HELP - purchased - LED rear light clusters

[ninja]

i've just bought a set of these

do i need to fit fuses inline to avoid the things randomly blowing out the LEDs?

thanks

ninja

[steve_weegie]

Fuses wont help the problem, as they will only blowout with excessive current. I suspect these LED problems are down to putting too high a voltage across the LED, so perhaps a carefully calculated resistor might help

Not seen a light cluster to poke with electronic gizmos so I couldn't honestly tell you what resistor value you'll need, but dropping it a couple of volts is probably what you're looking to do. My guess is that the light clusters are built for 12v operation, and struggle to cope with the near 14v of the running car....

Taking the years of rust of my electronics knowledge, a cunning zener diode arrangement might be the order of the day..... Hmm.....

[delands]

There's a kit to buy to retro fit these... costs around £10 a side or a light.
Lotus will be able to advise.

[delands]

Bell and Colvill should also be able to help!

(m) LED Lamp Resistor Jump harness
QTY 1 Needed £6.86
(m) LED Lamp Inductor Jump Harness
QTY 2 needed
£7.28

http://www.bell-colvill.co.uk/LotusShop ... hapter=E02

[ninja]

excellent my LED units came with these!

was wondering why all the extra wire...


ninja

[ninja]

i seem to have 2 extra inductor loops - if anyone is looking for some?

ninja

[ninja]

bugger the inductor loop that bell and collvil sell doesn't protect against teh additional voltage charge blowing out the LED's.

is there anyone on here who can tell me in idiot's terms how to fit the zenner diode thing that should help? i have no problem going to maplin and buying and fitting something - anything - if it's going to work...

help

please

ninja

[steve_weegie]

Oops, forgot about this

Probably easier just to drop a couple of volts by using a resistor in series with the light- a zener regulated supply is probably overkill and more tricky to fit neatly IMHO.... Can you find out how much current they draw when operating at the moment? You can then just use the usual ohms law stuff (v=ir) to find out what value of r you need in series with the load, and what wattage you need it at (p=vi).

Cheers,

Steve

[robin]

The problem with the resistor is that it gives poor performance - the LEDs are very sensitive to exceeding their current limits even momentarily, so you have to protect against the fast transient voltages produced by inductive switching, sudden changes in load on the alternator, etc. These can cause peaks of up to 50V!!

You can use the resistive load in conjunction with the zener diode.

What is the target forward voltage and current for the LEDs?

The best solution would be:

Code: Select all

Battery +ve ---- inductor ---- resistor ----- + ------- +
                                              |         |
                                          Zener        LED
                                              |         |
Battery -ve ----------------------------------+---------+

Without some specs for the LEDs I cannot tell you what values to use, but the general principle is this:

The LEDs want to operate with a fixed forward voltage and current. The resistor is set to drop the difference between the nominal alternator ouput voltage and the target LED forward voltage. The inductor resists change in current flow (this will help to remove the higher speed transients). The zener is like a switch that conducts only when the voltage across it exceeds a certain value - they come in many different values. If your LEDs are designed to operate at, say 10V with an absolute maximum of 12V then you would buy an 11V zener diode. Now when the voltage across the LEDs exceeds 11V, the Zener opens and clamps the voltage at 11V. This means that the resistor will have a higher voltage drop across it and more current will flow through it - but the additional current is flowing through the zener not the LEDs - they remain happy seeing 11v and constant current.

Give me the specs for your LEDs and I'll tell you what you need to do ...

Cheers,
Robin

[ninja]

thanks robin

i think i have the adapted set from lotus though, there is already a resistor in line along the +ve after the inductor loop. i can't see inside the unit so do not know if there is a zener in there somewhere.

i'll look at the units tonight and PM you with the spec mate. i fitted them at the weekend and they look brilliant but will look desidedly less so if they stop working!

ninja

[ninja]

the part numbers for my clusters are:

inner cluster - lotus part B120M0035F, Perie part CRL 1101
outer cluster - lotus part B120M0034F, Perie part CRL 1100

does anyone know if these are the first LED clusters, the ones that fried the LEDs? or are they the revised ones that are ok?

ninja