Failed start and run capacitors

[wirenut1980]

Hello, I have a customer who has been failing start and run capacitors at a small rural water treatment facility. The pump motor is a single phase 10 HP rated 230 V. Service is 120/240 V split phase. They have told me that ever since they bought the place (all existing equipment), these things have failed. There used to be a different start and run cap installed, but those failed in a few days. They replaced them with ones with a higher voltage rating and now they fail every few weeks. I'm not sure why they let this go for a couple years, but anyways...

I am guessing either the wrong caps are being installed, or they are wired incorrectly. I did install a monitor at the main in case there is something wrong with the supply.

I took pictures of the motor nameplate and start and run capacitor nameplates.

Can anyone tell me whether these caps are correctly specified for the motor? Anyone have any experience with these getting installed incorrectly and failing them over time? I plan on monitoring for a couple weeks and checking how the caps are installed.

Thanks!

 

[Hv&Lv]

Here is some information on that particular motor:http://attachments.temcoindustrialpower.com/product_info/Baldor-FDL3737TM.pdf

The capacitors listed are:
OC3050F09SP CYL OIL CAP 50MFD/370V
EC1216C06SP ELEC CAP, 216-259 MFD, 250V, 2.06D X 4.

 

[kwired]

What controls this motor and how possible is it to run "short cycles"? Even an intermittent problem in a control contact could be a cause for abnormal short cycling.

 

[wirenut1980]

What controls this motor and how possible is it to run "short cycles"? Even an intermittent problem in a control contact could be a cause for abnormal short cycling.

I'll have to find out what controls the motor, but I can tell you that I was there for about 45 minutes to an hour setting the monitor and talking with the customer and the motor ran the entire time.

 

[wirenut1980]

Here is some information on that particular motor:http://attachments.temcoindustrialpower.com/product_info/Baldor-FDL3737TM.pdf

The capacitors listed are:
OC3050F09SP CYL OIL CAP 50MFD/370V
EC1216C06SP ELEC CAP, 216-259 MFD, 250V, 2.06D X 4.

Thanks! Good wiring diagram as well. So it seems the caps are ok for this motor. The nameplate voltage rating on the caps is higher than needed, but I think that is ok. The capacitance will be less with lower applied voltage, but there should not be failure issues, right?

 

[Hv&Lv]

Thanks! Good wiring diagram as well. So it seems the caps are ok for this motor. The nameplate voltage rating on the caps is higher than needed, but I think that is ok. The capacitance will be less with lower applied voltage, but there should not be failure issues, right?

From the pictures and the Pdf. I think the caps are fine.
Like kwired stated, what is controlling the motor? I would also wonder if the centrifugal switch is working properly.

 

[Besoeker]

Can anyone tell me whether these caps are correctly specified for the motor? Anyone have any experience with these getting installed incorrectly and failing them over time? I plan on monitoring for a couple weeks and checking how the caps are installed.

Thanks!

I've seen a lot of failed capacitors. Not just on start/run configurations but on PFC capacitors too.
I think that in every case that I checked, the supply was somewhat distorted. There is a lot of electronic kit these days. No single item needs to produce much distortion but the huge proliferation of it adds up and can (and does) cause problems.
We supply and install variable drive systems. Usually, we are required to provide harmonic distortion data at the bid stage and this is followed up by measurements before and after installation to ensure compliance with specified limits. On one site, the distortion was outside the limits before any of our drives were put into service. This rather surprised me. The site was a relatively small pumping station in a residential area. With a background in power electronics and drives, I was used to dealing with harmonics. I just didn't expect a problem at residential level. But, as I noted earlier, it's the aggregate effect of lots of little effects. It was a lesson for me.

Anyway, if your monitoring programme doesn't reveal much, you might consider looking at the supply quality.

 

[Phil Corso]

Wirenut1980...

1) Have you confirmed the Electolytic-Cap is wired to Start-ckt?

2) Have you confirmed the Oil-Filled-Cap is wired to Run-ckt?

3) Can you provide members with measured Volt and Amp measuremtnts?

Regards, Phil

 

[Besoeker]

Wirenut1980...

1) Have you confirmed the Electolytic-Cap is wired to Start-ckt?

Is it an electrolytic capacitor?
I don't know of any that are rated to operate on an AC supply.

 

[wirenut1980]

I've seen a lot of failed capacitors. Not just on start/run configurations but on PFC capacitors too.
I think that in every case that I checked, the supply was somewhat distorted. There is a lot of electronic kit these days. No single item needs to produce much distortion but the huge proliferation of it adds up and can (and does) cause problems.
We supply and install variable drive systems. Usually, we are required to provide harmonic distortion data at the bid stage and this is followed up by measurements before and after installation to ensure compliance with specified limits. On one site, the distortion was outside the limits before any of our drives were put into service. This rather surprised me. The site was a relatively small pumping station in a residential area. With a background in power electronics and drives, I was used to dealing with harmonics. I just didn't expect a problem at residential level. But, as I noted earlier, it's the aggregate effect of lots of little effects. It was a lesson for me.

Anyway, if your monitoring programme doesn't reveal much, you might consider looking at the supply quality.

I will looks at that. My monitor is set to look at THD at the very least. I have also seen areas with large amounts of residential load show high 3rd and 5th harmonics.

Wirenut1980...

1) Have you confirmed the Electolytic-Cap is wired to Start-ckt?

2) Have you confirmed the Oil-Filled-Cap is wired to Run-ckt?

3) Can you provide members with measured Volt and Amp measuremtnts?

Regards, Phil

I will check this when I return to the site to download the monitor. I will be on vacation for the next week or so, so I probably will not be back up there until a week from Friday. I'll be sure to update the board on what I find.

 

[Besoeker]

I will looks at that. My monitor is set to look at THD at the very least.

You need that for voltage harmonics.

 

[Jraef]

I've seen a lot of failed capacitors. Not just on start/run configurations but on PFC capacitors too.
I think that in every case that I checked, the supply was somewhat distorted. There is a lot of electronic kit these days. No single item needs to produce much distortion but the huge proliferation of it adds up and can (and does) cause problems.
We supply and install variable drive systems. Usually, we are required to provide harmonic distortion data at the bid stage and this is followed up by measurements before and after installation to ensure compliance with specified limits. On one site, the distortion was outside the limits before any of our drives were put into service. This rather surprised me. The site was a relatively small pumping station in a residential area. With a background in power electronics and drives, I was used to dealing with harmonics. I just didn't expect a problem at residential level. But, as I noted earlier, it's the aggregate effect of lots of little effects. It was a lesson for me.

Anyway, if your monitoring programme doesn't reveal much, you might consider looking at the supply quality.

I think this is a good point. I have started seeing harmonics issue showing up in traditionally residential areas too, in the same way Besoeker did; someone wants harmonic mitigation for a VFD and to do it right, you need to know from whence you start. I've been surprised by the existing THD when I get there, even though it doesn't appear to be an "industrial" area where one would expect it. Could be the cumulative effects of all the CFLs, electronic ballasts, PC power supplies, big screen TVs and "energy efficient" appliances that all have SMPS or VFDs on them. Either that, or there is another VFD driven pump station near by with no harmonic mitigation, because "nobody will notice". One of the side effects is that the line harmonics can interact with capacitors and make them overheat and swell. If those are the kinds of repeated failures they were having, that might be an issue to look into.

 

[gar]

120625-1442 EDT

wirenut1980:

For many capacitor classes air, mica, Mylar, polypropylene, paper, oil filled, etc. the capacitance is moderately constant relative to applied voltage up to near breakdown. Electrolytic capacitors have a less well controlled capacitance than the above, but not largely voltage dependent. Most ceramic capacitors are voltage dependent and some greatly so. I have built voltage tunable oscillators with special ceramic capacitors. One was an FM transmitter. These ceramic capacitors are also quite temperature sensitive.

AC electrolytic capacitors are quite lossy and are not suited as run capacitors. They will overheat. Electrolytic capacitors are used as start capacitors because a large capacitance is possible in a moderately small package and cost compared to an oil filled or other low dielectric constant type capacitor. High capacitance is needed for low impedance compared to the start winding inductance to obtain a large phase shift. Start capacitors are only powered for a short time and therefore heating is not normally a problem.

The voltage rise on these start capacitors is less than on a run capacitor, but not less than line voltage. The run capacitor voltage might be in the range of 1.5 times line voltage or more. 330 V relative to 240 V is a ratio of 1.375, but if that is the rating specified for the motor, then I would accept it.

.

 

[texie]

I think all have made good observations. But I can't help but wonder if the start switch might be sticking sometimes. It would seem that the start cap should be safe from harmonics as it is not in the cicuit long. Also, depending on the setup, what if the OP had a mercury pressure switch bouncing and causing rapid on/off? Just speculating of course without more details.

 

[hurk27]

The parts list a oil for run and electrolytic for start, most times I have run into a motor blowing start caps was because of a sticking centrifugal switch that kept the cap inline too long, it might not always stick but worth looking at the contacts and see if it needs to be replaced.

Here's the source I had on this motor, but it list a electrolytic 216-250 MFD 250v cap for start
http://www.globalindustrial.com/site/images/universal/baldor/specs/FDL3737TM.pdf

It also had wiring diagrams to make sure it is wired correctly.

 

[ActionDave]

Hello, I have a customer who has been failing start and run capacitors at a small rural water treatment facility. The pump motor is a single phase 10 HP rated 230 V. Service is 120/240 V split phase. They have told me that ever since they bought the place (all existing equipment), these things have failed. There used to be a different start and run cap installed, but those failed in a few days. ..

I agree with Texie and Kwired, too many starts or bad switch and you get blown starting caps.

The part about failing run caps bugs me. They do not go bad near as often.

Wirenut, are the running caps failing at the same rate as the starting? Did you put an amp meter on anything?

 

[hurk27]

I think all have made good observations. But I can't help but wonder if the start switch might be sticking sometimes. It would seem that the start cap should be safe from harmonics as it is not in the cicuit long. Also, depending on the setup, what if the OP had a mercury pressure switch bouncing and causing rapid on/off? Just speculating of course without more details.

well we think alike, I started my post then went to the PDF and you beat me to it LOL.

 

[kwired]

The part about failing run caps bugs me. They do not go bad near as often.

Same thoughts here. I just don't see both failed at same time very often.

Someone mentioned whether or not the start and run had been switched to wrong positions. If OP says it was running for 45 min to 1 hr while he was there I say this was not the case. I only give that start capacitor half minute at most in the circuit before it spits all of its guts out - they will do that.

 

[wirenut1980]

Sounds like the top two options are harmonics in the voltage and a stuck centrifugal switch. If the switch is sticking, there will be visual signs of this? Or will something show up in the data? Something like a longer start time, or lower starting current, or maybe a leading power factor if it is a very long time (not sure what the interval is for power measurements). I'll also check to see if the caps are in the correct positions, not switched around.

Thanks!

 

[ActionDave]

If the switch is sticking you can check it physcally by pulling off the endbell of the motor or testing with an amp meter, and listening to the motor when it starts. This is the easier of the two.

On starting, the motor should have a high inrush reading and drop to close to nameplate amps in less than a second. There should be an audible "click" when the starting switch opens. You can double check by putting you amp meter on the wire going to the starting switch inside the peckerhead.

Are both running and starting caps failing? That would indicate miswiring of the caps IMO.