Motor Run caps - How to tell if Poly or 'Lytic?

[rongon]

I did some searching and couldn't find an answer, so please forgive me if this has been asked and answered before...

I have a few Dayton branded motor run capacitors, 10uF 370VAC. Short of dissecting one, I can't find any info on what their construction is. It's this one:
Run Capacitor, 10 MFD, 370 VAC, Oval - Capacitors - Motor Supplies - Motors : Grainger Industrial Supply

I've seen others that look identical and are specified as being film type, oil filled. I've also had a few vintage motor run caps that were easy to tell they were oil filled -- shake 'em and you can hear the oil sloshing around inside. The thing is, this Dayton cap doesn't make any sloshing noises, and it seems too light in weight to be filled with oil.

Do you think this light and dry Dayton cap could be (shudder) electrolytic? Can motor run caps be electrolytic? I thought they needed to be film for their self-healing properties and other safety/longevity concerns.

Any info much appreciated...

-=|=-

[AndrewT]

Motor run and Motor start capacitors can be electrolytic.

I can't see type either.
You will need to ask.

[jacco vermeulen]

Originally Posted by rongon

this Dayton cap could be electrolytic

Simple answer, yes.

[indianajo]

Suppliers have gotten a bit secretive about the content of their caps since the PCB fiasco, and WW Grainger doesn't say. Mcmaster.com doesn't say either. Sloshing could be oil, could be water. I bought motor caps for my organ from Newark.com, that has different selector charts for film (that I bought genelec, mexico) and electrolytics. Tagging onto another order from Mouser, I bought a film 3 uf 370 VAC motor cap for my second hammond organ, an An Hui Fidex industries part from China. I hate electrolytics so badly I bought Genelec 50 uf 440 VAC film caps for the B+ of the first Hammond organ; they were so huge I had to install a separate chassis to cover their death terminals from touch. But they will never wear out, (I hope). Bottom line, Hammond branded motor caps (installed 97 after the cap/wiring fire) don't say what they are either. It is easy to tell the 1968 motor cap in my newer Hammond organ is electrolytic, it came to my house sitting in a puddle of it's own acqueous slime.

[pjp]

Originally Posted by rongon

I've also had a few vintage motor run caps that were easy to tell they were oil filled -- shake 'em and you can hear the oil sloshing around inside.

(I've never used oil filled caps, but) This can't be correct ?
Oil and Air filled capacitors ?

Is the air gap provided so the hot oil has a place to expand ?

[indianajo]

Yes, motor run caps run quite hot. Also metalux lamp caps. You can't tell from the sloshing whether they are electrolytic or film, you have to drill a hole and see what drains out. WW Grainger and macmaster-carr are private label industrial suppliers. You cannot expect that a part you order will be from the same manufacturer or even the same technology from one day to the next. The capacitance and voltage rating, the type of hookup, as specified in the catalog, are assured.

[Pano]

I have a few Mars brand motor caps. Don't know what is inside them, might be worth a look.

[phaselag]

If the cap is a run cap, it is usually under 50 mfd. These are oil filled non-electrolytic caps. Start caps are generally cylindrical only and are higher value. These higher values are non-polar electrolytics. They can not be used in continuous operation and would overheat and vent, or worse.

paul

[indianajo]

Originally Posted by phaselag

If the cap is a run cap, it is usually under 50 mfd. These are oil filled non-electrolytic caps. Start caps are generally cylindrical only and are higher value. These higher values are non-polar electrolytics. They can not be used in continuous operation and would overheat and vent, or worse.

paul

You may have some knowledge of modern caps, which might be plastic film because it is cheaper. Older motor run caps are quite likely electrolytic. There is a guy here on craigslist trying to flog off some 20? year old Aerovox motor caps. Aerovox was primarily known as an electrolytic house, in my experience, and his caps are probably scrap. These Hammond organ branded motor run caps are definitely electrolytic, including the one that set the wiring on fire in my first H182 in '97.

[bichi]

Take a look at the "MSDS" tab on the product description page.
Run Capacitor, 10 MFD, 370 VAC, Oval - Capacitors - Motor Supplies - Motors : Grainger Industrial Supply

or

"MSDS" tab direct link:
Grainger MSDS Lookup

My guess, polypropylene film, aluminum deposition plates.

************************

SECTION 2 - COMPOSITION/INFORMATION ON INGREDIENT
COMPONENT CHEMICAL NAME FORMULA CAS NO.
ALUMINUM HULL ALUMINUM Al 7429-90-5
CUPULE OF INSERT POLYPROPYLENE (C3H6)x 9003-07-0
INSERT COPPER WITH TIN Cu 7440-50-8
Sn 7440-31-5
FILLER MICROCRYSTALLINE WAX 63231-60-7

CORE:
POLYPROPYLENE POLYPROPYLENE (C3H6)x 9003-07-0
ZINC ZINC Zn 7440-66-6
ALUMINUM ALUMINUM Al 7429-90-5

MANDRIL POLYPROPYLENE (C3H6)x 9003-07-0