Hey all,

This is not really a repair question, but most of you probably have
electronic skills to answer this question.

Short description of the problem: I want to use a series of LEDs to
replace the turn signal indicator globe on my bike.

My bike battery outputs 12.5V, and currently, the bike uses a 12V/10W
globe (on each side). I intend to replace each globe by connecting 6
LEDs in a row, so that way the total voltage required for all LEDs
would be ~13.8V (a single LED consumes 2.0-2.6V, so 6x~2.3V=13.8V).

So here comes my first question. Am I assuming correctly that because
I have a total of 6 LEDs in a row (~13.8V) I
don’t need a resistor
[b:6e8628ea4d]before[/b:6e8628ea4d] the LEDs?

Next, a single globe consumes 0.83A (10W/12V=0.83A) while all the LEDs
together consume less than half (~0.05Ax6=0.30A). So here comes my
second question, do I need to put a high-power resistor in
[b:6e8628ea4d]parallel[/b:6e8628ea4d] to the LEDs to match the
current consumption compared to the globe?

Sorry it’s long, but I would appreciate you help.

Cheers,
Ronen

slepax wrote:

Hey all,

This is not really a repair question, but most of you probably have
electronic skills to answer this question.

Short description of the problem: I want to use a series of LEDs to
replace the turn signal indicator globe on my bike.

My bike battery outputs 12.5V, and currently, the bike uses a 12V/10W
globe (on each side). I intend to replace each globe by connecting 6
LEDs in a row, so that way the total voltage required for all LEDs
would be ~13.8V (a single LED consumes 2.0-2.6V, so 6x~2.3V=13.8V).

So here comes my first question. Am I assuming correctly that because
I have a total of 6 LEDs in a row (~13.8V) I
don?t need a resistor
[b:6e8628ea4d]before[/b:6e8628ea4d] the LEDs?

Next, a single globe consumes 0.83A (10W/12V=0.83A) while all the LEDs
together consume less than half (~0.05Ax6=0.30A). So here comes my
second question, do I need to put a high-power resistor in
[b:6e8628ea4d]parallel[/b:6e8628ea4d] to the LEDs to match the
current consumption compared to the globe?

Sorry it?s long, but I would appreciate you help.

Cheers,
Ronen

Hi...

You're probably far far better off just going into your
local car part shop and buying a replacement led bulb to
install.

However, seeing you have a 12v supply I suspect that by
bike you really mean a motorcycle - or at least a motor
driven vehicle. If that's true, then be absolutely sure
to check your local laws to find out if you're allowed to
do so.

I think in most (if not all) places we can't use led's
unless they were used as original equipment.

Take care.

Ken

You shouldn't need a resistor - in theory - but when multiple LEDs are
connected in series like this, they are often fed via a simple constant
current source. This can be easily and cheaply realised with two or three
components. This will allow you to set the desired current through your
chain of LEDs for optimum performance ie light output vs life. Also, your
assertion that the individual LED currents will add up, is wrong. If you set
the LED current for say 30mA, and connect 6 LEDs in series, that same
current of 30mA will pass thru all 6. If, however, you connect them in
parallel, the current will add up, but you will definitely then need a
series reistor - 330 ohms at half a watt would do nicely. This would be my
preferred way of doing it anyway as, if one of the LEDs fails in your series
chain, they all go out, whereas if one fails in the parallel setup, the
others stay on, allbeit at changed brightness if a simple resistor is used
for the current limiting.

As far as needing to load the bike's electrics up to simulate the former
lamp load, this will depend on whether the flasher unit is a thermal
relaxation switch, based on a bimetal strip, or an electronically switched
relay. If it's the latter, no additional load other than the LEDs will be
needed - except you might want to put some in anyway to help keep the relay
contacts clean. If the former, then the full load of the original lamps will
be needed, otherwise the flasher unit won't work at all. If the simulated
load is too light, the flashers will run too fast.

Geoff

"slepax" wrote in message
m...
Hey all,

This is not really a repair question, but most of you probably have
electronic skills to answer this question.

Short description of the problem: I want to use a series of LEDs to
replace the turn signal indicator globe on my bike.

My bike battery outputs 12.5V, and currently, the bike uses a 12V/10W
globe (on each side). I intend to replace each globe by connecting 6
LEDs in a row, so that way the total voltage required for all LEDs
would be ~13.8V (a single LED consumes 2.0-2.6V, so 6x~2.3V=13.8V).

So here comes my first question. Am I assuming correctly that because
I have a total of 6 LEDs in a row (~13.8V) I
don’t need a resistor
[b:6e8628ea4d]before[/b:6e8628ea4d] the LEDs?

Next, a single globe consumes 0.83A (10W/12V=0.83A) while all the LEDs
together consume less than half (~0.05Ax6=0.30A). So here comes my
second question, do I need to put a high-power resistor in
[b:6e8628ea4d]parallel[/b:6e8628ea4d] to the LEDs to match the
current consumption compared to the globe?

Sorry it’s long, but I would appreciate you help.

Cheers,
Ronen

In article ,
slepax wrote:
Short description of the problem: I want to use a series of LEDs to
replace the turn signal indicator globe on my bike.

My bike battery outputs 12.5V, and currently, the bike uses a 12V/10W
globe (on each side). I intend to replace each globe by connecting 6
LEDs in a row, so that way the total voltage required for all LEDs
would be ~13.8V (a single LED consumes 2.0-2.6V, so 6x~2.3V=13.8V).

LEDs are actually current driven, so this isn't that good an idea.

So here comes my first question. Am I assuming correctly that because
I have a total of 6 LEDs in a row (~13.8V) I
dont need a resistor
[b:6e8628ea4d]before[/b:6e8628ea4d] the LEDs?

Given that resistors are cheap, I'd use one per LED, and drive them in
parallel. Then if one fails, you'll not overload the others as would
happen with one common resistor, or end up with no light, as when in
series. You should be able to use 0.25 watt resistors which are pretty
small and cheap. If it's a bayonet fitting bulb, then simply break away
the glass and use the bayonet plug for the resistors, and bend the LEDs so
they point in the right direction. After checking it works, pot the
resistors in car body filler, etc, to give some mechanical strength.

Next, a single globe consumes 0.83A (10W/12V=0.83A) while all the LEDs
together consume less than half (~0.05Ax6=0.30A). So here comes my
second question, do I need to put a high-power resistor in
[b:6e8628ea4d]parallel[/b:6e8628ea4d] to the LEDs to match the
current consumption compared to the globe?

Standard LEDs driven at 50mA are likely to have a short life. And six
standard ones will be brighter on axis than a 10 watt tungsten, when
driven at 20mA. Where they should last forever.

But you may be able to buy an LED replacement anyway. Not the same fun,
though.;-)

Sorry its long, but I would appreciate you help.

--
*I don't suffer from insanity -- I'm a carrier

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 14 Aug 2005 17:55:29 GMT, Ken Weitzel wrote:

[snip...snip...]
However, seeing you have a 12v supply I suspect that by
bike you really mean a motorcycle - or at least a motor
driven vehicle. If that's true, then be absolutely sure
to check your local laws to find out if you're allowed to
do so.

I think in most (if not all) places we can't use led's
unless they were used as original equipment.

Also (for the OP) there may be a significant impact on legal liability
in the case of a traffic accident.

Someday, the guy in the 18-wheeler that rolled nine of the eighteen
wheels right over you might get off with no fault and no liability if
the turn signal that you claim to have used to signal the lane change
turns out to have been home-made.

Make your own christmas tree decorations not your own automotive safety
equipment.

--
Rich Webb Norfolk, VA

"slepax" wrote in message
m...
Hey all,

This is not really a repair question, but most of you probably have
electronic skills to answer this question.

Short description of the problem: I want to use a series of LEDs to
replace the turn signal indicator globe on my bike.

My bike battery outputs 12.5V, and currently, the bike uses a 12V/10W
globe (on each side). I intend to replace each globe by connecting 6
LEDs in a row, so that way the total voltage required for all LEDs
would be ~13.8V (a single LED consumes 2.0-2.6V, so 6x~2.3V=13.8V).

So here comes my first question. Am I assuming correctly that because
I have a total of 6 LEDs in a row (~13.8V) I
don’t need a resistor
[b:6e8628ea4d]before[/b:6e8628ea4d] the LEDs?

Next, a single globe consumes 0.83A (10W/12V=0.83A) while all the LEDs
together consume less than half (~0.05Ax6=0.30A). So here comes my
second question, do I need to put a high-power resistor in
[b:6e8628ea4d]parallel[/b:6e8628ea4d] to the LEDs to match the
current consumption compared to the globe?

Sorry it’s long, but I would appreciate you help.

Cheers,
Ronen


Yes you do still need a resistor. Measure the forward voltage drop of the
LED's you're using, and wire up a series string that will run on the worst
case lowest voltage you're likely to have, 10-12v should do it. Subtract
that voltage from the highest supply voltage you'll get, say 16v or so and
use ohms law to select a suitable resistor. You can wire up multiple
series/parallel strings to get more LEDs if you'd like to cover the lense
area with them.