3 phase sewage scraper bridge with 24VAC control issues

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Discussion Overview

The discussion revolves around control issues with a sewage scraper bridge, specifically focusing on the chattering of drive contactors when activated. The control circuit operates at 24VAC, and participants explore potential causes for voltage drops affecting the contactors.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • Nick reports significant voltage drops to the contactor coils, down to 13V, despite replacing the control transformer and processor.
  • Some participants question the installation of polarity sensitive beacons, suggesting that if they are DC, they could be causing issues with the AC control circuit.
  • One participant advises checking for voltage drops along the circuit, suggesting potential causes such as bad cable joints, insufficient wire gauge, or an overloaded 24V supply.
  • Another participant emphasizes the importance of identifying any recent changes made by personnel, as these could be the source of the problem.

Areas of Agreement / Disagreement

Participants express various hypotheses about the causes of the control issues, with no consensus on a single cause or solution. Multiple competing views remain regarding the impact of the beacons and the sources of voltage drops.

Contextual Notes

Participants note the possibility of changes due to recent modifications or wear and tear, but specific details about the wiring or connections involved remain unresolved.

Who May Find This Useful

Individuals working with industrial control systems, particularly those involved in troubleshooting electrical issues in AC circuits, may find this discussion relevant.

NicolasW
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Guys,

I'm having a lot of issues where I work with a sewage scraper bridge chattering it's drive contactors when being called to run, the coils for
the contactors are switched on their neutrals from an Allen Bradley logix processor. The control circuit is 24v AC. I've spent a few hours on this over the past week with little success. I appear to be getting large volt drops on to the coils of the contactors, down to 13v in places. I've replaced both the control transformer and the Allen Bradley processor which has made no difference.

It's worthy of note that a new guy has started and installed polarity sensitive beacons on top of the control panels to signal when the bridge is running. Depending on where he's tapped into the supply, could this cause the issue, I've not been back to look yet to see if this is the problem, could it be likely?

Here are some drawings

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Hoping you guys can give me some pointers.

Thanks
Nick
 
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What do you mean by "polarity sensitive" beacons? If the controls are ac then there is no polarity.
Could the use of dc(?) beacons be causing an issue? quite possibly. I would disconnect the beacons and see.
If so get 24vac beacons.

Do the contactors for the scraper lift , and lower chatter only or are there more that chatter?
 
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If there are voltage drops on the coils work back from there to the power source to see where the drop is introduced.

Bad cable joint?
Wire gauge too small?
24v supply overloaded?

PS: Also check for problems with any common return (0V or earth). It might not be the 24V "coming down" but the return/earth "coming up".
 
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NicolasW said:
Depending on where he's tapped into the supply, could this cause the issue, I've not been back to look yet to see if this is the problem, could it be likely?

Analytical Troubleshooting training courses teach :
'if it used to work and now it doesn't work, something has changed.
Things can change by normal wear and tear,
or they can be changed by somebody tinkering around.
If somebody has been tinkering , that's the first place to look. '

What wires got moved?
 
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jim hardy said:
...they(things) can be changed by somebody tinkering around.
If somebody has been tinkering , that's the first place to look. '

What wires got moved?
Tinkering has brought on several tears over the years, for me. Very good point.
 
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