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RobbieKnobbie
12-15-2010, 04:52 PM
I have one of the Harbor Freight 6x12 surface grinders that come up around here every so often. I've had very good luck with it so far, I've owned it abotu 3 years, give or take.

It's set up out in my barn, which is unheated. It's 25-30 degrees in there.

So I'm out there grinding a thin steel ring down to thickness. The ring is about 1 3/4 OD with a 3/16 wall. The ring is .218 and I was bring it down to .210 (not in one pass!)

About five or six minutes into the job the capacitor on the side of the motor lets out a little 'POP' and then starts to sizzle and smoke. I shut down the grinder as quickly as I could, and then I noticed the sexy little appendage growing out the side of the cap housing:eek: ...

http://i96.photobucket.com/albums/l166/robbieknobbie/105_1710.jpg

http://i96.photobucket.com/albums/l166/robbieknobbie/105_1709.jpg

So my question is this... Do you think the cap crapped (sorry, couldn't help it) because of the cold weather, because I haven't used it in six months, or because it was just a crappy chinese capacitor and was bound to go sooner or later? You may not be able to see in the pictures, but it was literally wrapped in cut up newspaper! The NINGBO DAILY from May 4th 2007.

The grinder has fewer than 10 hours of actual run time on it. The cap itself is rated at 40uf +- 5%, 370V, 50/60Hz. Manufactured by Kaihong Capacitor Company.

Lastly, is there an alternate capacitor type (not electrolytic maybe?) that would be more reliable or suitable in this application (infrequent use, run in the cold)?

Carld
12-15-2010, 04:58 PM
Almost any motor shop can supply you with a replacement. It's hard to tell what caused it to fail, just replace it.

John Stevenson
12-15-2010, 05:03 PM
It's the papers fault.
May the 4th be with you.

gnm109
12-15-2010, 05:04 PM
I have one of the Harbor Freight 6x12 surface grinders that come up around here every so often. I've had very good luck with it so far, I've owned it abotu 3 years, give or take.

It's set up out in my barn, which is unheated. It's 25-30 degrees in there.

So I'm out there grinding a thin steel ring down to thickness. The ring is about 1 3/4 OD with a 3/16 wall. The ring is .218 and I was bring it down to .210 (not in one pass!)

About five or six minutes into the job the capacitor on the side of the motor lets out a little 'POP' and then starts to sizzle and smoke. I shut down the grinder as quickly as I could, and then I noticed the sexy little appendage growing out the side of the cap housing:eek: ...

http://i96.photobucket.com/albums/l166/robbieknobbie/105_1710.jpg

http://i96.photobucket.com/albums/l166/robbieknobbie/105_1709.jpg

So my question is this... Do you think the cap crapped (sorry, couldn't help it) because of the cold weather, because I haven't used it in six months, or because it was just a crappy chinese capacitor and was bound to go sooner or later? You may not be able to see in the pictures, but it was literally wrapped in cut up newspaper! The NINGBO DAILY from May 4th 2007.

The grinder has fewer than 10 hours of actual run time on it. The cap itself is rated at 40uf +- 5%, 370V, 50/60Hz. Manufactured by Kaihong Capacitor Company.

Lastly, is there an alternate capacitor type (not electrolytic maybe?) that would be more reliable or suitable in this application (infrequent use, run in the cold)?

I'm not the motor expert here but it's likely that you just got a bum capacitor. It could have something to do with the low temperature, but I sorta doubt it since high temps are generally more damaging to electrical components.

I don't know whether your motor has a centrifugal start switch inside. I'm just guessing that the cap simply gave out.

If you can get a US made one in the same size, you would probably be better off. I recently bought a pair of Mars brand for start caps for my new RPC. They were advertised as Made in US but when I got them, they said Made in Mexico. What a nice surprise!

The great preponderance of capacitors sold on eBay are made by Packard n China. They are OK but they have certainly flooded the market.

You need to determine whether your cap is a start cap or a run cap. After that, just get the right physical size and capacitance. Might even take it to a motor shop and let them install the caps and test the motor.

It just occurred to me that it was wrapped in newspaper since it was built only for "periodical" use. (pun intended). :)

RobbieKnobbie
12-15-2010, 05:04 PM
Carl: I plan to replace it... I'd just like to upgrade it to something a little more reliable, if possible.

GNM: I'm assuming it's a start cap, it's the only one. Most motors with run caps that I've dealt with have 2 caps: one start and one run(not that I'm an expert - obviously)

Thanks for the replies, guys. (except you, Mr Stevenson)

jugs
12-15-2010, 05:12 PM
You may not be able to see in the pictures, but it was literally wrapped in cut up newspaper! The NINGBO DAILY from May 4th 2007.

Lastly, is there an alternate capacitor type (not electrolytic maybe?) that would be more reliable or suitable in this application (infrequent use, run in the cold)?


You need to make sure the new cap is wrapped in one of these LINK (http://www.icenews.is/)

john
:)

MotorradMike
12-15-2010, 05:16 PM
It's the papers fault.
May the 4th be with you.

HaHa,
Yes, the Ningbo Daily is not a quality rag!

Seriously:
It must be a run cap because you were in 'run', not 'start' mode.
One advantage of electrolytics is small size. You could replace it with polypropylene but it worked for 3 years so why not buy another one that fits in the same place and go from there.
I'd go to an electric motor shop and pay what they want as long as they say they have good luck with the brand.

RobbieKnobbie
12-15-2010, 05:35 PM
I just did some googling and found this: Start caps are typically in the 100's of uf while run caps are typically in the to's of uf. So that, plus the 370volt rating suggest it's a run cap.

Live and Learn!

Looking for a motor shop now; failing that I see Digikey has a few Run Caps with matching, or higher, specifications in stock. Gotta love the internet-age!

DR
12-15-2010, 05:35 PM
Can we assume for 100% sure the motor wasn't still in start mode?

Cold plus not running it for 6 months, maybe the grease had solidified and it never got up to speed in run mode?

RobbieKnobbie
12-15-2010, 05:43 PM
I'm fairly confident that it was up to speed when it pooped... but you're right insomuch as Who's to say the centrifugal switch (if it has one) ever dropped out? it may be crudded up with frozen gooped up grease and kept the start circuit active!

I can say that I tried to start it up again (knowing that to be a bad idea) and even after I gave it a nudge by hand it just sat there and ran at about 10 or 20 rpm

Liger Zero
12-15-2010, 05:51 PM
You might be able to put that slag in your molding machine and make something useful out of it.

uncle pete
12-15-2010, 05:57 PM
Not to hijack this thread but there's two differnt comments on this thread that I thought were as good or better than the best standup comedy I ever heard. "May the 4th be with you" and "not a quality rag" Simply awesome.

Pete

DR
12-15-2010, 06:17 PM
duplicate post

darryl
12-15-2010, 08:42 PM
So the chinese crap cap crapped. What else is news?

gnm109
12-15-2010, 08:50 PM
So the chinese crap cap crapped. What else is news?


The real news is that you will have a difficult time finding any start or run capacitors that were not built in China.

J Tiers
12-15-2010, 09:33 PM
The part does not look like an electrolytic, although the Ningbo daily is obscuring most of it.

Replace with same type film cap.... Run caps must be film, or paper and oil, etc. Never electrolytic.

As for motors with a run cap only, they are common, and a surface grinder might be a good application for one...... They are known as "PSC" motors, and the run cap supplies a 'second phase" that increases the smoothness of rotation, a good thing for a grinder.

Bill736
12-15-2010, 09:50 PM
Very thrifty, those Chinese. I can recall from my youth fireworks also made from Chinese newspapers. In my experience, capacitors are odd devices. Some seem to last forever, some fail almost immediately, and most are somewhere in between. Back when most engines ( auto, tractor, lawn mowers, etc.) had ignition points, they also had a capacitor (condenser) attached. The reliability of those capacitors was so varied that I regarded a functioning used capacitor as superior to a new capacitor of unknown reliability. The more recent introduction of Chinese made capacitors introduces a new element of uncertainty.

Teenage_Machinist
12-15-2010, 10:04 PM
Oh god. As some of you know this happend to me a month or two ago. It's easy to find new capacitors online. Whether they are US made is unknown but imports can be pretty good.

RobbieKnobbie
12-15-2010, 10:37 PM
Yes they are, and here's the one I just ordered...Motor Run Cap (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=495-4346-ND)

J Tiers
12-15-2010, 10:48 PM
Little size and shape difference there?

RobbieKnobbie
12-15-2010, 11:35 PM
Do the electrons come out of oval capacitors differetly from round ones?

Evan
12-16-2010, 01:33 AM
It depends....

J Tiers
12-16-2010, 08:29 AM
Do the electrons come out of oval capacitors differetly from round ones?

It's more about the "gozinta" where the old one was...... I usually like to put the new part back where the old one was, and avoid using "Bubba tape". Not always possible.

jugs
12-16-2010, 08:47 AM
It depends....

On what :confused:

john
:)

Liger Zero
12-16-2010, 09:34 AM
On what :confused:

john
:)

Polarity. Some electrons are positive and some are negative. You have to make sure when you order that you order one full of the right kind.
























fer gosh sakes PLEASE don't start a flame war over this. :D

mike os
12-16-2010, 09:45 AM
... I thought some were round & others from the oval caps were hexagonal? sure I read it in 'tinternet someplace:eek: :rolleyes:


now we have +ve & -ve too.... do you get both shapes in each or is it one for each???

pcarpenter
12-16-2010, 11:15 AM
Before we go too far off into humor, there are a couple of things that should be figured out to prevent blowing another one.

The capacitance of the capacitor has less to do with the function than the size of the motor. If that were a higher HP motor, you would need a several hundred uf cap to start it...not so with fewer or fractional HP.

The fact that the motor will not start without it now tends to suggest to me that it is likely a start cap. As mentioned, if your centrifugal switch is not kicking the start cap out after the motor reaches speed, that could easily blow a new one. Since some of these designs slide on the motor shaft under spring tension, pull the cover off and look for a centrifugal switch...which answers the start vs. run question. Then, if it has a centrifugal switch, make sure it's not rusty, crusty, or prevented from proper operation by cold pasty lubricant etc.

Bearings that are full of grease do not turn so easily when cold and can prevent it from coming up to speed as easily as they should. This can leave the cap in circut longer than it normally would, too.

In any case, check the function of the centrifugal switch by hand to make sure there is not an issue there. I had one that merely had the spring-contact type contacts, that had the contacts melted together. It's a downhill spiral....if the switch doesn't function as it should, then it can burn the contacts together by staying in circuit when it would otherwise kick out. That then insures that it never disengages.

Paul

RobbieKnobbie
12-16-2010, 11:17 AM
OK, we've got some great debate going here, and I for one am certainly learning a lot.

I called Digikey about my order and they assured me that the capacitor I ordered would be able to capacitate both positive and negative electrons: That's one of the benefits of the oval case models over the more polarity-sensitive (cheap chinese made) round ones. I also asked about round v. hexagonal and they said that ALL electrons used in American made electricity are round, citing the round cross section of copper wire as proof. ( so much for the 'know it alls')

They were really patient with my questions, and even explained to me that the hexagonal electrons (and the square one so popular in Europe) are used for structural purposes - which is why the steel wire rope used in bridge building is so often hexagonal in overall cross section.

To be honest, I never even thought about any of this so I'm getting a real education. Thanks Guys, I really appreciate the help.

Oh, and as for mounting a differently shaped capacitor with 'Bubba Tape...' I'll misquote a wiser man than I and say 'that's why I have a $10,000 machine shop in my basement'

gnm109
12-16-2010, 11:22 AM
Before we go too far off into humor, there are a couple of things that should be figured out to prevent blowing another one.

The capacitance of the capacitor has less to do with the function than the size of the motor. If that were a higher HP motor, you would need a several hundred uf cap to start it...not so with fewer or fractional HP.

The fact that the motor will not start without it now tends to suggest to me that it is likely a start cap. As mentioned, if your centrifugal switch is not kicking the start cap out after the motor reaches speed, that could easily blow a new one. Since some of these designs slide on the motor shaft under spring tension, pull the cover off and look for a centrifugal switch...which answers the start vs. run question. Then, if it has a centrifugal switch, make sure it's not rusty, crusty, or prevented from proper operation by cold pasty lubricant etc.

Bearings that are full of grease do not turn so easily when cold and can prevent it from coming up to speed as easily as they should. This can leave the cap in circut longer than it normally would, too.

In any case, check the function of the centrifugal switch by hand to make sure there is not an issue there. I had one that merely had the spring-contact type contacts, that had the contacts melted together. It's a downhill spiral....if the switch doesn't function as it should, then it can burn the contacts together by staying in circuit when it would otherwise kick out. That then insures that it never disengages.

Paul


All good "points" you make (pun intended). It could be a combination of cold weather and a sticking start switch that led to the untimely demise of that Chinese, paper-wrapped chick...ahh, err, I mean capacitor. I would disassemble the motor and have a look at the switch and points as you suggest.

I see you are in Illiinois. I was born in Chicago and left right after high school. I couldn't take the weather. I admire anyone who likes snow and cold weather. I will do that from a distance, however. LOL.

RobbieKnobbie
12-16-2010, 11:24 AM
Before we go too far off into humor, there are a couple of things that should be figured out to prevent blowing another one.
Paul

Good points. This is what I was looking for when I started this thread.

I will try to get in there and check the presence/operation of the centrifugal switch this afternoon. I'll let you know what I find. Before I open it up though, I have a question...

How do I keep the electrons from pouring out when I open up the motor? Is there a special kind of electrical tape for keeping everything in there, or should I just use duct tape?

Amigo
12-16-2010, 11:44 AM
Had a friend that was an electrical engineer, who told me that in most applications whether electronic or simple electric, that a 20% increase (over OEM) in capacitance for most circuits would not cause any problems and when it came to motors usually beneficial. That was both for electolytic start and oil filled run.
In addition, I had a motor with an OEM 5mf (uf) run cap that would last only a year to 18 mos, after a couple 5 mf replacements, I replaced with a 7mf and is still running fine over 20 years later.

Liger Zero
12-16-2010, 12:10 PM
How do I keep the electrons from pouring out when I open up the motor? Is there a special kind of electrical tape for keeping everything in there, or should I just use duct tape?


Lockout-Tagout. Contrary to popular belief those locks aren't there to protect YOU they stop the electrons from spilling. Electricty is EXPENSIVE you don't want to pour it all over the floor.

Bill736
12-16-2010, 12:19 PM
This thread is proof that this forum will never constitute a Wiki source of technical information. But, we have fun !

Liger Zero
12-16-2010, 12:29 PM
This thread is proof that this forum will never constitute a Wiki source of technical information. But, we have fun !


Which is good. Wiki gets it glaringly wrong in many cases and no one catches it.

We have peer review here. If someone is WAY off, a correction is forthcoming.

RobbieKnobbie
12-16-2010, 12:40 PM
... If someone is WAY off, a correction is...

Fortunately that doesn't apply to this thread.

Tinkerer
12-16-2010, 12:51 PM
Good points. This is what I was looking for when I started this thread.

I will try to get in there and check the presence/operation of the centrifugal switch this afternoon. I'll let you know what I find. Before I open it up though, I have a question...

How do I keep the electrons from pouring out when I open up the motor? Is there a special kind of electrical tape for keeping everything in there, or should I just use duct tape?
Unplug the cord and kink it... then wrap with tape. As long as you keep the end lower then the top of the motor none will leak out when you pop the top. ;)

dockrat
12-16-2010, 12:57 PM
Unplug the cord and kink it... then wrap with tape. As long as you keep the end lower then the top of the motor none will leak out when you pop the top. ;)

Now thats an example of why I keep coming to this site. Sooooooooo many neat tricks to learn :)

pcarpenter
12-16-2010, 01:17 PM
Amigo is largely correct. The "correct" cap value for a starting cap is usually really a range. That's a good thing, because when you buy most starting caps, they have a nominal value and if their real values are within 20% of that you are doing pretty good.

True, more capacitance will often result in faster startups, but you can go overboard and get a really harsh start and high inrush currents to the start windings. The goal is not to shake the motor apart on startup. Likewise, if the value is too low, the startup is slow enough that the cap is not taken out of circuit very quickly and it's more prone to failure.

Buying a starting cap with a higher *voltage* rating than you need is often a good move. On the other hand, higher voltage ratings often result in a larger form factor.

Edit-- P. S. I am in central IL, and our winters do still suck...especially when they start off this cold this soon, but you don't have to *love* snow or winter to live here. I just tolerate it. I would miss not having the seasons.

Paul

mike os
12-16-2010, 04:42 PM
Personally I woud get the cap from a place that deals with motors, & take their advice as to size, type etc.


all this has got me thinking.....you know how cable is different sizes (CSA)? so are the electrons different sizes to fit, or is it a bit of a bodge job with one size fits all? (or indeed are they elastic to accomodate?)

also is it possible to use different patters within the same system eg if I buy a tool from the US will it work with the octagonal ones we have over here?

and with multicore cable...do they use smaller ones in each wire or does it kind of strech to fit over them all?


one other tip... kinking & taping is all well & good, but a simple knot will prevent leakage in smaller sizes

Stepside
12-16-2010, 09:35 PM
Worried the electrons will spill out? Hook a shop vac to the nonopened end of the motor. It is the end away from the starting switch thing-a-ma-bobby. Place some panty hose over the end of the vacuum hose so you can suck but the electrons will stay inside the motor. As a side benefit this gets rid of any of the "magic Smoke" that has been contaminated.

J Tiers
12-16-2010, 10:25 PM
Before we go too far off into humor, there are a couple of things that should be figured out to prevent blowing another one.

The capacitance of the capacitor has less to do with the function than the size of the motor. If that were a higher HP motor, you would need a several hundred uf cap to start it...not so with fewer or fractional HP.



If itis not an electrolytic, AND based on the value, it should be "both" a start and run.....

A PSC motor has one cap, which is never switched out. No cap, no run.

They are a little more fussy about correct value than a plain start cap.... But for any, the right value, while a range, is not unlimited..... the cap is in for a reason, and teh reason is phase shift.

Too small a cap has plenty of phase shift, but no current to speak of.....

Too large a cap has plenty of current, but very little phase shift.

You need BOTH current (to produce torque) and phase shift (to produce a rotating field from single phase voltage). As a result, there is indeed a range, and within the range, there is an optimum value.

Krunch
12-17-2010, 04:58 AM
It's the papers fault.
May the 4th be with you.

OUCH! ROFL! :p

bob_s
12-17-2010, 02:01 PM
Go with non-polarized electrolytic or Mil-Spec tantalum capacitors.

Just beware that the Mil-Spec capacitors could set you back $200 a pop (so to speak) :)

J Tiers
12-17-2010, 10:27 PM
Go with non-polarized electrolytic or Mil-Spec tantalum capacitors.



Do not do this.

if ir is electrolytic start cap, which would be VERY surprising,. replace with similar type.

But at 40 uF, it will be a film type run cap almost certainly......

Yes, I know the OP already bought a good run cap. I'm just counteracting some bad advice... You know, "wait a minute, I'm typing... someone on the internet is wrong"......