Simple capacitor question - Page 1
Forum section: electronics / projects

author: wguibas
author_rank: Unknown
timestamp: October 03, 2015, 12:07:55 am
content: I bought some 470uF panasonic caps for a project from mouser, part#667-EEE-HAE471UAP. After getting them I notice they spec for 1000 hours @105c, what does that mean? Are they gonna have a short life in my board that hangs out in the back of a car? Thank you in advance.

author: DanielS
author_rank: Frequent Contributor
timestamp: October 03, 2015, 12:30:06 am
content: Does the back of your car typically reach anywhere near 105C?In general, for each slice of 10C below the rated temperature, you double electrolytic capacitor' operating lifespan. If the operating temperature maxes out around 55C, then your "1000h" capacitors should last at least three years assuming none of its other specs are exceeded during that time.

author: wguibas
author_rank: Unknown
timestamp: October 03, 2015, 01:01:28 am
content: Thank you, thats what I wanted to know. I would imagine the back of the car could get up to 60c in the summer when parked.

author: Fungus
author_rank: Super Contributor
timestamp: October 03, 2015, 11:30:52 am
content: Quote from: wguibas on October 03, 2015, 01:01:28 amCapacitors generate heat. How hot will your capacitors get in a 60c ambient temperature?

author: wguibas
author_rank: Unknown
timestamp: October 03, 2015, 11:56:23 am
content: It doesn't get hot at all at room temperature. It just smooths the 12V input feeding a recom 785-1.0 switching voltage regulator, the whole circuit draws about 30mA/12V on my powers supply.

author: DanielS
author_rank: Frequent Contributor
timestamp: October 03, 2015, 12:45:10 pm
content: The 1000h rating is at max temperature, max ripple current and max operating voltage simultaneously.At 1/2 the rated temperature, 1/2 the rated operating voltage and likely much less than 1/12th the rated ripple, I imagine the only two reasons it might fail are manufacturing defect and load dumping if your circuit has no protection against that.

author: Fungus
author_rank: Super Contributor
timestamp: October 03, 2015, 01:07:45 pm
content: Quote from: wguibas on October 03, 2015, 11:56:23 am470uF of capacitance probably isn't needed for that. Use a 10uF ceramic instead - problem solved!Edit: And in fact the datasheet only recommends 10uF...http://www.recom-power.com/pdf/Innoline/R-78xx-0.5.pdf

author: wguibas
author_rank: Unknown
timestamp: October 03, 2015, 02:03:52 pm
content: I also have a 2.2uF in front and after the regulator I'll update it to a 10uF, before adding the 470 the circuit worked fine in a modern car, but when I put it into a 67 thunderbird it was glitching out from the noisy 50 year old brake pedal switch. Adding the 470 before and a 47 after the regulator stopped the problem. I recently started redoing this board in SM and thats when I bought the new caps and noticed the 1000 hour rating. The old caps in this pic were rated 7000 hour@105c.

author: Fungus
author_rank: Super Contributor
timestamp: October 03, 2015, 04:47:57 pm
content: Quote from: wguibas on October 03, 2015, 02:03:52 pmIf you need more capacitance you could maybe use polyester.Electrolytics should usually be a last resort, when you really can't get enough capacitance any other way. They dry out and stop working when they get old/overheated.

author: rdl
author_rank: Super Contributor
timestamp: October 03, 2015, 07:48:02 pm
content: Maybe switching to solid polymer aluminum caps would be an option. I've seen some with endurance ratings up to 15,000 hrs.

author: wguibas
author_rank: Unknown
timestamp: October 03, 2015, 09:04:12 pm
content: I'll check them out. Thanks