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RichardD Marshall
Joined: 13 Mar 2003 Odometer: 22856 Location: State of Confusion
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Posted: Sat May 12, 2007 12:15 pm Post subject: Led indicators not flashing
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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?
__________________________________ Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him. |
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:) Mud Obsessed
Joined: 06 Feb 2006 Odometer: 4337 Location: Norfolk
1995 Land Rover Defender
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Posted: Sat May 12, 2007 2:09 pm Post subject:
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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.
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Tim.
__________________________________ -- Timothy Birt -- |
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RichardD Marshall
Joined: 13 Mar 2003 Odometer: 22856 Location: State of Confusion
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Posted: Sat May 12, 2007 2:20 pm Post subject:
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I've got resistors but fitted them in series. I'll try parallel at 10 ohms
__________________________________ Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him. |
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br00n1e Just got MTs
Joined: 27 Mar 2005 Odometer: 498 Location: Angus Scotland
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Posted: Sat May 12, 2007 2:33 pm Post subject:
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you can get led flasher units
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:) Mud Obsessed
Joined: 06 Feb 2006 Odometer: 4337 Location: Norfolk
1995 Land Rover Defender
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Posted: Sat May 12, 2007 2:55 pm Post subject:
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rdover wrote: | I've got resistors but fitted them in series. I'll try parallel at 10 ohms |
10 ohms would be more appropriate for a 12V vehicle, it will dissipate too much (78W @ 28V) power on a 24V system. I stand by my back-of-envelope calculation above. You could however connect a pair of 10 ohm resisters in series to make a 20ohm resistor and then wire the pair in parallel with the LED lamp.
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Tim.
__________________________________ -- Timothy Birt -- |
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RichardD Marshall
Joined: 13 Mar 2003 Odometer: 22856 Location: State of Confusion
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Posted: Sat May 12, 2007 3:16 pm Post subject:
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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
__________________________________ Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him. |
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RichardD Marshall
Joined: 13 Mar 2003 Odometer: 22856 Location: State of Confusion
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Posted: Sat May 12, 2007 3:22 pm Post subject:
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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!
__________________________________ Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him. |
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:) Mud Obsessed
Joined: 06 Feb 2006 Odometer: 4337 Location: Norfolk
1995 Land Rover Defender
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Posted: Sat May 12, 2007 3:38 pm Post subject:
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rdover wrote: | 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! |
Slight confusion here ohms are not the same as watts. Ohms are a measure of resistance and watts are a measure of power.
But if it is working then that's a good start. It would be worth checking that the resistors don't get too hot.
--
Tim.
__________________________________ -- Timothy Birt -- |
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RichardD Marshall
Joined: 13 Mar 2003 Odometer: 22856 Location: State of Confusion
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Posted: Sat May 12, 2007 5:42 pm Post subject:
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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!
__________________________________ Poking the Grim Reaper with a stick then running away. The devil made me do it but God said it was okay with him. |
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