3Ph switch

[tom horse]

Hi, i have a 3 ph tyre changer here which seems to have lost power. Everything works ok when doing small size tyres but the motor wont turn when trying to removing a larger size tyre, it just hums. The motor seems fine when checked with a multimeter. However the switch has one phase live at all times. The other swap as they should do when the switch is operated between forward and reverse. Should the wire that isn't swapped to obtain reverse, be live even when the switch is in neutral? What else could cause a lack of power?
Thanks for any advice help
TH

 

[Pete999]

Hi, i have a 3 ph tyre changer here which seems to have lost power. Everything works ok when doing small size tyres but the motor wont turn when trying to removing a larger size tyre, it just hums. The motor seems fine when checked with a multimeter. However the switch has one phase live at all times. The other swap as they should do when the switch is operated between forward and reverse. Should the wire that isn't swapped to obtain reverse, be live even when the switch is in neutral? What else could cause a lack of power?
Thanks for any advice help
TH

Best advice Tom get a Sparks to do some testing

 

[Lucien Nunes]

Hmmmmm.
A 3-phase motor won't generally start at all with a phase missing, so it seems likely that the supply is all there, although deserves checking for correct voltages on-load. My next check would be to current-clamp all 3 lines and compare with nameplate FLA. This will give a better indication of possible motor problems than a continuity test with a multimeter. Lines equal and overloaded would suggest a mechanical problem e.g. geartrain binding at higher torque. Lines unequal would suggest a motor winding fault. Etc.

 

[James]

this is likely to be a fairly simple job for any spark used to dealing with 3 phase motors.
where in the country are you?

 

[tom horse]

Hmmmmm.
A 3-phase motor won't generally start at all with a phase missing, so it seems likely that the supply is all there, although deserves checking for correct voltages on-load. My next check would be to current-clamp all 3 lines and compare with nameplate FLA. This will give a better indication of possible motor problems than a continuity test with a multimeter. Lines equal and overloaded would suggest a mechanical problem e.g. geartrain binding at higher torque. Lines unequal would suggest a motor winding fault. Etc.

I've just finished checking the supply and all voltages are there and within a few volts of each other. The windings are showing as correct I.E continuity where it should be no continuity between phases. I suspect now that you might be right when you say mechanical fault. I'll probably take the bevel box out and check the bearings etc.
My main concern now,electrical wise , is should one line be live at all times, even with the switch in the middle/neutral position? This one line stays live while the other two are not live in neutral and swap over depending which direction you use.

 

[ipf]

Are you a car mechanic in a French garage? The neutral you're talking about seems to be referring to being mechanically out of gear.

 

[DPG]

I think he means when the switch is off.

 

[ipf]

I think he means when the switch is off.

Aye...but forward, neutral, reverse...

 

[Lucien Nunes]

should one line be live at all times, even with the switch in the middle/neutral position

This is an economy method used to control 3-phase motors with a 2-pole reversing switch. The windings remain live in the stop position so the switch does not serve as an isolator. In the good old days, smaller 3-phase machine motors without starters would sometimes be controlled with a DP toggle switch; we last had this on a gang drill from the 1940s that we retired in the late 90s.

If the control is instead a 3-pole switch and all three lines visit it, then it's more likely that one pole is welded shut.

 

[tom horse]

This is an economy method used to control 3-phase motors with a 2-pole reversing switch. The windings remain live in the stop position so the switch does not serve as an isolator. In the good old days, smaller 3-phase machine motors without starters would sometimes be controlled with a DP toggle switch; we last had this on a gang drill from the 1940s that we retired in the late 90s.

If the control is instead a 3-pole switch and all three lines visit it, then it's more likely that one pole is welded shut.

The neutral I refer to is 'off' I.E Forward, off/neutral, reverse.
It is a 3-pole switch, which is why i thought it odd that one remained live. I'll pull it out tomorrow and see if i can check that it is indeed welded shut. If it is I might just swap to single phase and do away with the only equipment I have that is 3 phase. I have a suitable motor and switch just waiting for something to come along that I can use them in.
I can then use the motor on my lathe (in another building without 3 phase) using an inverter for speed control instead of having to swap belts around.
Thanks for all the help i'll let you know if it is welded contacts.