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can bad cap = hot motor?
I have an old Baldor grinder that's at least 80 years old. It is a
cap start and run motor. So the cap is always in the circuit of the phase shifted winding. There is no centrifugal start switch. It has always taken a long time to come up to speed but these types of motors do that. However, it seems to take much longer to spin up than my newer Baldor grinder motors that are wired the same. The capacitor is a rectangular shape about 5/16ths of an inch thick and maybe 1.5 x 2.0 inches. It has a brass case with cloth covered wires coming out of the tar used to seal the case. I mention the cap construction just to give an idea of how old it is. I went through the motor a few years ago because the bearings were bad. They had rawhide seals that had dried out, shrunk, and let grit in. I replaced them with modern sealed bearings. The motor runs very smooth. Just like a grinder motor should. Today I used the grinder for about 1/2 an hour and it got pretty hot. I was not loading the grinder very much because I was just grinding points on tungsten TIG electrodes with a diamond wheel I have mounted. Still, the motor got pretty damn hot. Could a bad cap do this? I suppose there could be some shorted windings. In any case, if a bad cap could cause hot running I'll take the thing apart again and replace the cap. Thanks, Eric |
can bad cap = hot motor?
If the cap is original to the motor, replace it. 80 years is a very long time for such a device, keeping in mind that AC-rated capacitors (80-year-old style) will deteriorate just by sitting on the shelf. A modern polyprop cap of the correct rating and voltage will outlive most of us here.
As to the motor itself, do you have an AC ammeter, with specific reference to the clamp-on type? If so, check each leg of the feed - they should be substantially the same when running, and substantially below nameplate when unloaded. If either of those statements is untrue of your motor, it is on its way out, however slowly. But, to answer your question directly, yes, hot-running is a symptom of a failed cap - as is slow starting and poor load handling. Peter Wieck Melrose Park, PA |
can bad cap = hot motor?
On Fri, 14 Aug 2020 05:00:41 -0700 (PDT), "
wrote: If the cap is original to the motor, replace it. 80 years is a very long time for such a device, keeping in mind that AC-rated capacitors (80-year-old style) will deteriorate just by sitting on the shelf. A modern polyprop cap of the correct rating and voltage will outlive most of us here. As to the motor itself, do you have an AC ammeter, with specific reference to the clamp-on type? If so, check each leg of the feed - they should be substantially the same when running, and substantially below nameplate when unloaded. If either of those statements is untrue of your motor, it is on its way out, however slowly. But, to answer your question directly, yes, hot-running is a symptom of a failed cap - as is slow starting and poor load handling. Peter Wieck Melrose Park, PA Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric |
can bad cap = hot motor?
On Friday, August 14, 2020 at 6:32:11 PM UTC-4, wrote:
Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? If the capacitor's value is wrong, it doesn't provide the proper phase shift. That causes the motor to require more power to do the same work. |
can bad cap = hot motor?
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can bad cap = hot motor?
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can bad cap = hot motor?
On 8/15/20 12:20 PM, Paul Drahn wrote:
A grinder has no reason the have a heavy load when it starts, which is the reason for motors with two caps. Well, actually it does. It has the inertia of both grinding wheel to get up to speed. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
can bad cap = hot motor?
On Saturday, August 15, 2020 at 11:33:43 AM UTC-7, Fox's Mercantile wrote:
On 8/15/20 12:20 PM, Paul Drahn wrote: A grinder has no reason the have a heavy load when it starts, which is the reason for motors with two caps. Well, actually it does. It has the inertia of both grinding wheel to get up to speed. The motor could certainly get it up to speed fast with a high torque, but the user of a grinder can wait a few seconds before applying his workpiece... so "low startup torque" :== "low startup load" is acceptable in this application. |
can bad cap = hot motor?
On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery
wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric |
can bad cap = hot motor?
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can bad cap = hot motor?
On Saturday, 15 August 2020 22:19:46 UTC+1, wrote:
On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric Maybe you can restuff it rather than dispose. NT |
can bad cap = hot motor?
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can bad cap = hot motor?
On Sat, 15 Aug 2020 10:20:08 -0700, Paul Drahn
wrote: I suspect your motor has a single capacitor and is a split-phase motor. Cap start, cap run requires two capacitors and the mechanism to switch between the two. A grinder has no reason the have a heavy load when it starts, which is the reason for motors with two caps. Paul Agreed. However, the official name is a "Permanent-Split Capacitor Motor" which has one permanently connected run capacitor. The "Split Phase" motor has no capacitors. See: Two-winding Machines https://people.ucalgary.ca/~aknigh/electrical_machines/other/split_phase.html Permanent-Split Capacitor Motor If run efficiency and vibration are important, but start torque can be compromised, the capacitor can be left in the auxiliary circuit at all speeds. Sizing the capacitor to provide balance at a particular load point, the backwards field can be eliminated, improving efficiency and eliminating torque pulsations. Eliminating the centrifugal switch can reduce the manufacturing cost significantly. The trade-off is lower starting torque, since the capacitor is not sized to provide balance at starting, but for run conditions The design has the disadvantage of having low starting torque, which is the cause of the slow start. At 80+ years old, I would guess(tm) that the capacitor is as dead as the bearings that were replaced. As it gets old, the ESR starts to climb which I presume was the cause of the observed heating. Drivel: My experience with motors was mostly with industrial sewing machines at my father's lingerie factory. At the time some of the older motors would exhibit the symptoms of a shorted winding. What was happening was that some motors were not designed to handle sustained high temperatures. The copper motor wire would expand slightly, cracking the old enamel insulation. New enamel was quite flexible, but old enamel became brittle. My guess(tm) is it took about 40 years to cause problems. Insulation failures were mostly around sharp wire bends. I think varnish insulation did the same thing, but at the time, I couldn't tell the difference between varnish or enamel insulated motor wire. Therefore, when working with really old motors, I always look for loose insulation flakes, which might be an indication of impending shorts. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
can bad cap = hot motor?
On Tuesday, 18 August 2020 16:54:25 UTC+1, wrote:
On Mon, 17 Aug 2020 14:14:28 -0700 (PDT), tabbypurr wrote: On Saturday, 15 August 2020 22:19:46 UTC+1, wrote: On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric Maybe you can restuff it rather than dispose. NT While I can see the draw of keeping all the old stuff intact or appearing so this cap is weird. It's a rectangle about 5/16 inch thick. Modern motor caps are a lot different in shape. Eric You gave its dimensions earlier. It is presumably a flat paper cap. I meant restuff with higher v non-motor caps. NT |
can bad cap = hot motor?
On Tue, 18 Aug 2020 20:11:15 -0700 (PDT), wrote:
On Tuesday, 18 August 2020 16:54:25 UTC+1, wrote: On Mon, 17 Aug 2020 14:14:28 -0700 (PDT), tabbypurr wrote: On Saturday, 15 August 2020 22:19:46 UTC+1, wrote: On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric Maybe you can restuff it rather than dispose. NT While I can see the draw of keeping all the old stuff intact or appearing so this cap is weird. It's a rectangle about 5/16 inch thick. Modern motor caps are a lot different in shape. Eric You gave its dimensions earlier. It is presumably a flat paper cap. I meant restuff with higher v non-motor caps. NT Modern motor run caps are all large. They use a lot of material. It can't be they do this just because of tradition. Eric --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
can bad cap = hot motor?
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can bad cap = hot motor?
On Wednesday, 19 August 2020 17:15:06 UTC+1, wrote:
On Tue, 18 Aug 2020 20:11:15 -0700 (PDT), tabbypurr wrote: On Tuesday, 18 August 2020 16:54:25 UTC+1, wrote: On Mon, 17 Aug 2020 14:14:28 -0700 (PDT), tabbypurr wrote: On Saturday, 15 August 2020 22:19:46 UTC+1, wrote: On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric Maybe you can restuff it rather than dispose. NT While I can see the draw of keeping all the old stuff intact or appearing so this cap is weird. It's a rectangle about 5/16 inch thick. Modern motor caps are a lot different in shape. Eric You gave its dimensions earlier. It is presumably a flat paper cap. I meant restuff with higher v non-motor caps. NT Modern motor run caps are all large. They use a lot of material. It can't be they do this just because of tradition. Eric You could always look up what properties motor run caps have. But did you also notice that even a 1930s paper cap lasted 80+ years? Modern film caps are massively better & smaller. NT |
can bad cap = hot motor?
On Fri, 21 Aug 2020 02:26:26 -0700 (PDT), wrote:
On Wednesday, 19 August 2020 17:15:06 UTC+1, wrote: On Tue, 18 Aug 2020 20:11:15 -0700 (PDT), tabbypurr wrote: On Tuesday, 18 August 2020 16:54:25 UTC+1, wrote: On Mon, 17 Aug 2020 14:14:28 -0700 (PDT), tabbypurr wrote: On Saturday, 15 August 2020 22:19:46 UTC+1, wrote: On Fri, 14 Aug 2020 19:56:04 -0400, Ralph Mowery wrote: In article , says... Yeah, I'm betting that the cap is as old as the motor. I'll take your advice and replace it. I don't understand how the current can be different if there are only two wires feeding the motor. What am I missing? Thanks, Eric Not likely, but if one of the windings is shorted to ground or the capacitor is leaking to ground the current could be different. I guess the cap could indeed be leaking to ground. It has a brass case after all and the case may be touching metal. I will be replacing the cap and that will hopefully solve the heating issue. I'm certain it will speed up the startup. Eric Maybe you can restuff it rather than dispose. NT While I can see the draw of keeping all the old stuff intact or appearing so this cap is weird. It's a rectangle about 5/16 inch thick. Modern motor caps are a lot different in shape. Eric You gave its dimensions earlier. It is presumably a flat paper cap. I meant restuff with higher v non-motor caps. NT Modern motor run caps are all large. They use a lot of material. It can't be they do this just because of tradition. Eric You could always look up what properties motor run caps have. But did you also notice that even a 1930s paper cap lasted 80+ years? Modern film caps are massively better & smaller. NT I know modern caps are much better than old caps. However, why do you suppose it is that motor run caps are so big for their voltage and capacitance ratings compared to other non-polarized caps? I'm serious. Eric --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
can bad cap = hot motor?
I know modern caps are much better than old caps. However, why do you
suppose it is that motor run caps are so big for their voltage and capacitance ratings compared to other non-polarized caps? I'm serious. That is not a bad question at all: a) Because they are AC-rated caps. b) Because the nature of a motor starting puts a tremendous load on the cap for a very short time, so they must be robust enough to absorb that shock, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage. c) Typical NP caps are used a great deal in audio applications, where the voltages are small, and the frequencies high. d) Motor Run caps start around 370V, or so, are typically of much lower capacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM). Hope that helps. Peter Wieck Melrose Park, PA |
can bad cap = hot motor?
On Friday, 21 August 2020 18:27:09 UTC+1, wrote:
I know modern caps are much better than old caps. However, why do you suppose it is that motor run caps are so big for their voltage and capacitance ratings compared to other non-polarized caps? I'm serious. That is not a bad question at all: a) Because they are AC-rated caps. b) Because the nature of a motor starting puts a tremendous load on the cap for a very short time, so they must be robust enough to absorb that shock, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage. c) Typical NP caps are used a great deal in audio applications, where the voltages are small, and the frequencies high. d) Motor Run caps start around 370V, or so, are typically of much lower capacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM). Hope that helps. Peter Wieck Melrose Park, PA Of course motor rated caps have advantages. So do higher rated non-motor caps. But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. NT |
can bad cap = hot motor?
But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA |
can bad cap = hot motor?
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can bad cap = hot motor?
On Sat, 22 Aug 2020 16:11:03 -0700 (PDT), wrote:
On Friday, 21 August 2020 18:27:09 UTC+1, wrote: I know modern caps are much better than old caps. However, why do you suppose it is that motor run caps are so big for their voltage and capacitance ratings compared to other non-polarized caps? I'm serious. That is not a bad question at all: a) Because they are AC-rated caps. b) Because the nature of a motor starting puts a tremendous load on the cap for a very short time, so they must be robust enough to absorb that shock, repeatedly and reliably, in addition to the actual voltage involved. So, whereas the actual operating voltage may be say.... 240 VAC, the start-cap must be rated (at a minimum) of 150% of the operating voltage. c) Typical NP caps are used a great deal in audio applications, where the voltages are small, and the frequencies high. d) Motor Run caps start around 370V, or so, are typically of much lower capacitance than a start-cap (and whereas replacement voltage may be higher, replacement capacitance should remain very close or identical to OEM). Hope that helps. Peter Wieck Melrose Park, PA Of course motor rated caps have advantages. So do higher rated non-motor caps. But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. NT So you suggested that I stuff the old cap with a new cap(s). I knew new motor run caps were too big to fit in the old cap case. You suggested I use modern caps with the same ratings. I wondered why motor run caps are still so much physically larger than caps with the same specs but which are not motor run caps. Then you post the answer above. I am not sure why you even bothered. Eric --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
can bad cap = hot motor?
On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), "
wrote: But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Eric --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
can bad cap = hot motor?
On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, wrote:
On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), " wrote: But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Good stuff with orange juice and 2 or 3 banana liquors. I wonder what an 80 year-old gin bottle would fetch today. |
can bad cap = hot motor?
On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, wrote:
On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), " wrote: But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Eric If you get that time machine working, go back to 1964 and tell Ford to use galvanized sheetmetal on the Mustang. Thanks. |
can bad cap = hot motor?
On 31.12.20 15:48, bruce bowser wrote:
On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, wrote: On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), " wrote: But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Good stuff with orange juice and 2 or 3 banana liquors. I wonder what an 80 year-old gin bottle would fetch today. How do you teach a gin bottle to fetch????? |
can bad cap = hot motor?
On 12/31/2020 11:15 AM, Sjouke Burry wrote:
On 31.12.20 15:48, bruce bowser wrote: On Sunday, August 23, 2020 at 8:11:26 PM UTC-4, wrote: On Sun, 23 Aug 2020 07:20:43 -0700 (PDT), " wrote: But the key point the op appears to have not noticed is that his crude paper cap has already lasted over 70 years. That is more than good enough. We do not know that at all. What we do know is that *FINALLY* Eric has gotten around to dealing with it. Peter Wieck Melrose Park, PA I was going to go back in time to replace that cap but my time machine was serviced byb me after a few gins so instead I waited until I bought the grinder in real time, used it for a couple years, posted a question about it here and now I have a new cap coming. Good stuff with orange juice and 2 or 3 banana liquors. I wonder what an 80 year-old gin bottle would fetch today. How do you teach a gin bottle to fetch????? You can't teach an old gin bottle new tricks. |
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