230V relay

[tgen]

A novice but frustrating question --
When a 230V load goes on, I want to close a switch (very low load). I see 230V coil relays, but is there something smaller/more elegant I could use?
thanks

 

[Willbe]

A reed switch with a homemade electromagnet closing it?

 

[tgen]

thanks. can you help me with setup? A 230V water heater element (10 gauge solid wire) when powered will close the switch, grounding a mV circuit.
Will a parallel stranded wire work for the electromagnet, and can I be sure the reed switch is sensitive enough to switch?

 

[Willbe]

thanks. can you help me with setup? A 230V water heater element (10 gauge solid wire) when powered will close the switch, grounding a mV circuit.
Will a parallel stranded wire work for the electromagnet, and can I be sure the reed switch is sensitive enough to switch?

Try 10 turns of 10 or 12 AWG wire around, or near, the switch. It carries the water heater current, 20 or 30A.

I've never done one so you might want to ask the switch vendor for an app. note.

Since it's alt. current and the reed has very little inertia, it might buzz. Design Rev A will then be necessary!

 

[stevez]

A small transformer could drop the voltage to something more useful. A voltage divider might also work with appropriate caution. The voltage divider might power the coil of a relay - or the input of an LED. You might carefully tinker around to see if you can find a voltage drop within the equipment that can provide enough voltage for a light or LED. You don't need much current for an LED.

 

[Willbe]

1 foot of 10 AWG = 1mΩ. At 30A this would be 30 mV; input this to a diff amp and you can drive LEDs or whatever.

If you put a skinny lead at each end of the same long power lead you could get several volts to power an LED through a dropping resistor, but the insulation of these voltage-pick-off leads has to withstand 230vac.

 

[tgen]

I picked up both a reed switch and a 230V relay (I plan to also switch a 110 circuit). Just to verify --
the relay is 32500 ohm, rated 230V across the coil. I plan to connect it with 18 AWG wire across the 2 heating element terminals. Yes I will be careful. I don't think anything will pop, but little plastic parts with large voltages scare me. Is it OK?

 

[Thunderchild]

just get a 230 v relay and put it in paralel with the appliance, when it gets turned on the relay will switch and you can switch on whatever else you want

 

[Willbe]

I picked up both a reed switch and a 230V relay (I plan to also switch a 110 circuit). Just to verify --
the relay is 32500 ohm, rated 230V across the coil. I plan to connect it with 18 AWG wire across the 2 heating element terminals. Yes I will be careful. I don't think anything will pop, but little plastic parts with large voltages scare me. Is it OK?

That is the most resistance for a relay coil that I ever heard of. 230/32k = 7 mA coil current. If a less sensitive relay was available you might have paid less for it.

It's not the voltage, it's the current over time that does the damage, even for people.

With 20' of #10AWG at 30A you have enough voltage to turn on a germanium xsistor, if you want to go all solid-state.

 

[SpawnyWhippet]

Another question on a similar topic - I have a 230V air-con unit in my boat, but the 12V coolant pump is on its own 12V switch and both need to be switched on seperately. If someone forgets to turn on the pump, I think the aircon unit could be damaged by running dry. How can I wire this so that turning on one system (eg the 12V pump switch) automatically turns on the other? I thought of using a relay, but I am not very electronically minded and would appreciate some advice with designing the circuit.

 

[MikeMl]

Another question on a similar topic...

Is the aircon unit an evaporative unit, or a refrigeration unit? If it is evap, then running dry wont hurt it; it just wont cool.