Hi all,

I am a newbie here. Currently, I am thinking of using my analog timer to connect to an old mobile phone transformer (output 12v 1000ma) and then a relay (30A 12v) used for auto horn for switching my hot water cylinder. Is it feasible? Is it necessary any resistors, capacitors or diode required for the relay input end?

Thank you very much for your advice!

 

Is it feasible?

If the relay is rated for the heater voltage (AC?) and current.

Is it necessary any resistors, capacitors or diode required for the relay input end?

No.

 

Get yourself some spade crimp terminals.

 

I bought a couple of those analogue timers a few years ago. They didn't last long. The digital ones are much better quality in my opinion. Also look at din rail mounted version, then you can fit it in a control box with a contactor (much better than a relay for high amperage mains switching)

 

The ice maker in our fridge stopped working. The reset button did not fix it, even though Google said it would. Then I noticed if I cycled the power, the ice maker started to work again. So, the fix was to run the fridge via one of those analog timers. At 3AM, the fridge powers off for 1/2 hour. That has run quite well now for a couple of years.
If the ratings of the timer are ok, it should switch your heater directly.

 

The ice maker in our fridge stopped working. The reset button did not fix it, even though Google said it would. Then I noticed if I cycled the power, the ice maker started to work again. So, the fix was to run the fridge via one of those analog timers. At 3AM, the fridge powers off for 1/2 hour. That has run quite well now for a couple of years.
If the ratings of the timer are ok, it should switch your heater directly.

Too bad that my timer rating only 10A while the heater required 30A and therefore I start to think about using the timer to control a relay for switching.

 

Too bad that my timer rating only 10A while the heater required 30A and therefore I start to think about using the timer to control a relay for switching.

In that case, a relay or contactor is the way to go. But I think the relay you have shown may not be a mains rated one.

 

If the relay is rated for the heater voltage (AC?) and current.
No.

See if the following Relay spec fits (my heat water cylinder required 30A, 220v AC)

Heavy Duty Chassis Mount Relays - 30A

Relay

Contact format	SPST
DC Contact Voltage	12V
DC Switching Current (Opening)	30A
AC Contact Voltage	250V
Coil Resistance	120Ω

Power Source Details

DC Current Draw	30A
DC Voltage	12V
AC Voltage	250V

 

In that case, a relay or contactor is the way to go. But I think the relay you have shown may not be a mains rated one.

yes, therefore I found another relay instead. is it look goods for my application?

Heavy Duty Chassis Mount Relays - 30A Cat. No: SY4040

Relay

Contact format	SPST
DC Contact Voltage	12V
DC Switching Current (Opening)	30A
AC Contact Voltage	250V
Coil Resistance	120Ω

Power Source Details

DC Current Draw	30A
DC Voltage	12V
AC Voltage	250V

 

As the load is 30Amps, I would look for a relay rated at 50 Amps. It is best to have some margin. And the wiring will need to be quite heavy. Go for screw terminals too, not lugs.

 

That is an automotive relay that plugs into a cars fusebox. I doubt if it will switch nearly 7kw without melting. Use a big contactor and parallel up the 3 contacts.

 

As the load is 30Amps, I would look for a relay rated at 50 Amps. It is best to have some margin. And the wiring will need to be quite heavy. Go for screw terminals too, not lugs.

Thank you very much!!

 

Good luck!