X3 Milling machine Motor Overheating and tripping house RCD

[raynerd]

  Although I've been pottering and tinkering, I'm finally stuck into a project after nearly 2 years out due to house moves, work and kids. Got a bit of time, a lot of enthusiasm and finally building something worth showing you guys.

Went to my mill yesterday and faced off a piece of aluminium. Turned on the machine and took a few light cuts and pop, the electricity went with the house RCD tripping. Turning it all back on, nothing had broke or popped and I carried on suspicious but without an issue.

I've gone into my workshop tonight to cut some gears, turned on my mill and pop - mill immediately tripped out the electrics again. Turned it all off and I got back into it...very suspicious and keeping an eye out. Ran the machine for a minute or 3, took a cut again , then stopped and then pop, out it went. Obviously not turning it on again... But the motor is scorching hot so I can only presume it is a motor issue. The motor was far too hot to touch,

I'm not a motor expert and I'd appreciate anyone's advice. After a few years out, I've already got a scrap bin full of dead parts so this has just made me feel like the engineering gods are against me. I am determine to fix it if anyone could give me some advice as to where to look short of buying a new motor :-(

All the best

Chris

[raynerd]

...just doing some googling and as it is the x3 with brushed motor, could it be the brushes? Would this cause it to over heat and trip the RCD?

[Sid_Vicious]

I'm not an expert but I would opened it up (the motor) and looked at the brushes. Once in a motor I had it was only dust that made it difficult for the brushes to move so a good cleanup and they moved freely again and the motor worked again.  It's worth a try.

[Kjelle]

If the RCD trips, thehre is a leak between phase ande ground.. Check all connections, from the outlet on. It sounds like something isn't quite there, either a short in the motor, or a loose connection...

Kjelle

[lordedmond]

Does it have a mains filter for high order harmonics ( small box befor the main board )

These have delta cap in them eg two caps one from live , one from neutral the free end go to earth they can be the cause of the RCd trip

Note the mill will run without this but I have not said this because it can cause troubles with other household stuf

Motor hot how hot ? Can you keep your hand on it ?
Maybe the mill is a birth tight due to the cold weather

As a side note again I have not said this my Myford tripped the RCd from new one switch on and switch off due to the filter so dump the RCd they are overrated IMHO

You can get a RCd with a higher trip setting to get round the problem then it defeats the safety of the domestic RCd

As a old school sparks I believe in correctly fused/MCB and a good earth ( tested and proved) and a good equiptential Earth bond in the workshop and house

Stuart

The above is my view and not recommendations for others to follow

[raynerd]

Stuart - thanks for the advice.

The motor is REALLY hot. It was only running for about 2/3 minutes on a very slow speed before it tripped and it is so hot you can not put your hand on it. This surely isn`t normal. I can`t smell any burning but it can`t be far off.

I`m not too sure with regards to a mains filter - there are three fused trip switches in my garage which are NOT blowing and it is blowing the house main trip switch and killing all the house electricity (it is not even tripping the "garage" fuse on the main board).


Sid & Kjelle - thanks also for your input. The googling I did last night also suggested a leak to ground with others having a similar issue. I`ve only a basic understanding of the DC motor as I`ve never opened one. What exactly am I looking for and is there any way to test the motor is leaking to Earth? Could the brushes be the issue?

I know there are lots of posts about the boards going dead and killing the machine - I presume if the board was dead my motor would not run at all or could it still be a board issue?


I`ve not much experience with motors and I`ve come on here for help but the more I think about how stupidly hot it was, the more I can`t help think that that is the issue. Could a leaky motor also cause the heat issue.

Any more advice as to what I could do tonight when I get home to test and check everything would be much appreciated!

Chris

[lordedmond]

Chris
The filter if present will be in the mills elect box small shiny thing

Small earh leaks will not trip/blow a MCB/fuse but a small leak will do the RCd


If it's that hot and the magic smoke is still in , then you need to isolate the problem

Is this a old style one you can see the brush holders on the motor , it will only have two wires going to the motor or is it a new style one with a brushless DC motor, these have more than two wires because of the feed back Hall effect devices ,a quick squint at ark's site may help

Slip off the belt and run it off load see how it goes it should spin very freely

If you have a brushed motor you can ( turn off and unplug) take th out for inspection , but do not remove the end cap unless you mark its position very carfully as its rotation position is critical for the brush magnet relationship

If it's a brushless one you can do the same off load test but I have no knowledge of these ( I know how it works but not had my mitts on the insides of one

As you know diagnostic of the web is difficult but the off load test should split the problem from electrical/mechanical source

A note I had a early X3 not from ark that got hot and released the magic smoke and that was a duff motor

Stuart

[raynerd]

It is a brushed motor.

I`m sorry for such a basic question but what exactly can I 'inspect' on the motor? I.e would would be your process?

So I can easily remove the belt and pull the motor assembly out of position. I can remove the bushes and check those - I`ve never actually checked brushes before so do they wear down. A new one is apparently 6x12x18 so I guess if it is worn it could be an issue? If the brushes look good - then what should I do. I`ve never removed the end cap so do I mark it position on the outside in relation to the lower main body section?

Sorry - I`d just rather know what I`m looking for. It hasn`t smoked yet so I`m guess it can still be rescued or is the best bet to just replace the entire motor?


EDIT - I may be totally wrong but I can`t help thinking it all tripped when I touch the machine itself! It was running OK when I was only touching the hand wheels - it could be my imagination. I`ll try and assess tonight!

[lordedmond]

Chris

You have me worried

It tripled the RCd when I touched it .
Ok let's go though it one step at a time

Make sure the earth lead ( machine to 13 a plug ) is sound test with meter by thi I mean test from the metal parts of the mill to the earth pin .

If that's ok the you need to check or have checked the earth conductor in the socket , back though to the house consumer unit , because it sounds to me that it's not correct .


The above is very important and needs to be done

Now on to the brushes you remove the plastic cap and the brush should just pull out nicely , quite free as you know the new size you can make an assessment on that , they should not be chipped but look like they fit the commutator nicely

Chris take care

Your situation is why I am of the old school with bonding , I have a 10 MM. earth conductor connected to all the machines independent from the power cables an this is bonded back to a 2 metre earth rod that is also bonded back to the consumer unit in the workshop , this is then bonded back to the house consumer unit and then to another earth rod

As I had acces to the test gear to prove all this I know it's ok the reason for all this is to make sure that all the metal you can touch with both hands ( eg across your heart ) is at the same potitential

Run the motor off load and see what happens but until you are sure about the earthing put som marigolds on 

Stuart

Chris

If you do not have one of these I recommend yo get one they are not expensive

http://www.amazon.co.uk/13-Amp-Plug-Socket-Tester/dp/B004BLPIBK

Other site do have them as well well worth a check round now and then for peace of mind

[John Rudd]

Chris,
You can disconnect the motor altogether from the controller and in its place wire a 100watt domestic light bulb....if the rcd/breaker stops tripping, my money is on a leaky winding on the motor to earth.
This can be checked with a megger/insulation tester, ( but I doubt you will own one... )
A new motor I'm afraid....

Stuarts advice on wearing rubbers is good, you could also stand on a rubber mat too if you have...

[lordedmond]

Thanks John

Hoping you would drop by and help out

I was concerned when Chris said it tripped when he touched the machine.

yes a leaky armature will do it bad brush holder to earth would not do it because if memory cell is OK the end bell were plastic , or I would suspect a carbon build up


These little doc jobs are a wee bit small for me after working on 75hp jobs during the year I spent in the winding dept

Stuart

[John Rudd]

Thanks John

Hoping you would drop by and help out

I was concerned when Chris said it tripped when he touched the machine.

yes a leaky armature will do it bad brush holder to earth would not do it because if memory cell is OK the end bell were plastic , or I would suspect a carbon build up


These little doc jobs are a wee bit small for me after working on 75hp jobs during the year I spent in the winding dept

Stuart

Not a problem Stuart, but I'm far from your level of expertise.....

[raynerd]

OK, motor removed, turns freely without the belt and with it on. Brushes are fine - making good contact with plenty left - not looking dirty.

I have time later when the kids are in bed but does it look like it is time for a new motor?

£160 from arc eurotrade - two lots of xmas presents and both birthdays in the same month - no chance I can get a motor! If I remove the end cap will that show me anything more...

[lordedmond]

Not really without test gear . If you do mark it if you get it back 1 degree out the motor will not run correctly .

before you shell out have you done the test John recommended it's important to isolate the problem .

Have you run the motor off the machine but still connected to the controller . Note if you mix up the two wires the motor will only run the wrong way no other problem

As a side note I did read on this forum or MEM that ARK will test the motor and controller for you for a small fee worth ringing to see how the ground lies

Stuart

[John Rudd]

If I remove the end cap will that show me anything more...

A long shot, there might be capacitors, one each connected to each brush and earth( casing )....
Otherwise a photo mught help us....

Chris,
Just read Stuarts post re testing, I can test the controller and motor for the postage costs...but you need to do the light bulb test first....

[Bluechip]

It should motor slowly on  12v battery, may have to give it a bit of help to start it.
If it runs but often stops in the same place(s) you have a dead winding(s). Motor shot!

Does it smell hot shellaccy ?? Unmistakable stink!

What does the commutator look like? Should be an even polished brown colour.

Gaps between commutator segments? No blast marks on edges of copper bars.

Dave

[lordedmond]

John there was not any suppression caps in my X3 motor when it released its magic smoke

Stuart

[raynerd]

Commutator looks black with carbon powder.

no smell

Lots of black between commutator bars, blown that out.

Not done the light bulb test - not 100% confident in what to do 

I'll give it a clean out and run it off the machine see if it goes again now!! 

[John Rudd]

Not done the light bulb test - not 100% confident in what to do 

Chris,
Take a mains bulb holder with its wiring, connect the two wires in place of the motor, the lamp should be out at zero speed, and brighter as you advance the speed pot without tripping any fuse/rcd/mcb....
If I remember correctly, the controller used on the X3 is similar to that of the mini lathe/mill fitted with the American KB board....in as much as they use scr's not mosfets..so some resilience/consolation there
My offer stands to test for you...

[raynerd]

[ Invalid YouTube link ]
Ok John, I'll go and do the test now. I took the video before reading your post.

[raynerd]

Ok I've done the lamp test and no problem:

Thanks for the offer to test the motor John but in Colne their is a motor place, might try and pop there. If the lamp test has worked as it has, I presume it means I have isolated the motor as the issue.

[bertie_bassett]

have you tried running the motor off the machine, now that its clean of carbon dust?

might just be a few small issues causing it to trip out

[lordedmond]

Chris

That test looks ok

Danger Will Roberson  . If you do take it to the motor shop make sure that you tell them is a 180 volt DC motor , I know of a couple that have been damaged by motor shops not reading the name plate and testing on AC .



These are not a universal motor as they do not have a field winding they have permanent magnet fields

Have the RCd tripped again ? When you touched the machine

Stuart

[raynerd]

Hi guys,

Took the motor in at 8am this morning and they rang me at 12 noon saying the motor is unquestionably dead - apparently there are shorts to the armature from the wire and hence why it is tripping my house RCD. They said they could repair it but they would have to send it to their repair facility and it would cost many hundreds to get it rewound and I`m better just buying a new one. I said I could get a new one for £160 which made my eyes water but he said at that price I should snap their hand off. He didn`t charge but I gave him some beer money for the diagnosis.

So the motor is dead.

As always, I appreciate everyones help - it was very well received. Thanks Stuart & John for all the detail as well as everyone else that has chipped in. I`ll let you know when I install and new motor and hopefully the issues go away.

Chris

[PekkaNF]

The way I see:
Nothing wrong with wellmade DC motors that has brushes and commutator, but chinese motor and speed controller is a temporary solution.

Do you want commit to a temporary solution?

Alternative is more work, but robust three phase AC induction motor can be had about same price. Also new VFD is more or less same money than the speed controller that is going to break next....Just don't buy cheapest e-bay specials, but a brand name, it really does not pay off to save here last 10-20 whatever currency you have.

There is some work ofcourse and I understand that electrical installation is not trivial. But that what I would do, but then again: I'm and electrical engineer and I may fail to see the problem on your eyes.

Hope it will work out fine,
Pekka

[lordedmond]

Chris

Well it's good and bad news at least you now know what's what.

It was about 48 years ago when I was in the winding dept and knowing the size it would only be a 1 hour job if the com was ok and a over night stove

But alas the charge like rhinos for small one offs

Stuart

[PK]

I burnt the motor out on my X3 in about a week. YMMV, but I don't have much time for those cheap DC motor/drive combinations.
You can see my, perfectly sensible and understated fix here: http://www.caswa.com/cncathome/X3.html

[raynerd]

Hi PK. I Actually have a .75hp inverter that I had on a motor horizontal mill once and I can get a brand new matching 3 phase motor for £110. I'll go with this if the motor goes again or controller goes. For now I'm just going to shell out and buy a new motor. Ordered it from Arc yesterday, it arrived this morning. I've hooked it up and it spins so that's a good start. However, I've had to go my inlaws and school Christmas fair so I can't tell if the problem has been cured....I will use the mill properly this evening and check but first signs look promising,

[lordedmond]

Chris

one point has made me look back through this thread.

you were cutting gears in your pic , by nature of this operation you would have been at low speed for a while. consider fitting a extra fan to help with the air flow for the motor , they blow down

the same will apply if you do go the VFD route you will need a extra fan to cool the motor , don't forget in both cases they are designed for proper cooling at rated revs not at slow speed

many large motors that have speed controllers have a large independent  fan/motor that is at full speed all the time

Stuart

[PK]

Stuart makes a good point.
Even cheaper, and this has saved me once, is the 50 cent thermister that most VFD'a have an input for. It'll stop the drive if the motor gets too hot. 

You'll think something has broken, curse and rant, then you'll touch the motor and realise that 50c just saved you $200....

[raynerd]

Stuart, pk, -  what sort OD additional fan should I be buying?

[PekkaNF]

one that fits on shroud over the motor

Visually like this:
http://www.wistro.com/index.php?co=en

Here is some commercial unit data:
www.kmmp-usa.com/products/FBI/Massblaetter/kMMp_0M_technische_Daten_2014.pdf

What is OD of your motor? Something like 63/71 motor size?

PDF, 2/3 down "Forced ventilation unit" 20W seems to get you up to 71 frme size
http://www.rotor.co.uk/forcevent.html

What sort of air duct fans there are in britain for buildings, like toilet extractor fans, or inline air duct fans? Here stadard cheap bathroom fans are not that expensive.

Found this sort of:
http://www.screwfix.eu/manrose-xf100s-20w-axial-bathroom-fan.html


There are few things to consider:
* flow must be good enough. Compuer fans are generally too small. Air is not that great conductor, therefore you need a good flow of it. Bit like a blow on angle grinder. Few wats will not do, 20W a starting point, idustrial ones seems to be 20-40w smallest sizes.
* Check that you will be not fighting agains internal fan on greater rpm.
* Air duct reducer might provide smooth transition and correct size for the shroud.

I don't know how this motor looks, i'm assuming it has internal fan and cooling air entry is at brush end, exhaust at power take out end.

Pekka

[lordedmond]

Chris

A muffin fan as used in a PCs but please fit a guard they do chop fingers , power from a 5 v Dc wall wart but you can get mains voltage ones


Stuart

[PK]

Well, right now you have no fan. So any extra air is good. If you're never going to run a VFD+motor below 50Hz, then you don't need a fan. If you are, then you might need one. 
Personally, I hate fan noise so I don't fit them. I prefer the to go up in motor power and set sensible current limits on the drives. My motors rarely get more than warm..

[raynerd]

  All up and running now!!

Is it just one of those things or is there anything I can do to stop this happening again - I.e speeds and such

[chipenter]

Not so mutch speeds but time my X1 motor got hot enugh to melt the nylon drive gear , I kept feeling the motor and iff it got to hot let it kool down , a pain when you are near the end of a job .