Relay coil burning out

**Clive S** · 09-10-2015

Originally Posted by cropwell

The only thing I can think of that caused the problem was that the relays are 24vAC and the power supply is a solid 24vDC. The next relay will be DC rated, and I can only think that the AC relay coil limits current to a 'safe' level due to its' inductance.

Rob

Rob I am sure it is because as you say A DC relay with have a higher resistance and the AC relay will be lower R because inductance will come in to play and limit the current. It would be interesting for you to measure the current with the AC relay fitted and then check again with the DC relay in circuit.

..Clive

**magicniner** · 09-10-2015

I suppose that if they just put the voltage on it would be fair to assume that AC or DC didn't matter ;-)

**cropwell** · 09-10-2015

Originally Posted by magicniner

I suppose that if they just put the voltage on it would be fair to assume that AC or DC didn't matter ;-)

That's what I thought when I used the relays (which I happened to have). The other relays in the main panel are OK, but they don't operate in a 'pulled in' mode 24/7, but this one has a safety relay function, if the gas fails or the electricity goes and the furnace drops below 800C then the air blower won't come back on and air pressure operates the gas solenoid. Above 800C the furnace will relight itself OK when the electricity supply comes back on, but then it will only operate in a low fire mode (reaching about 1000C) until manually reset to full operation, when it will go to the set temperature, normally 1250C.

**Clive S** · 10-10-2015

Originally Posted by magicniner

I suppose that if they just put the voltage on it would be fair to assume that AC or DC didn't matter ;-)

The relay states 24V AC on the picture. Thinking about it 24V AC will be RMS so the peak with be higher about 34V !!

**magicniner** · 10-10-2015

Originally Posted by Clive S

The relay states 24V AC on the picture. Thinking about it 24V AC will be RMS so the peak with be higher about 34V !!

Yes, indeed it will and you will then have AC running through an inductance, which should tell you something, if it doesn't then at least it tells you why AC or DC is included in component marking and should be observed ;-)