Relay in a Box

[Mustwin351]

I had to troubleshoot an exhaust fan and figure out why it was not turning on when the emergency generator kicked on. It is controlled by a relay (Relay in a Box by functional devices) through our building automation. The problem ended up being on the programming side of the building automation but in the process of troubleshooting I found zero resistance across the coil of the relay. The relay works just fine when voltage is applied to the coil. I tried to google to find out how this relay is designed but have had no luck. It is also not a solid state relay as I can hear the contacts close. Anybody know how the coil circuit might be designed?



It is a model number RIBX24SBA

 

[Mustwin351]

Cut sheet

 

[hbiss]

If you look at it, it's not a simple relay. Although the "coil" is drawn as a normal coil, there are electronic components in its circuitry that are probably giving you that reading. Do you have your meter set to the lowest range (Rx1) if it isn't autoranging? Note that the coil is 24V AC or DC so suspect a diode or FW bridge. Did you try to reverse your test leads?

-Hal

 

[Mustwin351]

Yeah tried reversing and no luck. I got 600 kilo ohms across the coil. Just curious as to how it’s designed.

 

[synchro]

I agree with Hal that there may be a full-wave diode bridge in front of the coil to allow AC and also DC with either polarity. It's likely that your meter does not apply enough voltage in the "ohms" mode to get the two series diodes of a bridge to conduct any significant current. You'd need at least 1.3 to 1.4VDC before conduction begins.

If you have the time you could try applying 1.5V and 3V DC using a couple of dry cells (AAA, AA, C, or D, etc.) and have a meter in series set to measure DC current. If there's a diode bridge then the current at 3V will be much more than 2X the current at 1.5V.

 

[n1ist]

There may be a capacitive dropper in there to drop the 120V down to 24V that drives the relay; if so, you would be seeing the discharge resistor for the series capacitor
/mike

 

[kwired]

He said he had zero ohms one way and 600k with leads reversed.

Analog meter might be because of a charged capacitor in the circuit, most digital meters will often give you a negative reading, at least in one direction, when there is a voltage source in the tested circuit

 

[Metallicbeing]

This is an Electronic Current Sensing Relay. It seems very similar to a Motor Controller.

Functional Devices RIBX24SBA

Functional Devices RIBX24SBA : Enclosed 20 Amp Relay/Current Switch Combination, Adjustable + Override Switch, Made in USA, UL Listed

www.energycontrol.com