12th January 2009, 15:23 #1
Newbie level 1
impedance of a solenoid
Did some searching of the forum, but didn't find an answer to my question.
If you used an ohm meter, and measured across a solenoid coil are you measuring the resistance of the coil or the reactance?
What I want to do is calculate the inrush and holding currents of a solenoid valve in a 24V AC 60 Hz application.
So if I take a measurement of the solenoid coil with the plunger in the open position and the closed position would I use this ohms value to calculate the inrush and holding current with ohms law? I'm currently reading 23Ω in the open position. Which should equal 1.04 Amp but the manufacturer rates the inrush at 0.41 Amp.
If not is there a way to calculate the inrush current and how do I do it? Also is there any possible way that the inrush current could be made larger. (Other than pulling the solenoid plunger further out of its open resting position) Say something like the plunger having a greater amount of pull, or a lower than 24 voltage applied to it. Or is the inrush current for a specific coil set by the resistance and just the amount of time the inrush current would be present before lowering to the holding current would be changed by these things such as voltage and pull.
Thanks for any help you can provide.
12th January 2009, 15:23
12th January 2009, 18:14 #2
coil inrush resistance/reactance
You can't measure the AC impedance of a solenoid valve with an ohmmeter. For an exact measurement, you should use a shunt or current probe and an oscilloscope. But usually, manufacturers specify inrush and holding current and holding power consumption. So there is to need for measurements.
12th January 2009, 18:14
13th January 2009, 02:35 #3
Advanced Member level 5
acceptable solenoid valve coil resistance
The current into an inductor rises slowly. A solenoid is an inductor. There is no "inrush" current like there is into a capacitor.
13th January 2009, 02:35
14th January 2009, 05:08 #4
amperage measurement coils
I am also not clear about the term inrush current, unless due to activation of the plunger, the effective inductance increases.
Any how, you can measure the Operate and release current by applying a variable AC voltage source in series with an AC current meter to the solenoid. For AC coils it is the inductance that matters more than the DC resistance that you measure with an Ohm meter. The resistance gets added vectorially to the AC reactance of the inductance.
By the way, why do you want to increase the inrush current ? Obviously if the plunger is moved away, you need more force and therefore more current to operate it.
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14th January 2009, 06:05 #5
solenoid coil measurements
To understand the usual solenoid valve terminology, you have to know a bit about the specific properties of AC operated valves. As the first point, inrush is the usual term for the higher turn-on current of AC solenoid valves, found in any datasheet.
It happens, cause the inductance of the solenoid is considerably lower in off state. When the coil is energized, the plunger moves and closes the magnetic path. The effect is utilized to get a faster and more powerfull action with higher initial current and lower static power consumption. It's an inherent advantage of AC solenoids (the same with AC driven contactors BTW, this should be rather known by interested engineers).
14th January 2009, 14:22 #6
Advanced Member level 5
how to measure induction of a coil
Yes, of course. The plunger is the core of the inductor and the inductance changes as the plunger moves.
So there is a useful inrush higher current.