General > General Technical Chat
The unfortunate shrinkage of capacitors
IanB:
--- Quote from: magic on January 11, 2022, 10:22:28 am ---
--- Quote from: IanB on January 11, 2022, 03:45:37 am ---I'd rather pay twice as much, and not have to worry about replacing it.
--- End quote ---
There may be a way if you are willing to pay 4x more ;)
--- End quote ---
;D
It makes mounting and wiring a bit more complicated though...
IanB:
--- Quote from: TERRA Operative on January 11, 2022, 01:00:24 pm ---You can always use a new capacitor with a higher voltage rating to get something with thicker plastic laminations inside that will last longer.
--- End quote ---
I am using a 440 V capacitor on a 120 V system. I understand 600 V capacitors are available, but they are harder to source.
cvanc:
I have used polypropylenes from Digikey to replace both of my furnace run caps. Works fine.
I don't think it's motor spikes killing these, I think it's powerline spikes. One way to increase life is to use the highest voltage cap you can find (or fit). These are self healing types so a lifetime of power glitches eventually reduces the capacitance. A higher voltage rating slows this down.
And I bet adding a varistor across the furnace's AC line input would help, too?
coppercone2:
I think the key to this might be the improvement of QC practices for film materials.
I am not sure on the specifics (heard something about radiation casks being used as test equipment for aluminized films), but the idea might be that the material is the same but the increased quality of testing and production methods lead to designers being more confident in thinner materials.
But of course proliferation of intense bean counters is a known thing, so its unlikely to be entirely a positive change.
jonpaul:
Bonjour, our wise Solons and The mandarins with sinecures in Wash DC banned the best capacitor oils due to PCBs decades ago.
The newer subs are not as good.
Finally all old line USA cap mfg like Sangamo, Mallory and Aerovox long closed.
The current "USA" ballast firms like Magnetek offshored ALL capacitor and other manufacture to China were the materials, quality control, fabrication and seals are the cheapest possible.
Look for old 1950s...1980s parts,
Jon
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