Replacing a car globe with a series of LEDs

Hi...

You're probably far far better off just going into your local car part shop and buying a replacement led bulb to install.

However, seeing you have a 12v supply I suspect that by bike you really mean a motorcycle - or at least a motor driven vehicle. If that's true, then be absolutely sure to check your local laws to find out if you're allowed to do so.

I think in most (if not all) places we can't use led's unless they were used as original equipment.

Take care.

Ken

You shouldn't need a resistor - in theory - but when multiple LEDs are connected in series like this, they are often fed via a simple constant current source. This can be easily and cheaply realised with two or three components. This will allow you to set the desired current through your chain of LEDs for optimum performance ie light output vs life. Also, your assertion that the individual LED currents will add up, is wrong. If you set the LED current for say 30mA, and connect 6 LEDs in series, that same current of 30mA will pass thru all 6. If, however, you connect them in parallel, the current will add up, but you will definitely then need a series reistor - 330 ohms at half a watt would do nicely. This would be my preferred way of doing it anyway as, if one of the LEDs fails in your series chain, they all go out, whereas if one fails in the parallel setup, the others stay on, allbeit at changed brightness if a simple resistor is used for the current limiting.

As far as needing to load the bike's electrics up to simulate the former lamp load, this will depend on whether the flasher unit is a thermal relaxation switch, based on a bimetal strip, or an electronically switched relay. If it's the latter, no additional load other than the LEDs will be needed - except you might want to put some in anyway to help keep the relay contacts clean. If the former, then the full load of the original lamps will be needed, otherwise the flasher unit won't work at all. If the simulated load is too light, the flashers will run too fast.

Geoff

LEDs are actually current driven, so this isn't that good an idea.

Given that resistors are cheap, I'd use one per LED, and drive them in parallel. Then if one fails, you'll not overload the others as would happen with one common resistor, or end up with no light, as when in series. You should be able to use 0.25 watt resistors which are pretty small and cheap. If it's a bayonet fitting bulb, then simply break away the glass and use the bayonet plug for the resistors, and bend the LEDs so they point in the right direction. After checking it works, pot the resistors in car body filler, etc, to give some mechanical strength.

Standard LEDs driven at 50mA are likely to have a short life. And six standard ones will be brighter on axis than a 10 watt tungsten, when driven at 20mA. Where they should last forever.

But you may be able to buy an LED replacement anyway. Not the same fun, though.;-)

Also (for the OP) there may be a significant impact on legal liability in the case of a traffic accident.

Someday, the guy in the 18-wheeler that rolled nine of the eighteen wheels right over you might get off with no fault and no liability if the turn signal that you claim to have used to signal the lane change turns out to have been home-made.

Make your own christmas tree decorations not your own automotive safety equipment.

Yes you do still need a resistor. Measure the forward voltage drop of the LED's you're using, and wire up a series string that will run on the worst case lowest voltage you're likely to have, 10-12v should do it. Subtract that voltage from the highest supply voltage you'll get, say 16v or so and use ohms law to select a suitable resistor. You can wire up multiple series/parallel strings to get more LEDs if you'd like to cover the lense area with them.