AB Output Card and Power Supply

Hi,

I was checking out these two identical panels and some weird things happened. The first thing is that we are using allen-bradley 24V power supplies with a redundant module. On the one panel without any outputs hooked up we are reading about 40V but the other panel is fine. The panel builders said it was because there was no load on it. Does this sound reasonable? Why would it be with one and not the other.

Second we have a couple of 1756-OW16i digital output cards and with nothing hooked up and the output off we are reading about 20-21V. Again the panel builders said this was possibly because of leakage current of the card. Just wanted some more expert opinions of the situation. Thanks in advance
Tim

What is the model number of the power supply?
40VDC is not right, even for a typical unloaded switching supply. What if you just hook a light bulb up to it?

1756-OW16I modules are isolated relay output modules. I don't know how they can possibly "Leak". It's a contact.

More information is needed.

rdrast said:

1756-OW16I modules are isolated relay output modules. I don't know how they can possibly "Leak". It's a contact.

Click to expand...

See picture below for spec on leakage. Some of AB's cards have build-in surge protection. Or a led to indicate the output is on.
We would have to see a circuit diagram to know. But the spec.does say there is leakage.

I dont have the model number on me right now, but they are the same module in both panels. We switched the modules and nothing changed. The panel builders hooked up a relay and said that everything was fine but why is it only happening in one?

Could you get 20V off a 1.5ma leakage current? Do meters have a resistence of 13k?

timmyh said:

Could you get 20V off a 1.5ma leakage current? Do meters have a resistence of 13k?

Click to expand...

Yes you can. Most meters have a lot more resistance then that.

http://www.allaboutcircuits.com/vol_1/chpt_8/3.html