WM18 Earth Fault - Looks like Controller blew

Hi

Just wondering if anyone else has come across this? Ive had the mill only a few months (WM18 from Warco) and from the start it had a bit of a strange tendency to 'hunt', with sudden spikes in speed generally when you first turned it on and began to dial up to machining speed. I let it go for whatever reason.

I started it up today to do some drilling, and all of a sudden the effect was much worse, speed jumping up then down. It did this three times and then all the lights went out and the mill went off. It had tripped the earth leakage fault protection back in the house.

Now the mill does not work at all. The box powers up, I can hear the transformer running. I have checked all three fuses (plug and the two in the base of the control box), the blue light up display illuminates and the LCD works. The spindle and gearbox all turn freely.

After measuring with a multimeter, there is zero voltage on the motor (you can access the screw terminals to the brushes by taking a cover off) even with power on and rpms turned up, so it looks like something has shorted to earth inside the controller, given that it was the earth leakage trip that went and none of the other fuses blew in the mill.

Ahead of contacting Warco on Monday, any clues as to what might have gone and likely resolution? The mill is well within warranty. Do warco just send a new part or does someone come out to fix it?

Cheers

Ross

Likely blown one or more of the large three legged switching devices on the main control board. I would be very surprised if Warco would send someone out to fix it, more likely to send you a new board to change out yourself assuming it is still carrying some sort of guarantee.

If you do have to swap it out yourself take plenty of photos and notes as to what goes where. and unplug from the mains first. Good luck

Thanks Nige, I thought it might be something along those lines. I am quite happy to replace myself, always good to learn what the insides of any machine are like.

They will probably ask you to send them the board for repair/replacement, so take a few photos to help make sure you can get it back on right.

Neil

From your description above, "none of the fuses have blown, and it tripped the earth leakage breaker", suggests to me that the motor is faulty...

The thyristors or ' three legged devices' have isolated tabs, that means even if they failed short circuit across their junctions, ( anode/cathode...) that would not cause an earth leakage trip....

The circuit board can be tested in isolation by disconnecting the motor from the board and substituting a 100 watt light bulb, the brightness should vary when the speed pot is turned up and down....

Testing the motor for leakage to earth will require an insulation tester ( 'megger'....)

Hopefully Warco will resolve this for you without delay.

Edited By John Rudd on 11/08/2018 22:04:57

Edited By John Rudd on 11/08/2018 22:05:24

Hi John

If the board was ok, wouldn't you expect to see voltage at the motor terminals? When measuring across the screw terminals there was no voltage at all. As the terminals are connected directly to the controller, I would expect to at least see a voltage across them even if the motor was faulty?

Cheers

Ross

If you have had it only a few months it is THEIR problem, not yours. I would suggest that you are careful not to do anything that dilutes their responsibility for fixing this.

Ross,

Oooh my bad.....I missed your statement about there being nothing at the motor terms...,( assuming you had good contact with the wiring and your meter works ok. on dc volts range ..😀 )

Have you checked the motor commutator? Does it look burnt/carbon'd up?

Bottom line here is the machine is under warranty, so rather than speculate on what is/isnt ....let Warco decide and act accordingly to your satisfaction

While you check the commutator take a look at the brushes, when my lathe started running irratically like you describe this was the cause.

As it’s under guarantee I would suggest you don’t start playing with it, Warco have a 6 month on site option to use.

Dismantling could void your warranty.

It's because these machines have a tendency to minor assembly faults like loose screw terminal connections. As these are easily fixed, it's worth having a look because of the time and trouble saved.

I agree though that some go a bit mad and tear the whole machine apart. That's not a good idea. If a machine is under warranty and the supplier can see you've been at it, you went too far.

I bet the suppliers of these machines could tell some stories about the occasional unwise customer...

Dave

I had the same problem as Jason a couple of weeks ago, re: carbon brushes on my WM-16 mill which resulted in one of the glass fuses blowing due to over-current.

If it's an earth fault I'd look inside the control box to see if there has been a short to earth of some kind from the PCB to the case itself, a bit of loose wire or swarf left over from manufacture perhaps.

If possible I'd also check the outputs of the PCB to see if voltage is actually leaving it.

Ed.

[This posting has been removed]

Personally, I can’t really undestand why anyone posts on here re in-warranty failures, except to warn others of the frailities of the machine or control electronics.

The first port of call should always be the supplier. Even if a weekend fault. Also, a record of the conversation, or otherwise exchange, should be retained for future use, should it become necessary in the event of further problems.

Unauthorised ‘fiddling around’ is a simple way to void any warranty.

This thread seems to be one of arming the poster with information as to whether the failure is common. How the supplier might approach the warranty claim is entirely up to them and no prior conjecture will alter that.

The replies confirming you should not interfere with it prior to contacting the supplier are likely the best replies you have or are likely to get.

It would seem that you have had, for whatever reason, a fault which was apparent earlier, but you failed to inform the supplier - until it has escalated tonthe point of complete machine stoppage. Not good for either party.

Hi chaps, just an update. Spoke to warco today and they are sending out a replacement board tomorrow first thing It falls to the customer to replace 'simple' components like boards, so I have removed the board ahead of it arriving. Warco said I could keep the old one. If that doesn't work they will send someone out.

Here's the culprit. Looks like a few factory attempts at drilling went awry, and the swarf embedded itself in and made its way through the insulating tape (I checked and the tape is not electrically conductive, though may be thermally so. Top pic shows the mosfets in situ on left, note the insulating grommets keeping the bolts from touching the mosfet tab. Bottom shows the worn-through tape and chewed up drill holes after removing.

NOTE: Warco suggested I open the box to remove the board and said I could dispose of it.

May be worth checking if you own this or similar mill, especially if you don't have an RCD capable of tripping on earth leakage.

.

Thanks for sharing that, Ross ... it speaks volumes.

MichaelG.

Thanks Ross - most interesting. Just goes to show how a small fault in the wrong place can cause chaos. Attention to detail is important. They build an entire milling machine and then a silly factory mistake spoils it.

The 'tape' is a silicon thermal conductor and electrical insulator. It needs to be fitted! Not difficult to source. More or less anyone who sells semiconductors - Farnell, amazon etc. Try searching for 'Heatsink insulator pads' or transistor insulator etc.

Dave

as the fault was swarf shorting the semiconductors metal tab to the heatsink

it looks like the speed control is a copy of KB electronics KBLC-240D (or some thing similar )

KB electronics use devices that have isolated TAB's on the 3 diodes & 2 thyristors ( forming a controlled bridge rectifier ) & does not require the insulator

the copies use cheaper devices that don't have isolated TAB's and there for requires the insulator

john

Edited By john swift 1 on 13/08/2018 21:32:13

Many thanks Dave, I will add that to the shopping list!

Cheers

Ross