120V Capacitor start/stop Mill motor

[mattbesquare]

My DM45 mill's motor is all wacked out. Switched it back to 110 volt from 220, now it runs will slow with a lot of noise, and the breaker pops after about 5 seconds..

Could this be as simple as a run or start capacitor?

[Al_The_Man]

Sounds like it could be capacitor.
If it is an original R.O.C. motor then this is likely, what were the symptoms in 220?
If it has a centrifugal switch in the motor, then disconnect the cap and give the shaft a sharp spin when turning on the power.
Al.

[mattbesquare]

Thanks Al, always right on it. I swear you are bot or something. When running on 220 it was going at half speed. But running that way since I first got it, took about 25 broken end mills and a month running my feed-rates at half of every calculator in existence until I started measuring the basics again. Turns out the motor was wired by some tool.... (me). Without a tach, if you start wrong, you always assume it is running at the spindle speed it is supposed to. I had no previous experience to compare to.

Switched it to 110 again according to the diagram, new 30 amp breaker, one of the 220 hot lines stripped back to be a ground. And it is doing this now.

I wish didn't try doing everything myself, everything has to be the hard way. Ill reorder two new caps from surplus supplies, only a few bucks there.

[mattbesquare]

Hey Al, surplus center has a huge selection of capacitors, some cheaper than others. I grabbed a few extra that were bigger than the size that came with my motor. From my experience with car radios many years ago, I would assume that larger isn't really a bad thing. But then again, I have been wrong with everything else...

Any reason to not use larger caps? I dont meed mean 88 farads or anything like that, but then again why not...?

[Al_The_Man]

If the motor manufacturer designed things right, then the value of the cap in conjunction with the start winding impedance, is to try and achieve 90 deg phase angle difference with the run winding, so yes, value cannot be too far off the mark.
Al.

[mattbesquare]

If the motor manufacturer designed things right, then the value of the cap in conjunction with the start winding impedance, is to try and achieve 90 deg phase angle difference with the run winding, so yes, value cannot be too far off the mark.
Al.

Ok, way over my head i will follow the advice, thanks Al.

[mattbesquare]

I think i am starting to understand what you mesnt about phase shift..becaus i am running on 110 instead of 220 the motor can get an extra kick from the another phased power surge...does this phased second loop continue or is it only for starting?

The caps coming off the motor sai plu or minus five percent. I couldnt find these, all my searches came up woth the same results, would plu or minus twenty percent cause damage to the motor?

Also one of my caps os rated to 250 volts instead of 450. The capacitance, charging and discharge properties should be the same right? I just has a different sheet thickness perhaps?

Also, i know with dc, dialectric caps are very sensitive to polarity, is this not the case with ac applications? I ask becaue neither the wiring diagrama, nor the capacitor seems to be marked for polarity.

I feel too stupid to be trying tofigure this out, i just dont know where else to go. Thanks so much for the help, it is an incredible learning experience.

[Al_The_Man]

The inductance and capacitance is the same for both 120 or 240v.
I wouldn't run on 240 with a 250v cap, on 120 would be OK.
Any cap that is left connected in run should be AC motor run variety,
Caps that are in for start only and are switched out with a centrifugal motor switch can be AC motor start rated.
If you have two caps on the motor, you usually have a start cap and a run cap.
AC caps are bi polar, so they are not polarity conscious, large caps on DC are generally Electrolytic variety which are definitely polarity sensitive.
Al.

[mattbesquare]

The inductance and capacitance is the same for both 120 or 240v.
...
I wouldn't run on 240 with a 250v cap, on 120 would be OK.
....
AC caps are bi polar, so they are not polarity conscious..

Al.

Ok, starting to get some of this into my thick skull.

I ordered the two capacitors calls for a 20 and a 150 uf. I have rebuilt one of the centrifugal motors before for my band saw, I was very intrigued the first time I saw that. The motor on the DM45 is a capacitor start capacitor run variety, B3/B5 base I think is what it is called.

So when looking at a motor, say a replacement, the base and frame will be specified differently? maybe?

[mattbesquare]

Ok, got both sets of capacitors, big size difference (two different buyers).

I am thinking the 150uf 450v capacitor is sized based on its build (only as large as it has to be), while the larger capacitor with smaller capacitance (20uf 250v) is based off of a standard tooling set or size? A larger dialectic? maybe just full of filler material?

Any reason to not use these as direct replacements on my motor (same capacitance)? I assumed before, and have had nothing but frustration so I am asking before I wire this up and burn the block down....

sorry about the image size

[Al_The_Man]

The larger caps appear to be AC rated caps OK, the smaller ones look like polarized electrolytic which CANNOT be used on AC.
The construction is very different, the larger ones most likely are oil filled and paper dielectric or similar, the smaller ones use a chemical that depends on a DC voltage to produce the dielectric.
You may see Non-Polarized Electrolytic Motor Start capacitors, these are constructed of two polarized electrolytic's back to back and can only be in circuit for a second or two for the start sequence.
Al.

[mattbesquare]

The larger caps appear to be AC rated caps OK, the smaller ones look like polarized electrolytic which CANNOT be used on AC.
The construction is very different, the larger ones most likely are oil filled and paper dielectric or similar, the smaller ones use a chemical that depends on a DC voltage to produce the dielectric.
You may see Non-Polarized Electrolytic Motor Start capacitors, these are constructed of two polarized electrolytic's back to back and can only be in circuit for a second or two for the start sequence.
Al.

Woah, I am very glad I asked. I can't believe I did that. Was looking at the auction angry thinking it was mislabed. But no, it clearly said... VDC. I am feeling like a complete tool today.

I owe you a six pack, instant message me your address or paypal account!

Really, after all the hours of looking I cant believe I bought clearly marked VDC capacitors ...maybe Ill make a stun gun or something...