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After reading recent posts about hot master
solenoids I ran a brief test today. I placed a solenoid (Master Relay, 12
Volt, Continuous, part number 5485 from Aerocraft Parts) out in the open on
my workbench, not mounted to anything, and hooked it up to a power
supply and put a current meter in line with it. I adjusted the power
supply so that I had 13.5V between the connection posts. This was in a
closed hangar so there was no air movement over the workbench but it was
completely open. The ambient temperature was 60 F. The initial
current reading was 0.80 Amps. At 13.5V that means the solenoid was
dissipating 10.8W. After 30 minutes the voltage was still at 13.5V but the
current had dropped to 0.58A (7.83W) because the solenoid had warmed
up. How warm? According to a thermocouple the hottest spot I could
find was almost 130 F. I can see where a longer energized period combined
with higher ambient temperature would make the solenoid to hot to touch
comfortably, possibly hot enough to burn your fingers. Note that this was
a sample size of one and I don't have any data on the variability one should
expect to see from part to part.
I stopped the test after 30 minutes because my wife
called and said she was starting to cook dinner. Dinner sounded better
than watching a solenoid heat up so I went home.
Tom Gourley
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