Current operated switch

[Andy Bennet]

Decided to fit a 14.4kW electric boiler to replace our old ageing sold fuel boiler (getting too old to hump hods of coal around the place). I'll add we are off the gas grid. Yeah I know I could go oil or LPG but prefer electric. We have an EV (electric vehicle), our DHW is electric immersion, we cook by electric .... you can see where this is going yet? Had the supply upgraded to 100A when we got the EV. The EV and immersion are generally only run overnight on economy 7. Now, if the heating comes on at 6 in the morning AND the immersion is heating AND the EV is charging and I put the kettle on and thje misses does a fryup I think I have an over 100A problem.

The boiler has a shower switch input - if you have a 10kW shower then apparently you can get a flow switch that tells the boiler to shut down while the shower is running ---- (we dont have an electric shower)

Does anyone knowledgable know if I can get a current monitoring relay that detects if the car is charging and I use relay output to hold off the boiler if the car is pulling (say) more than 5A??? (The car initially charges at 7kW (32A) when eco7 starts.) Any helpful suggestions welcome. Andy

[John Rumm]

Here is one we prepared earlier for you:

[Andy Bennet]

Thanks for the suggestion - seen that - was really looking for an off-the-shelf-solution Surely I'm not the first person on the planet to have this problem?

[Andy Burns]

No status light on the EV charge point you can tap into?

[Andy Bennet]

There is, but it gives 'plugged in' status rather than whether its charging or not. The car has a timer which I set to start charge at the start of the economy 7 period.

[nothanks]

Modify one of the "slave power" controls used for PCs

[tabbypurr]

A relay/contactor. Rewind the 240v etc coil to give the right number of amp-turns with wire as thick as possible. 5A seems an odd threshold though.

NT

[spuorgelgoog]

You can get shower priority units eg

EV as 'no 2' and boiler as 'no 1' so the EV gets continuous charging except when the boiler control is calling for heat.

Owain

[Andy Bennet]

Thanks for that, almost exactly what I need - with a bit of bodgery I think it will do the job.

Andy

[Andy Bennet]

Digging around further, I think I only need one of the componets of this unit, the priority relay. A quick google finds several DIN mounting types - a lot cheaper than buying the whole shower controller. Just put the EV load through the relay, and the clean contacts tell you if it pulling over 13A or not - absolutly ideal. Didn't know these things existed!

[John Rumm]

Most of the off the shelf solutions will assume the load you want to monitor can be fed from a 13A plug. Less useful for high load fixed radial circuits.

[nothanks]

True, but I believe they use the voltage drop across a pair of back-to-back diodes as the sensing circuit, so these could easily be beefed-up. The output would drive a contactor. But it seems that a "priority relay" is the thing - I hadn't heard of them until this thread.

[John Rumm]

Yup, not looked at them before either...