Need to drop out solenoid valve with NO Form A contact?

[AJ2002]

I need a high speed form A contact (Normally Open commanded closed) be used to drop out a solenoid valve. The form C contact is much slower and millisec's count in the application.

The valve is 125 VDC requires a 180 milliamps to be be held in. Pull-in Voltage: 95-70 vdc & Drop-out 50 to 20 vdc.

If I shunt the solenoid valve with the form A and add a resistor in series with the solenoid valve and shunt contact may work. Any other better ways?

 

[VEBill]

Interesting question.

The concept of shorting out the solenoid makes one think...

The current in the coil would briefly spike, that might drive the plunger (mechanically) further in the wrong direction, thereby adding ms. This possibility obviously depends on the mechanical characteristics of the solenoid.

I was also thinking you could just use a diode to dump the current, but of course it's AC. But maybe a triac would be a better shorting device than another contact. A hefty triac, properly applied, would be indestructible.

There should still be an series open, even with the shorting system. It depends on the timing scheme. But also consider carefully what happens with various failure modes.

Could you use a DC driven, permanent magnet solenoid where you could actively slam it in either direction?

 

[Skogsgurra]

First, I think it IS a DC solenoid already.

Second, shorting a DC solenoid creates a drop out delay (same as a parallel diode does) because the circulating current is only dissipated in the coil and nowhere else.

Question: Is the C contact slower than the A contact? I cannot really see why. Breaking part of an ordinary C contact opens before the closing part closes (normally, although there are also overlapping contacts - but that's less common).

I would say that your coil's time constant is the problem - not the contact.

To get a really fast coil current break down with a closing contact, I would use a transistor with high enough Vce and power capability and use it to open the path when its base is closed to gnd by the A contact. I would also add a MOV to keep voltage within the transistors safe operating area.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[VEBill]

DC - it only says "dc" three times LOL. Sorry.

 

[waross]

Thinking "Outside the box",--
We improved the response time of motor-generator DC drives with field forcing. Applying an overvoltage for fast action and then cutting back to the needed voltage.
Applying a reverse voltage would shorten up the operating time of the circuit considerably. Rather than trying to control the time of application of the reverse voltage pulse, I would charge a capacitor and discharge it across the coil to force it open quickly. Will your application justify this level of sophistication?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AJ2002]

Thanks for the replys:
1st) It is 125 DC there is a snubber installed around the coil.

2nd) The high speed output form A closes in 10 microseconds and the form C drop out is 8 milliseconds. It is designed to energize circuit breaker trip coils. Not drop out fuel valves. It is unfortunate the contact timings are not the same. The standard output is 6mS either form A or C.

The fuel valve is 80 mS closing time on drop out. And as stated previously every millisecond helps. I will use the standard 6 mSec but it would be nice to take advantage of the faster form A contacts. But this is outside my area of expertise. I was trying to see if this has been before? Using Form A to drop out a solenoid?
Has this trip been before

 

[waross]

Have you considered using a normally open valve in hydraulic series for fast shutdowns? If you are energizing instead of de-energizing you can force the crap out of it for fast action.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

AJ,

I was telling you how to do it in my answer. Use the A contact to short out the base drive of the controlling transistor.

The reverse voltage mentioned by Bill will develop automatically when you switch the transistor off.

What type of snubber do you have? A diode delays the coil a lot. An RC snubber may be optimal, if correctly designed. A MOV is almost always best when you need fast drop out. It shall have a rather high clamping voltage.

You haven't given us any background information. We cannot guess what you are trying to do. There are fuel valves and breaker trip coils mentioned. But still not sure what you want to do. And no good explanation about the 'high speed form A contact' either.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

I've done controllers that paint glue dots in special sequential patterns on beer and cereal boxes traveling under glue heads at over 65MPH. If you want 'fast' get a commercial high speed solenoid driver.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[OperaHouse]

I've done glue dots, a lot of fun. Surprised you didn't say get rid of that 125V coil. You ain't going nowhere with that. Go to a 6V coil if you want speed and a good driver.