Opto Isolator - solenoid not energizing


Thread Starter


I have a Daniels RTU output that is using the board 6VDC and the output is tied to the input of a wiedmuller Opto-Isolator. The output of the isolator is 24vdc for energizing a solenoid. For some reason everything checks out(Voltages etc..) with no load. Once the Solenoid is connected the output of the opto-isolator shows 0Vdc instead of the 24vdc needed to drive the solenoid.

The current limit on the isolator is 20mA and I think the solenoid draws just about that.

I was wondering if I may need a "Free-Wheeling Diode" since the opto is driving a solenoid, which I believe to be an inductive load. Would not having this cause this type of problem?

Anybody have any thoughts or ideas on this?
I suspect you may have destroyed the isolator or it's current limiting. To prove it out I suggest you connect an LED in series with a 1200 Ohm resistor in place of the solenoid.

You don't say if this is a new fault with an existing system. Please give model Nos for solenoid and the opto Isolator

That's what we had originally thought so we replaced the Isolator and still the same problem. The isolator is a wiedmuller EG01. I believe the Solenoid is an ASCO. I'm not sure of the specifics. I'll have to check monday.

From what I was told this circuit worked when they used it last; which was about 2 years ago. The valve is very rarely used but very important. I know that doesn't make sense. That's what I thought, but now its become important to test every month. So I don't know if this is a new problem or if it never worked.

Alan Balcombe

Thanks to Roy for your comments.

Can I also ask, what current does the solenoid need to drive it? Many need much more than 20mA.

Weidmuller does have a solenoid driver opto for up to 10A and 5 - 33VDC on the load side - model MOS 24DC/5-33VDC 10A (8937940000).

As Roy asked, please tell us (or me) the product you are trying to use.

Alan Balcombe
Weidmeller, Richmond VA
[email protected]
I couldn't find the specs for the Opto Isolator but I notice it has an LED on the front. Presumably this lights when you power the input.
Does your's light up?

The ASCO coil information is easily available but if you cant find it give me the coil No, I have a catalog

Is it possible you have the power switched, wrong polarity?

Ok, I ve been in training for a few days and havent had a chance to get back here. I have the ASCO valve information:

Nameplate info
S/N: A997498

Etched on the side of the Solenoid:
24/DC FT

I notice on the solenoid it states 10.6 watts power. If this is nominal power then this would draw around .4 amps which I dont think the Wiedmuller can handle. I'm not sure since I cant seem to find any data sheets on the Weidmuller EG01 55816 unit.

Thanks for all the input gentlemen!!!

from ASCO catalog 34 (page 77):

8344G044 with general purpose (not hazardous area) 238310 coil
DC watts = 10.6
VA Holding = 16
VA inrush = 30

The arithmetic with those numbers is a far cry from the 20mA mentioned in the first post.


Can this unit be energized by the 6V i have coming from the Daniels unit? I need 6v on the input and 24vdc load for the solenoid.

Feel free to contact me if necessary

[email protected]

Alan Balcombe

Martin - sorry for the slow reply - I am travelling.

The device I mentioned before is limited to a 24Vdc control voltage, but we do have another i our Micro-Opto Series (6mm width) with 5Vdc control voltage and 24Vdc/2A load drive, article no. 8633000000 Description MOS 5Vdc/24Vdc 2A.

We also suggest fitting across the load connections a parallel diode (reversed) as a little extra protection for the opto while switching off.

Hopes this helps
Alan Balcombe
[email protected]
Alan-Does this unit replace the EG04.....I think we have used those in the past but I believe they are obsolete.

Alan Balcombe

Not sure what you mean - the 8633000000 item I mentioned is current. There are no EG housing types now in our current relays/optos catalog i.e. Section C in the Number 4 electronics catalog.

Francois Reyneke

The EG01 is realy intended to give an isolated output to drive high/low 24v control signals to plc's or digital input modules of process control bus systems. To put a solinoid is not a good idea because when it switch of the back-EMF can be up to 7 x the nominal current. Better let it drive a solid state relay and let the relay drive the solinoid.

Francois, Media24 Corporation.
Well gentlemen, I have set up a test bench with a similar circuit to the one in the field and everything works fine!? I'm still stumped on this as the math doesnt add up with the EG01(26616) isolator and the ACSO solenoid. The output capabilites of the isolator from the specs is 20mA, but the solenoid is energizing and drawing .4amps through the isolator.

Still no resolution to the field issue where the isolator does not pass the 24vdc through to the solenoid......