LED Tail light question

[techno]

No, it wouldn't fit.

- Dual rear lights (= double security if one light breaks down) - Won't happen on mine - well unless the fuse blows.
- Number plate illumination - Included.
- Standard rear reflector - Included on the standard lens (not included on the clear replacement ones you get though )

 

[Timolgra]

I had the NN LED unit on my last 1150ADV but some of the LEDs failed.
I now have the TT twin light unit which IMO is much better:cool

 

[Roger Chatterton]

I had the NN LED unit on my last 1150ADV but some of the LEDs failed.
I now have the TT twin light unit which IMO is much better:cool

Yes, I prefer the TT double bulb rear, but my GS1150 ABS doesn't like the LED bulbs....not enough current draw....
So where did you fit the resistor, and how ?? That's really my "problem" !!

Thinking that I may be able to find a take-off point from the contacts in the number plate light bit, and run wires to a suitable 8 ohm 5watt resistor from there-it has to be the same supply as to the rear light surely ??

 

[Timolgra]

Yes, I prefer the TT double bulb rear, but my GS1150 ABS doesn't like the LED bulbs....not enough current draw....
So where did you fit the resistor, and how ?? That's really my "problem" !!

Thinking that I may be able to find a take-off point from the contacts in the number plate light bit, and run wires to a suitable 8 ohm 5watt resistor from there-it has to be the same supply as to the rear light surely ??

Sorry that was confusing and not very helpful, my previous 1150 ADV was non ABS so didn't need a resistor.
I thought NN did a different version for the ABS models, presumably with a resistor.
As a matter of interest, does the resistor go in line?

 

[Peter Rankin]

Nippy Normans LED rear light fitted to late '04 GS, transferred to '07 model in August, absolutley no problems on either bike.

 

[Roger Chatterton]

Apparently, in-line (series) would only reduce VOLTAGE...
connecting across both terminals (parallel) will increase apparent CURRENT draw, and thus fool the "Fault" light into thinking that there is sufficient current draw.
Bloody pest really -I'll try to sort this out asap, as I don't want to return lights to filament type bulbs. Just got to find somewhere for the resistor, which will get quite warm, as it's acting as a current dump.
Must state that I'm no expert on electronics, just Audio type wiring and soldering (being a Sound Engineer, and ex PA tech !!!)

 

[Roger Chatterton]

Nippy Normans LED rear light fitted to late '04 GS, transferred to '07 model in August, absolutley no problems on either bike.

Was that an ABS bike though ?? There has to be a simple way round this surely ?? As I said, mines a TT light -dual bulbs, and separate number plate bulb.

 

[techno]

I think the GS can have IBS without ABS and ABS without IBS...if that makes sense.

Basically the IBS is a current sensing circuit, so you need a ballast resistor to simulate the filament current as you say. 8 ohms will mean you draw 1.68A which will is 22.6 Watts. Your 5W resistor wouldn't last too long at that power and something will melt!

You are thinking of the brake light perhaps? The IBS senses current on the tail light circuit. If there is no (or little current) it then decreases the current flow to the brake filament to simulate a tail light. it doesn't work the other way round.

Ohm's Law is V=I/R and Power = (I^2)R

Using the above R can be found assuming 5W bulb and 13.5v battery/alt output you have:

P=IV, I=0.37A
R=V/I R=36.5 Ohms (33R or 39R)

So you will need a resistor capable of handling 5W (go for a wire wound 7W or alu clad 10W)

Parallel is the way to connect to shunt the current.

One thing though, if the unit has a separate number plate bulb (effectively another tail light), the current draw should be sufficient to fool the IBS. If it is lower than 5W try changing that bulb to a 5w version. Bear in mind the power use (i.e. effective resistance) of this bulb when calculating the shunt resistor.

 

[techno]

Not wishing to blow my own trumpet....but my tail light replacement will have a switchable IBS function. If your current 1150 doesn't have it, your next one might.

 

[Roger Chatterton]

I think the GS can have IBS without ABS and ABS without IBS...if that makes sense.

Basically the IBS is a current sensing circuit, so you need a ballast resistor to simulate the filament current as you say. 8 ohms will mean you draw 1.68A which will is 22.6 Watts. Your 5W resistor wouldn't last too long at that power and something will melt!

You are thinking of the brake light perhaps? The IBS senses current on the tail light circuit. If there is no (or little current) it then decreases the current flow to the brake filament to simulate a tail light. it doesn't work the other way round.

Ohm's Law is V=I/R and Power = (I^2)R

Using the above R can be found assuming 5W bulb and 13.5v battery/alt output you have:

P=IV, I=0.37A
R=V/I R=36.5 Ohms (33R or 39R)

So you will need a resistor capable of handling 5W (go for a wire wound 7W or alu clad 10W)

Parallel is the way to connect to shunt the current.

One thing though, if the unit has a separate number plate bulb (effectively another tail light), the current draw should be sufficient to fool the IBS. If it is lower than 5W try changing that bulb to a 5w version. Bear in mind the power use (i.e. effective resistance) of this bulb when calculating the shunt resistor.

HI Techno, many thanks for the info,and just a couple of queries;

a/. swapping the number plate bulb back to a filament doesn't help, even though it is 5w bulb, Fault light still shows !

b/. are you saying that my 7w , wirewound resistor should be 33 ohm ? My 8 ohm would therefore not be high enough resistance ?

help much appreciated

 

[techno]

Resistors

HI Techno, many thanks for the info,and just a couple of queries;

a/. swapping the number plate bulb back to a filament doesn't help, even though it is 5w bulb, Fault light still shows !

b/. are you saying that my 7w , wirewound resistor should be 33 ohm ? My 8 ohm would therefore not be high enough resistance ?

help much appreciated

Strange about the number plate light. Can't see how it can be wired independently of the tail light. I would need to see a wiring diagram of the unit.

As for your resistor, if you put an 8ohm resistor across a 13.5 volt source, 1.68A will flow through it and that will generate heat in the form of 22.6 watts. This will fry your 7W resistor.

It doesn't matter if it is a 7W or 100W resistor, if it is 8ohms you get 1.68A.
To reduce the current flow (and reduce power) you need a bigger resistor.

Your 7W rating will be fine but it needs to have a bigger resistance -

for 33 ohm
13.5/33=0.4A -> 0.4^2 x 33 = 5.5W

for 39 ohm
13.5/39=0.35A -> 0.35^2 x 39 = 4.8W

for 47 ohm
13.5/47=0.29A -> 0.29^2 x 39 = 3.8W

These are calculated values not actual as the resistor tolerance and values change with heat/batch etc. Also your LED clusters will use some current and have resistance too. Don't know what that would be - depends on their specs and internal resistors.

As Maplin don't do a 33R in 7W or 10W (I don't use Maplin - but I assume you would) I would go for a 10W 39R AND a 10W 47R and try them both. Go for the 10W as it will be able to dissapate the heat better. If both work, go for the 47R as that is a whole Watt saved

Hope that helps.

 

[Roger Chatterton]

Hi Techno,

thanks again for the info , and that's exactly what I needed to know , and makes a lot of sense, so I'll pop back to Maplins !!
Re the light assembly in the TT-from what I can gather, the 2 rear bulbs and number plate bulb are paralleled-up, and I guess this would account for why returning the number plate bulb to filament doesn't affect the Fault light, as it won't therefore show the required resistance ?

Anyhow, very grateful for the help, -if I'd had the original BMW tail light I'd have gone with your mods, and the extra "Running lights" ...and saved a lot of faffing about !! They look very neat ( and trouble free )
Electronics is not my strong point....but I think you've guessed that

Cheers, Roger

 

[Roger Chatterton]

Strange about the number plate light. Can't see how it can be wired independently of the tail light. I would need to see a wiring diagram of the unit.

As for your resistor, if you put an 8ohm resistor across a 13.5 volt source, 1.68A will flow through it and that will generate heat in the form of 22.6 watts. This will fry your 7W resistor.

It doesn't matter if it is a 7W or 100W resistor, if it is 8ohms you get 1.68A.
To reduce the current flow (and reduce power) you need a bigger resistor.

Your 7W rating will be fine but it needs to have a bigger resistance -

for 33 ohm
13.5/33=0.4A -> 0.4^2 x 33 = 5.5W

for 39 ohm
13.5/39=0.35A -> 0.35^2 x 39 = 4.8W

for 47 ohm
13.5/47=0.29A -> 0.29^2 x 39 = 3.8W

These are calculated values not actual as the resistor tolerance and values change with heat/batch etc. Also your LED clusters will use some current and have resistance too. Don't know what that would be - depends on their specs and internal resistors.

As Maplin don't do a 33R in 7W or 10W (I don't use Maplin - but I assume you would) I would go for a 10W 39R AND a 10W 47R and try them both. Go for the 10W as it will be able to dissapate the heat better. If both work, go for the 47R as that is a whole Watt saved

Hope that helps.

Hi Techno,

looks like the 47 Ohm 10 watt does the job -on turning on ignition, the Fault light comes on, thinks for a moment, and then goes off. Guess it's the electronics checking the system.
I ran off the number plate light, and hid resistor, with a bit of heat-shrink and silicone, under the seat, where it can get a bit of air, and not touching any cables.
Job done I hope. Will road test this weekend.
So, many thanks- I owe you one !!!

 

[techno]

I am sure it will be OK. Remember the resistor will/should only get as hot as the bulb so as long as it is in 'free air' it will be fine. Still wouldn't mind knowing why it wouldn't 'see' the number plate bulb as sufficient load though....My tail light uses the aluminium type and the copper board as a heat sink. Sounds like you have done a good job.

The fault light does come on for a few seconds, but goes off. That is normal with or without your mod.

Got the LED side light boards today so they will soon be ready for all those waiting!