Immersion control

[jpdw]

We're about to lose our gas boiler during 3 months of building work. Which mean for hot water we'll have to use the immersion heater that we have never used other than the occasional test. It has not timer (not a problem when we were not using it!). So, I'm gonna get the builder's 'lectrician to fit a simple timer, but at the same time, why not add a parallel module so I can add it to Cortex....

Question is: the immersion is rated around 3Kw, so around 12.5A @ 240v. I dont think there are any Idratek modules with relays rated above 13A ...?

If so, what solutions have people used, if indeed anyone else has hooked the immersion up.

A simple option would be a relay unit energising another relay that is higher rated but that seems wasteful to have 2 relays energised.

Next up, would be a digital output with some drive circuitry (aka transistor & resistor(s) probably) to drive higher rated relay. Would be my preference over the previous.

Any other suggestions / precedence?

jon

[Karam]

The relays used on the higher power modules such as QRH, DRH, SRH are actually 16A rated relays and the tracking/connectors are also overspecified. So there is already a small margin beyond that of the component manufacturers when we state 13A (~3KW @ 230V resistive load). The SRH 10A fuse will preclude its use but a DRH or QRH should be ok though you should obviously feed via a suitable circuit breaker or fast fuse.

[jpdw]

Thanks Karam. I've actually got a spare DRH but "knowing" the spec was 13A hadn't bother looking at the actual relay !!

I think the normal "immersion timers" are only single pole, switching the live only, so I only need to use one of the 2 relays. (hm.. what can I use the other one for...)

Now I just need to convince the electrician to install it.....

[alldone]

We have got a DRH wired to our immersion heater although the element is only 2.5kW. The electrician was a bit nervous initially but he cheered up when he saw the relays were 16A ones (the cylinder is on a 15A MCB anyway). Had no problems in 6 months so far...

We have a solid fuel boiler so use that in winter to heat the water but immersion heater is to be used in summer when we don't also need central heating. Have used the second relay in the DRH to control the zone valve for the central heating coil in the cylinder.