Relay .. Reactor

[Prickle Donating Member Find all posts View Profile Close Prickle]

Hi
I need / want to have my heater element (hot water service element .. 2400 watts) run through a relay fired by the PID temperature controller. Anyone care to suggest a suitable relay ??

Regards

Stuart

[Matt Senior Member Find all posts View Profile Close Matt]

Re: Relay .. Reactor

25 Amp Solid State relay is what you are after, ebay is good if you choose carefully (lots of fakes).

Here you go, I assume no liability of course but given the high positive feedback I have no reason to think they are fake

http://www.ebay.com/itm/Output-24V-3...-/310702225734

Matt

[craigcurtin Senior Member Find all posts View Profile Close craigcurtin]

Re: Relay .. Reactor

25 Amp Solid State relay is what you are after, ebay is good if you choose carefully (lots of fakes).

Here you go, I assume no liability of course but given the high positive feedback I have no reason to think they are fake

http://www.ebay.com/itm/Output-24V-3...-/310702225734

Matt

The other two things to think about/keep in mind

1) You really want to get a relay that has Zero Crossing support built in - as this will be much nicer to anything else that happens to be on that phased circuit in your house
2) You should also (for longevity) mount the Relay on a heat sink

Craig

[Prickle Donating Member Find all posts View Profile Close Prickle]

Re: Relay .. Reactor

Thanks for the reply chaps .. much appreciated

Craig what is "Zero Crossing support" ...

Stuart

[tillyfromparadise Senior Member Find all posts View Profile Close tillyfromparadise]

Re: Relay .. Reactor

The zero-cross effect means that if the input signal is applied at any point during the AC output wave other than very close to the zero voltage point of that wave, the output will "wait" to switch on until the AC wave reaches the following zero point.

[craigcurtin Senior Member Find all posts View Profile Close craigcurtin]

Re: Relay .. Reactor

The zero-cross effect means that if the input signal is applied at any point during the AC output wave other than very close to the zero voltage point of that wave, the output will "wait" to switch on until the AC wave reaches the following zero point.

And what this means in the real world is that it will be much nicer to any other electrical equipment on the same phase in your house - otherwise if your PID controller is trying to rapidly cycle the relay and it does not have this support it can switch on an off at any point in the AC cycle and potentially (and in reality) throw spikes through your AC circuit.

Craig

[Matt Senior Member Find all posts View Profile Close Matt]

Re: Relay .. Reactor

Given its a water heater its purely resistive and the load will not have any power factor issues or harmonics, the relay will be fine as it should be a FET. Its only an issue if its in a switch mode supply where FET will dissipate power whilst turning on with heavy currents, being in a linear response range and not fully on ie low Rds. PID response rate of seconds should be fine. Kilohertz is another matter.

Sorry all from engineering background.