Re: WRT54G in the attic

Frazer Jolly Goodfellow <no-spam@xxxxxxxxxxx> hath wroth:

One other thing to consider is the lifetime of unit. At
elevated temperatures the consumer-grade electrolytic capacitors
just aren't going to last very long. Its probably not a big
deal with a $50 access-point, but still needs to be figured into
the equation.

Well, yeah, sorta, maybe. There are two basic types of electrolytics.
85C and 105C. Tearing apart my handy WRT54G v1.1, I find that it uses
G-Luxon 105C electrolytics with various values. Ok, they're not junk.
The caps appear to be rated at 3 times the applied voltage, which is
very conservative and should yield a long lifetime:
Power Supply input: 220uF 25v and 470uf 35v
PS output (3.3vdc): 220uF 16v

The problem with electrolytics is that the voltage rating and lifetime
decrease rapidly above the rated temperature. Capacitor life drops
rapidly with increasing temperature. See the graphs at:
http://www.bhc.co.uk/pdf/TD003.pdf
which are for much larger caps, but are generally characteristic of
electrolytics. There's no much on the Luxon web pile, but the basic
data shows that rated lifetimes are something like 2000 hrs at maximum
ratings.
http://www.luxon.com.tw/radialcap.htm
Lower voltage or temperature will last longer per the previous graphs.

Incidentally, "end of life" is typically 105C for 85C rated capacitors
and 120C for 105C rated capacitors.

A good point. But don't automatically assume that Linksys uses
consumer-grade electrolytics - e.g. most consumer market
motherboards use high-spec aluminium components.

I've seen motherboard CPU filter capacitors, where heating is far more
extreme than with routers, using 85C capacitors. It's one of the
things I look for in rating a quality board.

I'm somewhat bemused to read the upper operating temp (40C) - not
unknown even here in the UK.

It will not be the electrolytics that limit the upper temperature
specification. It will be something like the flash ram, MAC/radio
chip, or "power amp", dissipation that will cause problems. I've seen
a few reports of users tweaking the tx power to the 250mw maximum
output and blowing up their WRT4G routers. My guess is that it
overheated by itself or with some help from high ambient temperatures.

BTW: wikipedia is not a reliable source of factually accurate
information.

That's easily solved. We have a Wi-Fi FAQ at:
http://wireless.wikia.com/wiki/Wi-Fi
that is looking for user contributions, corrections, and editing. If
you find something wrong, then you're always welcome to make
corrections or debate the point with the authors. Other articles on
Wikipedia have similar policies. Controversial issues are always
handled by providing multiple points of view. Personally, I find the
Wikipedia quotation on capacitor lifetime to be quite accurate.


--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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