WM250 speed control board

[Mark P.Participant @markp]

Hello all, I think my speed control board has died. I had been using the lathe this morning when there was a “pop” and the lathe stopped also the workshop elcb tripped. I opened the panel to have a look but nothing untoward could be seen, I disconected the motor and pressed the start button elcb tripped again so I concluded
that the motor is ok. I am guessing the scrs have shorted to earth could I be right? I pulled the motor apart and except for some carbon dust there appears to be no damage to the armature and the com. Now is there a generic control board available or do I get one from WARCO.
Cheers Mark P.

[Mark P.Participant @markp]

[Richard MarksParticipant @richardmarks80868]

Ring warco and ask their advice.

[Les Jones 1Participant @lesjones1]

When you use the term "elcb" what do you realy mean as it is unlikely to be an elcb. Do yo mean an MCB, an RCD or RCBO ? It is possible it could be an SCR short to earth IF the SCR is mounted on an earthed heat sink with an insulating washer and the insulating washer has failed. I HAVE NEVER SEEN THIS METHOD USED. All the speed controllers I have seen have the SCR anode in contact with the heat sink which is insulated from anything else.

Les.

[Mark P.Participant @markp]

Hi Les,I should have said RCD.Just waiting for warco to get back to me.
Cheers Mark P.

[John RuddParticipant @johnrudd16576]

Wether its the KB board or the Chinese clone, none should have any leakage to earth.

The semiconductor devices used in the KB boards have isolated tabs. The Chinese clone boards actually go one better, they use isolated tab devices too but belt and braces uses mica washers and bushes.

To isolate the cause of the tripping, disconnect the motor from the F/R switch, mark the leads so you know where they go. You could try resetting everything and tr0ying again….If your elcb/rccd or whatever protective device you have trips again, then quite possibly the board has a fault to earth. If the device doesn't trip then it could be the motor and you would need an insulation tester (Megger) check the insulation between commutator and shaft…..Oh…just re-reading your opening post….ignore the last bit, sounds like the board has gone west….

 

Want it repairing? pm me…

 

 

Edited By John Rudd on 02/02/2017 16:11:16

Edited By John Rudd on 02/02/2017 16:38:12

[John RuddParticipant @johnrudd16576]

I've uploaded some fotos of the two boards in an album…..this foto is the Chinese board, you can see white/black washers and grey thermal insulators

Edited By John Rudd on 02/02/2017 16:35:03

Edited By John Rudd on 02/02/2017 16:38:41

[Mark P.Participant @markp]

Hello John, I did disconnect the motor from the fwd/rev switch and tried again same result plunged into darkness when the RCD tripped. It is a KB board. Have since spoken to Warco and he said the same thing that it is the board. I must say I was taking quite a heavy cut when it “popped”! Well ?110 for the board, but I will check out the motor before I order it.
Cheers Mark P.

[Mark P.Participant @markp]

Thanks for the offer of repair John, I will bite the bullet and get a new board, but I may contact you and have it repaired so I have a spare.
Regards Mark P.

[John RuddParticipant @johnrudd16576]

Posted by Mark P. on 02/02/2017 16:39:42:
Thanks for the offer of repair John, I will bite the bullet and get a new board, but I may contact you and have it repaired so I have a spare.
Regards Mark P.

No problem…..

[John RuddParticipant @johnrudd16576]

Seems during my editing a post, I lost the second foto…a KB board no insulation on the devices….

Edited By John Rudd on 02/02/2017 16:45:19

[Alan VosParticipant @alanvos39612]

Posted by Les Jones 1 on 02/02/2017 15:06:08:

When you use the term "elcb" what do you realy mean as it is unlikely to be an elcb. Do yo mean an MCB, an RCD or RCBO ? It is possible it could be an SCR short to earth IF the SCR is mounted on an earthed heat sink with an insulating washer and the insulating washer has failed. I HAVE NEVER SEEN THIS METHOD USED. All the speed controllers I have seen have the SCR anode in contact with the heat sink which is insulated from anything else.

Les.

I had a simillar "pop" from my speed controller last year. Now fixed. I did some research. Insulating washers are avoided by using 'isolated tab' SCRs (and diodes). Unlike the more common devices, their tabs are not connected to the anodes. If they were, all the anodes would be connected together via the heatsink.

In my case, one SCR was shorted anode to cathode. The speed controller switched on, but at minimum/off, gave half-wave full power. As soon as the speed controller was advanced, the other SCR was triggered, instand dead short, another vaporised fuse.

[Mark P.Participant @markp]

Just wondering if it would be an idea to fit an extra heatsink to the one already fitted, wouldn’t hurt would it?
Mark P.

[CirclipParticipant @circlip]

Seems to be a constantly requested help line for the control boards. Wonder if replacing the motor and using an inverter might be a better solution. A friend with one of "Those" lathes went through two boards in short order. Is infinitely variable speed control REALLY necessary on toy lathes?

Regards Ian.

[John RuddParticipant @johnrudd16576]

I'd be interested to know what fuses are fitted to the main plug….I bet they are 13amp…..

Considering the boards are rated at 6Amps for the smaller machines …….from the information given here lately, fitting an 8 amp fuse is questionable….

[Mark P.Participant @markp]

Hello John, the lathe is fitted with a 10 amp fuse as standard, I expect it is a quick blow type. The main fuse at the plug is 13a.
Mark P

[DustyParticipant @dusty]

Hi Mark, I see we are having similar problems. I can confirm that the fuse on my lathe is 10amp. For Circlip's benefit the WM250 is a 5" lathe not one would normally call a toy lathe and yes variable speed is very useful. John Rudd has been an absolute diamond in helping me.

[Mark P.Participant @markp]

Dusty, I’ll second that, mine is used maybe 6 days a week for 5-6 hours a day and has been since for the last 7 years. Apart from motor brushes have had no real problems with it.Yes thanks John.
Mark P.

[John RuddParticipant @johnrudd16576]

Hello John, the lathe is fitted with a 10 amp fuse as standard, I expect it is a quick blow type. The main fuse at the plug is 13a.
Mark P

Mark given that 10amps is more than 2000 watts….that's approaching 3hp territory……

What size motor is in your machine?

Even if the fuse is a quick blow type, the scr's will blow a lot a faster….

My recommendation fwiw, is to replace the fuse with that of a lower rating, even going to the lowest value that doesn't blow under normal use….

My Chester mini mill is fitted with a 3 amp fuse in the plug, the motor is rated at 550 watts (3/4hp….) ok the fuse is borderline at say 690 watts (230v ac nominal? )……

Cheaper than buying a new board or the cost of the repair…..

Its down to individual choice…..

[Mark P.Participant @markp]

John the data plate on the motor says 750 watt.
Mark P.

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