Control circuit woes

Working on an Italian machine, 4 motors run the 5 heads, motor for feed beam up/down and one motor for the feed.

Everything works except the feed. Feed has two sets of jog buttons forward/reverse, a test/auto switch and the start and stop buttons.

Everything on the machine works, except the feed. I can push in contacters and feed motor runs in either direction.

Found all 3 limit switches which I believe are tied to the feed, had no continuity when in the NC position. Overnighted 3 new pizzato switches, installed, no difference. Replaced aux contactors on the two starters, no difference.

Finally pulled the pushbutton panel and checked voltages on the stop buttons and on one side of start buttons. All are correct at 120v (480v machine, 120v controls) except for all the ones in the feed circuit. I read voltages from 20 to 30v on those.

Obviously I found the issue.

But, my question is, what could cause this?

I have seen this with control transformers wired wrong, but this issue is just on the feed.

Everything else functions correctly.

Is it a almost broken wire somewhere in the machine (probably inside one of the pieces of liquid tight conduit) voltages read exactly right on all circuit breakers in the control panel.

I guess I need to find my really long leads I made up and start checking ends of wires in that circuit.

Any guesses? Something obvious I'm overlooking?

All components are Klockner moeller, so plastic IEC stuff, but at least what I consider good IEC stuff.

All the pushbuttons are making contact and working as they should.

Sorry, don't have a picture of panel, but for being 30 years old, it's nice a tidy and other than being switched from 230 to 460 no one has messed with it, or if they did they obviously cared about their work.



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Ok, the low voltage reading is probably just leakage from all the other wiring in the machine.

I need to establish which wire/wires are feeding the control voltage. (I believe there are a couple) but something some where in the machine is killing that control circuit.



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You have certainly done some great troubleshooting. N/C push buttons pass control voltage through them to whatever device they are controlling. Have you looked at the N/C side (STOP) of the push buttons to make sure there isn't a mashed bug or piece of detritus between the contacts offering a high resistance.

Is it possible to hook your volt meter to the 20-30 volt funky voltage, then jiggle and wiggle any flex sealtite or cord or anything to see if the meter jumps.

Stuart

Try to determine the input side of each switch.

Then check voltage on switched side.

Or place voltmeter across switch and see what. Happens when you hit the switch.

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atomarc said:

You have certainly done some great troubleshooting. N/C push buttons pass control voltage through them to whatever device they are controlling. Have you looked at the N/C side (STOP) of the push buttons to make sure there isn't a mashed bug or piece of detritus between the contacts offering a high resistance.

Is it possible to hook your volt meter to the 20-30 volt funky voltage, then jiggle and wiggle any flex sealtite or cord or anything to see if the meter jumps.

Stuart

Click to expand...

When I first started troubleshooting, I pulled pushbutton panel out and started testing all the stop and couple other NC parts. I ended up taking 5 of the buttons apart to clean the contacts inside the plastic (I really don't like these delicate little things)



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Floating voltages on an AC system are often "phantom" readings caused by parasitic capacitance and/or inductance. That generally means you've got an isolated section of wire between two open contacts that is picking up a minute charge from other wires. You could think of it sort of like radio interference.

Start at the source where you do have voltage and work your way along until you don't. Easiest way to find the cause of an open circuit.

Best guess is a loose connection or failed contact/operator. Could be an open fuse too, depending on the layout. Try having a buddy hold in some of the N.O. pushbuttons too. Could be open on the load side of the control elements/coil. Motor starter with open overloads/bad coil?

Just a Sparky said:

Floating voltages on an AC system are often "phantom" readings caused by parasitic capacitance and/or inductance. That generally means you've got an isolated section of wire between two open contacts that is picking up a minute charge from other wires. You could think of it sort of like radio interference.

Start at the source where you do have voltage and work your way along until you don't. Easiest way to find the cause of an open circuit.

Best guess is a loose connection or failed contact/operator. Could be an open fuse too, depending on the layout. Try having a buddy hold in some of the N.O. pushbuttons too. Could be open on the load side of the control elements/coil. Motor starter with open overloads/bad coil?

Click to expand...

It's still not resolved, got tied up rebuilding a couple forklift engines.

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So after making my own diagram for feed control circuit, testing all 120v control wires, I determined that the feed control circuit was two dead end loops, nothing sending any power to that circuit.

Determined the beginning of that circuit, looked at control wires termination strip again and noticed what I thought to be a jumper wire that should be there, wasn't.

So, this was fixed with left over wire 3" long.

At least I know all the other wiring is good...ugh

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Mr.Green said:

So after making my own diagram for feed control circuit

Click to expand...

Now you did it. Passing on that bit of advice will cause a flurry of diagram drawing before even thinking about making a post question...

The activity here will be reduced by 2/3.

rons said:

Now you did it. Passing on that bit of advice will cause a flurry of diagram drawing before even thinking about making a post question...

The activity here will be reduced by 2/3.

Click to expand...

It's like reading the directions. [emoji38]

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