LED lights - any problems?

Post by **indigolemon** » Wed Jun 29, 2016 2:58 pm

But you wouldn't know with a resistor either, unless the resistor pops?

'92 Si VTEC · Post by **jjmartin349571** » Wed Jun 29, 2016 3:52 pm

I was just assuming that if the bulb stopped allowing a current to pass through it then the warning would come up, but the more I think about it the more I realise I'm not actually sure how an LED behaves when it fails

alinton · Post by **alinton** » Wed Jun 29, 2016 10:40 pm

An LED has a very high resistance one way, low the other, but possible not as low as a filament lamp. It's the current they draw that confuses the car's systems; if the current being drawn is too low the system assumes that the bulb is open-circuit and either flashed the indicators fast or shows a warning.

I tried a 10-ohm resistor across an LED today in the indicator circuit (the value that people sell to supposedly combat this), and it didn't work. I think it should be lower.

In fact, for a 21w lamp at 12v:

P=IV,
I=V/R

=> P=V sq / R
And R=V sq/ P

So R is 9 ohms. Two lamps on each circuit, so the car's expecting about 4.5 ohms.

But I don't know the dissipation of the LEDs, so can't work out what resistance they present.

Suffice to say it's hassle.

A.

alinton · Post by **alinton** » Thu Jun 30, 2016 1:58 pm

Further experimentation shows that the indicator circuits need a 2.2-ohm resistor across one led bulb to be happy.

As the dissipation is then 80-watts, I've used two 4.7-ohm 50w resistors in parallel, mounted at the rear indicator wiring. the resultant 2.35-ohm is fine. The flash rate is then good.

I have the front, side repeaters and rear indicators all working fine now on LEDs.

LED bulbs don't really blow very often; as you're shunting them with resistors the bulb failure circuits won't work if they do.

I haven't experimented with the stop/tail lights yet.

But I will...

alinton · Post by **alinton** » Tue Jul 05, 2016 5:06 pm

Does anyone know what's the module inside the nearside rear lamp cluster, that's not present in the offside cluster?

Ta

Post by **indigolemon** » Tue Jul 05, 2016 9:25 pm

That's the blown bulb sensor on the brake circuit.

K30DPC · Post by **K30DPC** » Tue Jul 05, 2016 11:51 pm

alinton wrote:As the dissipation is then 80-watts

So you say that you are waisting 80watts plus whatever LEDs need instead of 47watts (21+21+5) of standard light bulbs, also cheeting blown bulb warning light which won't work ever again just for having LED indicators?

And you wanna do the same with tail/brake?

Well...

alinton · Post by **alinton** » Wed Jul 06, 2016 11:06 am

Yea, that's a valid point.

Although defeating the brake light fail circuit means you don't have to use resistors...

I might try to be a clever sod and build a new flasher relay which is happy with LEDs. Shouldn't be difficult - just an astable multivibrator circuit running a pair of relays.

A

Post by **indigolemon** » Wed Jul 06, 2016 11:20 am

alinton wrote:I might try to be a clever sod and build a new flasher relay which is happy with LEDs.

Have a look on ebay, you can buy LED compatible flasher relays for about six quid.

alinton · Post by **alinton** » Wed Jul 06, 2016 1:13 pm

OK thanks - then to interface it with the Prelude's circuit. Shouldn't be a prob.