Replacement Lathe Motor

[alan wParticipant @alanw]

We have a DB8VS Chinese lathe from chester. It's been working OK for 7 yaers, but recently it blew a fuse, then another then wouldn't come on. We sent the controller board off for inspection. Chester told us it was blown and sent us another for £120. We fitted it, and the fuse blew again – and perhaps the board – don't know yet.

A local engineering firm tested our motor and tell us a winding is shorted and want £300+ to rewind it.

Chester cannot yet tell us how much a new motor will be nor when we might receive one. Since they took three weeks to get around to looking at the controller board, we're not holding our breath on a rapid response on this.

The motor is 220V DC, 750 Watts. The rating plate says it's type is ZYT95-02T1. I cannot find it anywhere online.

If anyone has any useful comments, I would be very grateful to hear them. Do you have a spare you can sell us for a pittance? Can you rewind ours for a Kit-Kat? Do you know where we can get a replacement or of other names this motor goes by, or which company ZYT is? Or maybe alternative motors which will do the job?

What other options do we have?

Thanks for your time.

[alan wParticipant @alanw]

What options remain?

[JourneymanParticipant @journeyman]

Alan, see this current thread where Dusty is replacing the motor on his WM250, similar to yours, with a VFD and 3-Phase motor. For another possibility.

John

[John RuddParticipant @johnrudd16576]

Alan,

I sent you a private message, check your inbox at rhe top of the screen

[John RuddParticipant @johnrudd16576]

 

 

Without doubt, a 3 ph conversion is the most efficient way of spending your hard earned….

The motors fitted to these machines are of the permanent magnet type, cheap to make ( no field coils to wind, etc…)

And they are easy to control speed of….Sadly when they become faulty ( shorted turns….due to heat..) they take out the speed controller too. I'll bet if you checked the fuses, ( plug or on the machine) they are greater than 5amps in rating…..which is why the controllers go pop….

Ok, none of this helps you get going again…..but does illustrate why things might go bang..

Best way forward, a new or s/h 3ph motor and inverter….Do becareful, to maintain something like the original spindle speeds you need a 2 pole motor not the standard 4 pole offering running at 1400 rpm. The original motor would have had a shaft speed of around 4500rpm, geared down to get you the 50-2000…..Rating wise, I'd go for a 3/4hp motor. Some might say it is less powerful than  the original, Chester's specs say it is 750watts, but what is that ? ( no pun intended…) inout power? Debatable….any way..

As for your speed controller, that can be repaired…probably blown thyristors…( I have spares and spare boards too).

Have the controller repaired, sell it on and fund the inverter from the proceeds….

Should you decide on reading the other thread referred to, get yourself a cup of coffee…..its like War n Peace but with a happy ending….

Edited By John Rudd on 04/04/2017 16:31:51

[MikelkieParticipant @mikelkie]

Go for John Rudd's suggestion!

[John RuddParticipant @johnrudd16576]

Ok,

Here is an inverter that I would recommend…..

http://www.ebay.co.uk/itm/0-75kw-1-HP-Single-Phase-In-Three-Phase-Out-Motor-Inverter-AC-Drive-NEW-/221180221237?hash=item337f5e5735:g:d1QAAOSwGIRXbmIV

I have two of them myself on my own machines and I'm sure there's more than 1 forum member that has one or more….

[not done it yetParticipant @notdoneityet]

Another project by someone who had trouble with a mini lathe motor, with several options carried out over a period, which possibly might be worth reading is this one:

http://www.model-engineer.co.uk/news/article/3-phase-conversion-and-other-alternative-methods-of-powering-a-mini-lathe/18752

The only comment I made about it was that I would investigate using the dead motor as an auxiliary shaft as a possibility for housing almost any frame size under/behind the machine.

[alan wParticipant @alanw]

Bang. Just like that – instant help. Heh. Chester – if you're watching – see that? These people are more helpful for free than you people are at £1,200 a pop.

Gents, thank you all greatly for your interest, ideas and advice. John Rudd – thank you especially for your kind email. I will meet with my brother today and discuss what you have all said, and decide on our way forward and John – I'll get back to your email after that.

Best Wishes,

Chris

[John RuddParticipant @johnrudd16576]

Posted by alan w on 05/04/2017 10:15:29:

Bang. Just like that – instant help. Heh. Chester – if you're watching – see that? These people are more helpful for free than you people are at £1,200 a pop.

Gents, thank you all greatly for your interest, ideas and advice. John Rudd – thank you especially for your kind email. I will meet with my brother today and discuss what you have all said, and decide on our way forward and John – I'll get back to your email after that.

Best Wishes,

Chris

Off to a good start there Chris/Alan…..nothing like a bit of vendor bashing first thing…..true but true….

Whatever course of action you take, I wish you well on recovering your lathe, and if you need any more assistance with motor selection/ vfd choice then do ask. There's a multitude of folk here willing to help. Ok they may not be at the end of a fone ( well I've been known to assist this way…) but an answer will be forthcoming….

[alan wParticipant @alanw]

OK well, surprisingly, Chester got back to me this morning to say they have a direct replacement DC motor for shipping today and arrival tomorrow. I have heard what people have said about superior AC motors, but because we have clients waiting on projects, this is our fastest easiest route back to production, so it's what we'll do. Contrast this to yesterday when they didn't know anything.

We may take the upgrade route when things are less hectic and funds allow.

John, as we may have blown even the new controller board, any guidance on how to fix it would be welcome. I have an electronics background, and oscilloscope, multi-meter and soldering iron, but I have no knowledge of or experience with these boards. I assume they're PWM controllers? Even if the new one is OK it would be nice to fix the old one and maybe sell it on to recover some of our £120 outlay. I could also clobber Chester for not offering to repair it at a far lower price.

BTW, I am Chris, Alan, the lathe owner and my older brother is Alan, the subscriber to model engineering. As his underling (I'm only 57) he's delegated the clerical drudgery to me.

Also tea making.

[John RuddParticipant @johnrudd16576]

Chris,

The boards use a full wave scr/ diode bridge arrangement with phase angle triggering with zero crosspoint detection.

If the fuse blew when the new board was fitted, it may have survived.

Action plan:

Fit new motor, but dont wire it up yet.

Check the new board by dvm checks on Ohms, between the two L connections on the board, across the A+ and A- connections, then each L to A+ and A- . This should cold check the scr/diodes for shorts. ( you can also check the old board out too, assuming chester have returned it to you!)

Fit a new fuse appropriately rated. Now connect a domestic light bulb to the A+ and A- connections on the board or to where ever the motor was connected. Apply mains power and adjusting the speed pot, does the bulb brightness vary with the speed pot? If all is good, disconnect and replace the motor wiring.

You should now be good to go.

Repairing the boards requires a delicate touch, components although are thru hole, the holes are plated thru' use plenty of flux to remove the solder. If you need to replace the thyristors, make sure you get the right ones, the originals have an isolated tab….most dont….result? Bang when you apply power….( I can supply new replacements…) When unstalling bew thyristors/diodes, bend the leads appropriately, use long nose pliers to prevent straining at the entry point of the device body…

After completion of the repair, clean the area on the board with flux remover ( I use celly thinners)

Ensure you fit the correct value horsepower resistor, otherwise the controller wont work properly….

Keep us posted with progress..and good luck with the repairs.

 

Edited By John Rudd on 05/04/2017 13:54:49

[alan wParticipant @alanw]

John, many thanks for all of that. You're a kind a patient man.

I'll give it a go. I may come back to haunt you – no good deed, after all, should go un-punished.

Thanks again,

Chris

[John RuddParticipant @johnrudd16576]

Posted by alan w on 06/04/2017 09:54:29:

John, many thanks for all of that. You're a kind a patient man.

Yes it has been said….

I'll give it a go. I may come back to haunt you – no good deed, after all, should go un-punished.

Well it happens all the time…..

Thanks again,

Chris

No problem….

[alan wParticipant @alanw]

Hello again. I'll post here in case it's helpful to others.

John – we followed your procedure. The resistance on the A+ to A- (armature) leads on both the old and new boards is about 132 ohms. We connected an incandescent mains bulb as suggested to the new controller board where the motor would be. With the controller speed set to the slowest, the bulb was at full illumination.

That's not what we'd expect, but – what to do now? We bit the bullet and connected the new motor. With the controller still set to the slowest speed, the motor ran very fast for a very short time then the fuse blew.

Hopefully, the motor didn't have enough time to overhead and break down the lacquer on a winding as before.

So it looks like both boards are faulty. Wonderful.

Your repair description looks like special knowledge is a real benefit, so – if the offer is still available – we'd like to ask you to fix one of them for us. We'll happily pay for your time and of course the postage. If the offer IS still on, please message me your postal address and payment details. If not, I'll do my best with the instructions you've already kindly provided.

Many thanks,
Chris

[John RuddParticipant @johnrudd16576]

Chris,

I guess you realise now, you should not have connected the new motor up…..The thyristors/diodes are shorted hence the reading and you have applied effectively ac to the motor….result fuse blows…

Ok, the fuse has blown, hopefully, the motor is ok. You could try the motor on a bench power supply…anything up to about 60-70volts if you can or else connect a full wave bridge rectifier to a variac and increase the voltage to around 60-70dc….the motor should run nice and smoothly…no sparking from the comm( or very little as the brushes bed in)

I'll turn the controller around as soon as I receive it….assuming it just needs thyristors……

Address pm'd to you…

[alan wParticipant @alanw]

John,

I took the 133 Ohms reading to be a sign that all was well with the thyristors, not that they were faulty. I was wrong on that.

I reasoned that the worse the controller can do to a motor is dump full WPM into it. For the short time I had it connected I didn't think it would do any harm. I was wrong on that too – not realising it might dump AC.

Clearly I should have stuck to the experienced advice you offered us. I'm afraid urgent desperation got the better of us.

Luckily, it doesn't seem to have done the motor in. At least it turns evenly on a 12v battery charger.

Meanwhile, the motor Chester sent us – though working – is clearly second-hand and it squeaks. I've taken that up with Chester.

I will email you about the controller board repair John.

Thanks,

Chris

[Neil WyattModerator @neilwyatt]

The poor motor should run (slowly) on a 12V battery (e.g. car battery) if its still OK.

Neil

[JonParticipant @jon]

They may have removed it from a new dead machine or 6 months delivery. Seen the shipping containers round the back stacked three high full of defunct machines for whatever reason.

[alan wParticipant @alanw]

Final update(?):

Neil, the old, blown, motor, also turned slowly on a 12V charger which really convinced us it HAD to be OK. But if you pinched the shaft whilst it was turning though, you'd feel it kick once a revolutions. One of the windings was shorted out. The new motor doesn't do this.

POST MORTEM:

Almost certainly, I caused the problem whilst spending a morning taking 2mm cuts on a large piece of stainless 303. I had a lot of material to remove, and everything seemed happy – no bad noises, vibrations or poor finishes, so I pressed on until, apparently, the motor got so hot the windings' lacquer presumably melted, then shorted, That blew the controller. My understanding is that this problem is exactly why you all prefer AC motors.

Chester advised we return the controller to base. More than two weeks later, they told us is was blown and sold us a new one which we fitted. However, because the motor was blown, fitting the new board also blew that, though we didn't know it at the time.

So we bought a new motor from Chester. Actually, it was an old motor – grubby, rusty in parts, chafed labels and obviously-used wire connectors. Also it squeaked when on the battery charger. It didn't work on the machine because the controller was now blown.

I complained to Chester about faulty advice and the squeaky second-hand motor, being £200 down, nearly a month older and no working lathe. I have to say Tony in sales, did a fantastic job. THE NEXT DAY we received another motor and another new controller board. I fitted them and they work. Chester will pick up the faulty board and the squeaky second hand motor free of charge. So – all ended well, but we're about a month down, and no work on client projects. Now my car's failed it's MOT so I'll be bussing to the workshop when I can.

LESSONS LEARNED:

1. The 12V charger test does not guarantee a good motor.

2. Fittng our bad motor blew its controller in an uneventful instant.

3. Do John Rudd's bulb test to verify a controller board

4. Working this lathe hard will burn out the motor with no warning

LOOKING FORWARD, I think I might fit a fan in the motor compartment to help keep it cool and a temperature sensor with a display up on the lathe where I can see it. Has anyone done this or is there a better way?

Chris

[John RuddParticipant @johnrudd16576]

A number of folk have fitted supplementary fans to their dc mill motors to counter the excess temperatures.

Fitting a temperature sensor to the body is probably a good idea, but bear in mind the thermal mass of it compared to that of the windings…. The windings will be hotter than than the motor casing, so try and keep the temperature down… Or Phut…..

[Jim NicParticipant @jimnic]

Alan w – thank you for posting your story and the conclusions. I recently burnt out the motor on my similar Warco lathe by working what is a light hobby machine far too hard to the point of overheating it to failure. Luckily in my case the controller survived and Warco were able to supply me with a replacement motor from stock. Let this be a lesson to all of us with lightweight hobby machines.

John Rudd – as an interested spectator to this tale may I take this opportunity to offer my thanks for your input here and in other threads which while helping with a particular problem add to my understanding of my machines workings.

Jim

[alan wParticipant @alanw]

Thanks John. I think we'll do that.

[Brian OldfordParticipant @brianoldford70365]

Posted by John Rudd on 11/04/2017 08:56:50:

A number of folk have fitted supplementary fans to their dc mill motors to counter the excess temperatures.

Fitting a temperature sensor to the body is probably a good idea, but bear in mind the thermal mass of it compared to that of the windings…. The windings will be hotter than than the motor casing, so try and keep the temperature down… Or Phut…..

If you use a three phase motor with VFD the addition of a fan is also a good idea if you use it at reduced speeds for extended periods.

[Author]

Posts