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Car Forum / Land Rover Cars / December 2007LED dash bulbs
mixed results... the indicator warning lamps on the LDV are especially naff, and in pursuit of making them brighter I bought some LED ones, superbright have some high-intensity ones... got a full set of green, amber, and a blue (not super bright) for the main beam. interesting results, though. The indicator ones work well and look brighter than the bulbs. You can't change the no-charge one for an LED as the alternator then doesn't charge. The ABS warning lamp and the handbrake/brake fail warning lamps don't go out properly with LEDs, so they have to stay with bulbs. The main beam lamp is plenty bright, even with a "normal" as opposed to "bright" LED. Still, I now have some spare ones to play with.  SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > You can't change the no-charge one for an LED as the alternator then doesn't > charge. Shunt it. What current flows through the original bulb ? Steve >> You can't change the no-charge one for an LED as the alternator then doesn't >> charge. > >Shunt it. What current flows through the original bulb ? Depends on what wattage the original bulb was. R = V(sq)/P So if it was a 2w bulb, a 75ohm resistor will provide the same current. Although that is only a 160mA current, would think an alternator will need a bit more than that. Could be a 5w bulb which will require a 30ohm resistor. Alex > Although that is only a 160mA current, would think an alternator will > need a bit more than that. I think it will be OK as once the alternator gets up to battery voltage it supplies its own field current and no current runs through the warning light. AJH >> You can't change the no-charge one for an LED as the alternator then doesn't >> charge. > >Shunt it. What current flows through the original bulb ? could do, but it's not a big issue having a bulb there. and not a lot, it's only about 1.2W. It's more down to reference voltage for the alternator, I think. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > could do, but it's not a big issue having a bulb there. and not a lot, it's > only about 1.2W. It's more down to reference voltage for the alternator, I > think. It's current rather than voltage that matters. >>> You can't change the no-charge one for an LED as the alternator then doesn't >>> charge. [quoted text clipped - 3 lines] > only about 1.2W. It's more down to reference voltage for the alternator, I > think. There may be another advantage to sticking with a bulb for the charge light. LED's are pretty much on/off devices with nothing in between so you won't get the typical "dimly on/flickering" effect that you'd see with a bulb if, say, your alternator belt were slipping. SignatureRegards Steve G > There may be another advantage to sticking with a bulb for the charge > light. LED's are pretty much on/off devices with nothing in between so > you won't get the typical "dimly on/flickering" effect that you'd see > with a bulb if, say, your alternator belt were slipping. That's simply not so - unless you're driving them off a constant current source. Otherwise their light output is proportional to the voltage same as any other bulb - and I'd guess more linear than tungsten. Signature*Husband and cat lost -- reward for cat Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >> There may be another advantage to sticking with a bulb for the charge >> light. LED's are pretty much on/off devices with nothing in between so [quoted text clipped - 4 lines] > source. Otherwise their light output is proportional to the voltage same > as any other bulb - and I'd guess more linear than tungsten. Dave, you're so right. I have no idea what I was thinking when I wrote that drivel. Excuse me while I get my coat :-) SignatureRegards Steve G > >> There may be another advantage to sticking with a bulb for the charge > >> light. LED's are pretty much on/off devices with nothing in between [quoted text clipped - 5 lines] > > voltage same as any other bulb - and I'd guess more linear than > > tungsten. > Dave, you're so right. I have no idea what I was thinking when I wrote > that drivel. Excuse me while I get my coat :-) You could have been thinking of HIDs - since those are being discussed here too. They need special techniques to dim - and can't be dimmed fully. But high power LEDs are best driven using a pukka driver which produces constant current - and that effectively prevents them being dimmed by a simple voltage dimmer. Signature*When I'm not in my right mind, my left mind gets pretty crowded * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. > But high power LEDs are best driven using a pukka driver which produces > constant current - and that effectively prevents them being dimmed by a > simple voltage dimmer. You need a constant current source and a PWM drive..... Steve > mixed results... > [quoted text clipped - 16 lines] > > Still, I now have some spare ones to play with. I reckon you could frig the alternator one with a resistor of the correct value. SignatureNige, talking utter shite since 1967. Ducati 916 BMW K1100LT MT-03 Focus ST3 Land Rover Discovery Xtreme Range Rover 4.6 HSE NIGE#1 > You can't change the no-charge one for an LED as the alternator then > doesn't charge. The current flow from the battery to alternator field is via the warning light so you need to make your LED draw the same current by fitting a parallel resistor across it and its series resistor. To work out the value you'll need to find out the wattage of the bulb. If say 2.2 watts it goes like this. Watts = Volts x Amps (W = V x I) W so I = --- V 3 I = --- 12 = 0.18A The LED will take probably 0.02 A so we're looking at 0.16A via the shunt resitor. From V=IR, V R = -- I So 12 -- = 75 ohms. 0.16 This isn't a preferred value of resistor, so use a 68 ohm 3 watt type. Signature*Go the extra mile. It makes your boss look like an incompetent slacker * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. |
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