General > General Technical Chat
The unfortunate shrinkage of capacitors
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IanB:
I just replaced the motor run capacitor on my furnace blower, due to the gradual failure of the old one. It is rated 7.5 µF, 440 V. The size is kinda sorta 1 inch x 2 inches x 3 inches. It measured 2.2 µF when I pulled it out.

I remember, back in the 1970's, I had a fluorescent tube ballast capacitor, which was described as 8.5 µF, 250 V AC. It was probably 2x or 3x the size.

I really don't know if material science has advanced that much that they can shrink down the volume that much today compared to the old days? I've got to think it is cost cutting.

From what I understand, run capacitors are considered to be a consumable now, they are guaranteed for up to 5 years, and are a regular replacement item. I'd rather pay twice as much, and not have to worry about replacing it.
Ed.Kloonk:
I've got to do the one for my compressor in my A/C and I know the replacement I got won't be as good and the original that has lasted about 12 years.

Ed.Kloonk:

--- Quote from: IanB on January 11, 2022, 03:45:37 am ---
I remember, back in the 1970's, I had a fluorescent tube ballast capacitor, which was described as 8.5 µF, 250 V AC. It was probably 2x or 3x the size.


--- End quote ---

To address this specifically, these were included here in Oz to counteract the effect of inductance. The particulars in the issue have be explored at length elsewhere, but I think in recent years before LED 'flouros', the installed cap had only to be good enough to pass a test at the compliance level. The bloody thing didn't last 5 minutes. It used to annoy me that they would often fail short.
IanB:

--- Quote from: Ed.Kloonk on January 11, 2022, 04:03:38 am ---To address this specifically, these were included here in Oz to counteract the effect of inductance.
--- End quote ---

Yes, I think they were for power factor correction. Given that all industrial and commercial premises were lit with fluorescent tubes using magnetic ballast, I imagine  this was a matter of some importance.
IanB:

--- Quote from: Ed.Kloonk on January 11, 2022, 03:57:15 am ---I've got to do the one for my compressor in my A/C and I know the replacement I got won't be as good and the original that has lasted about 12 years.

--- End quote ---

I suppose I should check the one in my A/C unit. However, it seems to work fine and has been in use for at least 20 years.
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