when buying diodes higher current rating and voltage never hurts. in
continious duty the higher current rating is usually larger physically
which helps keep it cool for long trouble free operation.
generally doubling voltage and tripling current rating is a good idea,
plus diodes are very cheap:)
The only time there is any significant current is when the doorbell is
ringing. It's a pretty short duty cycle. I"m not disagreeing with
your general statement but this is not a very stressful application.
I don't think I've ever had a button burn out either. I'm on my
second button and the house is 34 years old, but I think the house
came with an unlighted button, so I changed that almost right away,
and after 15 or 20 years, the new button got so weathered the light
didn't show through. (Or maybe it burnt out but it was still after 15
or 20 years.)
I bought the 2nd button at Home Depot. It's just like the first one,
pretty much the cheapest lit button that they sell, other than the
round one that goes almost entirely in the hole. (This is a black
plastic rectangle which sits on top of the wood, with a metal cover
that wraps around the top, front, and bottom, with a white or cream
colored plastic button in the middle**.) . When I put in a doorbell
in the basement, in parallel, I had to put in a bigger transformer, so
I got either 16 or 18v (whichever the bigger doorbell transformer is)
from Home Depot. In other words nothing special.
The OP's voltage may be too high. Maybe the previous owner didn't use
a standard doorbell transformer. Or maybe it's broken.
**Actually all the buttons by the same maker are probably of the same
quality, just the cases are different. I know in 1967 when my car
compass didn't work, I wrote to Airguide, I think the name is, and
asked if I bought a more expensive compass would it work better? And
they wrote back, "No. All the compasses are the same. Only the cases
If they dont sell them, find one where you can access the bulb. Wiring
a LED would be simple. Your doorbells are usually running off a 24v AC
transformer. So, you'd need a diode to convert to DC, then a suitable
resistor (someone on one of the electronics newsgroups could help with
selecting the right size), and of course the LED itself (probably
white). 3 parts, and a little solder, and you'll have a LED lighted
To wire it, one power lead goes to the diode, then to the resistor, and
to the LED. The other lead on the LED goes right to the power wire.
Polarity of the LED and diode are important. There are likely lots of
simple circuits for them on the web. Or buy it at Radio Shack and there
will be a wiring diagram on the package.
The Xmas lights might not ever go reverse current because I'm pretty sure
it's higher than forward voltage to conduct. I don't like the look of
blinkys. A bridge rectifier would double the frequency.
A bridge would increase the efficiency a little. Probable too little to
be concerned about here. If you do use one, consider that it adds an
about 1.4V voltage drop.
I wouldn't use a bridge here, because of the increased complexity and
Unlikely unless current was excessive (resistor too small).
BTW, I have (accidentally) connected 12V (1.5A supply) to a LED without
a resistor. It popped and split in half immediately.
AFAIK, the reverse threshold (voltage that must be reached for a diode
to conduct) is usually higher (AFAIK) than the forward voltage.
If there is ever any reverse current, it'll be too small to be concerned
On 04/24/2013 08:37 PM, email@example.com wrote:
For xmas LED lights, the series I've seen have 25, 30, or 35 LEDs.
Longer strings have multiple series, in different polarities. These have
diodes. That's what LEDs are.
However, some LED strings seem to have full-wave rectifiers (4 diodes)
in them, in addition to the LEDs.
On 4/24/2013 10:07 PM, firstname.lastname@example.org wrote:
I thought a regular 5mm red LED used 2 volts DC at around 30ma. A small
switching diode rated at around 50 volts DC and a suitable resistor to
limit the current with everything in series with the LED should work
across the doorbell button since it's working as a simple continuity
indicator across an open switch but in series with the doorbell and
power transformer. ^_^
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