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Most are electrolytic for practical reasons including cost and available capacity+voltage rating. Electrolytes in the capacitors dry out in the hot weather as w

by gh02t 2y ago

Most are electrolytic for practical reasons including cost and available capacity+voltage rating. Electrolytes in the capacitors dry out in the hot weather as well as other things like other components going bad and drawing too much current, both of which cause further overheating. Overheating makes the electrolyte dry even faster (making the capacitance plummet and resistance increase, i.e. stop capacitoring) and generate gasses (=>swell/pop). Tldr hot weather is hard on them. They have a finite lifetime and suffer most when you need the AC the most.

trq01758 2y ago
For AC these units use non polarized, oil-filled metallized polypropylene film capacitors. But overheating is a problem for them, as it is for electrolytics.
- Log_out_ 2y ago
  Would be neat to have an AC to keep the electronics nice and cool.
- gh02t 2y ago
  Indeed, I did some basic double checking before I posted but I guess the info I read was bogus+I was also having a brain fart to not know better because you're definitely right. Thanks for correcting.
sidewndr46 2y ago
No one uses an electrolytic type capacitor for the 60 Hz winding of a "single-phase" induction motor.
steve_adams_86 2y ago
Are more robust capacitor designs not an option because the capacitive properties of the paper ones are better for the use case?
- ssl-3 2y ago
  More robust capacitors exist. They just cost more. In HVAC world, the practical differences between a motor start cap and a motor run cap are price, physical size, and longevity. A start cap is cheaper, but is meant only for intermittent duty and is unsuitable for use as a run cap. Meanwhile, a run cap costs more but can serve as a run cap or a start cap. All things (except for outliers like the McLaren F1) are built down to a price.
himinlomax 2y ago
Aren't electrolytic caps polarized? That can't be used for AC. Iirc these capacitors are film types instead.
- ssl-3 2y ago
  Non-polarized electrolytics are somewhat uncommon, but they definitely do exist. They get used rather frequently in things like crossover networks for loudspeakers[0]. They tend to cost more, and tend to be larger than their polarized kins. They're not advantageous in circuits that always have some DC bias, so they only get used where it is necessary. 0: https://www.bennic.com.tw/en/ec/index.asp https://www.bennic.com.tw/en/ec/index.asp
- deleted 2y ago
  [deleted]

by gh02t 2y ago

trq01758 2y ago

For AC these units use non polarized, oil-filled metallized polypropylene film capacitors. But overheating is a problem for them, as it is for electrolytics.

Log_out_ 2y ago
Would be neat to have an AC to keep the electronics nice and cool.
gh02t 2y ago
Indeed, I did some basic double checking before I posted but I guess the info I read was bogus+I was also having a brain fart to not know better because you're definitely right. Thanks for correcting.

sidewndr46 2y ago

No one uses an electrolytic type capacitor for the 60 Hz winding of a "single-phase" induction motor.

steve_adams_86 2y ago

Are more robust capacitor designs not an option because the capacitive properties of the paper ones are better for the use case?

ssl-3 2y ago
More robust capacitors exist. They just cost more. In HVAC world, the practical differences between a motor start cap and a motor run cap are price, physical size, and longevity. A start cap is cheaper, but is meant only for intermittent duty and is unsuitable for use as a run cap. Meanwhile, a run cap costs more but can serve as a run cap or a start cap. All things (except for outliers like the McLaren F1) are built down to a price.

himinlomax 2y ago

Aren't electrolytic caps polarized? That can't be used for AC. Iirc these capacitors are film types instead.

ssl-3 2y ago
Non-polarized electrolytics are somewhat uncommon, but they definitely do exist. They get used rather frequently in things like crossover networks for loudspeakers[0]. They tend to cost more, and tend to be larger than their polarized kins. They're not advantageous in circuits that always have some DC bias, so they only get used where it is necessary. 0: https://www.bennic.com.tw/en/ec/index.asp https://www.bennic.com.tw/en/ec/index.asp
deleted 2y ago
[deleted]