Motor Capacitor?

[RonRock]

I have a Marathon 5 hp, single phase 240v motor on my air compressor. It's an oldie and assumed discontinued motor. The tag is pretty beat up but I am pretty certain that the Model number is VN 184TCDR7630AN L. I haven't been able to find anything in my Google searches.
Anyway I figure that it would probably be a good idea to replace the capacitors based on their age. Motor still runs good, but seems like it could be quieter. So I opened it up and the caps have a paper label that is deteriorated to the point of no readable print. I was able to test them and they both test at about 830 uF. Both pretty close the uF reading kept bouncing, so I figured that was about max. Other than old and bad label they "look" ok. No leaks, the dot looks ok. Overall OK.

So is there anyway to determine what to replace them with? I'd like to replace them, but mostly just because it seems like a good idea.

They are wired in series with a motor lead going to 1 terminal of each with a jumper between the two.

 

[RonRock]

 

[wyliesdiesels]

replacement caps will not make the motor run quieter.

the noise is probably a bearing going out. what does the noise sound like?

if it aint broke dont fix it.

 

[Bert_]

Since you tested them I'd write 830mfd on them with a paint marker. Then if they ever actually go bad you will know what size you need!

 

[RonRock]

Don't capacitors get weak over time?

 

[whateg01]

Since you tested them I'd write 830mfd on them with a paint marker. Then if they ever actually go bad you will know what size you need!

You mean uF? There's a big difference between u and m.

 

[ching0n]

Don't capacitors get weak over time?

if the electrolyte is still there, they should be good, .....they look physically fine to me (no cracks or bulges)....do you notice any hard start? If not, your start cap is probably fine. If you measure the current draw while running it'll tell you if your run cap is good or bad too.....a run cap makes the motor draw less current/more efficient. If there's significant drag on the motor due to bad bearings though, this reading may be a false negative. .

 

[Bert_]

You mean uF? There's a big difference between u and m.

Mfd is a very common abbreviation for microfarad. Tons of capacitors out there labeled this way from the factory.

 

[RonRock]

All helpful information thanks. I'll check the running amps. That needs to be done anyway.

What brought this on for me is that I am in the final stages of a compressor overhaul. I want to do my best to get the unit in it's best shape for another 65 years of service. The compressor is a Worthington 2 Stage, 2 cylinder with a casting date of 4-25-60 in the crankcase. 1 day younger than me. Haha

 

[whateg01]

Mfd is a very common abbreviation for microfarad. Tons of capacitors out there labeled this way from the factory.

Was a common abbreviation. The standard abbreviation is u for micro vs m for milli.

 

[Meursault74]

Was a common abbreviation. The standard abbreviation is u for micro vs m for milli.

This is true, but it's μ

I don't think I've come across a capacitor that was marked mF. In this case if would be 0.830 mF. I've seen both uF and MFD to mean the same units on a capacitor.

I've seen some pharmacy notations come into my work where they use mc instead of μ to denote 10E-6/micro I know what they mean, but I'm traditional and use the μ. This came up last week. Working with a pharmacist, she put it mcL to denote microliter in a report. I told her to change it to μL as it was a chemistry validation at this point and not pharmacy.

 

[Bert_]

Was a common abbreviation. The standard abbreviation is u for micro vs m for milli.

Mf would cause confusion, nobody is suggesting that. MFD is a common and understood abbreviation. Anyone who has any business working on a motor knows exactly what it means.

 

[dave*99]

Yup, like this

 

[fitter30]

Call the factory they might know but all these companies have changed ownership probably three or four times. Motor shop might know. Never heard of a 800+ mfd cap.
+1 833-697-3203
[email protected]

 

[Bert_]

Motor shop might know. Never heard of a 800+ mfd cap.
+1 833-697-3203
[email protected]

Would bet on it being (2) 830MFD 110V capacitors wired in series. Two wired in series gives a combined rating of 415MFD and 220v.

I think 830 is a common size and 400ish microfarads is about right for a 5hp motor.

 

[RonRock]

I'd like to replace those old caps. My compressor is not starting when cold. It is up in my shop attic/loft. At night temp drops and the compressor will not start until the attic gets warm from shop heat. Also just seems like a good idea to replace them with a new set. I am having trouble finding 830mfd caps. Where should I look? Can I use one that is variable like a 200-830mfd? Just an example number.

I am in process of getting a different motor in order, but if the new caps work the Baldor can set on my shelf for when needed.

 

[Mike007]

I'm hesitant to replace older USA made capacitors with a new cap these days if they test good. I'd definitely try and find a quality capacitor if I had to.

 

[mm08822]

I'd like to replace those old caps. My compressor is not starting when cold. It is up in my shop attic/loft. At night temp drops and the compressor will not start until the attic gets warm from shop heat. Also just seems like a good idea to replace them with a new set. I am having trouble finding 830mfd caps. Where should I look? Can I use one that is variable like a 200-830mfd? Just an example number.

I am in process of getting a different motor in order, but if the new caps work the Baldor can set on my shelf for when needed.

What is happening when not starting - any noises, motion, etc.?

Zoro and Supplyhouse have a decent selection. Granger, too, but is pricey w/o any corporate discounts. Stay away from Amazon no name brands.

 

[Bert_]

https://www.supplyhouse.com/MARS-11928-708-850-MFD-Round-Start-Capacitor-125V

https://www.supplyhouse.com/MARS-11982-710-852-MFD-Round-Start-Capacitor-165V

If it fits use the 165v capacitors.

 

[RonRock]

What is happening when not starting - any noises, motion, etc.?

Zoro and Supplyhouse have a decent selection. Granger, too, but is pricey w/o any corporate discounts. Stay away from Amazon no name brands.

It is like it is under load. It tries to start, but before getting up to speed the breaker pops. Once running it sounds fine, and will run and start fine for the rest of the day. I'd like to oil the bearings but the oil caps are seized in. If I push it I'm sure something is going to break or strip threads. I checked the caps last week and they were still good. As far as my test was. But they are very old. No readable label.

I opened up the union coming off of the compressor to see if it was a back pressure issue. There was no pressure when I opened the Union, and I started the motor with the union loose. No joy. Motor tried but would not come up to speed before breaker popped.

I have a "Load Genie" in my compressor to tank pipe. Every couple years I need to replace it, no big deal 40-50 bucks and good to go. Well this one is due, I can hear it loosing air when running and it just isn't "right." So I need to replace it, but the one that I use has been discontinued. My luck. So I figure I'll remove it and install a check valve and new pressure control with pressure unloader.

But I don't think that is my motor issue now.

 

[Bert_]

What size breaker you have it on?

 

[mm08822]

Ohm out the two windings.

Disconnect belt and try the cold startup next am. Same issue?

Is the cent sw moving? contact(s) welded shut?
Does the shaft spin quietly when spun by hand? and at the same time does is coast down to a stop really fast?

May be a good time to change out bearings with the motor halfway apart.

Next is the compressor head. Start with an oil change.

A failed unloader valve (or equivalent in your case) can make for an almost locked rotor condition when there is residual pressure in the tank. It shouldn't matter when starting from a zero pressure tank.

 

[mm08822]

Post pics of nameplate to help scrounge any info from it.

 

[RonRock]

What size breaker you have it on?

30 Amp breaker. Been running that way for many years. I used to use the breaker as a switch. This summer I finally took time to install a switch and disconnect . the switch is on main floor, easy access. Disconnect next to compressor.

 

[Bert_]

30 Amp

Too small. Put it on a 50A

 

[mm08822]

30 Amp

What are FLA's on the motor nameplate? I'm sure a 40A can be used, possibly 50A....need nameplate info.

 

[RonRock]

Ohm out the two windings.

Disconnect belt and try the cold startup next am. Same issue?

Is the cent sw moving? contact(s) welded shut?
Does the shaft spin quietly when spun by hand? and at the same time does is coast down to a stop really fast?

May be a good time to change out bearings with the motor halfway apart.

Next is the compressor head. Start with an oil change.

A failed unloader valve (or equivalent in your case) can make for an almost locked rotor condition when there is residual pressure in the tank. It shouldn't matter when starting from a zero pressure tank.

Will do tomorrow AM.

I did some work on the compressor this summer. Rings, gaskets, seals. Paint and fresh oil.

I'll remove the belt and see what happens. Good idea.

I'll have to read up on how to Ohm out the windings. But good to know, not only for this motor but others.

 

[RonRock]

Post pics of nameplate to help scrounge any info from it.

 

[Bert_]

What are FLA's on the motor nameplate? I'm sure a 40A can be used, possibly 50A....need nameplate info.

If it's really 5hp, code allows all the way up to a 70A breaker. 70 is more money and this application doesn't need it.

40A is bare minimum for 5hp motor in my opinion. I like 50 or sometimes a 60A because they cost the same and I don't have to come back for nuisance trips.

 

[mm08822]

Will do tomorrow AM.

I did some work on the compressor this summer. Rings, gaskets, seals. Paint and fresh oil.

I'll remove the belt and see what happens. Good idea.

I'll have to read up on how to Ohm out the windings. But good to know, not only for this motor but others.

The cb may be the fastest answer and the simplest to accomplish. Do the cb and caps.
Hold on the rest if start-up issues are solved or create an optional baseline and data/new parts.

 

[RonRock]

Good thinking on the breaker size. I did work on the compressor this summer. Probably a bit tighter than it was previously. But it ran and started fine until it got cold. That seems odd to me. Easy enough to swap breakers.

 

[mm08822]

If it's really 5hp, code allows all the way up to a 70A breaker. 70 is more money and this application doesn't need it.

40A is bare minimum for 5hp motor in my opinion. I like 50 or sometimes a 60A because they cost the same and I don't have to come back for nuisance trips.

Yes, at 26.4A, OP can use 60 or 70A (250% of 26.4A). I'd do the 60A if you have to go buy one.

 

[RonRock]

If it's really 5hp, code allows all the way up to a 70A breaker. 70 is more money and this application doesn't need it.

40A is bare minimum for 5hp motor in my opinion. I like 50 or sometimes a 60A because they cost the same and I don't have to come back for nuisance trips.

I have a 50A on hand. Yay!

 

[mm08822]

Good thinking on the breaker size. I did work on the compressor this summer. Probably a bit tighter than it was previously. But it ran and started fine until it got cold. That seems odd to me. Easy enough to swap breakers.

30a may have been just squeaking by when the oil was at a lower viscosity due to higher ambient temps.

 

[RonRock]

Great help guys. I appreciate it. Thank you.

I'll report back.

I still intend to replace the Marathon with the Baldor, if I can get the Baldor in order. But a guy can't be without his compressor.

 

[whateg01]

If you determine that the motor is good, what's the point in replacing it?

 

[wyliesdiesels]

30 Amp breaker. Been running that way for many years. I used to use the breaker as a switch. This summer I finally took time to install a switch and disconnect . the switch is on main floor, easy access. Disconnect next to compressor.

yeah thats too small for a true 5HP. the FLA is gonna be about 23a and the in-rush will be 4x-8x that, which could cause a 30a breaker to trip.

how do you have this compressor connected? hardwired or cord and plug?

EDIT: I see the FLA is 26.4a which is really high for a 5HP motor built in the last decade or so. the NEC FLC table lists 5HP @ 28a so this one is older....

 

[wyliesdiesels]

If you determine that the motor is good, what's the point in replacing it?

some people love wasting money

 

[exmaxima1]

I don't think I've come across a capacitor that was marked mF. In this case if would be 0.830 mF. I've seen both uF and MFD to mean the same units on a capacitor.

Agreed

 

[RonRock]

yeah thats too small for a true 5HP. the FLA is gonna be about 23a and the in-rush will be 4x-8x that, which could cause a 30a breaker to trip.

how do you have this compressor connected? hardwired or cord and plug?

EDIT: I see the FLA is 26.4a which is really high for a 5HP motor built in the last decade or so. the NEC FLC table lists 5HP @ 28a so this one is older....

Yes the Marathon is much older than 10 years.