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from the Automation List department...
AC 110V solenoid valve vs. DC110V
Application Questions and Problems topic
Posted by reza heydari on 8 March, 2007 - 11:07 pm
Please let me know, what's the difference between AC 110V solenoid valve and DC 110V?

Thanks in advance.


Posted by Michael Griffin on 10 March, 2007 - 7:04 pm
One requires AC, while the other requires DC. The AC solenoid will have a lower resistance than the DC solenoid because the current will be limited by the inductance. If you use DC power on an AC coil, the coil will probably burn up. If you use AC power on a DC coil, the coil may not develop full force due to the current being limited by inductance.


Posted by Mickaleto on 31 March, 2007 - 12:30 am
Hello guys,

I wonder, what if you're in hurry and don't have time to order DC solenoids, and decide to use AC 110V solenoids? Is there any way to prevent burn up? How about using resistor in series with solenoid to make resistance larger and prevent burn up in that way? What do you think? How "big" resistor to use with DC 110V (how much ohms)?

Thank you all.


Posted by Michael Griffin on 1 April, 2007 - 3:46 pm
First, read the data sheets (or contact the manufacturer) to see if this particular solenoid is AC/DC. It is possible to design a solenoid which is compatible with both AC and DC, although it is not very common (it means over sizing the heat dissipation capacity).

It may be possible to use a series resistor to limit the current. It would not however be my preferred solution to a problem. It sounds as if you are trying to repair a machine in a hurry. I don't know what your valves look like or what the problem is, but if the problem is the old valve spool and not the actual solenoid coil, then look to see if the old solenoid will fit on the new valve body.

If this is an existing machine, you could also re-wire it to use AC valves instead of DC valves. This would also make future repairs easier.

If this is a new installation, then why not design it to use AC? I always try to design a control system to use whatever is the most common version of a part in order to make replacement easy.

In order to run an AC valve on DC, you would have to size the current limiting resistor by making some measurements and doing some calculations. Alternatively, you may be able to get enough information from the valve data sheets without doing the measurements. Essentially, you are looking to have the same current through the coil in both cases. The AC impedance is a combination of resistance and inductance, so there is no fixed "factor" which applies in all cases for calculating the extra resistance required for DC operation.

You might still have a problem if there are any lights on the valve solenoids. The AC lights may not be compatible with the DC power.


Posted by Anonymous on 4 May, 2007 - 12:31 pm
A DC solenoid operation is understood. It will generate force in one direction. But how would an AC solenoid lift the plunger? The AC will generate alternating flux and there-by the force will keep changing at the freq of the supply. By this logic the AC solenoid should never be able to lift the plunger inside?

Pls explain the operation of AC solenoid/relay coils.

Regards,


Posted by Michael Griffin on 6 May, 2007 - 12:55 pm
AC solenoids have a "shading coil" which acts to delay the collapse of the magnetic field during zero crossing of the current. The shading coil is a single turn of large conductor (usually a stamping) around the solenoid. When the magnetic field begins to collapse a current is induced in the shading coil which then creates its own magnetic field. This tends to "average out" the magnetic field, and so prevents "buzzing" at line frequency. Coil size, inertia, and spring tension of course all have a part to play in the design as well.

For a normal AC or DC solenoid, the direction of the magnetic field doesn't matter. The armature (the moving part of the solenoid) is just plain steel, and is attracted to a magnetic field of any polarity.


Posted by John NJ on 25 July, 2008 - 12:32 am
This is excellent info! I've been going through 120V AC solenoid valves like mad, and this "shading ring" sounds like the problem, but I can't see how I'd burn it out! I take the valves apart and all seems well. Put it back together and all it does is buzz! I've swapped coils with no luck! It appears to be a problem with Normally Open valves, 2 or 3 way. They fail in a short period of time. I'm not abusing them, I hope! I cool the coils and even add air filters, with no luck. Just handling low pressure ~15hg vacuum. These are direct acting valves, though some appear to be poppet valves. I'm lost, but thanks for the info!


Posted by Roy Matson on 26 July, 2008 - 1:25 am
John NJ,

If the valve buzzes the chances are the shading ring is broken, or perhaps the solenoid was originally intended for DC without a shading ring. The shading ring causes a delay in the field so that you effectively have 2 fields out of phase: as one passes through zero the other maintains the pull.

Look for a copper ring on one of the pole pieces.

Roy


Posted by Curt Wuollet on 6 May, 2007 - 1:25 pm
Think about that for a minute: Either DC polarity will pull the armature in. Switching quickly will cause vibration but will still operate the solenoid. In relays, where the vibration might be enough to cause the contact to chatter, they use a shading ring (google) to keep flux more constant.

Regards
cww

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