Short #77 - What Causes Capacitors to Fail

HVAC School - For Techs, By Techs

Bryan Orr

Careers, Business, Self-improvement, Education

4.9 • 1K Ratings

🗓️ 22 October 2019

⏱️ 17 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this short podcast, Bryan talks through (once again) what REALLY causes capacitors to fail and what we can do about it.

High temperatures and overvoltage (NOT undervoltage) are what cause capacitors to fail. (There are also some poor manufacturing practices out there. Remember: they should be just foil and oil.) Capacitors create a phase shift to assist split-phase induction motors. Normally, a three-phase motor can start and run just fine because the sine waves are all angled. That is not the case for split-phase motors. Start capacitors help startup, which is difficult for the motor.

The capacitor stores and discharges each time there is a cycle change (usually 60 times per second). That rapid storing and discharging helps create a lag that gets the motor get moving. However, capacitors are limited by their design: their charge capacity (current) is dictated by size (microfarads), voltage, and frequency. If you measure amps on the start winding, you will notice that the amps are lower than on the run windings; the capacitor acts as a limiting factor.

When the run capacitor fails, you have no current on the start winding. The motor does NOT cause the capacitor to fail; there is a slim-to-none chance that a motor's back EMF can cause capacitor failure. Excess temperature or voltage is what really causes capacitors to fail, and THAT can negatively affect the motor. The hotter a capacitor runs, the shorter its life will be. Locations with high temperatures year-round and lots of thunderstorms will have more capacitor failures than places with more temperate climates.

Capacitor oil also plays a role in longevity. Oil exists for heat dissipation and should be mounted with the terminals up. Condenser cleanliness and temperature can also help or hinder the oil's efforts.

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Transcript

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0:00.0	This is the HVAC School Podcast. It's known as the podcast that helps you remember some things
0:09.1	you might have forgotten along the ways. Well, it helps you remember some things you might have forgotten in the first
0:13.8	place to at least that's what my friends tell me I'm Brian and this short episode is going to be
0:19.1	about capacitors what actually causes them to fail and I've talked about this a lot. I know I've talked
0:24.3	about this a lot. I know that I've made a video about this but some of you still aren't
0:28.1	getting it so I'm going to try it again. Our sponsors are refrigeration technologies at refriggedec.com.
0:33.8	Love those guys.
0:34.5	They make some of the best chemicals out in the marketplace today.
0:38.0	If your current supply houses do not have refrigeration technologies products such as
0:42.0	Nylog or Viper Cleaner or the pan and
0:44.8	drain treatment spray then you need to ask them to bring it in because it's good stuff
0:49.0	you're gonna like it give it a shot you can also get it from true tech tools if you'd
0:52.3	like TRU tech tools if you'd like.
0:52.6	TRU tech tools.
0:53.6	Use the offer code get schooled.
0:55.8	Also I need to thank fieldpiece.
0:57.2	fieldpiece.com another great so-cal company southern California company
1:00.9	just like refrigeration technologies. They make some of the best
1:03.7	test equipment out there so multimeters and gauges and probes and all that sort of stuff
1:09.8	they make really good products, monometers, so on and so forth.
1:13.0	If you haven't tried the new S-Man's, the new S-Man 380 and 480,
1:18.6	it's the new S-Man's, not the older ones.
	...

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