LED Bulbs

[Ben Stratford]

want to change indicator bulbs to LED. But they flash too fast. Do i need a resistor? One per side or one each lamp? Thanks

 

[StarCruiser]

Just a load resistor on each lamp should be good Ben. The suppliers may do some for 'Canbus' (rather than 'old bus') correction, otherwise you could put one resistor on the output of the flasher relay which would do just the same. You need the resistance of the lamps, all of them, to calculate the single ballast resistor.

 

[AdamKZJ78W]

Hi Ben,

When picking a load resistor keep the resistance between 5-10/ohms and the capacity in the range of 15-30watts. Also remember that these resistors can get hot so mount them away from any precious plastics.

 

[Ben Stratford]

Thanks guys, will recall this info when I get round to it - it sounds complicated.

 

[StarCruiser]

It's not to complicated Ben. If you buy an over rated resistor then it won't get so hot or will at least be able to shift the heat much easier so won't even feel warm as it's not on for long anyway. I haven't done any calculations but what Adam says sounds right.

Adam, were those values for a single resistor or for each indicator?

 

[Towpack]

Using a nominal 13.5v the resistance of each (21w) bulb is around 7.7ohm. Don't think it'll be that critical if you go higher by a few ohms as LED's draw little current but too high and the relay could 'see' an open circuit as in a dead bulb. Can't you by replacement LED bulbs with the resistance built in so it's just plug and play?

Digressing slightly, I fitted a small LED volt meter in the dash today wired through the accessory position of the ign and the voltage drop compared to direct to battery connection is 0.2v which is more than I expected.

 

[David]

Using a nominal 13.5v the resistance of each (21w) bulb is around 7.7ohm. Don't think it'll be that critical if you go higher by a few ohms as LED's draw little current but too high and the relay could 'see' an open circuit as in a dead bulb. Can't you by replacement LED bulbs with the resistance built in so it's just plug and play?

Yes I think I have those in my rear flashers, I just put them in and worked ok

 

[StarCruiser]

Are your lamps 12 or 24v Ben? If 12v and based on that 7.7 ohms then, the resistance overall works out at just shy of 2 ohms at say 50 watts if it was constantly running. At a 50% duty cycle (on, off,on,off) I expect a 25W one wouldn't get especially hot unless you left your indicators on for hours on end.

 

[Ben Stratford]

Are your lamps 12 or 24v Ben? If 12v and based on that 7.7 ohms then, the resistance overall works out at just shy of 2 ohms at say 50 watts if it was constantly running. At a 50% duty cycle (on, off,on,off) I expect a 25W one wouldn't get especially hot unless you left your indicators on for hours on end.

Everything is 24v Rich except the radio which runs to just one battery

 

[SamW]

I’m pretty sure you can but an led flasher relay or an adjustable flasher relay so you wouldn’t need resistors

 

[StarCruiser]

I’m pretty sure you can but an led flasher relay or an adjustable flasher relay so you wouldn’t need resistors

That would be the ideal solution, though fitting a resistor shouldn't be expensive or difficult it does involve a bit of work whereas that would be plug and play.

 

[David N]

That would be the ideal solution, though fitting a resistor shouldn't be expensive or difficult it does involve a bit of work whereas that would be plug and play.

Were you able to find a 24v flasher?