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Electric Motors/capacitor failures on electric motors Kansas City


QUESTION: Our exhaust fans on our roof(commercial) keep failing. The capacitors melt down. But this only happens with the Marathon single phase 1/4 hp. motor. We switched to GE and rarely have this problem. I'm thinking because we have occasional power outages here, that it's our line, and a surge protector would solve the problem. Our supplier does not carry the GE's anymore and we can only get Marathons from them.

ANSWER: It is possible a surge is ruining the caps, but only on the Marathon?   Check the voltage ratings on the caps,   some might be 220  some 370 volts   the UF should be the same or close,  have you spoken with Marathon about this problem?    I am assuming you are talking motor brands  what  capacitor brands are you using?   Generic capacitors in the rated volt and uf  should be available          sounds more like the voltage rating of the cap is low  220 versus 370   that or the Marathons have a different rating on the MOTOR         

Explain are you exchanging motors with caps or just caps?

shop email     any more detailed history and what exactly the replacement process is    would be a big help resolving this,        a Marathon cap should hold up under what a GE does,        so something is different,          let me know anything else you can    and read the cap  data plate or send photos   also would help me figure this out,   

---------- FOLLOW-UP ----------

QUESTION: i was thinking the same thing, but the GE's are the same. Is or was there a problem with the Marathons? Average life span of the Marathons is about 3 years, the GE's are7-8. These are cotinuous duty motors too. If it's an inherant prob with the Marathons, we need to find a new supplier.

Gino, thanks for the kind words and sorry again for being slow on replies, just one of those things,    I do this to help people but some days I might get 5 to 6 questions, and some are very involved,     yours is so weird,    caps blowing on the same motors,  just different brands,     Marathon is/has been a middle level motor     what I mean is they are not stuffed with iron like Toshiba,   but pretty well built,        I would have always suggested Marathon,  but they sold this and that division,   these motor companies outsource and relabel so much it is nearly impossible to keep up,    so maybe on these motors they are not Manufacture by Marathon, maybe just labeled,     

Do any of the caps have a little resistor between the spade connectors?  I think you would have mentioned that,  but just to cover all bases,  are there resistors on one or any of the caps?

some values above

article about bleed off resistors on capacitors

In the article above it explains a little bit about discharge resistors and states there are other ways to accomplish the bleed off when the cap is taken out of the circuit,

But on a PSC motor the run cap is on line all the time,  but the motor does stop, and the built up charge has to bleed off,     

For example  we always short circuit a cap  after a test run    just not to be stung   no big deal  but surprises lead to worse things,   

a short weird stat,   more accidents from electrical problems causing injury are rooted in the injuries caused by the surprise,      for example    bench test a motor,   the cap is still charged,   tech touches cap, gets a little shock  [motor is now not energized]

as he jumps back or jerks back from the little shock, it stings no big deal,  but it is a surprise,  in reacting or jerking   he pulls the motor off the bench,  down onto his or her legs and down to her foot and crushes the bones in the top of her foot,    

It is those kinds of things that usually cause injury not the electrical power itself,    

Do this,  if you can,    take Marathon motor,  fire it up, run for two minutes shut down,  discharge the cap   by using a volt meter  first set to volts,  then set to ohms,   

Now try the GE,     get the same results?

Now swap the Marathon cap with the GE cap and measure each,    see where I am going?

pretty basic info on this video but worth a look  

another thing, you say exhaust fans,   they could be PSC motors or cap start motors with a belted transmission,          can you snap some photos to

I would like to see the nameplates of both brands,   

Also  it is amazing you are doing such a great job of measuring the reliability and length of service   most just replace stuff, and never find the root cause    good for you,   I am impressed,        

Instead of me explaining all the things I need to know on the nameplate, if you could get me photo I can look at service factors,   and other data that might mean something,   

Power outages as you know equal spikes      even a utility doing a sub station transfer will send a spike down the lines from the opening and closing of switches and circuits,   

The failing caps might have a tolerance of surge of xx     while the non failing  have a tolerance of x  this goes to the quality of the cap and or motor or both,       

Most all motors are rated constant duty,    but that is a tricky situation,  constant duty as related to warranty means the motor is fed with a constant voltage that fits the nameplate,  the amperage drawn or load is within the range of the nameplate, the ambient temp is within the rating,     any deviation is a voided warranty,      

Some motors have a service factor   NOT POWER FACTOR or at least not the same,   some are rated  SF   at   1  which means constant duty is exactly and no more or less of any parameter on the nameplate,    some motors are rated  1.15 which can be roughly used as  15 percent over nameplate rating on hp, amps, voltage  etc   and still run cont duty,   day and night,     

In this day and age surge suppressors are a great protective device but to find the right rating and capacity is a complex formula,   I have a whole house surge suppressor installed by the utility,    which is great for incoming surges, but it cannot do anything about surges created internally or past the protector,       but in a situation where there are constant outages a surge protector would be a must after doing a cost analysis of the equipment failing versus the cost of the suppressor,     some times if there are few components   at a low cost of replacement  ROI could be forever,        so it is a bigger study than it seems,    

The video says to use the exact capacitor,   but if a more expensive cap with the same ratings is used    that is fine,       UF and voltage,     and I am still not sure if you are using PSC motors with tin can run caps or cap start motors with plastic cases mounted normally on the motor under a cover,       

7-8 years for a constant cap duty, with outages is pretty damn good really,   take out the outages and not so good,     

how about applied voltage?  does it change?  have you ever recorded the daily or weekly voltage values to the building?  Renting a chart recorded is fairly inexpensive and easy to use,       my home voltage runs on the low side or the 115 side  from 109 to 119,   I have seen voltages on the high side as much as 249 to above and in one case the low side was 151   yep right out of the outlet,      I asked the owner if he had to change light bulbs often, and replied   yea how did you know     simple    you got 151 volts on a 120 rated bulb,    want to save some of your "devil" bulbs  that are killing the world?    Put them on dimmers,  even cheap dimmers that lower voltage to wasted heat,  seems stupid,   waste of power, but if the bulb lasts twice as long  the savings can be huge,        

Even lowering the voltage a few volts, not enough to make a difference in candle power or light availability.

If both caps are exactly the same   say  360 uF to 375 UF or whatever at 370 volt rating then the failures we will call premature based on just another brand,   have to be in a rating that is not published on the data plate,      only they know what amount of surge the cap will withstand and how many times,    and even way more data than that,          

Next if the voltage rating is the same,   nothing there,   again  they come in different voltage ratings  which is a maximum  has nothing to do with any thing but voltage withstand capacity,    like using one insulator or two,   you can always go up on voltage ratings on caps but not down,     

next bleed off resistors if the motors are cap start,  which I am not sure at this point  exhaust fans could be either PSC OR CAP START,   OR CAP START CAP RUN,  and bleed off resistors,  if the GE has them and the Marathon does not,    sounds like the problem,   but again you can use any brand of cap,      as long as it meets the uf and voltage,   and caps of the same uf can change in cost a huge range        from less than a couple bucks to over 30 bucks for the same rating,     it is all quality,   bulk pricing so on,       

I would love to hear Marathons thoughts,      and we would be happy to examine a cap or two or whatever if you want to shoot them down here,       

I would also be interested in the running current of each brand motor or in the same brand   are they all pulling   9 amps or whatever?   Have you clamped them?   How about megger readings?  Do you meg the insulation values?

A down and dirty and very effective predictive maintenance program is to chart megger readings,  for example motor a          megger in January  note humidity level, if possible,  megger in April,    every four months,    what happens,     ??

Here is what you might find,   in January the megger reading may be lower than in July or August,   humidity most likely,       but you are looking for a down trend,   January megger reading is  1000 megohms,    April  900     July  800     November  700     time to remove from service and find out what is contaminating the windings,    

A drastic drop say  1000 in January  and  500 in April  shorten the next test date to May  if down again  the insulation is deteriorating or becoming contaminated,

Vibration   are you monitoring vibration?    on a consistent basis?

I don't know if we are talking three motors or 300   so cost is up to you factor in how much you are trying to predict and nothing in predictive is perfect or a guarantee,      it is the best you can do,   and it depends on the equipment cost, downtime cost, labor,  all that,   

I know an insulation plant, that has a 150 HP three phase motor in an area down under a conveying system that is a major deal just to get to,   it gets covered with softened insulation   but the cost to get down there,  shut it down, loss of productivity  is dealt with this way,     let it run  covered with an insulating blanket, have a spare on site,   when it fails  put in the spare and have the failed motor rebuilt as the spare again,   this can happen a lot of times if the shop does the rebuild correctly     

But I am interested in this situation,  we can supply you capacitors or even motors,   if you want pricing let me know,    the motor details    maybe we try an AO Smith or Baldor and drop ship to you,    or maybe try a different brand cap    trouble is it will take three years  probably at a minimum to know anything,     do the motors also fail?   


My Mother in Law is near death,  some 600 miles away,  so we have been fighting when to go there when not, so I apologize for the lack of reply,     I cannot say Marathon has a problem, with a run on capacitors or their supplier,  but it seems to be the capacitor  not the motor  correct?

The problem could be their supplier,   some cheap cap,  to cut costs,    have you spoken to Marathon about the problem?

I would love to know what their response was or is,      because it is not an instant failure, it is going to be hard to prove what lasts and what does not,        

have you tried a generic capacitor     ??

You can purchase the same ratings of a capacitor from different suppliers and the prices are all over the board,        

I am going to keep digging on this,      got any photos of the failed caps   ???

1/4 HP can be PSC or Cap start,    if the running current is pushing the tolerance,  maybe there is a 1/3 HP motor that would be in the same frame  and might stand up longer,     but it seems you have done a great job and narrowed it down to brand,   it could be just that, but I would like to look at both nameplates just for anything that seems weird,      

But I reread the question,  seems the motors are not failing only the cap,  so that sounds like spikes and lower tolerance to spikes on the Marathon versus the GE,    again constant duty can have spikes     remember the utility switching spikes, and the obvious outage which IS A SPIKE<   you will find most caps at 30,000 to 60,000 running hours divided by 8700 or you can divide by 24 x 365  if you want to be exact which means not a lot  it is around 5-6 years for 50,000 hours,         info at the bottom will explain more in detail         

I do electronics also and I feel horrible for the people buying these cheapo big TVs that are subjected to all kinds of trashed and unstable voltage,   and within a few years   their new TV is shot, not worth repair,  shame       

If anyone reading this is in an area where outages are common, contact your utility and ask for a whole house surge suppressor cost,   normally it is so much a month like 10 bucks,   well worth it,     

Send me photos or any further data as you collect it, and I will stick with you until we figure this out, and again,   thank you for the very kind words it was very nice of you  

Why did my run capacitor fail?

The answer may be simple, but depending on how close the run capacitor is to its design life, it may also be difficult to nail the reason down to a single factor.

Time - All capacitors have a design life. Several factors may be interchanged or combined to increase or reduce the life of a run capacitor, but once the design life is exceeded, the internals may begin to more rapidly decay and drop in performance. Simply put, a failure may be attributed to it being "just old."

Heat - Exceeding the design limit of operating temperature can have a big effect on run capacitor life expectancy. In general, motors that are operated in hot environments or with little ventilation will experience a dramatically reduced lifespan on their run capacitor. The same can be caused by radiated heat from a generally hot running motor causing the capacitor to run hot. In general, if you can keep your run capacitor cool, it will last a lot longer.

Current - Motor failure causes the capacitor to be overloaded. This scenario is less commonly noticed, as it would usually be accompanied by a partial or complete failure of the motor. The motor is overloaded or has a failure in the windings, causing the current to climb. This can have an effect on the capacitor.

Voltage - This single factor can have an exponential effect in shortening design life. A run capacitor will have a marked voltage rating that should not be exceeded. Let's use 440 volts as an example. At 450 volts, the life may be reduced by 20%. At 460 volts, the life may be reduced by 50%. At 470 volts, there is a 75% life reduction, and so on. The same can be applied in reverse to help increase life by using a capacitor with a voltage rating significantly higher then needed, although to a lesser dramatic degree.

How long should my run capacitor last?

The mid point for a good quality aftermarket (didn't come with your motor) run capacitor would be 30,000 to 60,000 running hours. Factory-installed run capacitors sometimes have a designed lifespan of much less that this. In highly competitive industries where every part can have a significant impact on cost, or where a motor's intended use would likely be intermittent and infrequent, a lower grade of run capacitor may be selected with a design life of as little as 1000 hours. Additionally, all of the factors from the section above (run capacitor causes of failure) may dramatically modify the reasonable expected life of a run capacitor.

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Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site


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