Hi, new here but have a very similar problem.

I have a rotary phase converter rated at 4.5kW. It runs the Colchester 1800 lathe no problem but will only run my Universal mill on the low speed range (two speed motor), if I try and run it on the high speed range it won't start at all unless I take the tension completely off the belts. The mill is 2.2kW but I think the mechanical drag is just too much for it on start up.

David

Hi David,
I think you should start your own thread relating to your problem. It can get very confusing discussing a number of different problems in the same thread.

Hi Tony,
I think an extra picture of the isolator door with the camera moved to the left a bit or the door swung about 30 degrees more closed might help. In the original picture I can't decide if the terminals on what I think is the contactor are in the horizontal or vertical plane. ( I think from the fact that it looks like the contactor coil is at the bottom of the picture that the contacts are in the horizontal plane.) It might also help identify the two things either side of what I think is the contactor. ( My best guess on these is thermal overload cut outs, one for the main motor and one for the coolant pump.) I think the right hand set of the four contacts on the contactor is the maintainer set to hold the coil in when the start button is released. I will avoid making any more comments at the moment as Phil seems to be thinking along the right lines and recommending sensible actions to diagnose the problem.

Les.

Edited By Les Jones 1 on 14/06/2020 09:21:39

Are the measured phase to phase voltages off load? If so what do they measure on load, on both the lathe and mill.

Andrew

Is it a rotary converter or a tranverter. A rotary is a 3phase motor generater The unit you have looks like the ones with your original single phase as lets say L1 & a bank of capacitors to lead the sine wave which we will call L2, then an inductor to make the supply lag. L3. Creating artificial 3 phase. I know of 2 people who have these & watching them start there machines is weird. 1 has to hold a switch on the front panel in a certain position to get the lathe running , it buzzes like hell. Then he moves the switch to a different position to run. The artificial ones give slightly different reading on each phase. If your contactor coil is 240v then I suggest you try using a different phase. Move them twice in effect. Once reverses the motor twice back forward. I did not want to get into this. If I was there I could sort it for you. I am sure. You may kick yourself once it gets done.

Steve.

Looking at the picture of the contactor, it looks like there is two sets of overloads, the one on the left with the black wires, I am guessing is the main motor, the one on the right, with the red wires I am guessing is the coolant pump. Try running the coolant pump, and the table feed motor if it has one. Do you have a multimeter?

Phil

OK, it sounds like the motor is either off a phase, or maybe has got damp and has leaky insulation, have you tried the coolant pump/table feed to see if they run correctly? What are the earthing arrangments for the installation? If you have a multi meter you need to turn off the power, isolate the machine and start testing through each phase from the isolator on the machine, through the contactor with the contactor held in manually, through the overload, and to the motor. You could also do with a megger to do an insulation test on the motor. I think Emgee is right, we are coming to the point where you need someone on site with basic test gear to sort this out. If it was running at your previous premises, it can't be much wrong with it. there is a possibility that there is a phase off at the motor caused by a bad contact either in the contactor, , or in the overload. If the coolant/table feed works, and the main motor doesnt we have confirmed three good phases at the machine, if they don't work correctly we can suspect the supply to the machine. Incidentally, what type of lathe is it, and why does it need a neutral? Where are you in the country?

Phil

Edited By Phil Whitley on 16/06/2020 21:03:15

Edited By Steviegtr on 16/06/2020 22:11:24

You are right Les, but it would be a bit of a faff to set it up, I am working on the assumption that if it starts a 3hp motor, it should start a 5hp off load with the belts off, and it isn't. it is rated at 7.5 hp, and should be able to deliver about 15a peak, the 5hp should be demanding about 8-10a, so it shouldnt be a problem, especially so with the belts off. Of course we do need to test that the three phases that are running the lathe are also reaching the mill!

Original poster, can we have a pic of the inside of the rotary convertor pls?

Phil

It may be that the motor starting current is higher than the converter or the single phase mains supply can supply without too high a voltage drop.

Bearing in mind that the starting current will be about 6 times the full load running current, so the 3 phase starting current could be in the region of 50 amps.

The attached document shows the size of motors that can be connected to the DNO network. The largest 3 phase motor that can be connected without any checks is 6 HP and the largest single phase is only 1 HP. This is to avoid voltage fluctuations affecting other nearby customers.

**LINK**

This is something that never seems to be mentioned when discussing the use of single phase to 3 phase converters.

Stuart

You are right again Les, I can also see the fan cowl now you have pointed it out! I am going on the assumption that the maintaining circuit is not workin because the overloads have either already opened due to excess current, or one of the overloads is open circuit, or stuck in the overload position and is causing the motor to try to start on two phases. This would have the effect (depending on how it is connected), of preventing the contactor maintaining circuit working, but would energise the coil when the start button was pressed. The contactor type, with two seperate overloads, which is what appears to be in the hinged lid, is unfamiliar to me. It appers that in order to start the machine, the start button brought in the contactor, and started the main motor, and you could then select coolant with the rotary switch, and either motor overloading or faulting would stop the whole machine. Unusual, but saves using two contactors. The only Cincinnati of this type I have ever encountered was in the seventies in a local workshop owned by a mate of mine, and as I recall now I think the table feed is mechanical and run from the main gearbox, rather than by a seperate motor. Unfortunately it never broke down electrically, so I never got to tear into it!

Stuart, the transwave should be able to deal with the starting current without a problem, especially with the belts off, it is after all, rated for starting a 7.5 hp motor. Your point about the single phase supply to the transwave is another possibility to consider though, we always assume MCB's are installed, but this may not be the case. It seems that the tripping is not taking place on the single phase side, so once again, we need someone on site with an AVO and a Megger!

Phil

Edited By Phil Whitley on 17/06/2020 21:35:10