Solenoid/Power Supply Question

[elk84]

Hello,

I have a 12 volt solenoid which I have actuated using a standard benchtop power supply (30V and 5 A). When I supply ground to one lead, and 12 VDC to the other, the solenoid actuates as expected. However, I notice that the power supply voltage drops from 12 VDC to 6 VDC during the actuation while pulling 700 mA. If I put a 33 ohm resistor in series with the solenoid coil, the solenoid actuates and the power supply remains at 12VDC while pulling about 275 mA as expected. Why is this happening? The coil itself has a resistance of about 5 ohms, why does the power supply only maintain its 12 V when an extra 33 ohms are placed in series with the solenoid? I would like to actuate the solenoid while not affecting the voltage of the regulated power supply. Any insight would be helpful!

Thanks!

 

[FvM]

This won't happen with a simple DC solenoid. There's apparently some kind of initial current booster built inside your "solenoid". Otherwise the current would increase monotonically after connecting the power.

Or there's a problem with your power supply and it's not actually capable of sourcing 5A.

 

[crutschow]

There appears to be a problem with your power supply as FvM noted. If you are only pulling 700mA then the voltage should stay at 12V.

The initial current surge should be about 2.4A with no resistor.
Does the power supply have some sort of foldback current limiting or adjustable current limit?
What is its short circuit current value?

 

[jiripolivka]

What you see is a typical behavior of an underrated power supply. Its regulator cannot supply the proper current pulse for your solenoid to actuate.
Connect a large capacitor across power-supply terminals , like 10.000 uF electrolytic, 30 V DC, then your solenoid will work better and the power supply voltage will not drop.