Smithy Granite 1324-I MX Help

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Jay79
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Re: Smithy Granite 1324-I MX Help

Post by Jay79 »

liveaboard wrote: Tue May 18, 2021 2:15 pm
Jay79 wrote: Tue May 18, 2021 2:05 pm the motor was noticeably harder to turn which normally spun pretty easily.
I was reading controller until that line.
How hard is it to turn?
A brushless motor with the belt removed should spin almost effortlessly. If not, the bearing (s) are likely your problem.
And a cheap fix too.
I would say it feels like turning with gear oil in it. It was much easier before so I know something is going on with the motor.
Jay79
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Re: Smithy Granite 1324-I MX Help

Post by Jay79 »

Torch wrote: Tue May 18, 2021 2:33 pm Within a few months of getting my machine, the controller let out it's magic smoke. I repaired it (replaced the SCRs on the board) but it happened again real soon. Then I discovered there was a problem with the motor itself -- a brushed DC 1.5hp, 180v motor. Some of the windings were shorted, and the over-current was taking out the controller. The manufacturer replaced it under warranty and I replaced the controller with a KBWT-210 PWM type controller rated over 2hp and 260vdc. Never looked back, better low speed torque, quieter running -- no, scratch that, *much* quieter running -- and a few features like soft starting and overload protection.
Do you have a G1324 as well Torch?
Torch
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Re: Smithy Granite 1324-I MX Help

Post by Torch »

No. But same general layout.
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liveaboard
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Re: Smithy Granite 1324-I MX Help

Post by liveaboard »

Jay79 wrote: Tue May 18, 2021 2:33 pm
I would say it feels like turning with gear oil in it. It was much easier before so I know something is going on with the motor.
That's odd; usually a bad bearing will feel a little rough.
Anyway, if your motor is stiff something is mechanically wrong, so take it apart and look.

Personally, I'm very happy with my VFD and 3-phase motor, the setup works great and the units are independent and can be easily replaced.
But if all you need is a $10 bearing, then swapping out the whole power and control unit is a bit overkill.
Jay79
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Re: Smithy Granite 1324-I MX Help

Post by Jay79 »

Ok a little update. I had a chance to tear into the guts and here is what I found. I decided to try and turn on the machine one last time, I put in a new fuse, plugged in the cable and power on = no blown fuse this time.Motor still hard to turn.

I Unplugged the machine and started to disconnect the motor leads and found that two of the 3 leads actually cause The motor to be hard to turn. If I disconnect those two wires the motor spins freely like normal.

Pics:https://drive.google.com/file/d/1YQ5R05 ... p=drivesdk

https://drive.google.com/file/d/1YMIEg1 ... p=drivesdk
Torch
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Re: Smithy Granite 1324-I MX Help

Post by Torch »

That looks like a 3-phase brushless DC controller. The 3 wires are labelled "U", "V" and "W". Probably PWM. If there's no other wires going to the motor, then it must be a sensorless controller, that relies on back-EMF to detect the speed and direction when controlling the power transistor switching sequence. The 6 big capacitors would seem to support that theory.

Does the resistance change with the speed of rotation? IE: if you move it slowly there is little resistance to turning, faster causes greater resistance?

I suspect a problem with the controller.
Jay79
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Re: Smithy Granite 1324-I MX Help

Post by Jay79 »

Torch,

Yes I believe its PWM. Im unsure on the resistance as i never checked. There are other wires going to the borad seen here>>https://drive.google.com/file/d/1YSkbzP ... p=drivesdk

The odd thing is the motor is free spinning with both W and V wires disconected. As soon as i connect the two back up the motor is very hard to spin by hand. This is with the machine unplugged.
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Bill Shields
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Re: Smithy Granite 1324-I MX Help

Post by Bill Shields »

For how long? A few minutes, an hour or a day?

Power must be coming from somewhere.

Can you measure voltage across any of these terminals?
Too many things going on to bother listing them.
Torch
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Re: Smithy Granite 1324-I MX Help

Post by Torch »

Ok, so it's not a sensorless motor then, but it's definitely a 3 phase DC brushless. The small wires go to Hall effect sensors that provide the feedback to the controller.

Bill, the power is provided by the motor itself. Rotating the motor causes it to act like a generator -- fancy term is "back-EMF". Current flowing through one or more coils causes the resistance -- same principle as an electric brake. If so, then turning slowly causes less resistance and turning faster causes more because the faster you turn the higher the current generated. Disconnecting the two wires interrupts the current flow, so the motor can be turned without resistance.

That is why I suspect the controller. I think something is shorted in the controller, possibly one of the mosfet power transistors. My theory is that the short provides a current path for the back-EMF. If there was some sort of short inside the motor windings, I don't think disconnecting the wires would have an effect. If this was normal operation, then Jay would not have been able to spin the motor freely by hand previously.

I also suspect that disconnecting a different pair would have no effect. It might even be just one of those wires. The current path could be between V and W, U and W or U and V. If it's one blown mosfet, then disconnecting just one wire might point to which one (or which pair, there might be 6 of them) EG: what happens if you reconnect V and W then disconnect just U?
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NP317
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Re: Smithy Granite 1324-I MX Help

Post by NP317 »

If you choose to repair the controller by replacing a mosfet, replace ALL the output mosfets.
My electronics experience suggests when one is bad, others are damaged and might also fail later.
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liveaboard
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Re: Smithy Granite 1324-I MX Help

Post by liveaboard »

It seems to me that a three-phase motor and VFD are now looking very attractive.
Jay79
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Re: Smithy Granite 1324-I MX Help

Post by Jay79 »

Thanks for the replys guys,

Bill, no there is no measurable voltage on any of the terminals but there is continuity. Torch, If I Disconnect "U", the motor no longer turns hard with "W" or "V" but with it connected Both "W" and "V" individually or together cause a hard turning motor.

Liveaboard, Yeah I think your right. However I am trying to learn about this, its all foreign to me right now so I'm not sure what to get at the moment if I went that rout.
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