Micro mill desperate help for a novice please

[///]

Mine looks the same and has a field winding.

Interesting. I've just inspected my two Sieg branded machines and they're both definitely permanent magnet motors.

 

[BaronJ]

Hi Baron
Permag? I'll take your word for it. Mine looks the same and has a field winding.

Armature windings are difficult because they are normally buried on one side. That's why I only suggested it for the field winding.

Some of these motors do have field windings and I agree it is not always obvious without taking the end plate off. I remember years ago coming across a permag motor for the first time. It was fitted to a Philips washing machine. At that time they were so new that in order to get a new one you had to return the old one, and you couldn't take them apart either. There were four long pins running the full length of the casing, dome heads on one end and a funny squeezed crimp on the other.

The excuse or reason given for this construction was that if the armature was removed it would damage the magnets by reducing their strength.

As far as armatures go I've rewound a few ! It's not a job that I relish even with preformed coils and pre-made replacement commutators.

 

[Wizard69]

Hi Baron
Permag? I'll take your word for it. Mine looks the same and has a field winding.

Armature windings are difficult because they are normally buried on one side. That's why I only suggested it for the field winding.

I can't say for sure but I was under the impression that the motors on these machines are in fact universal motors. The motor is run off a DC controller. Of course it is possible that the motor wound stator DC motor. However with the motors stamped for both AC and DC that is unlikely.

 

[///]

However with the motors stamped for both AC and DC that is unlikely.

It isn't though, one sticker is for the individual motor and only mentions DC-230V on it, the other label is for the mill as a unit.

 

[BaronJ]

I can't say for sure but I was under the impression that the motors on these machines are in fact universal motors. The motor is run off a DC controller.

"Of course it is possible that the motor wound stator DC motor."

I'm not sure what you mean here ?

However with the motors stamped for both AC and DC that is unlikely.

One of the major problems with universal motors is that without some form of loading they will theoretically run away with themselves at very high speeds. Indeed I've seen a number of motors that have destroyed themselves because the unloaded speed has caused the commutator to loose segments.

A permag motor will only run on DC because of the permanent magnet field, and the speed is controlled by the voltage that is applied to the armature and ultimately by the amount of current that can be passed through the windings before they burn out.

Because of the inductance of the armature windings you can apply a fixed DC voltage, but if you rapidly switch this voltage on and off, you can control the average voltage seen by the motor and thus it's speed. This is basically what the controller is doing when you turn the speed control knob.

 

[zebra7493]

I came across this page which may be useful for anyone having controller troubles with the mills of lathes
http://www.littlemachineshop.com/Reference/DriveTroubleshooting.pdf

 

[pmdevlin]

progress so far, I have the motor back in my possession. Whilst the guy who was the so called expert agreed he had misread the label and tested on 110v ac, when there was another sticker saying 230dc on it, he wanted to test again (why he didn't do this 3 weeks ago baffles me, it would have saved all these problems!) saying if he was replacing the motor he wanted to be sure it was infact burnt out. He had run it for seconds, it had smoked. So, after testing on 60v dc for a period of time, the motor showed no signs of failure, it was on a variable supply, it ran on tick over, and then up to 60v dc continuously, so I think it seems ok. I have taken it apart, no signs of damage, no smell of death, so hopefully its ok when it runs again on the machine.

The control board has been sent to someone who graciously offered to repair (on another forum, uk based) He has the test equipment, and the knowledge. All things are pointing to the pot as the motor was trying to run once the control was turned on, even with the pot off, or a reparable component on the board, it has been explained, but I was totally lost with the explanation.

Thanks to all who have so far contributed, I will report back when I have the info about the controller.

 

[pmdevlin]

controller came back, I was so grateful for the help, a mosfet was tested to be faulty and repaired. The controller was wired to a 60w bulb, and the pot altered the brightness, which was not happening before that repair, so all looked good. Connected all up last night, after a min or two, all was well, with variable speed, then a flash from the motor, and the original symptoms are back, blowing fuses, and the pot having no input, as soon as the controller is turned on, motor wants to run with pot turned off, so its back to square 1!
I did the bulb test again, its on real bright and pot does not alter brightness. I've ordered a couple of new mosfets, as I have been instructed how to change them, I'm thinking of getting a new pot incase that is faulty, just trying to take the cheapest way here!

 

[Wizard69]

controller came back, I was so grateful for the help, a mosfet was tested to be faulty and repaired. The controller was wired to a 60w bulb, and the pot altered the brightness, which was not happening before that repair, so all looked good. Connected all up last night, after a min or two, all was well, with variable speed, then a flash from the motor, and the original symptoms are back, blowing fuses, and the pot having no input, as soon as the controller is turned on, motor wants to run with pot turned off, so its back to square 1!
I did the bulb test again, its on real bright and pot does not alter brightness. I've ordered a couple of new mosfets, as I have been instructed how to change them, I'm thinking of getting a new pot incase that is faulty, just trying to take the cheapest way here!

I really think you need a new motor. These Chinese motors, at least a good portion of them, are known to be unreliable. The fact that you saw a flash from the motor just seals the deal here, the motor is shorting. If it was me I'd invest in a good American made motor.

 

[pmdevlin]

looks like I will have to bite the bullet ion the very expensive motor then

boohoo!

 

[DJP]

It does look like a short in the motor is causing the FET failure. Before you buy a new motor get yourself a really big diode at an electronic surplus store and rectify the line voltage to make DC for the motor. See if it will run well enough for your needs. The diodes that I am thinking of come with thick braided wire leads and threaded studs for mounting in a heat sink. They are probably rated at 300 amps and placing a few of them in series will reduce the voltage and speed of the motor. You won't have variable speed control but you may be able to use the machine.

Once the motor short becomes a serious recurring issue then buy a new motor.

My motor control board is acting strangely and I'm thinking of a simple and more robust solution as well. You might as well go first.

 

[pmdevlin]

I fitted the new fet tonight, but, didn't realise that the screw holding the heatsink had to line up, so then had to remove the new fet and fit the spare. Whilst getting it off, I "could" have damaged the board, really don't know, because when I powered it up with a test light, all was well for a few minutes, then one leg of the fet sparked, and that was the end of that .
I possibley (likely) need a motor, and now need a board, its really not worth it, too expensive, and the board is out of stock anyway at the only place with one, arc euro trade.(uk)
I have to call it a day, and will consider selling the machine for parts/spares. Buying both parts is the only way I will be sure that its fixed, luckily the board was not fitted back inside the case when I did the test, otherwise I would not have seen the fet sparking.
I need to pack it up, and think long and hard, almost £200 to get it working again, I bet the machine isn't worth much mort than that.
Many thanks to all that contributed
Paul

 

[DJP]

It looks to me as if you have proven that the motor is OK if the controller failed while powering a lamp. The basics of the machine are still there and all that you need is a 60VDC source of power. Check out surplus electronics stores or perhaps a router speed control will work.

In my opinion the controller for the mini mill only has value as a quick stop circuit to save the plastic gears. Once you give that up there are options to making it a usable machine. My controller board has strange symptoms and I'm waiting for a total failure to change it to a simpler design.

You shouldn't give up just yet.

 

[pmdevlin]

Thanks DJP for the time taken for previous post, although I can tell you wrote it in simple terms, unfortunately it was way beyond my understanding. With electronics, its turn it on, and expect it to work, although I have learnt a lot in this thread, and just found out you can damage a fet just by handling it wrong.

So, after sleeping on it, I decided to ring arc euro trade in UK, they are the only people who are showing original spares, and the machine originated from them a few years back, but not by me, it was my pals, and its a nice machine with some great accessories, long table, and spare short table, digital readout, rotary table, two vices, belt drive, so if broken for parts should fetch a few quid.

After discussing why I was chasing returned machines and second hand stuff, they suggested returning motor and controller, they would test in situ on machines, and report back. Its a fair charge for services, and at least I will confidently know if I need one, or both components, before I go spending money. The motor will now be tested at the correct voltage and speed

DJP maybe you are right, I don't need reverse as I don't use it, and its already belt driven, so there must be a cheaper motor alternative somewhere