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Bandsaw Help

Discussion in 'Woodturning Discussion Forum' started by Emiliano Achaval, Oct 19, 2020.

  1. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    I'm not sure how an old t-shirt, I use them for rags, landed on my Jet 18in 110V bandsaw motor. A friend came today, he was using the bandsaw for a while, at least 20 minutes. I started smelling something burning.
    The t-shirt was, I think, covering the vent holes and or fan, both I guess. Above the motor are 2 pieces, one of them melted. Question is, what the heck is that piece, I wonder if this happened because the motor heated because of the t-shirt, or it was going to happen anyway. Any damage to the motor, or can I buy this piece and it's all good? Thanks in advance for your help, as you can see, I'm no electrician, I just know how to turn a machine on, and off. Aloha from Hawaii.
     

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  2. Bill Boehme

    Bill Boehme Administrator Staff Member

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    That is a 40 μF (microfarad) 250 volt motor capacitor. They don't cost much. I would guess that it is a start capacitor, but it could be a run capacitor. The reason that I am uncertain is because of the black metal "bump" next to this capacitor. Open it ... there are usually a couple small screws holding it to see what if anything is inside. If I remember correctly you bought the bandsaw used and the previous owner may have bought a capacitor that was too big to fit inside the bump. If that's the case it is probably a start capacitor. Let me know what you find. Also the owners manual should help in the exploded parts diagram and parts list.

    As for the t-shirt draped across the motor, that's not a clothes rack. You'll notice that the fan on the end of the motor has a cowling around it. The purpose of the cowling is to direct air from the fan over the exterior of the motor in what is called a laminar boundary layer. This is the only thing, other than direct radiation, that cools the motor. by draping the t-shirt over the motor and cowling the motor is essentially getting no cooling at all and, yes, that is bad and may be the cause of the capacitor being cooked. However, motor windings are pretty rugged and replacing the capacitor may be all that is necessary.

    If it were me, I would open the back end of the motor. First remove the cowling and fan and then remove the end plate. The purpose is to check the springs, weights, and switch contacts. These parts make up the centrifugal switch that switches the start capacitor in and out of the circuit.

    It's possible that the motor doesn't have a centrifugal switch ... my fixed speed Jet 1014 mini lathe doesn't, so its capacitor is a type called start/run. It's important to get the right type of motor capacitor or else it might not hold up very long.
     
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  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I checked the manual for the current 18" 120/240 volt Jet bandsaw with 1¾ HP motor and it has a 300 μF 250 volt start capacitor and a 40 μF 250 volt run capacitor. This leads me to believe that your bad capacitor is a run capacitor. You could check Jet's price for the capacitor, but I think that you could get it for a lot less at Grainger or McMaster-Carr.

    Since it appears that the bad capacitor is a run capacitor, you probably don't need to open up the motor, but if it were me I would do it just to make sure that the insulation on the windings still looks good no sign of burning and no ozone smell that comes with burning insulation and arcing.

    It doesn't hurt to get a capacitor with a higher working voltage such as 370 volts.

    μF means microfarads and is sometimes shown as MFD or MF. Occasionally you will see the letter "u" used in place of the Greek letter "μ" (mu).
     
  4. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Thank you very much for your help Bill! I will order the part, I will open the motor to make sure everything looks good. Thanks again.
     
  5. Roger Chandler

    Roger Chandler

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    I was going to reply a start capacitor, but Bill, being the "sparky" among us has you on track. I, for one, have really appreciated Bill's readiness to help a fellow turner with electronic/electric issues over the years. Bill, you are and have been a great resource person.......I personally want to express my gratitude to you!
     
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  6. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Here is the part number of a run capacitor that will work: 7602K71
    The price is $13.50

    Before you order it, I would like to verify that the motor has both a start and a run capacitor. The owners manual that I looked at is for the current model. If your bandsaw is older then it might be different. If necessary we can do a Zoom meeting so that I would be able to see what everything looks like.

    The capacitors at McMaster don't have pigtails ... instead they have quick disconnect tabs. You will need the mating connectors that are crimped on the wires coming out of the motor. The kind that you want is like the ones shown here: ¼" Fully Insulated Single Crimp Female Quick Disconnect . Don't get them from McMaster because they only sell them in bulk. The big box stores should have them in small quantities. You'll also need a cheap crimping tool. If you have an electrician or EE friend this would be a good time to ask a favor. You might even be able to get them to do the job for you.

    The other thing that you will need is a rubber boot that covers the terminals on the capacitor. Whenever I have bought a motor capacitor it comes with the boot as well as mounting hardware, but I've never bought anything from McMaster ... I assume that they will also include those parts.

    If you have an electrical supply house on your island they might have a capacitor with pigtail leads which would save you some work. All that you would need are a couple wire nuts.
     
  7. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    I ordered the part. At first, Mcmaster quoted me $40 shipping for the tiny part. They finally agreed to mail it USPS for 11.50. I found the manual today. Motor seems to be the original, and I was surprised that it says that I can plug it into a 220 outlet, by changing the plug. Would I have more power if I do that? The manual doesn't say much about the motor, or the insides. The bandsaw is model 18" JWBS 18X I have a friend coming to open the motor, hopefully, Saturday.
     
  8. Bill Boehme

    Bill Boehme Administrator Staff Member

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    You can't just change the plug ... it is also necessary to open the motor power access and reconfigure the jumpers. Despite the impassioned testimonials that I see all the time on forums, changing from 120 to 240 on the motor won't change the power output ... not even the tiniest bit. The only thing that will happen is that the voltage to the start winding will be doubled. The start winding is in the circuit for just a fraction of a second while the motor is coming up to speed. When the speed reaches about 75% of the rated RPM the centrifugal switch opens and disconnects the start winding and the start capacitor. During this start up time the motor will accelerate faster at 240 volts than it would at 120 volts. We're talking about less than a second in either case. The downside of 240 volts is that greater stress is placed on the start winding.

    Access to the jumpers in the motor would be either a junction box on the motor or a cover plate on the motor. Generally when you open the motor access cover plate you will see a diagram on the inside of the plate showing the jumper configuration for 120 and 240 volts. Note: motor manufacturers normally state the voltages as 115 and 230 volts with the assumption that under full load conditions the line voltage might be pulled down slightly. I think that this is mainly a legacy thing from early in the previous century when utility power wasn't as robust as it is now.
     
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  9. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Do you have any of the insulated female quick disconnect connectors?
     
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  10. Mark Jundanian

    Mark Jundanian

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    Bill, I've also heard it said that a given motor will run cooler when wired for 240 vs 120. Any truth to that?
     
  11. Joe Kaufman

    Joe Kaufman

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    Bill, I haven't checked newer "high efficiency" motors. The common practice 30+ years ago in motors less than 2HP rating was to parallel the start winding with one run coil of a dual voltage motor. In this case the starting coil voltage always has a max of 120V. regardless of input voltage, 120V. or 240V. Capacitor run or dual capacitor motors were not common at that time. The question of the start capacitor voltage rating occasionally came up, how can the voltage rating be less than 240V.?
     
  12. Bill Boehme

    Bill Boehme Administrator Staff Member

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    There's not a shred of truth to that myth. When configured for 120 volt operation the field run windings are connected in parallel so that each coil has 120 volts across it. When configured for 240 volt operation the field run windings are connected in series so that half of 240 volts is across each coil.

    I've never seen a motor configured like that and I can;t wrap my head around why it would make sense to parallel the start winding with one run coil. That seems to be counterproductive since the goal is to create a 90° phase shift between the start and run windings. What would the winding configuration be for 240 volt operation? Now, I can envision splitting the start winding into two coils, but it's probably an unnecessary expense considering the trivial benefit.
     
  13. Joe Kaufman

    Joe Kaufman

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    The start and run coils (windings) are physically positioned so they are 90 electrical degrees apart in the stator and are connected in parallel to a single phase source. In a simple split phase motor (no capacitor) the windings do not have the same wire size and number of coil turns so the impedance is different and the currents are not equal and slightly out of phase. In a capacitor start motor the capacitor causes the current in the starting winding to lead the voltage as compared to the run winding. The time phase difference in in the windings produces a rotating field for starting. In dual voltage motors the stator coils are connected in series 240V or parallel 120V. The start coils are connected in parallel to one run coil and therefore always see approximately 120V. for either motor voltage. I guess the analogy to a center tap transformer is appropriate. Like I said, this was the common practice 30 years ago and I haven't really paid attention to motors since the efficiency requirements went into effect.
     
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  14. Joe Kaufman

    Joe Kaufman

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    You could make a case where a dual voltage motor could run cooler at the lower line voltage. If you had a relatively constant load such as a fan and a 120/240 volt motor but the power distribution was 120/208 (common in some areas), the total current would be more than 1/2 of the low voltage current. The reactive power would also be higher. Some motors will list a derating or higher temperature rise for such conditions. I saw one on a Craigslist ad last week, it had a US Motors nameplate.
     
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  15. Jim Selby

    Jim Selby

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    Power consumption will be the same on 220 or 110 volts, Heat is power so no change in heat on different voltages.
     
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  16. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Yes, my son has a whole kit, he has a crawler truck, always fixing that, added light bars, switches and more, he said he can do it for me.
     
  17. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I had to Google crawler truck since it turns out not to be in the top ten activities of geezers. Looks like you're in good hands.
     
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  18. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    I got the part today. Came super fast. It was a good idea to order a stronger one. But, it won't fit in the little housing now. That does not bother me. Looks like one of the uses that Duct tape was made for. Bill mentioned that maybe was going to come with a cover, I think. I got a cylinder, no cover. I have to see tomorrow, after I check the insides, how I'm going to hold it in place, maybe just let it dangle.
     

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  19. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    I need you or @Bill Boehme to come for a vacation to Maui.
     
  20. Gary Beasley

    Gary Beasley

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    Cut some pvc pipe and make a cover. Those exposed connectors are not too friendly to the act of living and breathing.
     
  21. Joe Kaufman

    Joe Kaufman

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    Good advise, especially if you have visitors in your shop. In thinking about it, if you glue the end caps on the PVC before you cut it to fit, the capacitor would be fully protected.

    Brings back memories of HS shop classes. Early in the school year someone would charge a capacitor and leave it on one of the workbenches. Invariably some student would pick it up and get a good jolt. Just takes once and you don't easily forget. A charged 300 μF capacitor could be lethal.
     
    Last edited: Oct 24, 2020
  22. Dean Center

    Dean Center

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    OK, I'm appropriately scared of capacitors now. Could someone explain how to tell if a capacitor needs replacing? And how to safely replace a capacitor? Or explain that this is one of those things best left to experts?
     
  23. Rob Fridenberg

    Rob Fridenberg

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    LOL - my high school autoshop teachers always pulled that trick - which also means I am an old dude :( because points were still the primary form of distributor design.
     
  24. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Thank you for the suggestion. That's what I did. Great idea. We checked the motor, looked OK. Attach the little gizmo and the bandsaw fired right up!! A big Mahalo to @Bill Boehme for his help getting me the part number. And thank you to all of you that took the time to make a comment. Happy turner in Maui. Aloha
     
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  25. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I'm glad that your bandsaw is humming along again.I'm surprised that the McMaster capacitor didn't include a rubber insulating boot. The Dayton capacitors that I have purchased from Grainger always came with a boot plus mounting hardware. Your capacitor will be happier in the PVC pipe than it would be in the metal "bump" on the motor housing where it is hotter.

    If you're going to put a cap on both ends of the PVC pipe it would be a good idea to drill some ventilation holes ... ⅛" to ¼" ... small enough to keep most sawdust out.
     
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  26. Bill Boehme

    Bill Boehme Administrator Staff Member

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    If the motor stops running and just hums that is a sure sign that the start capacitor is bad. Start capacitors can become weak resulting in it taking longer for the motor to come up to speed. A weak run capacitor will cause the motor to be noisier and not run as smoothly. If it develops an internal short it will get hot and look like Emiliano's capacitor.
     
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  27. Don Wattenhofer

    Don Wattenhofer

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    Since there is only one contact on the centrifugal switch and current is the main ingredient in contact wear then operating on 120 volts would double the current that the switch has to break causing a bigger arc leading to failure of the starting switch. The continuous current rating for a 1 HP motor is generally 16 amp 120 V or 8 amp 240 V and the biggest common 120 volt outlet is 20 amp. The loading on a circuit is generally 80% or 16 amps on a 20 amp circuit so even cheating on that will only get you to 1-1/2 HP.
     
  28. Joe Kaufman

    Joe Kaufman

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    In fact, auto shop was the introduction and it spread to from there. Old enough to remember being able to purchase Model T coils at Sears and Monkey Ward's? I still have a couple of 'em around. The wood cases with the box joints were a fine piece of woodworking.
     
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  29. Bill Boehme

    Bill Boehme Administrator Staff Member

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    The centrifugal switch has a very fast snap action with a very wide open gap. They have a very high reliability and typically last the life of the motor. If anything breaks on the centrifugal switch it is more likely to be a broken spring on the flyweights. It's also worth mentioning that it's not the current, but the high voltage induced by the rapidly collapsing magnetic field around the start winding that creates the arc. BTW, the typical FLC (full load current) of a 1 HP single phase induction motor is in the range of 12 to 13 Amps. That's the total motor current under full load. The current in the start winding at the time that the contacts open (when the speed is leveling off) would be just a small fraction of FLC.

    Start capacitors are usually back to back electrolytics in a single package and tend to be quite "leaky" (in other words, the dielectric is far from being a great insulator) in comparison to run capacitors which have a low loss polymer film dielectric.
     
  30. Don Wattenhofer

    Don Wattenhofer

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    Yes I was off on the switch wear, as to the amperage of the 1HP motor the 16/8 amp rating came from an old copy of the NEC so I looked at a Baldor 1 HP motor that I have and it has ratings of 13.2/6.6 so I guess the NEC is worst case.
     
  31. Bill Boehme

    Bill Boehme Administrator Staff Member

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    There is a "locked rotor current" (abbreviated on the nameplate as LRC) which is the motor current when the rotor speed is zero. This could be either abnormal like something that is preventing the rotor from turning or a normal condition such as when you turn the power switch on and the rotor speed is zero for an instant. The momentary LRC of a motor is greater than the FLC, but circuit breakers are designed to handle momentary overload surges without tripping. Maybe that accounts for the current value stated in the NEC or else there is a worst-case motor out there.
     
  32. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    We are so lucky to have Bill with all his knowledge. I greatly appreciate it, he got me back up and running in just days, for just a few dollars.
     
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  33. Don Wattenhofer

    Don Wattenhofer

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    IMG_20201026_140305.jpg No LRC on this one, but I suspect that the locked rotor current is much more than 16 amp.
     
  34. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Your suspicion is correct. The locked rotor current can be several times the full load current.

    My memory isn't what it used to be... I have several Baldor motors and none of them show the locked rotor current.
     
  35. Don Wattenhofer

    Don Wattenhofer

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    Which is why people with their shop in an older building with long runs of 14 ga. wire on the circuit could have starting problems due to volt drop on the wires.
     
  36. Bill Boehme

    Bill Boehme Administrator Staff Member

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    For a 1 HP motor on a 120 volt branch circuit, the NEC requires 12 gauge wiring for runs longer than 30 feet up to 50 feet. For runs over 50 feet up to 75 feet the code requires 10 gauge wiring. For runs over 75 feet up to 100 feet the code requires 8 gauge wiring. For runs over 100 feet up to 150 feet the code requires 6 gauge wiring. So yes, if somebody has wiring that isn't up to code it shouldn't be too surprising that they'll experience motor performance problems.

    The situation that you describe would be good justification to reconfigure the motor for 240 volts if that option is available on the motor and the shop has a 240 volt 15 Amp branch circuit..
     

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