On Sun, 05 Aug 2012 04:44:53 -0400, "Michael A. Terrell"
wrote:


"John B." wrote:

On Sat, 04 Aug 2012 10:25:10 -0400, "Michael A. Terrell"
wrote:


"John B." wrote:

A great many of those 12 VDC lights are just series circuits made up
of LED's and resisters. Try a resister in series with one side of the
circuit. It may well dim your lights. If that works you can replaced
the resister with a variable resister (potentiometer, rheostat,
whatever) for finer control.


Can and should are two different things. The proper way to dim them
is with a PWM controller which is dirt cheap on Ebay.

How so "proper"? More efficient as no resisters used to generate heat
but the O.P just wanted to make the lights less bright and a rheostat
will do that with the usual 12 VDC LED lights.


He would need a wirewound Rheostat, and the control would be very
touch, since LEDS are current operated devices, unlike incandescents.
They will change brightness with temperature changes when such a crude
method id used. A decent Rheostat willl cost more than a PWM
controller. Some LEDs will start to emit light at the microamp level.

I'm not arguing that a PWM isn't efficient. I'm merely pointing out
that the general, run of the mill, 12 VDC LED fixture is either a
series wired bunch of LEDs or a series parallel wired bunch of LEDs,
possible with resisters in the series circuits. They normally draw so
little current that there is no necessity for a wire wound resister.
If I remember correctly I used either a 1/4 or 1/2 watt carbon
resister to dim the lights in my previous boat. The OP just wanted to
dim some fishing lights and a variable resister will do the job.

At least it did on my 40 ft. sailboat that I converted from
incandescent/fluorescent to LED. I had no problems with the lights in
the three years before I sold the boat. Power came from the 12 volt,
600 amp hour house bank who's voltage would have ranged between 14+
volts when charging and probably 11.5 volts.
Cheers,
John B.