Here's an excellent explanation of diodes:
http://www.faqs.org/docs/electric/Semi/SEMI_3.html
It notes LEDs may have a lower breakdown voltage when reverse-biased, but this
won't necessarily fry the diode, just allow current to pass when you don't want
it to (like in an AC circuit).
Have reversed a few LEDs, and never seen one smoke. Anyway, the fact you tried
and it ruined the unit is sufficient for me--there is probably other supporting
circuitry that didn't like reversed polarity and may have given up their smoke.
It appears at least one other maker has constructed a polarity insensitive
unit. AFAIK, LEDs will only light when properly forward-biased, these units
must have some sort of circuitry--DC-DC conversion maybe--that allows this, but
it's beyond my knowledge.
bs
--------------------------------
Bob Spidell - San Jose, CA
----- Original Message -----
From: "Mr. Bill" <bn1@pacbell.net>
Hi Bob Larson, Bob Spindell and List,
First, I know absolutely nothing about the electrics and doubt I could
hold a decent conversation with either of you to Bob's! :-(
I use a homemade display case with three Lucas bulb sockets for my "show
and tell". The sockets hold a tungsten, halogen and LED bulb for
comparison. It's powered by my 12V battery charger. I had no problems
leaving the bulbs on both low and high brightness for extended periods.
When asked about the positive ground, I sacrificed one bulb by putting
the charger's positive clamp on the outer (ground) section and touched
the bottom electrode with the negative clamp. It went puff and let the
smoke out.
I anticipate being told that my charger was putting out more than 12V.
OK, if that's the case, why didn't it blow the LED in the comparison? I
don't have too many friends with Healeys that are still positive ground
but I'll try to quickly find one for a true test. Until such time I
will stand by my negative ground only warning.
I hope everyone's turkey is/was moist and tasty!
Bill
Red Car Enterprises
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