DIY Electric Car Forums banner

1 - 1 of 1 Posts

·
Registered
Joined
·
70 Posts
Discussion Starter #1
Re: [EVDL] LED Taillights - a money saver in gas cars? -rangeextenderin EV's? - an an

First off I should point out that I misquoted the specs <http://
www.superbrightleds.com/specs/115x-xLX3.htm>. I was looking at the ma
column instead of the lumens column. At full brake light power it
draws 240ma (current regulated.) That would be 2.88 watts of power
for the brake light function at 90 lumens. That is a lot less than
the 400 lumens of a 1157 bulb with both filaments lit.

I've tested a few cheap LED auto bulbs and found them lacking (not to
bright unless you are right in the center.) I have not yet tested
this bulb (I've been mostly occupied with the actual conversion of my
'66 Datsun right now, plus its not a cheap LED bulb.)

Danny Miller wrote:

> Well lemme point out something else.
> Unless you have a buck converter, the red 3W LED is like 3V @ 1A. But
> we start with a 13.8V system, so we have to burn off 10.8W in a huge
> resistor.
> Maybe you do have buck converter in there and if so great.
>
> With multiple LEDs, the situation is simpler. We can put 3x in series
> for a 9V forward voltage and the ballast resistor only needs to absorb
> 4.8W.

Look at the specs on the LED replacement bulb I was proposing. Try
finding lumen specs for cheap LED auto bulbs (I didn't have any
luck.) It is current regulated and mounted in a heat sink. It would
be internally dissipating 2.88 watts in the brake light condition if
the LED didn't convert any to light (note the .24 amps at 12 volts
spec.) I know that an incandescent bulb converts about 90% of the
applied power to heat (good ones are in the 80's, but this isn't a
"good" example.) So I can expect a 1157 bulb to make around 18 watts
of heat (and 2 watts of light - to be filtered and reflected.)

Using resistors as your voltage drop is not so simple. How many LEDs
do you want in series? 3 is typically less than 6 volts (for red
LEDs.) You would still be dropping 1/2 the voltage across each
resistor (around 1/8 watt per 3 LEDs, times HOW many?). If you put
more in series the current drops pretty quickly as the voltage drops;
the result is an LED lamp that dims about as fast as the incandescent
one (the incandescent bulb shifts toward red as the voltage drops.)

> The 7.6mm P4 pks are easy to use IF the red lens is screwed onto the
> back half. If the whole thing's one glued together piece and the bulb
> is socketed through the back, we may have a problem.

That package may be easy but how easy is it to find replacement tail
light housings for a 1966 Datsun 411? I'm *not* going to hack my tail
lights; I would rather run 1157 bulbs (it has kept the car intact for
over 40 years now.)

Paul Gooch

P.S. - there is no significant power savings in LED illumination for
on-road EVs at this time. The only advantage is faster brake lights.
That is nothing if they don't notice them!

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
 
1 - 1 of 1 Posts
Top