induced volage???

Status
Not open for further replies.
J

jcole

Senior Member
Location
Lawrenceburg, Kentucky
Hello guys and gals

I have a 480v actuator that has 120v inputs to open and close. The 120v power is supplied by a transformer in the actuator. The inputs are controlled by triac output card on an old Gould plc at least a hundred feet away in a control room.

I am picking up some voltages I dont really understand. When the 120 volt wires are hooked to the supply and inputs, without outputs on, I am reading about 108v to "neutral" on the open and close wires coming back from the output. But the actuator does not recognize this voltage because it does not try to move.

When the output turns on, the open and close wires coming back from the output turn to 120v and the actuator opens and closes correctly.

When I unhook the 120v supply and inputs on the actuator I read about 65v to ground.

I am using a fluke dmm for measurements.

Is this induced voltage? The control conductors are ran with the power conductors but doesnt there have to be current on the power conductors to induce voltage in the cotrol conductors?

I shorted these wires to ground to see if an overcurrent device would trip. Nothing.

If it was capacitive coupling wouldnt it have went away when I shorted it out.

I wouldnt worry about it much if the actuator sometimes didnt open when the closed input was energized. The manufactor says these voltages are what the problem is. The actuator is brand new.

Sorry for being so long, but I can usually get great help from you guys.


Appreciate all responses.
 
In this case, I think it is just leakage from the solid state output card in the controller. A long time ago I hooked a stobe warning light up to one of these outputs and about every 30 seconds this voltage would charge the strobe capacitor circuit to the point that we would get a single flash. The solution was to connect a standard pilot light in parallel with the strobe and the problem went away.
 
don_resqcapt19 said:
In this case, I think it is just leakage from the solid state output card in the controller. A long time ago I hooked a stobe warning light up to one of these outputs and about every 30 seconds this voltage would charge the strobe capacitor circuit to the point that we would get a single flash. The solution was to connect a standard pilot light in parallel with the strobe and the problem went away.
Click to expand...

It is a small transformer protected with a 200mA fuse. Do you think a 10k ohm resistor would help with leakage current and not blow the fuse? I am not sure what that impedenace is of the input.

I tried to replace card with relay output but cant find one. What I might do is just have output turn on relay and relay turn on input to actuator.

Thanks for the replies.
 
Just place a small resistive load across the two leads, this will draw the voltage off, 10k or 20k at 120 volts should do it. a 10k will only load your circuit 12 ma's and a 20k @ 6ma's 10k will be about 1.5 watt's and 20k about .75 watts, keep this in mind when selecting the resistor.
 
Last edited:
A triac will shock you when it is off from leakage current. When it was off an you read 100+ volts it was probably just leakage current and if you had any load at all it would get pulled down to 0v. The 60 volts you where reading is likely just ghost voltage because you meter has a high resistance.
 
090708-0829 EST

jcole:

You have a device, actuator, that has two inputs for controlling its function. Assume there is one common point for the two inputs. Label this "C". Label the other sides of the inputs "ON" and "OFF". These inputs nominally require 120 V AC to be asserted. There is a transformer secondary that provides the 120 V power. One lead from that transformer, call it "S1", is connected to "C". The other transformer lead is "S2".

To put your device in the ON state "S2" is connected to "ON" assuming that "OFF" is not energized. When "ON" is not energized connection of "S2" to "OFF" puts the device in the OFF state.

What is the input impedance of the control inputs to your device? Suppose these inputs are optical isolators and the threshold point is 25 V, then the impedance might be a 5000 ohm resistor, possibly higher. At 5000 ohms and 25 V the current is 5 MA. So at least 5 MA is required to trigger the input. If the input is a small relay the impedance is more likely about 2000 ohms and a higher pull-in voltage than an optically coupled device.

An OPTO-22 SSR OAC5 has a listed leakage current of 5 MA @ 120 V, and requires 20 MA minimum load. This may represent a typical specification for a small SSR.

When you measured a voltage of 108 V to neutral was this neutral the the point "C" as described above? I can not believe that it was. An input that requires a nominal input of 120 V for the asserted condition probably has a pull-in anywhere from 10% to 60% of that nominal voltage. Also was this measurement made at the control signal input terminals of the actuator? For a normal device with a nominal 120 V input a 108 V input would be way above its pull-in voltage.

.
 
090708-0846 EST

jcole:

Just now, at room temperature, I measured 10 V across a 5000 ohm resistor in series with the output of a Potter & Brumfield OAC5 supplied by 120 V. Thus, the room temperature leakage was 2 MA.

.
 
Status
Not open for further replies.
Top