Replies

1. 
   sawduster | Aug 08, 2003 06:04am | #1

   All I can offer is to parrot what little I have learned about electricity. However, if you think of electricity in terms of water, where amps is pressure and voltage is pipe size, then a capacitor is a bucket. When you switch on a large electric motor it immediately starts sucking up the juice. This creates a vacuum on the system which will collapse the pipe (the draw is too high and the circut breaker will trip). To overcome this you need a little bucket of electricity, the capacitor, to give you a little boost until the water, juice, can start to flow. Once the motor is running normally the capacitor recharges and is ready to give you a boost the next time you start it up.

   I also have had good support from jet/performax, and like you have been sent hunks gratis, even if it was my own stupidity that caused the problem.

   Hope the info helps.

2. 
   IMERC | Aug 08, 2003 06:24am | #2

   A few fast question.

   How many capacitors?

   How many terminals and there configuration?

   What the voltage and MFD rating on the cap?

   Is it dual rated?

   Did the motor get hot enough to small?

   Let's figure out if the motor has a start cap and a run cap. Lets also figure out if your motor switched from start to run. This is a internal centrifically controlled function.

   If your motor did not switch from start to run automatically you may have tosted your motor. The cap provides / gives the motor a jolt of high voltage to develope the torque to start. If the cap is split, half of it provides extra juice to the motor to maintain run torque. The mfgr does this to build motors at a rated horse power cheaper. Think of the cap as a battery, The stored electricty is then released in a fraction of a second to the motor. The liquid is oil. An older cap is loaded with PCB's in super high concentrations. I know the warning flags in your head just started waving. CLEAN UP THE OIL.

3. 
   JohnWW | Aug 08, 2003 07:25pm | #3

   Bear,

   First, the use of PCB's in capacitors was stopped a long time ago, in the 70's I believe, so unless your machine is that old you don't have a toxic material problem.  The oil served as an insulator between the layer's of foil that are wound up inside the can of the capacitor.

   Second, with due respect to the other two replies, neither quite explained the function of a capacitor accurately.  If the motor has only one capacitor, it is a start capacitor.  The start capacitor is connected to one of several sets of copper windings in the field coils that surround the rotating armature of the motor.  The purpose of the capacitor is to create a current lag in the winding it is connected to.  This lag creates a rotating magnetic field around the armature that gets it started spinning.  There are other ways of doing this, but using a capacitor is the best way to create the high torque needed to start the saw turning.  

   The windings that are connected to the start capacitor are only meant to be used for a fraction of a second during start-up, after that they are supposed to be disconnected automatically by a centrifugal switch hidden inside of the motor.  If the windings don't disconnect they get very hot after a minute or two and the capacitor gets fried, which sounds like your experience.  Being that the centrifugal switch is probably bad and the over heating must have done at least some damage to the motor's insulation, I'd try to get the motor replaced by Jet. 

   If the motor has two capacitors on the outside, the second one is a run capacitor, its purpose is to make the motor run more efficiently with less vibration.  It too can burn up from a manufacturing defect or, in some motor designs, a hung up switch.  Depending on the type of failure this could also cause the motor to overheat, causing damage that will shorten the motor's life even if the motor still runs after replacing the capacitor.

   In short, no matter why the capacitor failed, or why, I'd try to get a new motor from Jet.  If you decide to just replace the capacitor, I'd take the motor in to a motor repair shop to get the centrifugal switch checked.  If you don't the problem will probably just repeat itself, though maybe not right away, if the switch is hanging up intermittently.  A second failure will probably destroy the motor if it isn't toasted already.

   Good Luck, John W.    

   
   

   ---

   Edited 8/8/2003 1:44:30 PM ET by JohnW

1. 
   forestgirl | Aug 08, 2003 07:35pm | #4

   John, I want to thank and commend you on the excellent explanation you provided above.  Such a concise and directly pertinent reply involving electricity of all things is refreshing (Can you tell electricity isn't one of my strong subjects? LOL!)  I hope Bear can get Jet to replace the motor.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   Jimma | Aug 08, 2003 10:55pm | #5

   I agree that John's explanation and advice are right on, but did you happen to notice the motor laboring or bogging down as you ripped through that tough ol' oak? Maybe you just plain made that there lil ol' capacitor work too hard keeping things moving? However, it just doesn't add up that the capacitor would fail before the breaker opened up unless it was a defective centrifigal switch OR capacitor.

   Don't you just love it when those of us without the problem get to speculate all over the place?

   Good luck getting it fixed. I once had a Sears motor that wouldn't develop much torque and it wasn't until I took it to a motor repair place that I learned some of the windings had never been hooked up by the factory.

4. 
   riverr1 | Aug 09, 2003 01:22am | #6

   Jet has somewhat of a reputation for capacitors going. Might want to consider having a spare around. Just a thought.

   Don

1. 
   alias | Aug 09, 2003 02:01am | #8

   cheers don will do...b

5. 
   JohnWW | Aug 09, 2003 01:29am | #7

   Bear,

   I can't think of anything beyond the obvious, power loss, heat, smoke, etc. that would indicate a failed motor.  The bigger problem is that the varnish insulating the motor's coils has almost certainly been damaged, but perhaps not to the point that the motor won't run properly for now.  Once it is damaged, the chances are the varnish will eventually fail completely, even under ordinary use, a year or two (or ten years) from now when Jet won't feel obligated to give you a free replacement.  I'd push them hard to get a new motor while the machine is fairly new and they seem agreeable to giving you replacement parts.

   John W.

6. 
   forestgirl | Aug 09, 2003 08:30am | #9

   TB, how long is/was the warranty with the 18" saw?  If it's just one year (rather than two), and they resist providing a new motor for free, you could probably bargain for one at 40% SRP or something like that.  Hopefully not necessary to fall back on that though, right?

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   alias | Aug 09, 2003 05:53pm | #10

   hey fg- hope all is well and congrats on the nuptials, took twice to get it down for me, but well worth it : ) i'm gonna press for that new motor even with the capacitor i think there been damage, and will eventually will end up getting the dirty end of the stick. the odd thing is i've ran the saw through a heavier regimine of work without a wheeze . i was surprised to say the least.. i'll keep the place posted just for the sake of the rest of the rank and file ... stay well pal -bear-

1. 
   forestgirl | Aug 09, 2003 06:22pm | #11

   Thanks for the congrats, bear.  I hope Jet comes through for you.  Sounds like the capacitor is (was? hopefully) a weak link for that motor.

   I'm #2 for my sweetie, but then that one lasted 25 years, so shouldn't be too much to worry about, eh?  LOL!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

1. 
   ccampbell | Aug 15, 2003 10:10pm | #12

   Okay, this discussion has me paranoid about an incident I had several months ago.  My father-in-law (a PhD in Electrical Engineering) converted my Jet DC and bandsaw to 220 using the printed conversion instructions from Jet.  The first time I tried the bandsaw it ran noisily a few seconds and then the capacitor blew.  He came over immediately and we double checked the instructions and the wiring and everything looked good, although he admitted that he thought the instructions were a little odd, but had assumed they were correct.  While still trouble shooting, I turned on the DC but then back off in just a split second because it made the same noise.  It did not blow.  We called Jet and they admitted to a misprint in their wiring diagram and sent out a replacement capacitor.  After that was installed and the wiring was corrected, everything ran fine...

   ...except that I've been paranoid ever since that the motor was somehow damaged and that I'm not getting as much power.  It could be totally in my head, but I FEEL like the DC isn't pulling as hard now.  I did call Jet and ask if there could be a problem, and they assured me that the motor should be fine.  Now that I'm reading this thread I'm worried that I've lost power again.

   Thoughts?

1. 
   alias | Aug 16, 2003 06:05pm | #13

   c-i 've posted this for you to confirm my wiring , with yours i'm doing some mental backtracking to make sure all my base's covered. jet has a history of bad or weak capacitors, how old is your saw i forgot the warranty agreement'sif it's just a year or two. well let us know how you made out..bear - try below-

   Edited 8/16/2003 11:17:00 AM ET by the bear

2. 
   alias | Aug 16, 2003 06:14pm | #14

   try this

   
3. 
   ccampbell | Aug 17, 2003 10:47pm | #15

   The wiring on my saw is fixed now, but I'm still worried that the motors were damaged somehow and are not as strong any longer.  Does anyone know if this is possible based on my previous explanation?

   Bear - attached are a couple of photos.  One is the wiring on my saw motor now.  The other is the diagram from the inside surface of the cover.  This diagram is correct, but the one in the manual is incorrect.  My saw is about 9 months old.

   Edit - sorry for the quality on these - I didn't realize until they were posted that my program had converted them to gif's.

   Edited 8/17/2003 3:54:36 PM ET by CAMPBELLDUST