CVA Lathe Coolant Pump Tripping

[Trevanion]

So for a few years now I’ve been without the coolant pump on the CVA because it would trip the overload after a couple of minutes of use, I assumed it was something faulty with the overload and then the reset switch broke and I’ve only recently got around to replacing it and cleaning out the horrendous mess in the coolant tank that accrued from a lack of circulation.

So I thought with the overload replaced the pump would work flawlessly, but it still trips. Looking closer I realise now that the motor that’s been fitted by the previous owner is an American one and 60hz, not our 50hz. I know that running a 60hz motor on 50hz will make it run slightly slower, but does it have an appreciable effect on the current draw?

The current overload is the same as was fitted on it, a 1.7A - 2.4A, from what I can understand on the motor plate the overload should be set around 1.9A for when it’s running on 240v. Checking with a clamp meter it appears to be drawing a steady 3.4A, so my question is would there be any catastrophic consequences from fitting a higher rated overload? The pump won’t be run for hours on end but only a few minutes here and there, I could live with the tripping but it’s more of a case that it’s a pain when it cuts out in the middle of a cut.

 

[brightspark]

if you fit the bigger trip just keep an eye out that the motor does not get 2 hot and check the amperage with the clamp meter to make sure it doesnt rise in use

 

[Trevanion]

if you fit the bigger trip just keep an eye out that the motor does not get 2 hot and check the amperage with the clamp meter to make sure it doesnt rise in use

I just ran it for about five minutes while resetting the trip, the motor does get a little warm to the touch but not majorly. Checked again with the clamp meter while it was warm and it was still pulling 3.4A, but then compared to the 4HP main motor which is supposedly only pulling 7A according to the clamp meter, so not 100% sure I can trust the “Fuke” clamp meter!

 

[daleyd]

Do you have the links in the right place in the motor connection box?

1.9a rated and 3.4a actual seems a bit high to me? Maybe the frequency increase will affect it by that much (I don’t know a great deal about single phase stuff) but that’s not just a bit more, it’s getting on for double…

 

[Agroshield]

Could you rewire it to its 115v setting and run off a building site transformer, if only for a test period?

It is not clear to me if you have to change any internal links to go from 115v to 230v. If that is the case, are all those connections verified correct?

 

[brightspark]

I just ran it for about five minutes while resetting the trip, the motor does get a little warm to the touch but not majorly. Checked again with the clamp meter while it was warm and it was still pulling 3.4A, but then compared to the 4HP main motor which is supposedly only pulling 7A according to the clamp meter, so not 100% sure I can trust the “Fuke” clamp meter!

at 7 amp on the 4hp motor that must be 3 phase so 21 amp over the 3 phase . is pump motor single phase 3.4 amp it will be about rite

 

[daleyd]

Is it 1/8 hp or 1/6 hp it’s hard to make out from the pic?

 

[Brad93]

Single phase?

You potentially haven't wired the three pole overload relay correctly.
You need to have phase on all three poles.

 

[Trevanion]

Do you have the links in the right place in the motor connection box?

1.9a rated and 3.4a actual seems a bit high to me? Maybe the frequency increase will affect it by that much (I don’t know a great deal about single phase stuff) but that’s not just a bit more, it’s getting on for double…

I'm honestly not sure, There are no links but a connector block. I didn't check if there was a diagram behind the cover plate.

at 7 amp on the 4hp motor that must be 3 phase so 21 amp over the 3 phase . is pump motor single phase 3.4 amp it will be about rite

They're both single-phase motors, which is why I found the 7A reading on the main motor strange.

Is it 1/8 hp or 1/6 hp it’s hard to make out from the pic?

1/6HP.

Single phase?

You potentially haven't wired the three pole overload relay correctly.
You need to have phase on all three poles.

Possibly, but it does look set up similar to your diagram. When I replaced the overload, I put it back exactly the same as the old one. All of the electrics in the machine were supposedly professionally done when it was converted to single-phase by the previous owner. I do have the wiring diagram somewhere that the electrician who did it drew up.

 

[Martin-Sy]

My first thoughts were that the wiring in the motor terminal box was wrong and had not been set correctly for 230V. I trawled for a manual and this one seems to be close. If so (see last page for connection diagram) the motor connections in your photo are correct. The main winding is in two halves which should be in series for 230V and parallel for 115V.
Yours (if the colours are to be believed) are in series which is right.

Can you hear the centrifugal switch click over when the motor is turned off and slows down? Could this be stuck in the closed position leaving the start winding in circuit?

Its unlikely to be a duff capacitor as the motor wouldn't start.

The motor in the attached pdf is only rated for 60Hz operation. Yours appears similarly 60Hz rated from plate photo.
I would expect a higher current on 50Hz since the motor is predominantly an inductive load and hence its reactance (proportional to frequency) will be lower.

Is the pump turning freely?
Could it be a mechanical overload?
What voltage does your mains read?

Something isn't right tho. 3.4A for a 1/6 hp motor when the rating plate says 1.9A ....and that's at full load.

Sorry, I have no real answer just more questions!

 

[daleyd]

Something doesn’t seem right - a single phase 1/6 hp at that voltage shouldn’t be pulling 3.4a

I’d check the voltage setup of the motor is correct (it’s dual voltage on the plate so should have some links to configure it - or at least the combination of wires connected in the terminal strip) and also maybe direction (if it’s going the wrong way it could cause a high current)

If you don’t have a connection diagram how are you sure the wires used at the motor end are correct for your voltage? They seem correct for the pdf attached above (assuming direction is ok) but needs verifying for your exact motor -should be easy enough to measure the resistance for both configurations to see, one should read half the resistance of the other if it’s the same as the pdf.

 

[Agroshield]

Possibly, but it does look set up similar to your diagram.

Another diagnostic step would be temporaily to eliminate the contactor and wire the motor directly to a lead with a plug on its end. That will tell you if it is a motor or control issue.

 

[Trevanion]

Thanks everyone for your comments and help, I really appreciate it. This is the sort of question I would usually pose to Bob 9fingers on the Woodhaven2 forum but sadly he passed recently.

So I had another look at the motor and there is a diagram on the capacitor cover that I somehow totally overlooked.

1 = Blue
2 = White
3 = Orange
4 = Yellow
5 = Black
8 = Red

Looking at it, it seems the wiring is correct but lead 5 and 8 are swapped so that the motor runs in reverse, which might be correct for the pump but I wouldn’t know which way it needs to spin. I do have a photo of the pump impeller from when I stripped the pump to clean it out the other day if that’s useful. The motor runs clockwise when looking from above, so anti-clockwise when looking from below.

Can you hear the centrifugal switch click over when the motor is turned off and slows down? Could this be stuck in the closed position leaving the start winding in circuit?

Is the pump turning freely?
Could it be a mechanical overload?
What voltage does your mains read?

Centrifugal switch is operating correctly, can hear it click as it’s running down. The pump turns freely, there’s a little access hole in the side and I can turn it with the tip of my finger with no issue. Not sure about mechanical overload, but it’s definitely the pictured overload as you have to reset it for the motor to run again. I checked the voltage at the main contactor in the lathe with my multimeter as it was the easiest thing to measure and it read 253V.

 

[Martin-Sy]

Whilst I'm not 100% sure about this my gut feeling is that the lower mains frequency and high voltage are causing a degree of magnetic saturation in the stator.
When this happens the current goes up without any significant increase in flux and the current waveform becomes non-sinusoidal.
It's unfortunate that your mains is 253V which is right at the top of the UK mains voltage specification: 230V +10%/-6% or 253 to 216.

If it were mine I think I'd try a step down transformer to reduce the voltage to to the motor to say 220V.
It needn't be a isolating transformer, an auto-transformer or an isolating transformer with suitable (eg 240-220-200) tapped primary used as an auto would be fine.
But that's a lot of faffing around just to try.

Otherwise, as @brightspark says just put a higher rated trip in and keep an eye on it to see if it overheats.
This will be easy to monitor if your pump is mounted vertically behind the bed at the tailstock end as mine is (CVA Mk1A series III) but less so if it's hidden in the rear cupboard as on earlier CVA's

Worst case is that the motor will overheat possibly and burn out.

What is intriguing is why this motor was chosen for the conversion to single phase and how it came to be in the UK.
It's clearly designed for the USA market where 60Hz 115V / 230V mains is the norm.

The other point of note is that the CVA original pump motor would have been two pole 2800 RPM.
This one will only be around 1450 rpm on 50Hz.

From your picture of the impeller the correct rotation is ACW, but I doubt the current would change much if it were wrong.
The pump part certainly looks like mine:

I wasn't suggesting that there was a mechanical overload trip - just that a mechanical problem like a binding bearing would increase the current draw.
This clearly isn't the case if you can turn it with a finger through the access hole.

 

[Agroshield]

Looking at it, it seems the wiring is correct but lead 5 and 8 are swapped so that the motor runs in reverse,

Again, for diagnostic purposes, switch the leads back and see if it makes any difference to the current drawn.

Put a different motor onto the end of the contactor and see if everything runs normally.

There are only two items in this problem; it is one or the other or the combination. And the only way you will find this out is to divide and conquer.

 

[Trevanion]

So I bought a new clamp meter because the old "Fuke" was knackered (I had to hold one of the wires onto the 9v battery to make it work as the terminals had broken), and I wasn't 100% certain of the readings. So with the new meter it reads 3.5A, and as it was easier to use without having to mess about holding a battery and operating the clamp I had a second look at the main motor on the lathe. The typical brown live wire was still reading 7A while running, but there are five wires coming from the motor, presumably the live is brown, the neutral blue, and the earth is obviously yellow/green, but there is also a black and white wire and the black wire also reads 7A while running, but the white wire reads 17A while running. I thought perhaps if the motor was running in reverse the black or brown wire may read 17A but it was still the white wire that read 17A and the rest 7A, unusual and I admit I don't understand enough to know what's going on there, but it's not an issue.

Again, for diagnostic purposes, switch the leads back and see if it makes any difference to the current drawn.

Put a different motor onto the end of the contactor and see if everything runs normally.

I tried swapping the leads and the motor ran, but slightly noisier than when it was wired in reverse and it did pump but at a significantly slower rate. It also pulled a little more current at 3.6A. I'll have to try another motor but I don't think I have anything close enough to 1/6HP, I have a couple of 3/4HP motors, but they're closer to 4.5A when running.

Worst case is that the motor will overheat possibly and burn out.

What is intriguing is why this motor was chosen for the conversion to single phase and how it came to be in the UK.
It's clearly designed for the USA market where 60Hz 115V / 230V mains is the norm.

The other point of note is that the CVA original pump motor would have been two pole 2800 RPM.
This one will only be around 1450 rpm on 50Hz.

Interesting that the original motor was 2-pole 2800RPM, the coolant must come out at a rate of knots as it's pretty fierce with this motor at half the speed. I'm not sure why the motor was selected, I might have to dig out the documents that came with the machine and see if there's anything in there that would present a clue. The only thing I can think of is that the guy I bought it from seemed very interested in the Monarch 10EE, so perhaps this is a preferred replacement motor for one of those?

 

[Martin-Sy]

but there are five wires coming from the motor

If the motor is reversible from the apron control you need to have access to both ends of the start winding. i.e. Two wires for the run winding, two for the start winding and an earth.
The start winding connections are reversed to swap direction.

A 4HP single phase motor will have a very high start current!
A VFD would be the way to go now. Kinder to your supply & the machine.

 

[Trevanion]

If the motor is reversible from the apron control you need to have access to both ends of the start winding. i.e. Two wires for the run winding, two for the start winding and an earth.
The start winding connections are reversed to swap direction.

There's a rotating on-off switch on the apron along with the pump controls, but forward and reverse are controlled from the lever on the carriage and the sliding lever that rides on the square bar. A quirk of the machine is that if you're running it in forward (lever up) and you put it into reverse (lever down) before the spindle runs down, it continues running in forward or vice versa, rather than instantly going into forward or reverse as you have with three-phase machines.

A 4HP single phase motor will have a very high start current!
A VFD would be the way to go now. Kinder to your supply & the machine.

I can't complain about the way the 4HP motor works, it starts instantaneously every time without issue. I do have a Sedgwick LK Rip Saw which has a 4HP motor and the control box has very large capacitors in and three contactors, you have to hold the "ON" button for a few seconds while it winds up on the start capacitor and then once you come off the button it switches over to the run capacitor. If you don't hold the ON button down long enough, it just doesn't start, or it can trip the breaker.

 

[Martin-Sy]

but forward and reverse are controlled from the lever on the carriage

Yes, in the jargon that's apron control. For lathes the apron is the bit hanging from the front of the bit (saddle aka carriage) that slides along the bed.

you put it into reverse (lever down) before the spindle runs down, it continues running in forward or vice versa

Yes, that's the norm with single phase motors. Unless the motor slows down sufficiently for the centrifugal switch to re-connect the start winding, it will just run the same way as it was running.