Solenoid Valve puzzle

John.G

I might have referred to this before but someone might throw a bit of light on it.

The oil valve solenoid coil on my oil fired boiler burner has two windings, one is 1.4ohms resistance, the other is 1400ohms. When the solenoid valve is energised (to close on this one), 24VDC is applied to the 1.4ohm winding and I think, also to the 1400ohm winding but only for a split second or so, this means a power of 446watts from the 1.4ohm winding and 0.41watts from the 1400ohm winding, after this second or so, the 24VDC is switched off the 1.4ohm winding and 5VDC is supplied to the 1400ohm winding which gives a (hold in) power of 0.0179watts, this seems almost unbelievable?. I have measured these voltages numerous times with flying leads from the control box and can definitely confirm that I get 0VDC on the 1.4ohm winding supply terminal and ~ 4.8VDC on the1400ohm winding supply terminal when the boiler is firing normally. Any comments?.

Calahonda52

Watt exactly is the puzzle?

John.G

Watt Watt?, that 0.0179watts is sufficient, even if 20watts is sufficient to close this solenoid it still means that the hold in power is still less tha 0.1% of the pull in power, I thought it should be at least 10% or so.

whizbang

The resistance you measured is dc measurement only.

The Solenoid coil has inductance which opposes the current trying to flow, so the actual current is not really related to the dc resistance.

John.G

Can you tell me what is the power in watts of a 1.4 ohm Coil with a supply voltage of 24 V DC. and the power in watts of a 1400 ohm Coil with a supply voltage of 5 V DC