Power problems when going through PLC

[Lancie1]

Josh, for our education on future troubleshooting, how was the relay socket bad? Was it an open circuit, or a mis-wired terminal? What is your Omron socket catalog number? I want to be sure and avoid that one.

 

[milldrone]

Put a 24 volt lamp in series with one of the relays. That should help with troubleshooting.

keithkyll's suggestion would have lead you straight to the problem.

 

[Lancie1]

keithkyll's suggestion would have lead you straight to the problem.

Perhaps, if you put the lamp in series with one of the relay contacts and wired it to 24VDC power, it could tell you if the relay operated.

Keithkyll's suggestion to "Put a 24 volt lamp in series with one of the relays", although not clear, I interpreted to mean in series with the relay coil. Usually in electrical jargon, "the relay" means the relay coil. But if you put a lamp in series with a relay coil, the voltage is divided between the two devices, and there are several possible outcomes, depending on the individual impedances of the two devices:

1. lamp lights and relay operates,
2. lamp lights and relay does not operate,
3. lamp does not light and relay operates,
4. lamp does not light and relay does not operate.

Putting a lamp in series with a relay coil then seems to be mostly a waste of time, unless you have a known relay and have tested to see how it works with a particular lamp.

On the other hand, if you put a lamp in parallel with a relay coil, it could tell you that you had power to that relay.

 

[keithkyll]

A series lamp allows you to have a dead short without blowing anything up.
Someone suspected reverse wiring. A backwards diode would clamp the supply and put it into shutdown. A series lamp would light, and not clamp the supply.
If the relay was AC instead of DC, the lamp would still light.
Loose connections cause a flicker in the lamp.

You still need to use your brain, but a series lamp will tell you quite a bit. It's especially handy when you have something that keeps blowing fuses. Call it a poor man's Variac.

 

[jimbo3123]

Lights are flashing and parts are moving so everyone is happy around here.

Josh

Good to hear! Thanks for the follow-up letting us know what you found and how it went.

 

[Imracing]

It was a Omron PYF08A 8-Tab Relay Socket 7A 250V.

I did use a light as he said but I unhooked all my relays and used a 24V light to check each circuit. After that was checked I then started to hook each relay on its own. First socket I put in was bad and I didnt know it so I kept trying different cubes. After that I tried a different base and it worked. I guess I should of said 30min trouble shooting and another 30 hooking it all back up. I didnt think an hour was bad.

I didnt check the socket till a few min ago. I have not pulled it apart but from the multi-meter it seems to have a short across the positive and common lead screws.

 

[milldrone]

A series lamp allows you to have a dead short without blowing anything up.


You still need to use your brain, but a series lamp will tell you quite a bit. It's especially handy when you have something that keeps blowing fuses.

I have used this technique with a slight twist to find a 120V field sensor power supply short. The problem was the short was intermittant. I used a 500 watt quartz light in series, the circuit was fused with a 5 amp 5X20mm fuse. The conduit and sensors covered about 4 acres. A log had crushed a section of conduit, shorting the 120V field sensor supply. But we could not find the dammage. Whenever the light would light up I would begin tracing with a clamp on ammmeter. The other sparky's had been replacing the fuses for two consecutive production shifts. After placing the quartz light in series no more burned fuses. Plus being able to trace using the ammeter (clamped around any bundle of wires coming out of the conduits) helped to find the offending conduit run. The other benifit was the quartz light provided enough current to power the sensors when there was no short, so production could continue.

 

[keithkyll]

An excellent example of the point I was trying to make. Without a light, how else could you troubleshoot that problem? Replace stuff until you stop blowing fuses? We call that Easter-egging.
With a (properly sized) light bulb and your brain (Ohms law, ammeter, etc.), you can pinpoint the problem, explain to others exactly what happened, and still be home in time for dinner.