# testing relays

#### leon

Joined Aug 21, 2007
2
We have a high voltage power supply for a painting system and I would like to know if there is a way to test relays in the chain of things that give the high voltage output. Is there a way to use a test meter on a relay? The relays in the box are the common small clear plastic cube type with the contacts visible. It's an older system and there are a couple of vacuum tubes in it. The manual says when the tubes heat up voltage is delivered to the first relay. The other day we lost several hours production because of a lightning strike and the crew replaced several parts in the system without knowing where the problem was-but their technique worked. Since relays are a common element in many systems I have often wondered if there is an easy way to test them.

#### bloguetronica

Joined Apr 27, 2007
1,541
You can test relays with a multimeter with no problem.

First you should test the relay coil first by checking it with a multimeter. You should read about 50 to 500 Ohm, depending on the relay type of course. If you know the relay wattage, you can determine its resistance by usint the equation:
R = V^2 / W. Then you should confirm this value with the multimeter.

You can also check contacts with a multimeter. A closed contact should have less than 1 Ohm and a open one should have infinite resistance. When checking contacts, check them with the coil energized as well.

#### techroomt

Joined May 19, 2004
198
several checks can be made in circuit as well as bench testing with an ohm meter. first, the great thing about clear housings is that you can visually watch them change "state", from de-energized to energized. this will verify the coil is likely good and operating. you can then test the voltages at the contacts. if you are unsure about testing high voltages or any voltages, seek help! a decent technician with schematics should be able to follow the "loss of power" back through the relay contacts.

precaution here is that although contacts are closed, and show ohm meter continuity, and even the correct voltage, the contacts can be eroded away enough that they cannot carry the required current for the circuit.

if these are the socketed plug-in type, you should carry some spares on hand so that a quick swap can get you back on-line faster.