1970 Metal Lathe Control Circuit blowing fuses on the 120 volt section failing meager test below 60 mega ohms

[sam_sam_sam]

I was working on this machine yesterday and I now going to use an incandescent lights instead of a fuses to figure out what the issue is with it blowing control voltage rail but this not the only issue the coolant pump failed the meager test as well as the main motor as well this motor has 12 motor wire leads instead of the normal 9 wires

This metal lathe has a weird motor setup it has a soft start motor with a “Y” and a delta type of motor winding setup and it is not done in the motor pucker head enclosure it is with four different contactors wired in a configuration I have not seen before plus it has a timer module that appears to some how control the contactors the wiring diagram does not show this timer module at all so l have to manually figure out how it is wired in this system configuration

More to come next weekend is when I going back to work on it again

[sam_sam_sam]

There is an issue with this editing process for this post see below the quote function is not working correctly either

One note you know that I have been working on an enclosure for my battery testing machine computer rail cart and was going to cut the opening for the battery testing machines and the buck converter modules and I was going to do this with a drill bit and and a jigsaw and a cutting jig ( I am going to have two of them made and he is providing the material for this project just the metal plates that attaches to the computer cart )

Well the person ( I have known this person for at least 20 years now I work for him on a technical level and troubleshooting and board level repairs in the past ) that I doing this for has access to a laser cutting machine and we are going to trade services so this will make this project simpler in the long run

[stj]

lathes are reversable - thats why the motor looks strange
i would start by looking for bad caps in metal cans < a clue there.
and wires with cracked or damaged insulation.

[sam_sam_sam]

lathes are reversable - thats why the motor looks strange
i would start by looking for bad caps in metal cans < a clue there.
and wires with cracked or damaged insulation.

By the way this is a 480 volt 3 phase system ( but could be setup for over 500 volts according to the wiring diagram. ) that is used on this lathe and there is no controllers other than the timer module everything is done with relays and contactors no VFDs it does have motor overloads and that all it has that is the main reason in the title of this post I put the area when was made


I found what has caused part of this issue and it is that they use a coolant mister on this lathe and most coolant are not kind to rubber type of insulation that is used on OS cord at that what it is called in this country or a least what I know what it is called

Most Reversible motor might have three contactors at the most not four of them like this one does and most reversible motors do not have a timer module wired in the contactor circuit

That why I said that this a weird setup that I have never seen before

It might have to rewired at least high voltage cables going from the motor pucker head to one of power terminal rails and from this terminal to another terminal power rail and maybe some of control wiring depending on what I find when I do the incandescent light instead of the two fuses for the control circuit section

The motor is being sent to a rewinding company for evaluation and see what the actual issue is with it to why it failed the meager test I have used this company for many years when I have had issues with motors that cost to much money buying a new one I send it there first for evaluation then make a decision to weather or not to buy a new one or have it rewound or buy another new motor

This company has a very interesting testing station for testing motors this why I have used them several times over the years when I have issues with motors that are blowing fuses and they fail the meager testing that was done on my part

[stj]

is it a delta or star configuration?
if it's a star then the center phase stays the same and the contactors could be working in pairs to swap the 1st and 3rd phases.

a mist spray is new to me, the lathes i used to have acess to just had a jet system for the fluid that you directed at the cutter

[sam_sam_sam]

is it a delta or star configuration?
if it's a star then the center phase stays the same and the contactors could be working in pairs to swap the 1st and 3rd phases.

a mist spray is new to me, the lathes i used to have acess to just had a jet system for the fluid that you directed at the cutter

The wiring diagram says that it is a “Y” or Delta configuration depending on the configuration of the contactors —> one contactor has the contacts shorted across each other ( this set of contacts are not across the mains the other contactors are across the mains ) then you have the normal reversing configuration I am not sure what the other contactor how it is configured and I am not in front of right now

When I go back next weekend I will take some pictures of the wiring diagram that shows how it is wired but like I said the timer module is not in wiring diagram I will trace it out because I want to know how this configuration actually works because like said earlier I have not seen this configuration before

I have heard of the star configuration before but I do think I have actually seen one and how it is wired

[stj]

the timer is strange unless it's related to a cooling system or the cutting fluid pump - maybe it keeps something running for a while after the main motor stops.

[redwire]

Coolant residue is conductive. The slime is terrible for electrical/electronics. Never mind the operators breathing the stuff.

I got screwed troubleshooting CNC machines/lathes, a digital multimeter gives ghost voltage readings.
At mains voltages, even a 100MEG or pF's slime resistance will cause voltage readings due to leakage current or maybe it's the capacitance I did not check that.

You must have a LowZ voltage mode or use a VOM to avoid going on a goose chase.

[sam_sam_sam]

You must have a LowZ voltage mode or use a VOM to avoid going on a goose chase.

”You must have a LowZ voltage mode” what is this device?

I am aware of ghost voltages reading and ghost meager reading as well but when you have blowing fuses in the control circuit you need to figure out what is shorting out even if you have to apply voltage through an incandescent light to get to bottom of the issue with it blowing fuses first then you can go beyond this issue and concentrate on what other issues that have been caused by the coolant mister has caused but to complicate the issue it has been very humid the several weeks so this is going to make more complicated the process to remedy the issue

I have ran into this before and it is not easy to deal with because you can not just use degreaser and be done with it you might be able use a heater to dry out the control panel enclosure enough to figure out what has been leaking the voltage to cause the control circuit fuse to keep blowing after about 30 seconds being power on to the contactors

This is where an incandescent light bulb is your friend I found a short in a dryer that we have at work that the other maintenance personal could not figure out what the problem was ( they kept putting fuses in it to try to figure out what was causing the issue )

I was asked to figure out what was causing this issue about 30 minutes later I figured out what the issue was and repair the dryer the use of a multi meter would not help you in this situation ( this is where an incandescent light bulb is your friend ) because it was the gas controller that was shorting out when power was applied to it but the multi meter did confirm that the gas controller was the issue with it blowing fuses

I also got tripped up working on a CNC drilling machine/plasma/gas torch plate cutting machine that ever time the humidity was above 85% in the morning the machine would error out on the measurement sensor plasma cutter the torch spark ignitor circuit would not function correctly either the solution was to use a dehumidifier and put it in controller cabinet for a couple of hours and then the machine would work correctly for a couple of hour if the humidity did not go back to normal

Another issue is that the main control relay will not stay in gauged it is chatting which means that there is an issue with the holding circuit as well as it not latching this relay to stay on bypass the push button and wired it directly to the holding circuit and then it would still chatter and blow the fuse unfortunately I did not have my incandescent light bulb jig setup with me that day and I called it a day after this situation

[stj]

low-z mode is a setting on some meters that adds a load resistor to get rid of ghost readings.

[sam_sam_sam]

low-z mode is a setting on some meters that adds a load resistor to get rid of ghost readings.

Thanks for the information

[sam_sam_sam]

A partial determination of the issue with blowing fuses diagnosis was made using an incandescent light bulbs instead of the fuses
One of the main contactors coil was internally shorted 110 volt ac coil 4 ohms this is not a misprint the working ones has a resistance of 24 ohms first issue was this the second issue is with the control contactor a set of contacts of a 4 pole contactor are bad still can not get the the motor contactors to operate because of the controlled contacators not being turned on by the control contactor

The evaluation was not completed for the main motor of the lathe as of today because of the holidays hopefully by next weekend we have more information on the motor and if it has any issues ( one note the person that has the motor shop made the comment that he has never seen a motor setup like this one is )

Both items have been ordered and waiting for parts to come in for further inspection and determination if anything else is wrong with the control circuit

I personally have never seen a contactor coil short out internally like this one the majority of the time they short out and are an open circuit not like this one ( one note I took apart the contactor that has the shorted coil and you can see that it got extremely overheated and this is the burning smell that I smelled the first time I started working on it and who knows how many fuses was put in there before I started working on it )

[sam_sam_sam]

Update on main motor he says that the some of the motor winding are shorting between legs

The person that I am doing this project for has decided to go with a VFD drive so I will be doing some re-writing for the use of a VFD drive

More to come later

[sam_sam_sam]

Update I have the controls on the lathe the person I doing this for has to find a motor rewind shop that can do this motor because of its configuration is the issue now about getting this motor rework done

Here is a picture of the control box the control relay is in lower left hand corner the big contactor on bottom left hand side contactor number three in the wiring diagram which is one you see with the jumper wires on the top of the contactor which figure out is the brake function for the lathe because does not turn on unless it is neutral now if you forward or reverse the four contactor turns on and one of the top contactors also turns on as well

One note you will notice that the motor leads have been disconnected from the wire terminal block as we as the coolant mister pump because there is an issue with both motors but there is also an issue with main motor wiring as we land needs to be replaced as well but there is also person I doing this for wanted me to get the controls working first now he going to get the other things that are needed to complete this job

This person has finished my cutting out of the opening that I need for my computer rail rack battery testing machine enclosure that I asked him to for exchange for my services repairing his lathe

Now my fun begins with installing the controller boards the front plate of the battery testing machine and the battery cells metering module that I am also using for this project and the switching power supplies power switches and other miscellaneous things that also need to be installed

This person did a fantastic job on cutting out the opening that were needed and put the holes for battery cells volt meter module stand offs as well which will make it easier to install this is the third picture in this post

[stj]

if your going to use a vfd, wouldnt it be cheaper to grab a used 3phase motor from somewhere?
i used to see them all the time in abandoned factories and garages - probably not worth enough for asset strippers to remove from old equipment for auction.

[sam_sam_sam]

if your going to use a vfd, wouldnt it be cheaper to grab a used 3phase motor from somewhere?
i used to see them all the time in abandoned factories and garages - probably not worth enough for asset strippers to remove from old equipment for auction.

The person has decided to try to find some place that can rewind it first and if a place can not be found then we might have to go down this route but there are several rewind shops here in Jacksonville Florida that he going to try first because to put in a VFD drive it would have to partially rewired for it to work with the VFD for the controls of the lathe and would have to decide whether or not to have the forward and reverse done with contactors like it is done now or have the VFD drive do this function one of the contactors would not be necessary if it was setup for a VFD drive

One note 10 hp motors are not cheap neither is a 10 hp VFD drive either unfortunately ( Heavy duty ones )

One other note buying use electric motor of this size is hit and miss to weather or not you are getting a working motor or not and for get about getting a used VFD drive on eBay this would be really hit and miss endeavor to under take because these motors and VFD drive are very heavy to begin with the shipping cost on both of these items would kill your budget

Shipping cost have drastically increased over the last year for items less than 5 pounds

Yes there use to be places that you can buy used machine equipment ( in the past I been on some of these websites but have not done this in years so I have not kept up with what is available now ) but you have to have time to go there to see what you are buying first before you bid on it so you know what you are going to get ( I am not sure there is a place in Jacksonville Florida that has this available it most of time up north that has this type of place where you could find something like this )

[stj]

if you plan on buying a vfd driver then get one with a digital interface.
it will give an option in the future to automate it to create a cnc
you can get kits to motorise the controls for the cutter so it can all be done by a pc or raspberry pie!

[sam_sam_sam]

if you plan on buying a vfd driver then get one with a digital interface.
it will give an option in the future to automate it to create a cnc
you can get kits to motorise the controls for the cutter so it can all be done by a pc or raspberry pie!

Thanks for the suggestion and information

[sam_sam_sam]

I watched a couple of videos about 12 wire lead motors last night because I had some lingering issues about how these contactors are suppose to connect the motor leads in what configuration and what type of configuration is what and how are they suppose to be used and how it is suppose to work ( because they had a demo control circuit wired up and demonstrated on the two videos I watched ) —————> long pause————-> then an aha moment and went with what I saw and with what was happening with this lathe was not what I saw on the YouTube videos that I watched of how it is suppose to work the “Y” is used to soft start the motor until it reaches a certain speed point then it switches to the delta configuration for full power

So I have come to the conclusion that what I was seeing was the “Y” contactor turns on when you push the power on control relay but the main motor contactor does not turn on until you make a decision of weather or not use forward or reverse so apparently the timer control module has some type of issue but the controller module that I saw on the two YouTube videos I realized that they actually make a timer module that is actually made for switching from “Y” start configuration to the delta configuration and according to the two YouTube videos I watched it should take about 10 seconds or less depending on your configuration for it to complete this control function

Like I mentioned earlier that I have never seen this configuration but I wanted to understand the reasoning behind setting up this lathe in this configuration and why and how it suppose to work ( I try not to be just a part changer for what part I think are bad and have I really fixed the issue or is there more to this issue than meets the eye ( the motor being shorted between winding this why even though I have all the contactors working are they working correctly the way they are suppose to work and when they are suppose to be turned on and for how long ( this was still bothering me about how did the winding get shorted in the first place )