Help Please ---- with LED rear light

[Silverstripes]

Well I did a silly thing.

I bought an LED rear light from Ebay .

It looks realy good and does compliment the clear indicators.

It works OK, However I get the dreaded LAMPR warning.

Read all the previous threads about fitting a resistor so off to Maplins. Fitted a 1 ohm 7 watt resistor to the light circit and all was well, no LAMPR warning but the resistor started to smoke .

Put back to standard for now but can smeone tell me:

Based on the LED unit having 14 LED's with a further 3 for the number plate:

1. What resistor I need for the lights.
2. What resistor I need for the brake light circit.

Its got me beat for now

 

[shugie]

Well I did a silly thing.

I bought an LED rear light from Ebay .

It looks realy good and does compliment the clear indicators.

It works OK, However I get the dreaded LAMPR warning.

Read all the previous threads about fitting a resistor so off to Maplins. Fitted a 1 ohm 7 watt resistor to the light circit and all was well, no LAMPR warning but the resistor started to smoke .

Put back to standard for now but can smeone tell me:

Based on the LED unit having 14 LED's with a further 3 for the number plate:

1. What resistor I need for the lights.
2. What resistor I need for the brake light circit.

Its got me beat for now

12 volts across 1 ohm is 12A of current, 144W to be dissipated, no wonder it smokes. Try a higher value resistor, perhaps 150 ohm, you need to find the highest value that stops the LAMPR warning, my LED board has only small resistors, so it must be a high value otherwise they too would smoke.

At 150 ohms, current is low and power is less, just than 1W. This resistor goes between positive to the lamp and earth, so you need two, one for brake, one for side lamp, might try a 220 ohm for the sidelamp.

You should not need a resistor between the positive supply and the LED board

 

[The smudger]

Or,

You could just leave it as it is...........

No flashy light is worth setting MY bike on fire for.........

 

[Supertech]

personally I think people should stop buying new bikes until they make the electrical systems less complicated and more owner friendly.

 

[The Burpster]

Yawn....

personally I think people should stop buying new bikes until they make the electrical systems less complicated and more owner friendly.

Maybe with two large round stones as wheels, and best English Oak as a frame and axles.......

 

[Bengaz]

Well I did a silly thing.

I bought an LED rear light from Ebay .

It looks realy good and does compliment the clear indicators.

It works OK, However I get the dreaded LAMPR warning.

Read all the previous threads about fitting a resistor so off to Maplins. Fitted a 1 ohm 7 watt resistor to the light circit and all was well, no LAMPR warning but the resistor started to smoke .

Put back to standard for now but can smeone tell me:

Based on the LED unit having 14 LED's with a further 3 for the number plate:

1. What resistor I need for the lights.
2. What resistor I need for the brake light circit.

Its got me beat for now

First, What is the wattage of the standard stop and tail lamp - both values?

Second, Rather than keep guessing, you really need to measure the resistance of the LED fitting, between + and - for stop and tail - 2 readings.
When you have this value, it is quite simple to work out what resistor you require rather than buying loads.

ANd remember, if you put a resistor "across" the lamp, the combined resistance of the lamp and the resistor is halved!
Put it in line and the values are combined.

Hope this helps.

 

[Supertech]

Maybe with two large round stones as wheels, and best English Oak as a frame and axles.......

well what ever options turn you on. Perhaps a Harley is more for you? Go on Sir, suits you xxx

Personally I'd like to see ECU that displays fault codes on the box and a soft fault reset button.......as per the aircraft ECU I work with every day. So easy, so simple, but doesn't make your local BMW dealer a penny. But would make ownership that little bit more comforting.

FYI I'm an aircraft electrician, anyone who's worked on Miliarty spec electrics will know all wires are white and looms get up 4 inches in dia. So when i say a bikes electrics should be simple i mean in relation to the function they should perform, not your intellect.

Tosser

 

[Silverstripes]

First, What is the wattage of the standard stop and tail lamp - both values?

Second, Rather than keep guessing, you really need to measure the resistance of the LED fitting, between + and - for stop and tail - 2 readings.
When you have this value, it is quite simple to work out what resistor you require rather than buying loads.

ANd remember, if you put a resistor "across" the lamp, the combined resistance of the lamp and the resistor is halved!
Put it in line and the values are combined.

Hope this helps.

Ben gaz

Yes thanks Your comments did help.

The rear light is 5w and 21 w for light and brake.

I have tried measuring the resitance of the unit as ou suggested. However when set to 2000k my meter starts reading and stabalises around the 450 mark. Any other setting I get an out of range 1 appear on the meter.

I am also confused about your comment about across the lamp or in line. I placed the previous across. In the past to power LED always in line. Which way should the resistor be placed.

Thanks for your help. If its easier please email on [email protected].

 

[Pukmeister]

FYI I'm an aircraft electrician, anyone who's worked on Miliarty spec electrics will know all wires are white and looms get up 4 inches in dia. So when i say a bikes electrics should be simple i mean in relation to the function they should perform, not your intellect.

Tosser

You should try a warship for size mate, but I know exactly what you mean.

Any resistor will get hot, thats a function of its job after all to resist electron flow which generates heat. IF I had to, I would choose a metal bodied wire-wound resistor and bond it to the bikes chassis with epoxy or similar to dissipate the heat through the bike frame.

Personally I've just 're-engineered' my rear light fitting and wiring to make it fit for purpose (after seeing what the BMW design apprentices and bean counters came up with.)

 

[Bengaz]

well, my 21watt lamp is .5 ohm and my 5watt lamp is 2.5 ohm.
These are the figures you need to achieve by adding (or subtracting) resistance. Either in parallel or in line (series).

Your reading the resistance of the LED light on the 2 million ohm scale.
You need to be on the smallest setting like say 2 or 20 ohm.

DONT FORGET TO NULL THE TEST LEADS AS WELL...

 

[Silverstripes]

well, my 21watt lamp is .5 ohm and my 5watt lamp is 2.5 ohm.
These are the figures you need to achieve by adding (or subtracting) resistance. Either in parallel or in line (series).

Your reading the resistance of the LED light on the 2 million ohm scale.
You need to be on the smallest setting like say 2 or 20 ohm.

DONT FORGET TO NULL THE TEST LEADS AS WELL...

Bengaz

Sorry M8 I am a pain. Ok with std electrics and mechanics but Ohms law

With my meter on 20k alll I get is a 1 showing.

By Null do you mean touch them togeter before a reading

 

[Bengaz]

you need the meter on the lowest setting, not 20k.

When you get the true value, take the resistance of the leads off which will be around .1 or .2ohm.

 

[Silverstripes]

you need the meter on the lowest setting, not 20k.

When you get the true value, take the resistance of the leads off which will be around .1 or .2ohm.

With the meter on 200 and the leads together i get a reading of 00.7, which is the figure you have as .1 or .2.

However when connected to the + amd - feeds to the light unit I get a 1 show which I think is out of range.

I am doing something wrong but dont know what

 

[Bengaz]

Yes it seems its out of range of your meter.
When measuring very low resistances you need a really good meter.
Try a resistor of .5 ohm ACROSS the brakelight and 2.5 ohm ACROSS the tail light.
Its worth a try?
All I can help with without seeing it

 

[Silverstripes]

Yes it seems its out of range of your meter.
When measuring very low resistances you need a really good meter.
Try a resistor of .5 ohm ACROSS the brakelight and 2.5 ohm ACROSS the tail light.
Its worth a try?
All I can help with without seeing it

OK with a .5ohm across the brake connections (not in line) and the meter on 2000 (200 out of range) I get a reading of 538 (constant with no flucuation). The resitor on its own gives the same reading !!!! without the light unit.

Not got a 2.5 to try the tail.

I apprechiate is difficult doing this remote

 

[Silverstripes]

Got my hands on a better meter (Auto)

Taking a reading from the light unit the original figure does drop when the meter is connected and hovers around .470 for the Brake and .450 for the rear light

Does this make sense as I cant figure out why the value drops. On a resistor straight it remains constant.

 

[Bengaz]

ANd remember, if you put a resistor "across" the lamp, the combined resistance of the lamp and the resistor is halved!
Put it in line and the values are combined.

Hope this helps.

Sorry, when you put resistors in parallal, there is a furmula you need to use. Its not as simple as I said, I must be having a relapse today

The formula is 1/rt = 1/r1 + 1/r2 doh!

 

[Bear]

Sorry, when you put resistors in parallal, there is a furmula you need to use. Its not as simple as I said, I must be having a relapse today

The formula is 1/rt = 1/r1 + 1/r2 doh!

Correct. Its almost impossible to show the correct calculation using lines of text but here goes for the version I learned in school:-

Rtotal = 1/(1/R1 + 1/R2 + 1/R3 + ...).

As for resistors to take the current that the ECU expects for brake and tail lights, trying to measure the resistance of a bulb is doomed to failure because bulb filaments increase in resistance as they heat up. Given that power is calculated by squaring the voltage then dividing by the resistance that it's heating up, a bit of algebra shows that the value of resistor needed is given by dividing 144 (nominal 12 volts squared) by the wattage of the bulb in question. For a 5 watt bulb its 28.8 ohms and for 21 watts its 6.9 ohms. The resistor obviously has to be rated for the same power as the bulb it replaces otherwise it will eventually die. In practice, how about someone using LED bulbs telling us all what values actually work (or, better still, suppliers of such parts telling buyers the full story).

 

[Bengaz]

nice one bear!

so from 5ohm cold to 28ohm hot!

We must work on running temp.

Its worth a try.

Now work out what resistor he needs to bridge the lamps. My head hurts

 

[Supertech]

You should try a warship for size mate, but I know exactly what you mean.

Any resistor will get hot, thats a function of its job after all to resist electron flow which generates heat. IF I had to, I would choose a metal bodied wire-wound resistor and bond it to the bikes chassis with epoxy or similar to dissipate the heat through the bike frame.

Personally I've just 're-engineered' my rear light fitting and wiring to make it fit for purpose (after seeing what the BMW design apprentices and bean counters came up with.)

Yeah warships make aircraft looms look like playtime at the boffins tea party.

Doesn't get away from my orginal point, you aren't bombing people or hiding from them.....why such over complicated systems on basic personal transport!?

Just pisses me off when big companies try and baffle guys on the street into paying underqualified herberts for plugging in computers that said big companies have locked the guy on the street out of.

Off topic (sorry orginal poster) , but I have the biggest soap box and ain't afraid to step up on to it.