Mill capacitor centrifugal switch issue?

So you're saying this particular capacitor its taking a single line ?phase? off 220, so 220/2 = 110V in Taiwan. It is rated 125V so has 15V headroom.
But I have 240V, 240/2=120. So 125-120=5V headroom. But if it was lower spec to begin with or degrading, then that's why it bent boom?
I'm still confused, then why the recommended McMaster 250V capacitor?
 
Both the starter and ruin capacitprs should have a nominal voltage rating about double the intended - 250V for a 120V circuit, and 450V for a 24V circuit - this is pretty much standard in a Blador or other NA made motor...
 
Ya, I don't know if this generic info corresponds to my configuration or not, but it kind of infers same voltage both caps, no?
http://www.capacitorguide.com/motor-starting-capacitor/

I'm sure Technician will know right off. I'm just biding my time.... over Christmas & New Year break..... chewing my knuckles in chip making anticipation...
Why cant I type my motor manufacturer specs into Internetland & get the dang schematic?

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A voltage of 125VAC is not unusual for a start capacitor (which is blown), the start coil only see's 1/2 the voltage. The issue is often one of size, a 250VAC capacitor would be significantly larger. The run capacitor is usually oil filled and a rating of 250VAC is acceptable but marginal. Looking up a comparable Baldor motor 2 Hp 120/240VAC they spec a 125VAC electrolytic 850-1020 uF start cap and a 370VAC 15 uF oil run cap. The size "uF" of the caps is motor specific. I would be surprised if you could fit any higher volt caps under the metal cover, but I would try to buy higher quality motor capacitors. You run capacitor is a MPP (Metallized Polypropylene Capacitor) solid type which are often used for run capacitors, although the oil filled ones tend to be more durable. Once again, an oil filled 60 uF 370 VAC capacitor would be much bigger. Yo will often see much larger capacitor covers on some motors like Baldor's.

Since this is not an old motor, and the capacitor dates are recent, I do not feel it is an issue of deterioration seen with electrolytic's that sit unused for years. It is also possible that you have a faulty start switch, it doesn't take more than a few seconds for start capacitor to blow if the switch doesn't kick out, so it also needs to be checked.

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I pulled the cover of my 1HP Baldor motor -the only one easily reached - and the start capacitor is rated 300V and the run capacitor is rated 450V. This is, however a 30 year old TEFC motor, so more current designs (pun intended) will differ.
 
It is true that most dual voltage US spec motors only subject the start leg to half the supply voltage when running on 240 volts ac, so a 125 volt start cap will survive- for what the mfg. considers an acceptable lifetime; a few years, maybe less.
And yes, it's often a size/voltage issue which sets a limit of capacitors you can stuff in there- unless you mount it outside the cover(s).
Mark
Unless the centrifugal switch is stuck or broken, most likely the cap failure is just an infant mortality- it happens
 
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it is generally a (UK) rule that any start/run capacitor should have a working voltage (Wkg) of double the supply voltage, so for a 220/240v supply, the Wkg should be 450/500v. 125 is NOT enough! the capacitor will have to deal with transient supply spikes of many times supply voltage, and the big bang is the classic failure mode of an under rated capacitor!
Phil
 
The placard does not indicate the motor is split phase so I would assume a standard single phase motor. The start cap will be switched in parallel with the run cap. Parallel capacitors add the capacitance but the voltage across each capacitor will still be 240V not 120V.

125V capacitor is not enough for a start cap, when I had my single phase lathe both start and run caps were 400v. My lathe used to eat start caps and had the motor replaced 3 times under warranty. I got so sick of it blowing I removed the start cap altogether, the lathe was not starting under load so the run cap was enough to get the motor going albeit a little slower.

I would also have the tech replace the start switch, if this sticks it WILL kill the start cap in less than 2 seconds.
 
It is unclear as to the wiring of the capacitors in the motor circuit, so I would not assume that the capacitors are in parallel. Given that Jin Shin is a major Taiwanese motor manufacturer, I would not second guess their specifications for the capacitors. As I noted, Baldor (and a number of other motor manufactures) spec a 125VAC capacitor for the auxiliary start wiring as shown above. When the capacitors are run in parallel the Baldor motors spec a 250VAC electrolytic and a 370 VAC oil capacitors. The assumption is the start capacitor is in the circuit for a very short period of time, which may not have been the case in this situation. There is also a percentage of initial failure. Typically I see a much higher capacitor failure rate of the Chinese single phase motors, but rarely the Taiwanese motors. The Jin Shin motors are used in many of the PM mills and SB/Grizzly mills, and I haven't heard of any single phase motor failures. Given that the wiring connections to the capacitors do not look like something from the factory, it is possible that they may not be the original caps but they are both of Taiwanese origin which suggests they may be OEM? So some further details as to the brand of mill and if it was purchased new or used might shed some light on the discussion.

If you look at HVAC/Compressor motor start electrolytic caps rated at 400 uF 250 VAC you are looking at something in the 4 3/8 in x 2 1/16 can size, a 60uf 370VAC oil motor run would be a similar size. My compressor motor has a large compartment for these size of capacitors, but I have not seen this on mill/lathe single phase motors. I would start by contacting the mill manufacturer to get replacements capacitors/verify specs, and also checking the start switch.
 
Thanks. Its a very new model 935-VS1 mill of Taiwan origin. Very similar to a PM-935 but distributed & serviced through a large machinery company here in Canada where I live & they have handled the line for some time. It has maybe an hour of actual run time & still under warranty. The technician has been booked for a service call in the new year. I thought it would be beneficial to post in the meantime in case there was some similar experience or diagnosis. Thanks for the constructive comments. Hopefully this will be resolved soon & I will be sure to report back.
 
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