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Hello, a mechanic friend asked me to check his hydraulic vehicle lift controls as it had failed. When I arrived the lift started working again (of course) but with some contactor chattering upon initial start for approx 5 seconds.

He was happy it was working again and wanted to get home, I had a quick check and worked through the controls for loose terminations/crimps/continuity. Had a test of voltages and rotation and found that at the bs88 fuse holders there was 240 at L1, 260 at L2 and 220 at L3 +/-2% BUT from the bottom of the fuse holders all where 240 +/- 2%.

I've stewed on it all morning, and think I'll get called back at some point, any forthcoming wisdom would be appreciated....
 

littlespark

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Anything changed between testing supply and load sides of the fuses? Motor on load or anything?
Is the contractor got a 230v coil? Extra minuscule load on one phase, but if it’s faulty there could be much much more, causing a problem with one but not all phases.
Does contractor get hot?
Does motor get hot?

The chattering isn’t a good sign.
 

Pete999

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Try cleaning the pole faces on the contactor magnets, could be just dirty pole face causing the chatter, worth a try.
 

Lucien Nunes

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Are those fuses in the hoist panel? Clearly you can't have different voltages at the two ends of an intact fuse. Either those readings differ because of external load changes between taking one set and the other, or at least one fuse or supply line is dead / intermittent / high resistance and the affected phase is being regenerated by a motor or diverse balanced load, hence the odd voltages. The motor wouldn't start with the phase missing entirely though.

I would want to rule out, sooner rather than later, the possibility of a high-resistance connection in the neutral upstream, causing the voltages to be assymmetric. If it failed entirely there could be equipment damage when something expecting 230V gets 400. It doesn't explain why you got good readings at one end of the fuses, except that the load might have been very well balanced at that exact moment.
 

Marvo

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Maybe if the fuse or one of its associated terminations is arcing it could have caused the tester to give a confused reading.
 
  • Thread Starter Thread Starter
  • #6
Thank you for your insights gents, Im popping back at the weekend.

Anything changed between testing supply and load sides of the fuses? Motor on load or anything?
The workshop was busy when I was there, closed at weekend so will remove variables.

Try cleaning the pole faces on the contactor magnets, could be just dirty pole face causing the chatter, worth a try
Thanks Pete, big fan of simple, quick and easy. Would be my preferred cure!

Clearly you can't have different voltages at the two ends of an intact fuse.
Which is what bothered me!

high-resistance connection in the neutral upstream, causing the voltages to be assymmetric.
Thanks Lucien, hadn't thought through that far yet.

if the fuse or one of its associated terminations is arcing it could have caused the tester to give a confused reading.
Fuses looked good when I removed from holders but will look at them more closely upon return, cheers Marvo.

Again thanks all, many brains make light work!
 
The reason why the ac contactor cannot hold and shake is as follows:

When the power supply system is at a low voltage, it may cause ac contactor to suck up and shake. Please check the working voltage. If the power supply load allows, change the thick wire.

The main contact or auxiliary contact often has stains or burrs, resulting in the contactor can not hold or shake.

A short circuit between the coil turns of the ac contactor causes the contactor to not be able to hold or shake.

Ac contactor core mechanical plug or reset spring is not properly adjusted.

Bad contact of buttons or terminals in the control circuit.

Electromagnet end face enters foreign body, also can have such phenomenon.

The voltage of the control power supply is different from that of the coil.
 
Hello, a mechanic friend asked me to check his hydraulic vehicle lift controls as it had failed. When I arrived the lift started working again (of course) but with some contactor chattering upon initial start for approx 5 seconds.

He was happy it was working again and wanted to get home, I had a quick check and worked through the controls for loose terminations/crimps/continuity. Had a test of voltages and rotation and found that at the bs88 fuse holders there was 240 at L1, 260 at L2 and 220 at L3 +/-2% BUT from the bottom of the fuse holders all where 240 +/- 2%.

I've stewed on it all morning, and think I'll get called back at some point, any forthcoming wisdom would be appreciated....
change the contactor for starters after about 80k switch count contacts become worn / sticky etc.
 
The reason why the ac contactor cannot hold and shake is as follows:

When the power supply system is at a low voltage, it may cause ac contactor to suck up and shake. Please check the working voltage. If the power supply load allows, change the thick wire.

The main contact or auxiliary contact often has stains or burrs, resulting in the contactor can not hold or shake.

A short circuit between the coil turns of the ac contactor causes the contactor to not be able to hold or shake.

Ac contactor core mechanical plug or reset spring is not properly adjusted.

Bad contact of buttons or terminals in the control circuit.

Electromagnet end face enters foreign body, also can have such phenomenon.

The voltage of the control power supply is different from that of the coil.
tbf if the control voltage is higher than the coil voltage it will burn out if lower it wont work.
 
being that this is in a garage one thing to consider is possible oil contamination, fuse blocks that are contaminated can cause some flaky readings from corrosion resistance or contamination.
its not uncommon for oil vapor condensation to enter a contactor and build up carbon on the contacts either (usually evident from smoke stains)
 
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