dirtydiesel Posted October 5, 2010 Share Posted October 5, 2010 I need a dummy load unit to get my indicators flashing at the right speed after fitting led rear light units. But i carn't find a formular anywhere (that's simple enough for me to understand!) to work out what ohms i need. Something like this is what i'me looking at from RS Cheers in advance Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted October 5, 2010 Author Share Posted October 5, 2010 Found it 21watts @ 12volts = 6.8ohms & 1.75 amps Quote Link to comment Share on other sites More sharing options...
rtbarton Posted October 5, 2010 Share Posted October 5, 2010 Assuming it has to replace 2 bulbs you need a minimum power dissipation of 42 watts, each indicator bulb is 21w. Use the formual W = (v^2)/R W = power in watts, v = volts and R is the resistance in ohms. So R = (V^2)/W = 12*12/42 = 3.43 ohms (12 volts). You'll have to choose the nearest preferrfed value, and bear in mind they will get hot so the resistance may alter slightly from the nominal. Instead of buying a resistor, you could use 2 x 21 watt bulbs, these could be sited conveniently at the front and rear of the vehicle and protected by amber lenses Quote Link to comment Share on other sites More sharing options...
rtbarton Posted October 5, 2010 Share Posted October 5, 2010 Found it 21watts @ 12volts = 6.8ohms & 1.75 amps You may get the wrong flashing rate as the flasher unit will think you have 1 bulb blown. Quote Link to comment Share on other sites More sharing options...
fozsug Posted October 5, 2010 Share Posted October 5, 2010 I just used THESE , about 6 squid . Make sure you mount on the chassis or somewhere else metal as the get very hot Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted October 5, 2010 Author Share Posted October 5, 2010 You may get the wrong flashing rate as the flasher unit will think you have 1 bulb blown. I'd be using 2, one at each rear corner. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted October 5, 2010 Share Posted October 5, 2010 Or get a flasher unit for LED bulbs... Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted October 5, 2010 Author Share Posted October 5, 2010 Or get a flasher unit for LED bulbs... I've melted 3 of those so far, they arn't capable of driving the hazards or trailor lights. Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted October 5, 2010 Share Posted October 5, 2010 Hmmm...it surprises me that there is nothing out that would drive a combination of LED/normal bulbs. How are your soldering skills? I'll draw a diagram if you want! Quote Link to comment Share on other sites More sharing options...
pete3000 Posted October 7, 2010 Share Posted October 7, 2010 ultraleds sell them, ballast resistors, 1 per bulb, may work with less. http://www.ultraleds.co.uk/loada-solution-bulb-warning-turn-larger-bulbs-p-1213.html Pete Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted October 7, 2010 Share Posted October 7, 2010 Sort of defeats the object of fitting LEDs doesn't it? But if you have a problem with the trailer lights blowing the flasher relay then try fitting a trail-flash unit (slave relay). Quote Link to comment Share on other sites More sharing options...
pete3000 Posted October 8, 2010 Share Posted October 8, 2010 Sort of defeats the object of fitting LEDs doesn't it? Not really, as led's should last much longer, switch on quicker, be more shock resistant and run cooler than filament bulbs . If you do the unit wiring right they should be sealed against mud/water, they don't however like dirty power supplies i.e unregulated noisy supplies. Quote Link to comment Share on other sites More sharing options...
rtbarton Posted October 8, 2010 Share Posted October 8, 2010 And with a LED array as soon as one or two LEDs fail you can replace the whole lamp before it fails completely, much safer and makes you less laible to being pulled by the cops. Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted October 8, 2010 Share Posted October 8, 2010 I've used LED lamps myself but TBH I've never found one as bright as a filament bulb. I use them mainly to reduce the current draw in sidelights/brakeleights because I tow quite a lot. If I had to fit a resister to increase current draw then I really don't think I could justify the huge increase in price compared to a filament bulb.##I would agree that a brake light using LEDs can increae safety, provided it's bright enough Quote Link to comment Share on other sites More sharing options...
rtbarton Posted October 9, 2010 Share Posted October 9, 2010 You could use them on a trailer if you don't have a flasher unit that can handle trailer flashers, BUT the bulb failure indication facility would be lost, which would be illegal. No problem for brakelights though. Quote Link to comment Share on other sites More sharing options...
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