What happened? Solenoid mystery.

[Eric R Snow]

I have a solenoid actuated air valve that only occasionally is
operated. It is meant to be operated with 24 volts DC. I plugged in a
wall wart power supply and the solenoid just chattered. Looking at the
wall wart I see it's a 12 volt DC unit. Duh. So I grabbed the proper
24 volt DC wall wart off of the shelf and plugged it into the solenoid
and the thing worked! This was with the wall wart unplugged from the
wall. My first thought was that maybe the filter cap in the 24 volt
power supply had held a charge from a previous use but it has not been
powered up for at least 4 months. The solenoid valve has the coil as
the only electrical part. The two wires from the coil connect directly
to the power socket. The 24 volt wall wart has 4 diodes and one 2200
uf capacitor connected to the xmfr. The time from disconnecting the 12
volt wall wart and connecting the 24 volt wall wart was about 5
minutes. Could the solenoid coil have held a charge that long so that
when connected to the 24 volt unit the field collapsed like an
ignition coil and provided enough oomph to draw in the plunger and
actuate the valve?
Thanks,
Eric

 

[contrex]

I have a solenoid actuated air valve that only occasionally is
operated. It is meant to be operated with 24 volts DC. I plugged in a
wall wart power supply and the solenoid just chattered. Looking at the
wall wart I see it's a 12 volt DC unit. Duh. So I grabbed the proper
24 volt DC wall wart off of the shelf and plugged it into the solenoid
and the thing worked! This was with the wall wart unplugged from the
wall. My first thought was that maybe the filter cap in the 24 volt
power supply had held a charge from a previous use but it has not been
powered up for at least 4 months. The solenoid valve has the coil as
the only electrical part. The two wires from the coil connect directly
to the power socket. The 24 volt wall wart has 4 diodes and one 2200
uf capacitor connected to the xmfr. The time from disconnecting the 12
volt wall wart and connecting the 24 volt wall wart was about 5
minutes. Could the solenoid coil have held a charge that long so that
when connected to the 24 volt unit the field collapsed like an
ignition coil and provided enough oomph to draw in the plunger and
actuate the valve?
Thanks,
Eric

The solenoid coil could not have "held a charge". Inductors don't hold
charges. The magnetic field is only present when current is flowing
through the coil. Capacitors can hold charges, though, and I guess the
one in the 24v supply had enough to actuate the solenoid.