Help: Can someone assist with load resistor calculation for

[Lee Wilkinson]

Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made lamp
body).

I've made my own LED board and have found lots of resources on the web to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system that
has a bulb failure warning circuit. To get round this the aftermarket lamp
has a load resistor across each of the running and brake circuits - fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running light
and full level brake light and looks great. I guessed on the 100 ohms for
the running light but it looks about the same as the 5W tungsten to my eyes.

If I take one of the aftermarket board load resistors and connect it across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs are
already dim on the running light circuit, that they get too little current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work together.

Even better, if someone were actually able to explain to me how it's worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee

 

[Gyro]

On 04/06/2008 20:55, in article
e9OdncMvBq3WbtvVnZ2dnUVZ_h_inZ2d@giganews.com, "Tom Biasi"
<tombiasi***@optonline.net> wrote:

"Lee Wilkinson" <thepanda@btconnect.com> wrote in message
news:C46C9301.389%thepanda@btconnect.com...
Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made
lamp
body).

I've made my own LED board and have found lots of resources on the web to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system
that
has a bulb failure warning circuit. To get round this the aftermarket lamp
has a load resistor across each of the running and brake circuits -
fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running light
and full level brake light and looks great. I guessed on the 100 ohms for
the running light but it looks about the same as the 5W tungsten to my
eyes.

If I take one of the aftermarket board load resistors and connect it
across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs are
already dim on the running light circuit, that they get too little current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work
together.

Even better, if someone were actually able to explain to me how it's
worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee



Hi Lee,
Without knowing what you monitor circuit is looking for we can only make
some assumptions based on the circuits that work and the problems you have
with your circuit.
It would probably be easier to start with a high value load that works for
the LEDs and reduce it until it "fools" the monitor and the go a little
lower.

Tom


Hi Tom,

I can only presume it's looking for a 5w and 21w load on each circuit, the
same as supplied by a tungsten bulb. I have no idea how to calculate how
this equates to the 46 ohm load resistor that CA used on their board.

They used a low 43 ohm resistor on their running section and yet the LEDs
are too dim in mine and others opinion. If I were to drop on my board from
100 ohm down closer to the 43 used by CA, it may be too bright as a running
light without the load resistor but would that then be pulled back into line
when a load resistor was put across? - just a thought as a newbie!

What sort of value would you suggest as a high load across? I know these
need to be higher wattage resistors and can get hot but would a high value
resistor just force the current through the LEDs (an easier route so to
speak) or would it just dissipate the current as heat? Sorry if that sounds
silly but this really is new to me!

Cheers,
Lee

 

[Gyro]

On 04/06/2008 21:46, in article g26uv8$8aa$1@aioe.org, "Michael Robinson"
<kellrobinson@yahoo.com> wrote:

"Lee Wilkinson" <thepanda@btconnect.com> wrote in message
news:C46C9301.389%thepanda@btconnect.com...
Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made
lamp
body).

I've made my own LED board and have found lots of resources on the web to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system
that
has a bulb failure warning circuit. To get round this the aftermarket lamp
has a load resistor across each of the running and brake circuits -
fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running light
and full level brake light and looks great. I guessed on the 100 ohms for
the running light but it looks about the same as the 5W tungsten to my
eyes.

If I take one of the aftermarket board load resistors and connect it
across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs are
already dim on the running light circuit, that they get too little current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work
together.

Even better, if someone were actually able to explain to me how it's
worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee


Check your wiring.

If you connect the "running light" load resistor to the wrong end of the 100
ohm resistor, it will make the lights go out.


Hi Michael,

I was connecting it the same way as CA connected theirs - earth to the feed
side of the 'running light' 100 ohm reduction resistor not the LED/Brake
light feed side.

If I connect it to the LED side next to the brake feed I'll effectively be
adding another load resistor in parallel to the brake load won't I, and
halve the load resistance? I'm not sure how it would be 'seen' on the
running light monitor?

Cheers,
Lee

 

[Gyro]

On 04/06/2008 22:31, in article g271k3$imu$1@aioe.org, "Michael Robinson"
<kellrobinson@yahoo.com> wrote:

"Gyro" <thepanda@btconnect.com> wrote in message
news:C46CC395.744%thepanda@btconnect.com...



On 04/06/2008 21:46, in article g26uv8$8aa$1@aioe.org, "Michael Robinson"
kellrobinson@yahoo.com> wrote:


"Lee Wilkinson" <thepanda@btconnect.com> wrote in message
news:C46C9301.389%thepanda@btconnect.com...
Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find
some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made
lamp
body).

I've made my own LED board and have found lots of resources on the web
to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system
that
has a bulb failure warning circuit. To get round this the aftermarket
lamp
has a load resistor across each of the running and brake circuits -
fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running
light
and full level brake light and looks great. I guessed on the 100 ohms
for
the running light but it looks about the same as the 5W tungsten to my
eyes.

If I take one of the aftermarket board load resistors and connect it
across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs
are
already dim on the running light circuit, that they get too little
current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work
together.

Even better, if someone were actually able to explain to me how it's
worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee


Check your wiring.

If you connect the "running light" load resistor to the wrong end of the
100
ohm resistor, it will make the lights go out.


Hi Michael,

I was connecting it the same way as CA connected theirs - earth to the
feed
side of the 'running light' 100 ohm reduction resistor not the LED/Brake
light feed side.

If I connect it to the LED side next to the brake feed I'll effectively be
adding another load resistor in parallel to the brake load won't I, and
halve the load resistance? I'm not sure how it would be 'seen' on the
running light monitor?

Cheers,
Lee


Well, something doesn't jibe.

If I understand you correctly,

when the brake is not applied, and you don't have a load resistor installed
on the running light feed, the running light works;

but then, when you insert a load resistor from the "+14.4V Running Light"
node in your circuit to ground, the running light dies.

However, "+14.4 Running Light" is a low impedance power source, and
diverting some small fraction of an amp to ground from that power source
should have negligible effect; the voltage at that node should hardly change
at all with the addition of some small load. Either something's out of
kilter with your circuitry or else I misunderstood your post.

The points on your diagram labeled in red "+14.4V" signify a connection to
your bike's positive power source, do they not?


I'll connect all up again in the morning and double check, but yes I'm sure

you understand me & I've described the symptoms correctly. The circuits are
definitely as per my diagrams and I'm at a loss to work out why the CA
manufactured board works and mine doesn't - I know it's probably the
resistor values but don't know how to work them out hence posting.

For something being out of kilter, maybe it's my choice of the 100 ohm to
reduce the power for the running light. I don't know how to calculate what t
should be so took a guess by connecting a few different resistors until I
got something that 'looked' right. That's why I wondered whether changing it
for a lower value would be better.

Will check again as I say and come back.

Cheers, Lee

 

[Gyro]

On 04/06/2008 22:59, in article
__-dnbPOTpbNjdrVnZ2dnUVZ_qqgnZ2d@earthlink.com, "Dan Coby"
<adcoby@earthlink.net> wrote:

"Lee Wilkinson" <thepanda@btconnect.com> wrote in message
news:C46C9301.389%thepanda@btconnect.com...
Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made lamp
body).

I've made my own LED board and have found lots of resources on the web to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system that
has a bulb failure warning circuit. To get round this the aftermarket lamp
has a load resistor across each of the running and brake circuits - fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running light
and full level brake light and looks great. I guessed on the 100 ohms for
the running light but it looks about the same as the 5W tungsten to my eyes.

If I take one of the aftermarket board load resistors and connect it across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs are
already dim on the running light circuit, that they get too little current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work together.

Even better, if someone were actually able to explain to me how it's worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee

The short form of the answer is that you need to reduce the 100 ohm resistor.
If I were you, I would try 43 ohms (i.e. the value from the original circuit.)

Without more information about the monitor circuit, we can only guess about
the values for the green resistors. The 46 ohm value in the original circuit
seems
to have been chosen to give about a 5 watt load at 14.4 volts (actually 4.5
watts).
Since this value works, you can continue to use it. If you want, you can try
higher
values. Higher values will give you less power being wasted in these
resistors.
However at some point with higher values the monitor circuit will decide that
the 'light bulb' is burned out.

You chose the 100 ohm resistor to give the correct brightness for the running
lights. However, I assume, that the second 46 ohm resistor was not connected
when you chose that value. Put the second 46 ohm resistor into your circuit
and
try lower values for the current 100 ohm resistor until you get the brightness
desired.

The current combination of a 46 ohm resistor and a 100 ohm resistor creates
a 'voltage divider' circuit. I.e. (view in a fixed font):

_____
------| 100 |-----+--------o
| ----- |
+ ___
14.4 volts | 4 | Vo = 14.4 * (46 / (100 + 46)) = 4.5 volts
- | 6 |
| ---
| |
|__________________|________o

The voltage out of this circuit (Vo) is Vin * R2 / (R1 + R2) where Vin is 14.4
volts,
R1 is 100 ohms and R2 is 46 ohms.

For your values, this gives 4.5 volts. However your LEDs need a minimum of 7.2
volts (4 x 1.8 volts) before then will produce light. So you need to change
the
ratio of R2 / (R1 + R2) to give you a higher output voltage. Since you
probably
cannot increase R2 (46 ohms), you will need to decrease R1 (100 ohms).

Dan,

Thanks ever so much for the comprehensive reply- I'm going to check all
again in the morning anyway and will study what you've put here to make sure
I understand properly and make changes.

Cheers,
Lee

 

[google@woodall.me.uk]

On Jun 4, 10:59 pm, "Dan Coby" <adc...@earthlink.net> wrote:

The current combination of a 46 ohm resistor and a 100 ohm resistor creates
a 'voltage divider' circuit. I.e. (view in a fixed font):

_____
------| 100 |-----+--------o
| ----- |
+ ___
14.4 volts | 4 | Vo = 14.4 * (46 / (100 + 46)) = 4.5 volts
- | 6 |
| ---
| |
|__________________|________o

The voltage out of this circuit (Vo) is Vin * R2 / (R1 + R2) where Vin is 14.4 volts,
R1 is 100 ohms and R2 is 46 ohms.

Unless it's been wired up differently to the way it's been drawn then
this isn't the circuit the OP is using. He's using:

-----
------------------+--| 100 |------o
| | -----
+ ___
14.4 volts | 4 |
- | 6 |
| ---
| |
|__________________|________o


The only way I can see this failing is if there's a high resistance
somewhere (bad connection? Bad earth?). Occasionally you see a similar
problem in car rear light clusters where the indicator flashing causes
the brake light to flash in anti-phase.

Tim.

 

[Gyro]

On 05/06/2008 08:51, in article
6JudnUt4Z5V7B9rVnZ2dnUVZ_qPinZ2d@earthlink.com, "Dan Coby"
<adcoby@earthlink.net> wrote:

"Gyro" <thepanda@btconnect.com> wrote in message
news:C46CD344.756%thepanda@btconnect.com...



On 04/06/2008 22:59, in article
__-dnbPOTpbNjdrVnZ2dnUVZ_qqgnZ2d@earthlink.com, "Dan Coby"
adcoby@earthlink.net> wrote:

"Lee Wilkinson" <thepanda@btconnect.com> wrote in message
news:C46C9301.389%thepanda@btconnect.com...
Hi folks,

Don't have much electronics experience and have forgotten most of what I
learnt at school (well it was 25 years ago!) and am hoping I can find some
assistance in getting an LED lamp for my motorbike working correctly....

There is an aftermarket lamp made by Clear Alternatives that functions
correctly but has a very poorly designed LED board as far as vision is
concerned (very narrow beam and mis-aligned LEDs as well as poorly made
lamp
body).

I've made my own LED board and have found lots of resources on the web to
tell me what resistors to use with the LEDs to make the lamp function
correctly with the 14.4V my motorbike supplies the lamp. My problem has
arisen due to the fact that my BMW motorbike has a CanBus wiring system
that
has a bulb failure warning circuit. To get round this the aftermarket lamp
has a load resistor across each of the running and brake circuits - fooling
the onboard system into thinking there's a standard 5/21W tungsten bulb
fitted.

When connected, my lamp functions correctly with lower level running light
and full level brake light and looks great. I guessed on the 100 ohms for
the running light but it looks about the same as the 5W tungsten to my
eyes.

If I take one of the aftermarket board load resistors and connect it across
the brake circuit, the lamp still functions correctly and it fools the
warning system. However when I connect a 2nd load resistor across the
running light circuit the LEDs all go out!! I presume that as the LEDs are
already dim on the running light circuit, that they get too little current
when the load resistor is insterted and so go out.

What I need to know is what load resistors to use, and if necessary what
resistors to change on the actual lamp board so they can all work together.

Even better, if someone were actually able to explain to me how it's worked
out, I can learn something for the future too!

Here are the diagrams of the aftermarket lamp that works and my new home
built one for reference.
http://www.postimage.org/image.php?v=aV2gM5w9
http://www.postimage.org/image.php?v=Pq295j6A

Can anyone help me with the above or point me at any reference material,
online forums / guides on this that can help?

You'll make a very frustrated man happy!!

Cheers,
Lee

The short form of the answer is that you need to reduce the 100 ohm
resistor.
If I were you, I would try 43 ohms (i.e. the value from the original
circuit.)

Without more information about the monitor circuit, we can only guess about
the values for the green resistors. The 46 ohm value in the original circuit
seems
to have been chosen to give about a 5 watt load at 14.4 volts (actually 4.5
watts).
Since this value works, you can continue to use it. If you want, you can
try
higher
values. Higher values will give you less power being wasted in these
resistors.
However at some point with higher values the monitor circuit will decide
that
the 'light bulb' is burned out.

You chose the 100 ohm resistor to give the correct brightness for the
running
lights. However, I assume, that the second 46 ohm resistor was not
connected
when you chose that value. Put the second 46 ohm resistor into your circuit
and
try lower values for the current 100 ohm resistor until you get the
brightness
desired.

The current combination of a 46 ohm resistor and a 100 ohm resistor creates
a 'voltage divider' circuit. I.e. (view in a fixed font):

_____
------| 100 |-----+--------o
| ----- |
+ ___
14.4 volts | 4 | Vo = 14.4 * (46 / (100 + 46)) = 4.5 volts
- | 6 |
| ---
| |
|__________________|________o

The voltage out of this circuit (Vo) is Vin * R2 / (R1 + R2) where Vin is
14.4
volts,
R1 is 100 ohms and R2 is 46 ohms.

For your values, this gives 4.5 volts. However your LEDs need a minimum of
7.2
volts (4 x 1.8 volts) before then will produce light. So you need to change
the
ratio of R2 / (R1 + R2) to give you a higher output voltage. Since you
probably
cannot increase R2 (46 ohms), you will need to decrease R1 (100 ohms).



Dan,

Thanks ever so much for the comprehensive reply- I'm going to check all
again in the morning anyway and will study what you've put here to make sure
I understand properly and make changes.

Cheers,
Lee

A few more comments:

I suggested earlier that you replace your 100 ohm resistor with a 43 ohm
resistor
(the same as the original circuit). However that value may still be a little
large. With
a 43 ohm resistor, the output of the voltage divider is 14.4 * 46 / (43 + 46)
= 7.44 volts.
That voltage is still probably too low to get the desired brightness. (I did
not do the
math earlier, I simply assumed that the original circuit had reasonable values
and
that the LEDs were similar.) My guess is that something in the 33 to 36 ohm
range will
be better.

The 46 ohm resistors will dissipate about 4.5 watts. The other resistor will
also dissipate
about that much heat. Obviously they need to be sized to handle that power
level. I suggest
at least a 10 watt power rating. Even so they will get warm. Larger resistors
with more
surface area (or a heat sink) will run cooler.

The brightness of the LEDs in the 'running light' mode will be pretty
sensitive to the
battery voltage. (The original circuit had the same problem.) You could add a
diode
into the connection between the 'brake light' 46 ohm resistor and your 100 ohm
resistor.
This would reduce the voltage sensitivity by eliminating the voltage divider.
Thus you
could use the 100 ohm value that you already have. (The voltage divider is
eliminated
since the diode is reversed biased when the brake light switch is not
active.) The
voltage drop across this diode will reduce the drive signal to the LEDs by
about 0.7 volts.
You might want to reduce the 130 and 270 ohm resistors by 5% to compensate.

Both the original circuit and your version have groups of LEDs arranged as two
strings
of four LEDS in parallel sharing a single current limiting resistor. This is
not really a good
idea. (Its only advantage is minimizing the resistor count.) LEDs are very
non-linear in
their current/voltage characteristics. It is likely that the groups of 4 LEDs
will not share
the current equally between the two strings. A better design would have a
separate
270 ohm resistor for each string of 4 LEDs. (Note: Having the LEDs in strings
of at
least 4 is good since it helps reduce wasted power.)

My sincere thanks to everyone that replied. This has helped me out a lot and
I now have it sorted as per Dan's recommendations - a 33ohm 10W resistor
rather than the 100 has everything functioning correctly.

I now understand how to work out stuff a little more too.

Will look to adding a diode as per Dan & Bob for 'belt and braces'.

Cheers, Lee

 

[Gyro]

On 05/06/2008 16:50, in article
8fydndWJ_MLbltXVnZ2dnUVZ_gidnZ2d@giganews.com, "BobW"
<nimby_NEEDSPAM@roadrunner.com> wrote:

"Gyro" <thepanda@btconnect.com> wrote in message
news:C46DB058.775%thepanda@btconnect.com...

On 05/06/2008 08:51, in article
6JudnUt4Z5V7B9rVnZ2dnUVZ_qPinZ2d@earthlink.com, "Dan Coby"
adcoby@earthlink.net> wrote:


[snip]


The brightness of the LEDs in the 'running light' mode will be pretty
sensitive to the
battery voltage. (The original circuit had the same problem.) You could
add a
diode
into the connection between the 'brake light' 46 ohm resistor and your
100 ohm
resistor.
This would reduce the voltage sensitivity by eliminating the voltage
divider.
Thus you
could use the 100 ohm value that you already have. (The voltage divider
is
eliminated
since the diode is reversed biased when the brake light switch is not
active.) The
voltage drop across this diode will reduce the drive signal to the LEDs
by
about 0.7 volts.
You might want to reduce the 130 and 270 ohm resistors by 5% to
compensate.

Both the original circuit and your version have groups of LEDs arranged
as two
strings
of four LEDS in parallel sharing a single current limiting resistor. This
is
not really a good
idea. (Its only advantage is minimizing the resistor count.) LEDs are
very
non-linear in
their current/voltage characteristics. It is likely that the groups of 4
LEDs
will not share
the current equally between the two strings. A better design would have a
separate
270 ohm resistor for each string of 4 LEDs. (Note: Having the LEDs in
strings
of at
least 4 is good since it helps reduce wasted power.)



My sincere thanks to everyone that replied. This has helped me out a lot
and
I now have it sorted as per Dan's recommendations - a 33ohm 10W resistor
rather than the 100 has everything functioning correctly.

I now understand how to work out stuff a little more too.

Will look to adding a diode as per Dan & Bob for 'belt and braces'.

Cheers, Lee


Lee,

If what Dan and I suspect is truly going on, if you add the diodes then the
only values that would matter are the two fool-the-monitor-circuit load
resistors. These load resistors should only need to be some maximum value
(i.e. minimum sense current). After that, all the other brightness-setting
resistors will have no effect on the proper operation.

I would be concernced that without doing a lot of characterization with the
current circuit, you may get into trouble (e.g. lights not coming on) as
your battery voltage varies and the monitor circuit characteristics vary.
Again - if it were my bike I would spend the extra effort to see if the
diodes allow you to vary resistor values without concern for the operational
stability of your lights.

Bob

Will do, and thanks again for your and everyone else's help.

Next step after that is to find something that will remove the white hazing
that appears on the clear plastic around where 'super glue' (cyanoacrylate -
spelling?) has been used to join the halves. As it's dried the clear plastic
has gone milky - damn! If there isn't I need to find something that I can
run into the joints to seal it together as I don't want to use a glue that
will compress and ooze out as it looks nasty (especially on the inside where
I can't trim it off)!

Lee