Issue with changing a programmer

[jack101]

Hi,
Our current electromechanical controller - a Horstmann Diamond - has just failed. So I have bought a new Drayton Tempus 7 electronic programmer.
However, when trying to work out how to install it I noted that the mains supply seems to be fed through the controller to two relays, one for the hot water pump and one for the central heating pump.
I had thought that the point of relays was that they had a separate supply and only required a 'control' signal from the programmer/controller. I am slightly worried therefore about just wiring the new programmer in. Are they supposed to transmit the whole current to the relays/pumps? However, both old and new controller/programmer are protected by 3 amp fuses, so presumably if the old one works then the new one should be OK too - is that right?
Also, I want to move the new programmer to a better location, about 20m from the relays. Is it OK to assume that distance doesn't matter?
Thanks for any advice.
Jack.

 

[oilman]

Not sure what your realys are, but the programmer can drive directly, or you could wire it through relays. Your distance is no problem, just use 1mm2 or bigger

 

[jack101]

I've bought 20 m of 1mm 5 core so that I only have to use one run - do you you think that's OK?

 

[oilman]

Seems ok.

 

[breezer]

5 core 1mm? that's a new one on me, could you enlighten me a bit more? (colours, where did you get it?)

as for the relays ( i do know what they are) they will be fine so long as you wire them as they are now.

you are also right in your thinking as to what a relay is for, you said "I had thought that the point of relays was that they had a separate supply and only required a 'control' signal from the programmer/controller"

BUT, relays do not necessarily need a separate supply, it is quite ok to use the same "control voltage" as they will be using to supply .... (pumps in your case)

usually you would have a relay with a low voltage coil, and the relay will switch on or off something bigger that is on mains voltage. so in this instance you would need a 12v suppy to operate the relays.

Also relays are used (as in your case) for a small current to operate a big current device. so your current controller (no punn intended) probably has small switches that can not handle the current that a pump will draw, so relays have been used to save burning out the controls.

Most modern "programmers" are quite capable of switching "big currents" so your relays may be redundant, but for ease of wiring i would suggest you leave them where they are.

 

[jack101]

Brown, Blue, 2 x Black, Earth (yellow/green) - it's the flex type stuff (multi-strand) - £1.88 per metre from B&Q - a bit expensive but I thought it would make for a tidier easier job.

 

[breezer]

i wasnt thinking of flex

 

[masona]

Don't worry, you're our flex-ible friend

 

[jack101]

Thanks guys.

Another minor question as to why the relays had been originally fitted - presumably the old controller (and new one hopefully) can handle the current (what wattage would a pump normally be?) - so is it the actual switching of the pumps that causes the potential problem?

 

[breezer]

don't know how much current a c/h pump draws, but it is NOT a lot, i am curious as to why the relays were fitted in the first place, but i shouldnt worry about that. just change your "programmer"

you may even be really lucky and find that the old programmer uses a "standard" base, in which case the new one can just be "plugged on"