Electrolytic capacitors: overview, teardown and experiments [video] | Hacker News Reader

Electrolytic capacitors: overview, teardown and experiments [video]

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78 pointsdaneel_w14 comments

Very informative. Needless to say that most "brand" capacitors sold online from non reputable vendors are relabeled knock offs that would exhibit inferior characteristics and last a lot less than the real ones. There's no way you can buy a genuine Nippon Chemicon or Panasonic capacitor on Aliexpress, but beware also of unknown sellers on Amazon and Ebay. Always go to reputable vendors (RS, Mouser, TME, Farnell, etc) to be 100% safe. The cost of repairing a device that failed because of bad capacitors is always higher than the difference in price of the real capacitors.

Knock-offs tend to not pay for the patent licensing, but apart from that both reliability and performance seems to match in my experience.

I still wouldn't use them, but simply because if they do explode in my customers hands, then my chance of suing some noname brand for damages is low.

I can't ever see the words 'electrolytic capacitor' without getting flashbacks to the capacitor plague in the early 2000s

https://en.wikipedia.org/wiki/Capacitor_plague

I still look at any electrolytics on a board with a bit of suspicion, must be mild PTSD

Thanks for this, good stuff

There's even a site dedicated to it, with associated electronics repair forums: badcaps.net

Yes, we had months of replacing hundreds of motherboards one summer. At least Dell stood behind their machines and coughed them up readily enough.

Friday evening I came home from a concert and was greeted by a very warm upstairs. The A/C wasn't working. After a bit of diagnosis, I tracked it down to the blower motor starting but spinning very slowly. Internet research indicated the run capacitor[1] as a potential culprit. (For single phase induction motors, the run capacitor provides an out-of-phase voltage to the secondary winding to allow for a rotating magnetic field.)

By this point, it's 1:25 AM. I ordered a new capacitor from Amazon[2] and had it delivered less than 12 hours later. Replaced the capacitor and the motor was back to full speed. Total cost: $12.17. (A new motor would have been several hundred dollars.)

The original capacitor[3] lasted 20 years inside my air handler that's in my attic, so probably dealing with 100+°F temps for most summers. Not too bad.

1. https://en.wikipedia.org/wiki/Motor_capacitor#Run_capacitors

2. https://www.amazon.com/gp/product/B076RT8B61

3. https://imgur.com/a/2SCBETE

One interesting thing to consider (I have, sadly for power efficiency[1], a single-stage compressor) is a soft-start setup. Especially if planning to power HVAC from a generator for disaster recovery and not wanting to get a hugely sized genset just for HVAC startup current draw (mine has an LRA rating of 73A@240vAC, which is... non-trivial).

[1] One benefit, though, is compatibility with smart thermostats. Multi-stage/VFD setups tend to use proprietary signaling which makes using Ecobee or Nest a challenge.

Had a similar thing happen. It was later in the day, really hot, on a weekend, with high humidity and a crying baby in the house. My regular A/C company was closed, so I called another one. The person quickly diagnosed the issue and said he could "fix it for $450. I just wanted it fixed so decided to let him do it. But he then started acting shady, so I told him I'd take a picture of the old part before he offered to "dispose of it safely". He didn't seem to quite like that. I figured out why: it turns out it was a $15 capacitor. Oh well, lesson learned.

If he at least said, "look, it's $250 to come after hours", I wouldn't have minded that, maybe he had a crying baby at home too. But he made it sound like the part was expensive and I was "extremely lucky" he just happen to have this unique and special part in his truck. And then, to make it worse, he installed the capacitor without taking it out of the cardboard box it came with. That would have ensured the capacitor would overheat soon enough, so I, as sucker would be calling him again. Pretty sneaky. I opened the unit the next day and installed the part properly and filed a complaint with the Better Business Bureau.

i tried filling complaints in germany against behavior like this only to get ominous calls back from the guy warning me to retract my comments. this was some shady guy who has been at my home so I caved because I didn't want any trouble. not my proudest moment. but it was the last time I would use taskrabbit for anything. the guy was also a lockpicker so I had a video camera installed at the entrance since then.

>"But he made it sound like the part was expensive and I was "extremely lucky" he just happen to have this unique and special part in his truck"

Not to take away from your experience, however there is some truth to what your tech was saying. A capacitor is cheap when a part supplier/warehouse is open. You can call a warehouse to open after hours but you pay for the luxury and it isn't cheap (was at least $100USD, that was 20 years ago).

>"I was "extremely lucky" he just happen to have this unique and special part in his truck"

Actually, you were lucky if he had a capacitor that was the same farad rating. Most techs don't have a huge inventory in their vehicles, some times you get "weird" sizes that you dont expect. "Universal start capacitors" are available which allow you to "configure" the cap to the rating you require, however they are very expensive (over $150USD per cap). I would use a universal start to get you back up and running and then come back with a cheaper part.

> A capacitor is cheap when a part supplier/warehouse is open.

Well the warehouse was "open" so to speak. Capacitor failure is a fairly common failure and I bet he had quite a few of those in his truck. He didn't really have to go to the supplier to order one.

> Most techs don't have a huge inventory in their vehicles, some times you get "weird"

This wasn't a too weird one. It was either the 45/5 or the 35/5 uF one.

Installing it in the cardboard box and not clamping it with a metal clamp to the unit to dissipate heat was a confirmation this guy was shady.

How to Make Electrolytic Capacitors

https://yt.artemislena.eu/watch?v=ml2TdQ2_2mk

the process is not extremely difficult, but it turns out a lot better if you use a clean box and keep the dust out when assembling.

it is of merit among tesla coil buffs, to fab your own caps

nicely done - props to the vendor (which is one of the best), but not gross. excellent level of information, explanation, experimentation, teardown.

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