[RE-wrenches] Electrolytic Caps vs. Thin Film Caps

[Ryan J LeBlanc]

Dan,

Thanks for the E-caps post.

Could you briefly describe why the Thin-Film Caps guys continue to spread
this rumor?  

Perhaps give a brief description of the differences?

Perhaps some weaknesses of the thin-film caps? 

I'd love to get your take on this.

Thanks,

Ryan 


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Message: 3
Date: Thu, 12 Jan 2012 15:59:04 -0800 (PST)
From: Exeltech <exeltech at yahoo.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] SolarEdge v Enphase
Message-ID:
	<1326412744.14871.YahooMailClassic at web113303.mail.gq1.yahoo.com>
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Wrenches,

I wish this urban myth about electrolytic capacitors would die, but it
won't.? It's been a wonderful marketing ploy for some time now.

Simply stated, existence of electrolytic capacitors in inverters does NOT
mean the inverters are less reliable.? Satellites have been using
electrolytic caps for decades, and look how long THEY last!? (I know,
because I've helped to design power supplies for aerospace applications.)

What it boils down to is this: if a quality electrolytic capacitor is used
within its specifications, you can expect 60+ years of life from it in an
inverter application.? Conversely, if a circuit is poorly designed, you can
ruin any electronic part in a very short time.

What defines capacitor "life"?? It's defined as the doubling of the internal
effective series resistance of the capacitor from the value it had when it
(the cap) was new.

This is energy lost.? It also causes the capacitor to operate at a slightly
higher internal temperature than when it was new (all other factors being
the same).

Result?? It all depends on how the circuit is designed.? In our case, the
inverter efficiency decreases approximately a quarter to one half of a
percent. ? The waveform distortion also increases, but it takes lab grade
equipment to detect the change.? If you're worried about a 1/2 percent drop
in the inverter efficiency, your concern is misplaced.? After all, PV
degrades over time much more than that!

So why the bad rap on capacitors?

Like tires, they DO wear out.? 40 years ago, "premium"
tires were rated for 30,000 miles.? Could you wear them out in less??
Absolutely!? Drive like a 16 year old kid with a muscle car, and it's easy.?
On the other hand, I just bought a new set of tires.? The old ones still had
tread, but at 88,000 miles, they'd seen their better days.? This is a far
cry from 30k mile tires.

Capacitors have progressed in the same manner.? A long time ago, capacitors
wore out in 5 to 10 years.? Today, it's an entirely different story.

As long as the circuits in which the electrolytic capacitors are used are
well designed, you have nothing to worry about.
Electrolytic capacitors in a well-designed application will outlive all of
us.


Dan Lepinski
Senior Engineer
Exeltech