Relay or contact or available?

coopersim · 14 Sep 2021

I’d like to be able to take two 230v feeds to one output, do I need a contractor for this?

One input is from a vaillant vr71 to control a secondary pump and the other from an occupancy sensor. I would like both to be able to control a single pump.

I was thinking a contractor but they all seem to be setup for one 230v input?

Jackrae · 14 Sep 2021

You need to advise whether the two sources are considered as 'signals' for the pump to run or are they actually supplying the power for the pump to run. You cannot simply parallel two AC supplies together such that either (or both) will supply power to the pump.

The ideal method is for either source to be considered as a signal source, each driving its own relay. The relay 'output' contacts (N.O.) are then paralleled together to switch a 240v supply which powers the pump. Where you get the 240volt supply from is a separate issue.

coopersim · 14 Sep 2021

They’re both 230v sources

Jackrae · 14 Sep 2021

So you use 230volt AC relays - 'signals' can be of any voltage

oldbutnotdead · 14 Sep 2021

As above, you need 2 relays to buffer the voltages from the source devices (boiler and motion sensor). The switched contacts can then be wired in parallel to switch power to the pump. I've been using these for similar jobs https://www.amazon.co.uk/Aideepen-240V-Power-Relay-Electromagnetic/dp/B08DNDQYMR/

JohnW2 · 14 Sep 2021

oldbutnotdead said:
As above, you need 2 relays to buffer the voltages from the source devices (boiler and motion sensor). The switched contacts can then be wired in parallel to switch power to the pump.

Jackrae said:
The ideal method is for either source to be considered as a signal source, each driving its own relay. The relay 'output' contacts (N.O.) are then paralleled together to switch a 240v supply which powers the pump.

Indeed - and, in other circumstances, such a use of two relays enables one to have 'AND', rather than 'OR', functionality (i.e. pump only comes on if both sources are active), if one wires the two sets of relay contacts in series, rather than in parallel.

I suppose it would theoretically be possible for a single relay to have two coils, hence able to 'OR' together two source 'signals', but I can't see it's something I've ever seen done.

Kind Regards, John

bernardgreen · 14 Sep 2021

JohnW2 said:
be possible for a single relay to have two coils

Possible to have two coils when they are operated by DC, it is quite common in telephone and control equipment to have dual coil relays'

But when the coils are operated by AC then a "transformer" affect happens ( two coils on the same magnetic core ) and the power in one coil induces a significant amount of power in the other coil. This back feed could affect the operation of other items.

coopersim · 14 Sep 2021

I think I might have an spdt contactor that would fulfil what you’re describing but am head scratching at the wiring which suggests only one supply voltage across a1 and a2?

mattylad · 14 Sep 2021

2 sources means 2 realys is the simplest IMO.
One relay coil per source and wire the contacts in parallel/series as required.

NO messing around with any fancy stuff.

Coopersim, how do you want the relay to operate?
When both sources are supplying power or when either of them supply power?

I suspect that it's when the occupancy sensor is detecting and the valiant is on (so they would have the contacts wired in series)

What is the output of the occupancy sensor like? does it stay on for long enough?
If it's on/off/on/off as people walk around then the pump will do the same.

SpecialK · 14 Sep 2021

So an output from a thermostat and from a PIR? Will they be from the same source (isolator/MCB/RCD) ?

mattylad · 14 Sep 2021

bernardgreen said:
Possible to have two coils when they are operated by DC, it is quite common in telephone and control equipment to have dual coil relays'

But when the coils are operated by AC then a "transformer" affect happens ( two coils on the same magnetic core ) and the power in one coil induces a significant amount of power in the other coil. This back feed could affect the operation of other items.

If it was DC then a few diodes would negate the need for a fancy 2 coil relay

coopersim · 14 Sep 2021

Either source will trigger feed to pump but to isolate voltage to the other (I’m thinking of protecting the expensive vaillant electronics)

bernardgreen · 14 Sep 2021

mattylad said:
If it was DC then a few diodes would negate the need for a fancy 2 coil relay

True if the control signals had a common rail.

mattylad · 14 Sep 2021

They will be isolated as the coils will be separate.

You can connect the l/n to the relay common pins of both relays and the pump l/n to the n/o pins of both relays.

Why would you want the pump to be on when the occupancy sensor detects someone?

oldbutnotdead · 14 Sep 2021

mattylad said:
If it was DC then a few diodes would negate the need for a fancy 2 coil relay

TBH you could just halfwave the AC or even fullwave rectify it so you could use diodes for the buffering/switching logic referenced to neutral but then you need to find a DC relay running at 300v ish- might be a bit rare. Or some series resistors- but at £2 a go I'd just throw 2 relays and some chocblock at the job.
OP You need 2 relays, SPST will do, any more contacts are spare. Coil and contacts rated at 240v AC. Contacts 3a will be more than adequate for a standard heating pump

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Relay or contact or available?

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