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clearance light strobing

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Member - Posts: 44
Member spacespace
Joined: January 24, 2005
Posted: May 31, 2011 at 6:13 PM / IP Logged  
I'm adding some more emergency lights to my truck and am considering adding a flasher to the clearance lights in certain areas of the roof line of the truck. I know how to wire them as far as using an led flasher, but my concern is if I will need a diode or anything at each light to not have any kind of back feed. I want to be able to use them normally driving around at night, but have them flash when doing roadside work.
Thanks in advance.
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: May 31, 2011 at 9:45 PM / IP Logged  
Phew! I though you were going to have flashing lights whilst mobile and I was going to suggest that is probably illegal - and probably damned annoying for other motorists!
But your idea sounds pretty good as an alert to a stationary vehicle - much like flashing hazard lights (again, if not too annoying).
It might even become a Trucking standard one day. (© jimd2p 2011 - plus whatever conditions the12volt has...)
If you are flashing LEDs that are part of a parallel connected set, then yes, you will have to insert maybe 2 diodes for each LED you are flashing.
One diode from the flasher to the LED - or maybe 1 LED for all flashing LEDs if they can be commoned together, and one diode between the "normal" lighting power for each flashing LED - or as before, 1 LED for all if commoned together.
The first diode is to prevent the powered LEDs feeding back into the flasher. The second is for the flasher to prevent feeding the other LEDs.
I'm assuming the flasher outputs +12V and the LEDs are hot (+12V) switched. If they are all hot and the flasher or switch grounds them, then no diodes are required.
I'm also assuming a parallel array of LED strings - ie, usually strings of 3 to 6 LEDs in series (maybe with a series resistor) that are connected in parallel, but you can get to some of these strings or segments of the paralleled strings or LEDs. (A string could be one LED.)
Member - Posts: 44
Member spacespace
Joined: January 24, 2005
Posted: June 02, 2011 at 11:43 PM / IP Logged  
Excellent info. Thank you. I will be giving it a try and post an update.

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