Relays and Solenoids

glaverty

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Apr 2002
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This thread relates to this thread from last year.

I was recently talking to a company that does custom Hydraulic controls and they said that they never use Solid State Relays on Solenoids because when Solid State Relays fail, they usually fail in the on position, which could make for an unsafe condition.

I was wondering what you guys use when you control solenoids either Hydraulic or Pnuematic and what your experiences are with Solid State Relay Failures. Currently I am using Omron G3R-OA202SZN Solid State Relays with Zero Crossing on some Solenoids without problems but am wondering if I should use mechanical relays with snubbers.

Thanks for your thoughts.
 
1) we generally use 110vac solinoids.
2) we always relays, or high current relay output modules.
3) we always install MOVs accross the circuit to snub spikes.

That's what we do...
 
The third item on ElevMike's list is the most common cause for solenoid drivers (either relay or Solid State) failing in my opinion.

I consistantly hear from people that do not use any sort of CEMF supression who are surprised to find their relay contacts are burnt to a crisp, or their SS outputs fried.

Diodes or MOV's across the coil are a cheap way to solve the majority of problems with solenoids.

Personally I always use relays for solenoids that will not be switching quickly. Even if it means putting in a interposing relay, I still do it. Fuses are a must as well. Solenoids seem to have this nasty tendency to short and fry whatever they are connected to.
 
elevmike said:
1) we generally use 110vac solinoids.
2) we always relays, or high current relay output modules.
3) we always install MOVs accross the circuit to snub spikes.

Mike,

Do you use Mechanical or Solid State Relays?

Do you happen to have a part number handy for the MOV's?
 
glaverty said:


Mike,

Do you use Mechanical or Solid State Relays?

Do you happen to have a part number handy for the MOV's?

Electro-Mechanical... AD makes a 5 amp isolated relay module for the D-205, or just a KUP or KH relay. If we expect high current load (like a starter), then we will wire two contact in series then off to the coil.

I prefer Idec KUP or KH style relays relays. They have a model with barriers between the contacts, a test button and indicator LED. I cant think of the model number...Something like RLY4 bla bla 110 AC. A little expensive but cheaper then a service call..
 
Glaverty,

We have customers that use both...relays and solid state outputs for driving solenoids.

When using our relay output controllers, we strongly recommend noise suppression at the source of the noise...we provide this application note for their reference - http://www.entertron.com/support/apps/note2.pdf

For those who use our solid state outputs, benefit from the fact that the noise suppression is built in - diode for DC loads or MOV for AC loads. The design also includes snubbers, optical isolation and fusing.

Decisions as to which method to use, typically depends on the overall requirements of the application. Solid state is more expensive up front, but last longer. A small amount of I/O may put our solid state controller out of the price range of the application, making it less expensive to use a relay output with additional noise suppression.

To sum it up...it usually depends which device they use, depending on the overall application requirements. If solenoids are going to run 24/7 we strongly recommend going the solid state route, in order to provide a longer life for the controller they use.
 
Elevmike said:

"If we expect high current load (like a starter), then we will wire two contact in series then off to the coil."

Did you mean parallel?
 
No Series..... like so..


RUN RUN
-----||-----||--------( )---|
9 5 6 10 starter




In simple terms series contacts provides for more contact gap wich helps to preventing arcing... More gap = less arc = longer contact life = less chance for welding etc...
 
Last edited:
I'm not sure about MOVs, but we almost always use RC type surge suppressors in that type of application (120VAC solenoids).

Electrocube is our standard type. (I can't remember the part number offhand)
 
Last edited:

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