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daved20319
12-18-2010, 12:13 PM
I have several Grizzly tools in my shop, not a big fan of all things Chinese, but these have treated me well. Two of them are variable speed belt drives, my drill press and my lathe. Both work just fine, unless I try to set them at top speed. The motor will start fine, start speeding up, then it cuts out and coasts a bit, then catches again, and repeat. I've sometimes gotten the DP to settle down, but never the lathe, so my top speed is around 900 rpm, and I mostly work in plastics and aluminum, and mostly less than 1" dia. to boot.

So is this just a "normal" thing with Chinese motors and capacitors, or is there something I can do to fix it without having to replace the motor? Thanks, guys.

Dave

Lew Hartswick
12-18-2010, 12:17 PM
Are you sure they are wired for 115V and not 220V ???
...lew...

lakeside53
12-18-2010, 12:22 PM
No.. it's not "normal"... and likely nothing to do with the country of origin.

Arthur.Marks
12-18-2010, 12:51 PM
Are you sure they are wired for 115V and not 220V ??

I'm no expert, but that is my vote. Every dual voltage (110V/220V) motor on a machine tool I've encountered has been pre-wired the latter. If you run the former, my understanding is it will de-rate the HP significantly.

daved20319
12-18-2010, 02:45 PM
The DP is 120v., the lathe is 220. Both work fine on all but the highest speed. Not really an issue with the DP, but the lathe tops out at only 1300 rpm, and I can't go over 900. Was hoping someone had had a similar issue and could pass along the solution. Guess it's time to call a motor shop. Later.

Dave

Bill736
12-18-2010, 02:55 PM
I wonder if the motor has a thermal overload that is cutting in and out , or a run capacitor that is shorting out periodically ?
The last time I saw someone try to run a dual voltage motor wired for 240 volts on 120 volts, the motor just hummed, and would not turn at all.
Properly reconnected at the motor for 120 volts, the motor ran fine.

Black_Moons
12-18-2010, 02:58 PM
Id open up the guards and see how it runs. Check to see if its actualy the motor slowing down (Lack of HP to overcome friction losses? loose connection in motor? Etc), Or the belt sliping (Belt too long, Not enough friction on the belt (Thiers products to help that), etc)

There might be some tension adjustment if the belt is sliping at the highest speed. (The variable speed pullys automaticly adjust tension yes, But if one pully reachs its limit before the other, the belt will go loose)

MaxHeadRoom
12-18-2010, 03:47 PM
If you happen to visit other sites that where posters tend to use equipment and machines imported from R.O.C. The number of motor related problems and failures are prevalent.
Mostly capacitors and centrifugal switch related.
I know of least one importer of R.O.C. equipment that used to replace the motors before he sold the machines, just to avoid the aftermarket headaches.
Max.

metalmagpie
12-18-2010, 04:16 PM
Oh, come on! Squirrel cage AC motors are *not* hard to understand!

1. Check correct wiring for desired voltage. Don't believe anything nor assume anything.

2. Check correct voltage is reaching the motor.

If motor still not right, there's something wrong with it.

Single phase? replace the run cap, if not fixed, replace

Motors don't cost *that* much. Problem is if they don't use motors with NEMA frames. In that case, you call Bellingham and shoot for some of that legendary Grizzly customer service.

JoeFin
12-18-2010, 04:44 PM
Try checking the voltage drop at your top speed

If your trying to run those tools on 14 awg wire (house wiring, extension cords) that is exactly what they are going to do

Would also be a smart move to make sure you have the correct size fuse in the socket or that your circuit breaker is not so worn out from repeated tripping that it is actually holding too much current. As the voltage goes down the amperage proportionally goes up. In the case of your lathe motor running at full speed the amount of "Slippage" puts the armature in between opposing phases

Robin R
12-18-2010, 04:45 PM
It sounds like you are saying this only happens at the higher speed settings, does this mean they work as they should at lower speeds. If that is the case it would be worth checking the amps of the motor at various speed settings, to see if the motor is overloaded at the higher speeds. Otherwise I would say the checks Black_Moons suggested are a good place to start.

whitis
12-18-2010, 04:54 PM
It sounds like you may be overloading the motor by asking it to provide starting torque/acceleration at the mechanical disadvantage which exists on the highest speeds. The fluctuation may be due to the centrifugal starting switch disengaging and then re-engaging and the fact that some types of motors don't perform well until they are up to speed. Start on a low speed setting then ramp it up to high speed once it is running.

darryl
12-18-2010, 07:39 PM
If there's no electronic controls that might be responsible, then it's probably that what whitis is saying is right. The motor doesn't have enough torque to pass fully into run mode, for whatever reason. Too low a supply voltage would do it. Too much loading from the driven mechanism would do it. How would you have enough power left to actually machine with if virtually all the power is wasted in trying to get the mechanism up to speed-

gmatov
12-18-2010, 11:05 PM
Darryl,

Why would you start a cut, unless the machine WAS up to speed?

I don't think any machine would have been sold that could not get up to speed, at the factory. They may be crap motors, but I think they will all get up to the speed on the name plate.

That is a standard of electric motors. They all do that. Whether they can produce WORK is another thing altogether.

Buy a new 200 buck motor and see if it works better.

If it is a 56 frame motor, grab one out of the scrap pile and try it. If it works, you got a bad motor.

Cheers,

George

darryl
12-18-2010, 11:40 PM
I wasn't suggesting that you begin machining before the machine is up to speed, but I was suggesting that if it takes most of the motors power to get the mechanism up to speed, then there wouldn't be much power left to machine with. It wouldn't be right that a manufacturer sells a machine that works that way. Something is wrong, obviously. Maybe too much friction has developed in the drive system, maybe the motor is bad, maybe the start cap is weak- that's what I'm coming to on this, a weak start cap.

Terry L
12-19-2010, 12:10 AM
I'm sure that this has nothing to do with the problem described, however, I had an experience with a motor on a mill made in China that was wired for 50 cycles per second instead of 60. When hooked up to our current, the motor ran slow and overheated quickly.

J Tiers
12-19-2010, 01:07 AM
With a chinese motor, you never know...... anything could be wrong. This is not just me saying it, a while back I linked to an article where even CHINESE engineers were saying they made a lot of cheapo bad motors in china, and suggested standards and so forth to stop that.

Anyway.... You said 'variable speed"..... Do you just mean you can change pulley steps with the motor off? OR do you mean that there is a real variable speed, with a crank or knob that you use to vary speed when the motor is running?

If you just have pulley steps, yes, the machine SHOULD start in high speed. There is no other way to run it at high speed.

If you have true variable, you can presumably start slower and speed it up. If the problem is just starting a large inertial load at high speed, that could fix it to a usable condition.

You may as well call Griz, they will probably have heard of this before..... What they CAN do for you, or WILL do, I don't know. They HAVE been pretty nice, in general, they may have an acceptable solution for you.

The whys and wherefores are another issue:

Motor pulleys might have been mistakenly set up for 50Hz, which would be 6/5 too fast for 60 Hz.

Pulleys might just be "wrong".

Motor might have the wrong start cap, in which case it may be sluggish or fail to reach full speed at all.

Motor, if wired for a higher voltage, will start slowly, and may fail to reach full speed.

Presuming motor to be single phase, have you checked the start current with a clamp-on meter? It should start out with a huge current, possibly 4 to 7 times nameplate run current.

As it starts, the current should suddenly drop as the start cap drops out of the circuit due to the centrifugal switch. After that the run current unloaded should settle down to somewhere about 30 to 50% of nameplate current.

if that does NOT happen, you need to investigate the wiring of the motor for proper voltage, proper size cap (ask Griz) etc.

metalmagpie
12-19-2010, 09:47 AM
I'm sure that this has nothing to do with the problem described, however, I had an experience with a motor on a mill made in China that was wired for 50 cycles per second instead of 60. When hooked up to our current, the motor ran slow and overheated quickly.

This posting runs counter to what I had always been taught. I had understood that for a motor to run on 50Hz it needs slightly more copper than the same motor wound for 60Hz; thus, run at 60 Hz it would run a little cooler. In other words, all 50Hz motors should work fine at 60Hz but not vise versa.

metalmagpie

Terry L
12-19-2010, 10:41 AM
Perhaps that is true.....I have no idea. I know nothing about motors, so I can't argue with you. All I have to go on was what I was told by the person working on the motor. I do know that our plant's 3 phase power source was 550 volts and not 440. Whether that had anything to do with it is beyond me.

J Tiers
12-19-2010, 10:49 AM
This posting runs counter to what I had always been taught. I had understood that for a motor to run on 50Hz it needs slightly more copper than the same motor wound for 60Hz; thus, run at 60 Hz it would run a little cooler. In other words, all 50Hz motors should work fine at 60Hz but not <EDIT> necessarilyvise versa.

metalmagpie


As edited that would be generally correct. You really can't "wire" for 50 Hz, other than by the basic design.

However, it is true that the motor would have 6/5 the impedance/back EMF at 60 Hz, and the volts/Hz would be 5/6 that necessary to produce rated power. That, if the SAME voltage is used, would potentially overheat the motor same as low voltage.

The voltages may be related in such a way that it can work.... European 400/230 volts 3 phase corresponds to US 480/277, by a ratio of 6/5, and a motor for one could work on the other.

But a single phase 230V 50 Hz motor would be lacking in V/Hz if used on US 230/60Hz

daved20319
12-19-2010, 11:52 AM
Near as I can tell, you're the only one that really read my post :( . As stated right at the beginning, folks, this is a belt driven machine, I change speeds by moving belts on pulleys, the motor runs at the same speed regardless. It's a 1.5hp motor on a dedicated 30 amp, 240 volt circuit, that's only about 30 feet long. I installed it when I got the lathe, and although not a motor guy, I spent 10 years wiring houses for a living. The one thing I left out is that it's a 20+ year old machine. The only reason I didn't just assume it's an old motor issue is that I get the same thing with my much newer Grizzly drill press, which is why I posted in the first place. Thanks for the input, gents.

Dave

lakeside53
12-19-2010, 01:35 PM
Your drill press and lathe issue may be unrelated... even though they exhibit the same symptoms.

It's not uncommon for some lathes to have problems getting up to speed on higher ratios -anyone that owns an Emco v8 or V10 knows this well. Emco's solution was a two speed motor - start it in low speed; switch to high. I had real problems in the winter at any speed with my Emco, until I discovered 140wt gear oil (about the same weight 30-40wt engine oil) in the headstock instead on the required 10wt.. In my shop I figure I needed 5wt when miserably cold, but a block heats was a better solution :)


My bigger 4hp lathe will not get up to speed unless I run it for 10 minutes at 1000 (or less) rpm to warm up the oil. In this case it's my RPC not providing enough power when the cold oil is dragging, but it's related.


Your speeding up then cutting out is plain weird - not normal. To "cut out" there is some power disconnect happening, and the only "normal" switch is the centrifugal start switch(assuming it has one) in the motor.


As for the 50/60hz issue -very uncommon to find a motor that won't work on both... What does you motor nameplate say?

The Artful Bodger
12-19-2010, 01:42 PM
My Chinese 12x36 lathe came with a 2HP 230V 50Hz motor. It would not start on the high spindle speed ranges without tripping the wall breaker (10 amps). Then I replaced the start capacitor and it spins up fine now.

My knowledge of such things is very basic but I imagine a 'sick' run capacitor may cause loss of run torque?

Motor capacitors are cheap(ish).

JoeFin
12-19-2010, 03:28 PM
:( . As stated right at the beginning, folks, this is a belt driven machine, I change speeds by moving belts on pulleys, the motor runs at the same speed regardless. It's a 1.5hp motor on a dedicated 30 amp, 240 volt circuit, that's only about 30 feet long. I installed it when I got the lathe, and although not a motor guy, I spent 10 years wiring houses for a living. The one thing I left out is that it's a 20+ year old machine. The only reason I didn't just assume it's an old motor issue is that I get the same thing with my much newer Grizzly drill press, which is why I posted in the first place. Thanks for the input, gents.

Dave

Well I am glad you mentioned the "dedicated 30 amp 240v ckt". That eliminates any possible wiring issues as far as I'm concerned.

Still a bit perplexed by both the DP (110v) and lathe (240v) are doing this. Unless you are equipped to measure running amps vs: volts/ohms accurately I don't see how you can eliminate any more possible electrical conditions.

Just a guess mind you - but I would suspect the start cap in the lathe and mechanical load/stress in the drill press. You can simply remove the belts off both and hand spin the spindle of each to feel for any problems. Caps are dirt cheap compared to motors and have a shelf/service life less then the 20 year age of your lathe

derekm
12-20-2010, 02:35 PM
too much cold grease in the bearings?