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View Full Version : how common is it for a capacitor to blow on a mill?



hmcl281
03-11-2009, 10:11 PM
this is the second time that the capacitor on my mill has burn out. the first was about a year ago and took the manufacture about 6 months to send me a replacement. how often do they go bad? should i just try to find a capacitor made in america?



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Milacron of PM
03-11-2009, 10:22 PM
Do you mean on a single phase motor that drives the mill spindle.....or ??

aboard_epsilon
03-11-2009, 10:22 PM
it's quite common on Asian machines ..read quite a few stories in uk rec models engineering about it ..

motors fail as well in short time.

All the best.markj

hmcl281
03-11-2009, 10:24 PM
Do you mean on a single phase motor that drives the mill spindle.....or ??


it's the starter capacitor, or that's what they tell me



it's quite common on Asian machines ..read quite a few stories in uk rec models engineering about it ..

motors fail as well in short time.

All the best.markj

thanks, first time i called they seem to know it was common

Rustybolt
03-11-2009, 10:25 PM
I replaced both my run and start capacitors on my Chinese mill. I ot them from McMaster Carr.

Mad Scientist
03-11-2009, 10:31 PM
Not that uncommon, if the motor is made in china.
My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110. :eek:

hmcl281
03-11-2009, 10:35 PM
I replaced both my run and start capacitors on my Chinese mill. I ot them from McMaster Carr.

thanks i'll go check and see if they have mine, last time i looked all over the place and had to wait on the 6 months it took the manufacture to send me one



Not that uncommon, if the motor is made in china.
My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110. :eek:

i'm doing the same with with the 220 instead of using the 110. how do u tell if the capacitor is rated for 110?

J Tiers
03-12-2009, 12:43 AM
Not that uncommon, if the motor is made in china.
My motor had the option of being wired for either 110 or 220V. I wired it for 220. However it turned out, with a bang, that the capacitor was only rated for 110. :eek:

Normally, the start circuit STAYS across one winding, so it gets only 120V regardless of it being wired for 120 or 240. Sounds like you wired it incorrectly.......

40 uF is low for a start cap, but...... In any case, failures are all in the days work for chinese capacitors, which have had all sorts of problems, just like every OTHER chinese product. QC is not their strong point..... high production is.

A cap like that should be easily available from US sources...... much faster than your dealer got it from china. Grainger probably has it, or can have it in a day. Many other sources exist as well.

hmcl281
03-12-2009, 12:56 AM
there is a graiger near my house, i'll give them a try for the capacitor.

thanks


Normally, the start circuit STAYS across one winding, so it gets only 120V regardless of it being wired for 120 or 240. Sounds like you wired it incorrectly.......

40 uF is low for a start cap, but...... In any case, failures are all in the days work for chinese capacitors, which have had all sorts of problems, just like every OTHER chinese product. QC is not their strong point..... high production is.

A cap like that should be easily available from US sources...... much faster than your dealer got it from china. Grainger probably has it, or can have it in a day. Many other sources exist as well.

Paul Alciatore
03-12-2009, 01:35 AM
thanks i'll go check and see if they have mine, last time i looked all over the place and had to wait on the 6 months it took the manufacture to send me one

i'm doing the same with with the 220 instead of using the 110. how do u tell if the capacitor is rated for 110?

First, look at your picture, your old capacitor is rated for 450 VAC. However, the rated Voltage is not just the line Voltage. An inductive circuit, as in a motor with inductive coils in it, can have Voltages far in excess of the line Voltage. Hence, a 450 Volt capacitor in a machine that is intended to be run on 110 or 220 Volts AC.

I would suspect poor QC on the part of the Chinese manufacturers. Get a name brand capacitor with the same ratings from one of the sources already mentioned or any of a number of US companys and try it out. Chances are it will outlast you. If it fails, then try one with a higher Voltage rating.

Six months to get a capacitor is rediculous. If you can't locate one with under 2 week delivery, PM me and I will assist.

RancherBill
03-12-2009, 01:36 AM
It does not surprise me.

Capacitors can be made right or they can be made cheaply. When they are brand new you cannot tell the difference electrically. The cheap one fail prematurely.

There was a HUGE problem in computer 5 years ago with a fraudulent cap manufacturer that cheapened out on the caps. It was quite apparent when failure rate zoomed above 10% from normal .1%

lakeside53
03-12-2009, 01:50 AM
Very easy to find the right capacitors in the USA. WWW.Graingers.com has every start or run cap you'd ever want.

Any chance this case is a run cap? And it's a 3 phase motor wired to run on single phase?

Start caps are general larger, but are only in circuit for a short time. Run caps are generally smaller, but stay in circuit and pass continous current during operation.

Circlip
03-12-2009, 08:20 AM
Wouldn't be surprised if a local motor re-winder didn't have some in stock.

Regards Ian

ahidley
03-12-2009, 08:58 AM
The chinese ones blow all the time. This happens especially in the winter where starting loads are higher because of stiff belts and thick oil in the gear box.

Sparky_NY
03-12-2009, 09:27 AM
Caps for 220v motors are typically rated 370volt but more does not hurt.

The start cap should only be in the circuit for a second or two then switched out by the centrifical force operated contacts in the motor. If the motor does not start quickly and the cap stays switched in for too long it will go bang. These electrolytic type start caps are only rated for a few short seconds use each time. (guys building roto-phases know this very well)

When its working, how quickly does the machine start and come up to speed? You can usually hear a distinct click from the motor as the rpms increase and the switch trips, it should happen in just a second or two, no more.

As for a new cap, fleabay is loaded with new motor start caps, grainers is also a excellent source. There are two common types. One is the electrolytic type which you have and is quite common, the other is the oil filled type which is in a metal can, usually oval. The oil filled type are far more durable and not restricted to the very short duty cycle during starting.

You may also consider a larger value cap, in microfarads (uf), that will give the motor more of a kick to get it going. I am betting your problem is a combination of a poorer than average quality cap along with somewhat slow starting motor. Slow starting can be caused by low line voltage, poor connections, too small of a wire size and a few other things.

japcas
03-12-2009, 09:30 AM
The start cap blew on my Jet 13x40 lathe. I called the service dept. and they sent out a new motor, caps and all for free. I swapped them out and later took the old motor to a local motor shop and they verified that it was the cap. Cost about $20 to buy a replacement. I later swapped to 3 phase and a vfd and never looked back. Now I have two 2 hp single phase motors laying in the floor, just in case I decide to change it back.:eek: Which I wouldn't do.

J Tiers
03-12-2009, 09:57 AM
There was a HUGE problem in computer 5 years ago with a fraudulent cap manufacturer that cheapened out on the caps. It was quite apparent when failure rate zoomed above 10% from normal .1%

Actually, the real problem was that a chinese company stole the recipe for the electrolyte (an essential part of an electrolytic capacitor, which start caps normally are) from a Japanese company. What they didn't know is that the recipe they stole was not complete. The stolen recipe would not make a good part.

That recipe made its way into many manufacturer's products, via unscrupulous chinese capacitor companies who bought the stolen recipe.

Just about every capacitor made with that recipe WILL fail much sooner than it should.

Maybe these parts are "delayed fallout" from that problem.

A.K. Boomer
03-12-2009, 11:14 AM
My chineese run cap blew the first half hour - I replaced it with a dayco or dayton (I forget which) because I thought they were USA - removed it from the box and is said Made in china, its held for years now but im still keeping my fingers crossed.

Blackadder
03-12-2009, 11:37 AM
The start cap should only be in the circuit for a second or two then switched out by the centrifical force operated contacts in the motor.


Some single phase motors have the cap wired into the start circuit and do not have a cenrif switch but are known as capacitor start and run motors .

also if you do put a higher voltage electrolytic cap than the circuit requires be aware that after a period of use at a lower voltage that cap will not be able to be operated at its rated voltage.

caps are normally rated for RMS volts ac, the peak is root 3 ( 1.73 ) time the rms hence the apparent over spec. volts shown on the cap shown in the OP

hmcl281
03-12-2009, 12:17 PM
thanks for all the help and post. when it happen the first time i called the manufacture of the mill and they kept on saying it would be here next week and 6 months of next weeks i got the cap. i remember asking if i could get the cap somewhere else and they said no, i had to use theirs.

i pm one of the member here and he suggest these cap:


http://www.mcmaster.com/#capacitors/=yqy08


Grainger also has them, Dayton part number 2MDZ6.



i'm not positive if it's the start or run cap, but i was told from teh manufacture if was the start cap. when it happen yesterday, i remember hearing a click as i turn on the mill. the funny thing is that both time the cap went bad i was milling delrin.

lakeside53
03-12-2009, 01:10 PM
If you don't know if it's a start or run cap, for this samll size buy the run version. MUCH more durable anyhow.

hmcl281
03-12-2009, 01:20 PM
If you don't know if it's a start or run cap, for this samll size buy the run version. MUCH more durable anyhow.


called the manufacture and it's a run cap

pcarpenter
03-12-2009, 01:59 PM
the funny thing is that both time the cap went bad i was milling delrin.

Umm....if your starting cap failed while you were milling anything, you either have a problem with the centrifugal switch in the motor sticking, or are loading something so heavily that the motor slows down below the point where that switch would normally kick the capacitor out.

In a single phase motor, a second start winding with a capacitor to shift the phase slightly is used to start the motor. In order to keep this winding (and capacitor) from remaining engaged after the motor comes up to speed, a centrifugal switch is typically used. Flyweights rotating at speed separate a pair of contacts. If the motor slows enough, theoretically these contacts could close again, but not that likely. ON the other hand, the adjustment of the weight assembly and the contact assembly can go out of whack or for that matter the contacts could have become welded.

This could explain why you have blown two of them, too (if the root problem with the cap. staying in circuit has not been fixed.)

Another potential issue is that something is bound up, causing excessive motor load and the motor is trying to start heavily loaded. In a mill, this should not otherwise be the case as you don't start it up with the cutter in the works. Other possible causes could be siezed bearings or as someone else mentioned, cold, overly viscous lubricant.

But yes...as has already been stated, cheap capacitors are famous for puking their guts.

Paul

hmcl281
03-12-2009, 02:14 PM
Umm....if your starting cap failed while you were milling anything, you either have a problem with the centrifugal switch in the motor sticking, or are loading something so heavily that the motor slows down below the point where that switch would normally kick the capacitor out.

In a single phase motor, a second start winding with a capacitor to shift the phase slightly is used to start the motor. In order to keep this winding (and capacitor) from remaining engaged after the motor comes up to speed, a centrifugal switch is typically used. Flyweights rotating at speed separate a pair of contacts. If the motor slows enough, theoretically these contacts could close again, but not that likely. ON the other hand, the adjustment of the weight assembly and the contact assembly can go out of whack or for that matter the contacts could have become welded.

This could explain why you have blown two of them, too (if the root problem with the cap. staying in circuit has not been fixed.)

Another potential issue is that something is bound up, causing excessive motor load and the motor is trying to start heavily loaded. In a mill, this should not otherwise be the case as you don't start it up with the cutter in the works. Other possible causes could be siezed bearings or as someone else mentioned, cold, overly viscous lubricant.

But yes...as has already been stated, cheap capacitors are famous for puking their guts.

Paul


i found out that it was a run cap instead of the start cap. the motor load was on the low end, about 800 rpm with a small end mill cutting delrin. the weather was spring like.