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24 volt troubleshooting

rich p

Cast Iron
Joined
Sep 7, 2003
Location
plantsville ct. usa
I am working on A large tube bending machine and one of the hydraulic cylinders isn't working. If I manually actuate the solonoid on the valve , the cylinder works fine. The valve solonoids are 24 volts dc. My question is, are 24 volt dc systems similar to A car battery system in that + goes to load and has to return - in a closed loop back to the power supply? Can't find much info on the web for machine wiring. Thanks.
 
just stick a meter across the two wires to the solonoid, when actuated 24v will show on meter, also there usually is a LED in the coil connector that lights when power applied to coil, if none fitted then these are available, as its just a coil polarity is not that important, the 'return' is zero volts on the PSU, load +24v on PSU as you have indicated, however +24v is also an output voltage on a PLC, so a PLC can control solonid valves directly
 
You will find a lot of industrial equip is wired +24 to the device being activated and then it to the controller. I think its so that if the wire gets shorted less chance of frying one of the outputs of the controller.
 
One thing that can happen with a 24vdc system is if there is a shorted condition, the power supply will "crowbar" or be dragged down, rather than having the electrical a$$ to simply step up and put out enough current to blow a fuse.

If PLCs are involved, there are sourcing and sinking outputs, basically dealing with the polarity.

Determining how the power supply is wired for all outputs should give some clues about which sign convention will be used.

If you manually shift the spool on a valve, but can't electrically actuate it, your problem is close by. If a PLC and you can force the output on that will help to rule out some other possibilities within the program. As was stated above, checking for voltage at the solenoid coil is also a very good test point.
 
I've had to remove, clean, and re-install the same solenoids on a G&L horizontal tape machine literally hundreds of times. Go on a call, manually operate it, OK, pull it, clean out chewed up O rings, reassemble and all was well.

Rarely was the coil bad. Simply not enough oomph in the coil to pull the spool with rubber fragments in the way. Also, with the rubber fragments stuck in the spoolway, spring can't return the spool to closed when energy is cut off.

Operate with an Allen key. If it works, remove, clean, replace. If it doesn't move, remove, clean, replace.

Enegize the circuit, hold a screwdriver to it, if it is attracted, the circuit is live and making a magnetic field. No polarity to an electromagnet. Solenoids have normally 2 black wires coming from them. May be other color, grey, red, whatever, but both the same.

Cheers,

George
 








 
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