Today, An epic win, followed by a massive fail!

[Graham WhartonParticipant @grahamwharton]

[Graham WhartonParticipant @grahamwharton]

Just wanted to share my pain.

Due to some over enthusiastic machining last week I managed to completely melt the internals of the motor on my Sieg C6B lathe.

So, a quick hunt on ebay, and £10.00 later I was the proud owner of a Faulty treadmill with a working 1.75HP DC motor in it. This is a bit heftier than the existing 1HP motor from the lathe, however the controller on the C6B has over current protection, so my guess was that I might just have to live with it cutting out when I proper wind up the new motor. In time I would look at replacing the stock controller with something a bit more capable.

Well, I stripped the treadmill today, and pulled the motor. I did a quick check by hooking it up to the lathe controller. Tentatively wound the speed control knob up. To my glee, the motor purred into life and I was able to take it up to maximum speed just fine. Great, I thought. Took the speed control knob down to 0. I then noticed that the large pulley on the end of the treadmill motor that I hadnt removed yet, wasnt actually a pulley, but a flywheel. The motor spun down slowly, taking about 15 seconds to come to a stop. Mid way through this clouds of smoke, a massive spark from the controller board, a massive spark from the speed controller knob and the garage plunged into darkness as the fuse panel tripped.

So, I have a couple of theories

1. Because the motor is rated at 1.75HP and the controller was setup for a 1HP motor, Ive fried something because of this. However the speed knob was at 0 when it blew.

2. When the controller was off, but the flywheel was keeping the motor spinning, it was acting as a generator and pumped some current back into the controller board which wasnt expecting it.

I'm leaning towards No.2 as the thing blew when the controller was off, but the motor was spinning down. Is this technically feasible/possible?

So, an epic win, A 1.75HP DC motor for a tenner, and a massive fail to follow

Never mind, I'm £180 quid lighter now, but alteast I now have a shiny new KBCC-225 controller to look forward to fitting next weekend.

On the plus side, the motor itself fitted beautifully. Had to drill 1 extra hole in the existing motor bracket and that transferred over just right. All lined up perfectly on the pulley side. The spindle was the same diameter with the same keyway as the old motor. I dont think i could have asked for a better outcome from a stab in the dark 10 quid ebay special.

Edited By Graham Wharton on 14/04/2012 22:53:45

[John Stevenson 1Participant @johnstevenson1]

It's possible to get a 1Hp 3 phase motor and inverter onto a Sieg C6 lathe.

John S.

[Steve GarnettParticipant @stevegarnett62550]

Posted by Graham Wharton on 14/04/2012 22:42:32:

The motor spun down slowly, taking about 15 seconds to come to a stop. Mid way through this clouds of smoke, a massive spark from the controller board, a massive spark from the speed controller knob and the garage plunged into darkness as the fuse panel tripped.

So, I have a couple of theories

1. Because the motor is rated at 1.75HP and the controller was setup for a 1HP motor, Ive fried something because of this. However the speed knob was at 0 when it blew.

2. When the controller was off, but the flywheel was keeping the motor spinning, it was acting as a generator and pumped some current back into the controller board which wasnt expecting it.

I'm leaning towards No.2 as the thing blew when the controller was off, but the motor was spinning down. Is this technically feasible/possible?

Oh, yes – 2. is most definitely technically possible. If the reverse EMF diode happens to fail (because of rather more reverse EMF than it was expecting), then it's most definitely possible to release the small capsules of smoke programmed into every electronic device anywhere near it!

I very much get the impression that with DC motors of this power, the controllers are always tweaked to be able to cope with specific devices, and that replacing the intended motor with a completely different one can alter some of the characteristics in a way that's way out of proportion to the apparent size difference. It sounds very much like this is what's happened in your case.

I like John Stevenson's idea as a fix – I've had far less trouble with 3-phase motors and inverters than I've ever had with DC ones.

[Graham WhartonParticipant @grahamwharton]

Yeahh, I might look out for a 3 phase on the side as a future upgrade, however atleast I'll be back up and running soon.

[AndyfParticipant @andyf]

Hard luck, Graham!

If it’s any comfort to you, I fitted a 1.5HP motor from an Ebay broken treadmill (though at £15 it seems I was robbed!), to my milling machine and use a KBIC240 board to drive it. The on/off switch is on the input (AC mains in) side. The KBIC board survived initial experiments with the original flywheel in place, and has now been in use for 2-3 years.

Andy

[Graham WhartonParticipant @grahamwharton]

As an aside, the rubber tread from the treadmill, when cut up, makes perfect draw liners for my toolbox…… This one keeps on giving! Now to get the hacksaw out to break up the frame. Theres some good square and round tubing to be salvaged.

[Ian S CParticipant @iansc]

There should be a speed control on the tread mill, no reverse though. Ian S C

[Graham WhartonParticipant @grahamwharton]

Yeahh, the speed controller on the treadmill was trashed. I just hope it isnt something wrong with the motor that blew the speed controller on the treadmill, and also blew the controller on my lathe. I really dont want to plug in the KBCC-225 and have it blow that too!!!

[Les Jones 1Participant @lesjones1]

Hi Graham,

The picture of your controller board looks identical to the board on my X3 mill.

If it is any help I have traced out the schematic for it. It is on my website

Les

[Graham WhartonParticipant @grahamwharton]

Hi Les,

Yeahh, they are the same board, The big fat resistor on the front is a different rating though. I also have a board from an X3 which had some damage which I previously tried to repair using your schematics. I might send you some updates as I found a few minor errors. I think the fault on the X3 board that I have was less catastrophic than my latest frying as there is just a short on the low voltage side of things which caused the voltage regulator and zener to pop themselves off!.

[Les Jones 1Participant @lesjones1]

Hi Graham,

Thanks for the offer of the updates. I think it is always better for a second person to check something like this for errors. I will correct my schematic on my website and one I put on the Yahoo X-Series mills forum. I was lucky when the motor on my X3 failed with a short between winding which blew the fuse in a big way. The board was not damaged at all. I think Steves theory about the voltage from the motor when it was working as a generator driven by the flywheel is correct even though I cannot work out which component it caused to fail first. I will send you a PM with my email address so you can send the corrections.

Les.

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