Led indicators not flashing

RichardD · Posted: Sat May 12, 2007 12:15 pm Post subject: Led indicators not flashing

I've just fitted new LED indicators to both the front and rear of my 24v Volvo adn now they don't work. The hazards work fine so I know the lamps are working.

I suspect I'll have to fit some kind of resistor inline, but what type and where from?

:) · Posted: Sat May 12, 2007 2:09 pm Post subject:

The "usual" problem with LED indicators is that they take too little current, so the flasher unit operates as if a bulb is blown and flashes them too fast. If you were using the very old thermal flasher unit there would not be enough current to cause it to switch OFF, the lamps would be on all the time.
The crude cure for both is to increase the load by adding a resistor in parallel with the bulbs. The more subtle fix is to change the flasher unit for one which is designed to work with LEDs.

Neither of the above situations apply if the indicators never come on, but maybe the flasher unit requires some bleed current through the lamps when they are off (which it won't get with LEDs). If this is the case a parallel resistor should solve it.

I guess you want me to suggest a value?

Normally indicators use 2, 21W bulbs and a 5W repeater, so that is a total of 47W. I'll assume your LEDs take only 5W each, so that is 15W total. Based on this you need to waste 32W of heat in a resistor. Assuming the voltage is 28V, you will need a 24.5ohm, but since 22ohm is a standard size, that is what I recommend. Something like this. If you are fitting the resistor in parallel with the bulbs then you will need two, one for the right hand circuit and one for the left hand circuit.
--
Tim.

RichardD · Posted: Sat May 12, 2007 2:20 pm Post subject:

I've got resistors but fitted them in series. I'll try parallel at 10 ohms

br00n1e · Posted: Sat May 12, 2007 2:33 pm Post subject:

you can get led flasher units

:) · Posted: Sat May 12, 2007 2:55 pm Post subject:

RichardD · Posted: Sat May 12, 2007 3:16 pm Post subject:

10W 10 ohms resistors fitted adn everything working perfectly including the dash warning light which hasn't worked for months.

Difflock to the rescue again. Cheers

RichardD · Posted: Sat May 12, 2007 3:22 pm Post subject:

There are no repeaters and then leds (front and rear) draw a total of 20W per side. The 10W resistors are enough to do the job so I'll fix it when it breaks!

:) · Posted: Sat May 12, 2007 3:38 pm Post subject:

RichardD · Posted: Sat May 12, 2007 5:42 pm Post subject:

I'm aware of the difference as I have an Science Honours degree including physics, however my typing does not!
The resistors I had were from a led kit for my bike that I never used and each ceramic block had 10W10ohm printed on them.

You know what they say if it works that's half the battle!