Can the Multi relay drive a 240v contactor?

I have a MultiPlus-II 48/10000/140-100 and a Cerbo GX with 3 Pylontech US5000 batteries connected via a Lynx busbar. From AC1 out I have a new consumer unit with RCBOs and I am running in ESS mode which so far seems to work well.

I am now planning to add solar panels and an MPPT and anticipate excess solar in the summer so want to use a 3KW immersion heater to minimise feed in which I won't currently be paid for.

The new consumer unit is “Fusebox brand” and I have bought a 20A contactor of the same brand to maintain type test. This contactor has a coil listed at 230v but I can’t find any details of the current. I can test this to find out.

I plan to use the relay from the Multi to drive the contactor to power the immersion heater using assistants in ESS.

The Multi documentation says the relay is rated at 230V and 4A. The grid voltage is usually above 240v. I have seen forum posts saying not to drive the contactor from the Multi relay and to use an intermediate relay.

My question is can I use the multi relay to drive the contactor bearing in mind that the 230V rating is nominally mains and the likely current for the contactor is going to be much less than the 4A rating of the relay?

If it's not possible or sensible what would be a better option and in either case what would the recommended wiring solution be?

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1 Answer
matt1309 avatar image
matt1309 answered ·

Hi @Lazyterrier

I have a similar setup but I found the assistant criteria for activating the immersion heater too limiting.

I instead opted to use Node red (which allowed me to define more specific criteria) and if that criteria is met (for me it's when battery hits absorption, is exporting over 2500w and is not late in the day). Then node red activates a shelly smart switch (via http node). My immersion heater is smaller than yours so the shelly smart switch can be used to power the immersion directly. However given yours is much larger you could use the shelly smart switch to activate the contact to turn on immersion heater.

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