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1.1 kW electric motor burns up..

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Jens Eirik Skogstad22/08/2018 22:57:13
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Hi folks! I has used the milling machine at low speed (belts at low revolution) when i created gearwheel without problem. But the electric motor at 1,1 kW can't last more and burn up when i drilled the hole with 1 mm drill at high speed (belts at the highest revolution at 2050 rpm). Is it common problem with chinese electric motor?

Before i installed the 16 ampere fuse and 2,5 mm2 wiring to tool room where the milling machine is standing there, the 10 ampere fuse burst each time when i set the milling machine at high speed at 2050 rpm then i think the electric motor is too big for 10 ampere quick fuse. But not fact, there is some fault inside the electric motor since the house is hot. I learned out the belt gearing is over geared in high speed also the electric motor speed is lower than spindle speed, a weak engine who can't run the over geared belt with a load from 1 mm drill.

It's a Zhejiang ZX 30L mill/drill machine with belt.

Which electric motor can i replace? Want a reliable electric motor who can last long.

I will not repair the shitty chinese electric motor made by chinese city smith in backyard. This electric motor has taken away my pleasure to use milling machine.

Emgee22/08/2018 23:25:23
1046 forum posts
197 photos

Hi Jens

I guess the FLC on the 1.1Kw motor plate will be around the 10A, so when starting on load there will be a fair amount of extra current flowing, so 10A is undersize, especially so with a fast blow fuse.

I am not familiar with the mill/drill model you have but I think you need to check the gearing from motor to spindle, if it is all belt drive does your belt need to drive a second pulley geared to remove some load from the motor at high spindle speed settings.

Emgee

John Haine23/08/2018 06:21:36
2380 forum posts
132 photos

Are you saying the motor burned out, or does it just get hot when running continuously? Motors do get hot.

The problem (if there is one) is perhaps in your spindle, which may have too much friction so at high speed absorbs too much power from the motor. Might be worth checking the bearing preload.

Looking at the little data I can find on the machine it probably uses a standard 4 pole induction motor which will run at about 1480 rpm so needs gearing up for a higher spindle speed.

If you really want to replace the motor then a 3-phase type with a VFD would be the best way forward IMHO.

Jens Eirik Skogstad23/08/2018 06:29:23
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It came a lot of smoke from motor, all bearings is moving free without hard points. 1480 rpm geared up to 2050 rpm is too much can i think.
not done it yet23/08/2018 06:45:08
2652 forum posts
11 photos

A possibility, if the motor has starting windings, is it may never have reached the point where the start winding has been switched out of circuit (or the contacts are welded together). That would quickly overheat the windings and let the smoke out.

Martin Connelly23/08/2018 07:46:56
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Is this a new machine? It is usually recommended to run the machine for about 30 minutes at each speed starting with the lowest speed and working up to the highest one. This way the tightness of a newly assembled spindle can be eased so that it will run at the highest speed when first switched on in the future.

Martin C

Thor23/08/2018 08:52:21
1023 forum posts
23 photos

Hi Jens Erik,

Smoke coming from the motor is not a good sign. If the old motor is a single-phase I agree with John, get a 3-phase motor of the same frame-size as the old and a VFD. I did that on my lathe and I am very satisfied.

Thor

Edited By Thor on 23/08/2018 08:52:35

John Haine23/08/2018 08:56:57
2380 forum posts
132 photos

The gearing up should not be a problem as long as the spindle friction isn't excessive. If you get a 3 ph + VFD appropriately rated then you should be able to run the motor itself up to at least 100 Hz, so doubling its speed. My Myford VMB has a 3/4 hp 3 phase motor and VFD and I run it at 75 Hz max which is ~2500 rpm at the spindle on top gearing without the motor even getting warm.

Neil Wyatt23/08/2018 11:14:20
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15589 forum posts
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Sorry Jens, but if you uprate the fuse on a motor and then burn it out, it's your own fault, not that of the maker of the motor.

The 10A fuse would have blown if it was taking more than about 2.5 kilowatts. Is it any wonder it blows if it is being forced to work at over twice it's rated load?

I'm entitled to be blunt because I've done exactly the same thing myself.

The blowing 10A fuses were a warning that something is imposing too great a load on the motor. It's likely that the root cause was either not running in at high speed or, more likely, excessive belt tension.

It is possible that the spindle friction is excessive, see how free it is without a belt fitted.

Neil

Edited By Neil Wyatt on 23/08/2018 11:17:42

SillyOldDuffer23/08/2018 12:10:31
3871 forum posts
779 photos

Jens may have a faulty motor - it does happen. But don't forget the motor is often one of the limitations of a hobby machine. Hobby motors are rarely rated for continuous operation. It's important not to get them too hot.

Sometimes the motor plate gives the rating:

S1 Continuous duty The motor operates at a continuous load for sufficient time to enable machine to reach thermal equilibrium.
S2 Short Time duty Operation at a load for a time not sufficient to reach thermal equilibrium, followed by enough time for the motor to cool down.
S3 Intermittent periodic duty Series of identical duty cycles each a constant load for a period, followed by a rest period. Thermal equilibrium is not reached during the cycle.
S4 Intermittent periodic duty with starting Similar to S3, but there is a significant starting time within the periodic operation.
S5 Intermittent periodic duty with electric braking Sequence of identical duty cycles - starting, operation, braking and rest. Again thermal equilibrium is not reached.
S6 Continuous operation periodic duty Identical duty cycles with a period at load followed by a period at no load. Difference between S1 is that the motor runs at no-load, without actual stopping.
S7 Continuous operation periodic duty with electric braking As per S6, but with a significant starting and electric breaking periods. Again motor operates at no-load for period instead of stopped.
S8 Continuous operation periodic duty with related load/speed changes Series of identical repeating duty cycles, where within each cycle the motor operates at several different load levels and speed. There is not stopped time and thermal equilibrium is not reached.
S9 Duty with non-periodic load and speed variations Load and speed vary periodically within the permissible operating range. Frequent overloading may occur.
S10 Duty with discrete constant loads and speeds Duty with discrete number of load/speed combinations, with these maintained long enough to reach thermal equilibrium.

Hobby machines are usually S3. In this example (my grinding wheel), I think it means I'm allowed to use the wheel for up to 40 minutes, then I have to let it cool down for 40 minutes.

dsc05340.jpg

S3 motors are usually OK for hobby use because our machines usually work in short bursts and have plenty of time to cool off. BUT, once in a while, most of us will work our machines hard. Overheating breaks down the insulation causing short circuits inside the winding.

Dave

PS - Sorry the table has broken the forum.  The original is here.

Edited By SillyOldDuffer on 23/08/2018 12:12:05

Windy23/08/2018 12:29:38
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I had an old round column Warco with similar sized motor and at highest speed burnt out my friend found a similar size quality one at an auto jumble for £25.

Until he found it I had some Brook Crompton 1/2hp motors and managed with a bit of modification to fit one to keep mobile but just used the lower speeds.

Muzzer23/08/2018 12:46:40
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Posted by Neil Wyatt on 23/08/2018 11:14:20:

The blowing 10A fuses were a warning that something is imposing too great a load on the motor. It's likely that the root cause was either not running in at high speed or, more likely, excessive belt tension.

It is possible that the spindle friction is excessive, see how free it is without a belt fitted.

I think he had it right in his first post, last paragraph. Time to fit a proper motor, assuming it's past its warranty period. If it struggles to spin a 1mm drill (effectively zero spindle load), it's just not man enough for the job. Some of those Chinesium motors are just unadulterated crap.

Get a pukka European motor in there. Not sure where to buy one but a certain online auction site might be a place to look.

Worth checking the bearings aren't packed with the finest axle grease, as the load would increase significantly with speed. They should be only lightly greased (<20% of the space) and it probably wouldn't do any harm to clean them out and use oil instead.

Something should be getting hot if all that supposed shaft power is being absorbed in the bearings or belt. Suspect it's the motor though.

Murray

Jens Eirik Skogstad23/08/2018 17:49:31
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364 forum posts
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The spindle move free without hard points, same with other ball bearings in motor and the middle pulley without belt. The belt was not tightened for hard. Suspect that there are problems with centrifugal start switching inside the motor. The motor was new, ran a few hours before the start capacitor died out. Switched to a new start capacitor with the same capacity. The engine has 2 capacitors - start capacitor and running capacitor. And worked well in a few minutes before it ended, as I described in the first message. The condensers were not burned or developed smoke. Smoke came from the motor. A short life motor.

There is nothing wrote about running-in the motor or run the motor in 30 minutes before use, also not all is wrote in instruction created by chinese factory.

I read some of them in commends recommend 3 phase motor + VFD. Will it cost more than a new motor? Better in torque? I am thinking to replace with a 3 phase motor + VFD. Do you have a link?

Thor23/08/2018 17:55:40
1023 forum posts
23 photos

Hi Jens Erik,

When I upgraded my lathe to 3-phase + VFD I ordered a package from Transwave who advertise on this page. A single phase motor might be a bit cheaper, but I think 3-phase + VFD is worth the price.

Thor

Jens Eirik Skogstad23/08/2018 18:39:03
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364 forum posts
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Posted by Thor on 23/08/2018 17:55:40:

Hi Jens Erik,

When I upgraded my lathe to 3-phase + VFD I ordered a package from Transwave who advertise on this page. A single phase motor might be a bit cheaper, but I think 3-phase + VFD is worth the price.

Thor

Thanks! I must take a look at the homepage and find what they sell the 3 phase and VFD set.

Limpet23/08/2018 18:50:13
102 forum posts
3 photos

Hi Jens

When I upgraded my lathe to 3ph and inverter I used. **LINK** no problems at all

Inverterdrive.com 

Edited By Limpet on 23/08/2018 18:50:51

Jens Eirik Skogstad23/08/2018 19:39:33
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364 forum posts
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There is a lot of specifications of inverters, how can i select the right inverter if i select the motor at 1,1 KW 3 phase motor? And is variable revolution better when i want to select the required revolution via inverter?

mgnbuk23/08/2018 20:11:27
489 forum posts
10 photos

I have a TaiwaneseTrutool branded RF30 mill/drill , which appears to be identical bar the maker's name to the earlier (late 80's / early '90s) Warco Major.

This has a 1.5Kw (2hp) motor, not 1.1Kw as Jens Eirick's Chinese version (and the current Warco offering) has. Maybe the Chinese built versions have been downgraded from the original Taiwanese built machine specification ?

Nigel B

not done it yet23/08/2018 20:22:08
2652 forum posts
11 photos

Go for a 1.5kW inverter would be my advice. They can be turned down in power but not increased. Some motors are sold on power output, so need an extra few percent power for efficiency losses. Some cheap motors may be specc’ed on input power. Some motors will withstand a fair overload condition - VFDs usually don’t.

I have a variable speed lathe, but sill use the inverter for speed control at times. Just don’t run your motor at high load and low speed - the cooling fan will be compromised at low speeds. It is likely harder to get a motor, with the correct foot, than choosing an inverter. Some are more expensive because they are a well known brand name or because they use better components. Cheap Chinese tend to fail more frequently, but are getting cheaper all the time.

Also, I would recommend fitting a remote start/stop speed pendant as thay are very handy, and the actual VFD can be mounted well out of harm’s way.

Jens Eirik Skogstad30/08/2018 16:40:48
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364 forum posts
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I has installed the new 2 hp/1500 watt electric motor - 2700 rpm with only 1 condenser (The old motor 1,5 hp/1100 watt - 1400 rpm with 2 condenser). It works much better and i do not need set too high gear (pulley and belt) to keep same speed. Also it's less load on the engine for same spindle revolution. Less hot motor house.

The VFD + motor is not cheap for me.. 

Edited By Jens Eirik Skogstad on 30/08/2018 16:42:00

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