- How to size motor start cap? - 20 Updates
- Both caps blew! Why? - 3 Updates
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 19 10:29AM -0700 OK - keep in mind that the tolerance in electrolytic caps is typically +100%/-20% unless noted otherwise. Your larger caps will be just fine. Peter Wieck Melrose Park, PA |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 19 02:10PM -0400 In article <eb5f51d7-76a7-492f-9532-fbfc38381a48@googlegroups.com>, peterwieck33@gmail.com says... > Your larger caps will be just fine. > Peter Wieck > Melrose Park, PA There are two things wrong here. First this is an AC motor with AC capacitors. Electrolytics will not work on AC as a general rule. Newer capacitors, especially motor capacitors are much closer now in tollorence. I have one here that is rated +- 5% I keep as a spare for my heat pump. Many are rated for a range of capacitance of about +- 10 % now. |
| etpm@whidbey.com: Jul 19 11:21AM -0700 On Thu, 19 Jul 2018 10:29:29 -0700 (PDT), "pfjw@aol.com" >Your larger caps will be just fine. >Peter Wieck >Melrose Park, PA Thanks Peter. Do you know why the MFD value of motor starting caps is such a wide range? The specified caps are 485-582 MFD. Is that the min and max of the cap? Do they spec them that way instead of using a tolerance? Eric |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 19 11:24AM -0700 On Thursday, July 19, 2018 at 2:10:21 PM UTC-4, Ralph Mowery wrote: > There are two things wrong here. > First this is an AC motor with AC capacitors. Electrolytics will not > work on AC as a general rule. *Wrong.* From Wiki: Start capacitors above 20 µF are always non-polarized aluminium electrolytic capacitors with non solid electrolyte and therefore they are only applicable for the short motor starting time. ... If a motor does not start, the capacitor is far more likely the problem than the switch. A non-electrolytic cap, AC or DC of that rating would be as big as a football, or larger. The motor is 40+ years old. That is not 'newer'. That covers both *wrong* things. Peter Wieck Melrose Park, PA |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 19 03:21PM -0400 In article <f6bc1030-8362-47e2-8005-89352657ce64@googlegroups.com>, peterwieck33@gmail.com says... > That covers both *wrong* things. > Peter Wieck > Melrose Park, PA Winki lets anyone post anything. My 50 uF capacitor is not electrolytic and rated for AC. It is no where near footbal size. Not even beer can size. Even the 500 uF or so capacitors for motor starters are no larger than a beer can if that large. People are quoting very old data. Maybe in 1950 the capacitors were larger, but no today. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 19 01:55PM -0700 On Thursday, July 19, 2018 at 3:21:30 PM UTC-4, Ralph Mowery wrote: > large. > People are quoting very old data. Maybe in 1950 the capacitors were > larger, but no today. Go to any site, any manufacturer - and you will find motor-start caps to be electrolytics. Really. Better yet, just open one up. And, exactly, how do you think they are made? Peter Wieck Melrose Park, PA |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 19 06:09PM -0400 In article <b78946c6-8a01-46e0-93a3-b27b98dd9172@googlegroups.com>, peterwieck33@gmail.com says... > Go to any site, any manufacturer - and you will find motor-start caps to be electrolytics. Really. Better yet, just open one up. And, exactly, how do you think they are made? > Peter Wieck > Melrose Park, PA This will be my last post on this thread. There is no use in me trying to educate a person that will not be educated . Unless you can point me to a page that specifies an electrolytic capacitor for a run and/or start capacitor for an AC motor. And I do not mean the capacitors used in a varitabble speed drive, just an ordinary AC motor. If you go to the last sentence or two it will tell you that they are not suited for use on AC lines. Here is a quote from your belovied Wiki https://en.wikipedia.org/wiki/Electrolytic_capacitor Reverse voltage An exploded aluminum electrolytic capacitor on a PCB Standard electrolytic capacitors, and aluminum as well as tantalum and niobium electrolytic capacitors are polarized and generally require the anode electrode voltage to be positive relative to the cathode voltage. Nevertheless, electrolytic capacitors can withstand for short instants a reverse voltage for a limited number of cycles. In detail, aluminum electrolytic capacitors with non-solid electrolyte can withstand a reverse voltage of about 1 V to 1.5 V. This reverse voltage should never be used to determine the maximum reverse voltage under which a capacitor can be used permanently.[51][52][53] Solid tantalum capacitors can also withstand reverse voltages for short periods. The most common guidelines for tantalum reverse voltage are: 10 % of rated voltage to a maximum of 1 V at 25 °C, 3 % of rated voltage to a maximum of 0.5 V at 85 °C, 1 % of rated voltage to a maximum of 0.1 V at 125 °C. These guidelines apply for short excursion and should never be used to determine the maximum reverse voltage under which a capacitor can be used permanently.[54][55] But in no case, for aluminum as well as for tantalum and niobium electrolytic capacitors, may a reverse voltage be used for a permanent AC application. To minimize the likelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity has to be very clearly indicated on the case, see the section on "Polarity marking" below. Special bipolar aluminum electrolytic capacitors designed for bipolar operation are available, and usually referred to as "non-polarized" or "bipolar" types. In these, the capacitors have two anode foils with full-thickness oxide layers connected in reverse polarity. On the alternate halves of the AC cycles, one of the oxides on the foil acts as a blocking dielectric, preventing reverse current from damaging the electrolyte of the other one. But these bipolar electrolytic capacitors are not adaptable for main AC applications instead of power capacitors with metallized polymer film or paper dielectric. |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 19 03:32PM -0700 >Looking again I see that there are TWO model numbers on the motor >nameplate. The top one is 5K483-D, which is a good number as I found >it on the Grianger website. Bingo. <https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-5K483> More: <https://www.google.com/search?q=dayton+5K483+motor> There are TWO wiring diagrms for suffix BB and BA with different capacitor wiring schemes. I guess you have the BB suffix since it has 2 caps in parallel. <https://www.grainger.com/ec/pdf/5K483_4.pdf> BB suffix <https://www.grainger.com/ec/pdf/5K483_6.pdf> BA suffix I couldn't find a reference with the exact capacitor value(s). The parts list should have the Dayton capacitor part numbers on it somewhere. Possible source to double check the values: <http://www.emotorpro.com/capacitors.aspx> >caps and the motor has no run cap. I have two cap coming tomorrow but >they are 540-685 MFD. Will them maybe be a problem? In the meantime I >will try to get the proper caps. I've never seen anything like that but I guess it's possible, especially since Grainger was able to find documentation on the motor. The capacitance range of the new caps overlaps about 1/3 of the range of the originals. Not great, but it will probably at least start. Start caps are only used for increasing starting torque until the motor is up to speed. The motor might complain a little starting with too much capacitance, but once it starts, it should be ok. I've also never seen a 3HP motor without a run capacitor. Weird. To cover some of the other comments: Start caps are always non-polarized electrolytics. For the non-believers see this video where the mad bomber puts 220VAC across a start capacitor to easily disassemble it. <https://youtu.be/OMd9QkinXz4?t=360> Notice the electrolyte oozing out of the capacitor before it blows out. Looks like the guy has done this more than a few times in the past. Run capacitors are also non-polarized, but beside electroltyic, can also be oil filled. Not the best document on the topic but at least covers some of the details: "DIFFERENCE BETWEEN RUN AND START CAPACITORS" <http://www.capacitorindustries.com/wp-content/uploads/Run-and-Start-Capacitors.pdf> According to various web piles, the listed tolerance on most motor starting caps is usually +/-6%. When a range of capacitance is specified, that includes this tolerance. However that doesn't seem to be the case here as the 540-685 cap is a much wide tolerance range. If the capacitor is a nominal 612uF, then that range would be the same as 612uF +/-12%. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 19 04:09PM -0700 On Thu, 19 Jul 2018 18:09:05 -0400, Ralph Mowery >This will be my last post on this thread. Oh, be nice, or would trial by combat be a better way to settle the matter? >Unless you can point me >to a page that specifies an electrolytic capacitor for a run and/or >start capacitor for an AC motor. Are these sufficient? <http://www.keltroncomp.org/index.php/prdcts/ac-motor-start-capacitor> Note the lack of polarity markings. Keltron Aluminium Electrolytic Motor Start capacitors are manufactured... From the Gainger catalog under Dayton: <https://www.grainger.com/category/capacitors/capacitors-and-accessories/motor-supplies/motors/ecatalog/N-19eb> These electrolytic, nonplarized capacitors are designed for normal intermittent service on single-phase AC motor starting circuits. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| etpm@whidbey.com: Jul 19 04:12PM -0700 On Thu, 19 Jul 2018 15:32:39 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: >be the case here as the 540-685 cap is a much wide tolerance range. If >the capacitor is a nominal 612uF, then that range would be the same as >612uF +/-12%. Greetings Jeff, Thanks for the help. As it turns out the motor I have is suffix D. The guy at Grainger found that exact motor and he too was surprised that it did not not have a run cap. The power factor of the motor, according to the label, is 1.15. Wouldn't a run cap improve that a bit? Maybe because the motor was paired with a compressor with a large flywheel the pulsing torque from a single phase motor without a run cap was not considered a problem because the flywheel would smooth things out. My best bench and pedestal grinders are Baldor motors with run caps and they run very smooth. Virtually no vibration. This makes a difference when sharpening drills and grinding tools. In any case the motor never runs hot and the compressor seems fine. Since there are two caps connected in parallel I can connect caps of different values as long as they add up to the correct value needed, right? I ask because I was told that if a smaller and larger value cap are connected in parallel the lower value cap will work harder and so fail sooner. Changing the subject, this is the second time I have called Grainger where they have had to look in a filing cabinet for documentation not in the computer. The previous time was for a compressor and I was given the number for some guy in a warehouse in the Midwest. I told him what I needed and he riffled through some files, found what I needed, and then scanned and emailed me the documentation on the compressor. I think that's pretty good service. Especially since Grainger wasn't gonna be able to sell me new parts to fix the compressor. A part was missing from the unloader assembly and the documentation enabled me to make a new part and wind a new spring and now the compressor works properly. Eric |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 19 04:34PM -0700 >found that exact motor and he too was surprised that it did not not >have a run cap. The power factor of the motor, according to the label, >is 1.15. Wouldn't a run cap improve that a bit? Yep. That's the purpose of the run capacitor. Start on Page 19: <https://www.scribd.com/document/6883830/Tutorial-Motor-Basics-Lecture> The way it works is when stopped both the start and run caps are in parallel. When the motor gets up to speed, a centrifugal switch opens and disconnects the start cap leaving the run cap in the circuit. That means if you try to add a run cap, you'll need to decrease the value of the start cap by the same amount. Since you're already have too high a capacitance on the two parallel start caps, this will mean that you'll be replacing at least one of the two new capacitors. >flywheel the pulsing torque from a single phase motor without a run >cap was not considered a problem because the flywheel would smooth >things out. My guess(tm) is the start winding was intentionally undersized (which is why the start cap is so large). Exactly why, I don't know. >right? I ask because I was told that if a smaller and larger value cap >are connected in parallel the lower value cap will work harder and so >fail sooner. Nope. Two caps in parallel will distribute the current going through them by the ratio of the capacitive reactance (Xl - 1/(2Pi*f*c). The larger capacitor will have the smaller series reactance and therefore draw the most current. However, in the motor, we have a resonant situation, where the run capacitor has a capacitive reactance equal to the inductive reactance of the motor run winding, and therefore cancel each other leaving just the winding resistance to dissipate any power. That's also the ideal power factor point. So, if you parallel a mess of capacitors to make a run capacitor with the correct value for PF=1, then the capacitors will dissipate zero power. >documentation on the compressor. I think that's pretty good service. >Especially since Grainger wasn't gonna be able to sell me new parts to >fix the compressor. Impressive but what will they do when the warehouse guy retires? -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 19 04:48PM -0700 On Thu, 19 Jul 2018 16:34:42 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: >>things out. >My guess(tm) is the start winding was intentionally undersized (which >is why the start cap is so large). Exactly why, I don't know. Ok, I'm wrong. That's not the reason and nothing is wrong. <https://www.scribd.com/document/6883830/Tutorial-Motor-Basics-Lecture> See the drawing on Pg 20 of a capacitor start motor (as opposed to a capacitor start and capacitor run motor). It has only a starting capacitor and no run capacitor. According to the accompanying text: - Larger single phase motors with up to about 10 HP. - A split phase motor with the addition of a capacitor in the starting winding. - Capacitor sized for high starting torque. - Very high starting torque - Very high starting current - Common on compressors and other hard starting equipment. So, adding a run capacitor isn't going to do anything useful with this type of motor. Sorry for the bad guess(tm) but I'm not familiar with this type of motor. Everything I've seen has both capacitors. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 19 11:06PM -0400 In article <ak12ldpk619iljm0bbr1lpa3pf6dmqovfu@4ax.com>, jeffl@cruzio.com says... > least covers some of the details: > "DIFFERENCE BETWEEN RUN AND START CAPACITORS" > <http://www.capacitorindustries.com/wp-content/uploads/Run-and-Start-Capacitors.pdf> I guess it is my time to be educated. Those start capacitors are common but a special case for electrolytics. Good for a short time, but will let loose if AC is applied for very long at one time. |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 19 08:40PM -0700 On Thu, 19 Jul 2018 23:06:54 -0400, Ralph Mowery >I guess it is my time to be educated. Those start capacitors are >common but a special case for electrolytics. Good for a short time, but >will let loose if AC is applied for very long at one time. Maybe. There are different levels of quality in such capacitors. Since the heat generated is mostly from the ESR (equivalent series resistance) of the capacitor, a low ESR would heat up less and theoretically last longer. However, that's not what causes caps to die: <https://youtu.be/OMd9QkinXz4?t=345> He starts out putting a run capacitor across 220VAC and leaves it connected. It stays cold and nothing happens. Somewhat later in the video, he does the same to a large value start capacitor. It belches hot steaming electrolyte and then blows the end off. If the centrifugal start switch sticks or is delayed in opening, for example by line undervoltage, the switch stays closed for too long and cap dies. Part of this is ESR and ripple current heating, but the real culprit is junk centrifugal start switches with partly welded contacts. If the switches were good, methinks that even the lowest cost motor start capacitor would last forever. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Jeff Layman <jmlayman@invalid.invalid>: Jul 20 08:53AM +0100 On 20/07/18 00:34, Jeff Liebermann wrote: > Impressive but what will they do when the warehouse guy retires? Some time back there was an old guy whose sole job for 20 years was to make a product in a 1000+ litre reaction vessel with viewing ports, using several steps. Just before he retired, he wrote out all the info needed for the new guy to make the product. But try as he might, with the new guy the process always failed at a certain stage near the end. The company called the old guy and asked him to come in and make a batch with the new guy looking on. He started the process, peering through the viewing port, and the product came out perfectly at the end. The new guy asked him how he knew when to add ingredients at the step where it had always failed before. His answer? "It looked right". -- Jeff |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 20 06:49AM -0700 On Thursday, July 19, 2018 at 7:09:27 PM UTC-4, Jeff Liebermann wrote: > Oh, be nice, or would trial by combat be a better way > to settle the matter? On Trial-by-Combat: https://www.youtube.com/watch?v=ua_TZ84hmEA Peter Wieck Melrose Park, PA |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 20 10:26AM -0400 In article <pis4d6$764$1@dont-email.me>, jmlayman@invalid.invalid says... > asked him how he knew when to add ingredients at the step where it had > always failed before. His answer? "It looked right". > -- Sometimes you just have to go by looks or feel than by the book. Where I worked there was a device to pull a vacuum on the process. It was very simple. Five seperate stages of a long pipe with what looked like a trumpet horn in the end that steam was put through. Seemed that only me and another could trouble shoot them very well. Others just replaced parts tuil they stumbled on the right one. On more than one ocassion it went like this. The day shift worked on it most of the day and would leave about 11 at night. Then me and the other man would get it going in less than an hour. We had just worked out some tests that were very simple and easy to make, but were not in the book. |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Jul 20 07:56AM -0700 On Friday, July 20, 2018 at 3:53:12 AM UTC-4, Jeff Layman wrote: > > Impressive but what will they do when the warehouse guy retires? > Some time back there was an old guy whose sole job for 20 years was to > make a product in a 1000+ litre reaction vessel with viewing ports, Sometimes, this is much like making bread. Flour varies from day to day. Yeast will vary, even the dry stuff. Humidity, temperature, salt content. It comes down to the kneading - and getting that right, more importantly, when to STOP kneading. Peter Wieck Melrose Park, PA |
| Jeff Liebermann <jeffl@cruzio.com>: Jul 20 08:48AM -0700 On Fri, 20 Jul 2018 06:49:27 -0700 (PDT), "pfjw@aol.com" >https://www.youtube.com/watch?v=ua_TZ84hmEA >Peter Wieck >Melrose Park, PA At a former employer, I would sometimes bring my fencing kit (foils, mask, gloves, conductive jacket, helmet, buzzer, etc) to work. The kit would usually live in my truck, and only be dragged inside for a quick show and tell, or to repair the badly designed contact buzzer. Someone walked into my office, saw the foil, and decided that dueling must be my favored method of settling disputes. Within days, everyone knew that I was armed to the teeth and that I was prepared to do battle with anyone that criticized my decisions. I had no idea that the story had become so distorted. At the next design review meeting, I was asked to leave all weaponry at the door and that company policy forbids bloodshed during working hours. I still didn't understand what was happening, until someone mentioned the fencing foils. When I proclaimed that my kit was in my truck, everyone seemed to visibly relax. About a year later, I gave a quick fencing demonstration with a friend in the parking lot during lunch. It went well and we all went back inside when lunch was over. However, someone apparently called the police. At some point, fencing morphed into dueling, which the police interpreted as using dueling pistols. When the SWAT team eventually arrived, there was nothing to see, so they surrounded the building and started to evacuate the neighboring businesses. I'm going to skip over the next hour and just say the police left looking rather disappointed. Of course, management was not thrilled, but eventually concluded that it wasn't really my fault that things escalated out of control. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| etpm@whidbey.com: Jul 20 09:22AM -0700 On Thu, 19 Jul 2018 16:48:30 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: >So, adding a run capacitor isn't going to do anything useful with this >type of motor. Sorry for the bad guess(tm) but I'm not familiar with >this type of motor. Everything I've seen has both capacitors. I thought that maybe the really large capacitance was for higher torque, now I know it that it is. Thanks. Eric |
| Terry Schwartz <tschw10117@aol.com>: Jul 19 11:26AM -0700 > failed because of the extra work it had to do? > Thanks, > Eric The caps blew because they are decades old, in a high stress application. Once the first one blew the second was way overstressed. AC rated caps are tenuous beasts to begin with. My cousin in the HVAC business says compressor caps should be replaced every 5 years.... |
| Ralph Mowery <rmowery28146@earthlink.net>: Jul 19 03:15PM -0400 In article <115415f9-6239-409d-804a-71529c257af6@googlegroups.com>, tschw10117@aol.com says... > The caps blew because they are decades old, in a high stress application. Once the first one blew the second was way overstressed. AC rated caps are tenuous beasts to begin with. My cousin in the HVAC business says compressor caps should be replaced every 5 years.... I don't doubt that 5 year number for them. I had one to go out after about that ammount of time on my heat pump. A repair man replaced it and it took him about 15 minuits to find the problem and replace it for a cost of about $ 300. I bought one off ebay for less than $ 20. After about 5 years the capacitor went bad , so I replaced it myself and ordered another one for about $ 20 to keep as a spare. He also told me of a relay that often goes bad, so I bought one of those as a spare for about $ 20. Sofar it has not needed replacing. If replacing the capacitor , try to stay within the capacitance range,but you can go to a higher voltage rating. Get one rated for 440 volts if possiable. Also look at the temperature rating. While many are around 85 deg C see if you can find one rated for about 105 deg C. Those usually last longer. |
| jurb6006@gmail.com: Jul 19 05:08PM -0700 >"My cousin in the HVAC business says compressor caps should be replaced every 5 years.... " I had to replace ours a few years ago and the electric bill went down. |
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