Relay control circuit

[Vladpl]

Hello All

I have 2 questions.

1. I am trying to source a relay that is double pole, double throw(Change over) at 16A inductive. I haven't had luck finding one apart from the contactor relay which are very expensive.

2. I need a circuit to control the relay. I have built one and it doesn't work. I used a cap to drop the 240V mains with a 100nF which gave me about 8mA. From that it goes into a RC timing circuit and then a darlington pair. The realy I have for test has a 240VAC coil which I am trying to turn on using a bridge rectifier after the darlington pair so that they are conected to DC part of the bridge. Relay coil is conected to the mains on one side and other to the Bridge. So when the transistors turn on the bridge diodes conduct turning on the relay coil. It sounds good in theory but I had problems getting this circuit working.
If any of you have a circuit that would operate a relay like this please could you post it here. Thank you for your time.

PS sorry for such a long thread.

Vlad

 

[nbucska]

You haven't mention filtering of the 8mA DC supply
and perhaps regulating. The principle you describe
is correct otherwise, the problem must be in the details'

What is not too expensive ?

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[BrianR]

Switching 16A inductive requires a relay rated for approx 4x this current into a resistive load. This is into the contactor sizing. I think Digikey sell a solid state relay that might do what you want. I got one from there to switch a 1HP 240VAC motor and it needed 40A rating to be safe when allowing for temperature de-rating and stall current.