Relay voltage question

[FJ_Hooligan]

I believe LEDs are either on full or off.  There is a voltage threshold that will turn them on and if the voltage is less than that they will not come on.

However, a lower voltage could be over the LED threshold but the fan may not run fast enough to keep the heat down?

[movenon]

I believe LEDs are either on full or off.  There is a voltage threshold that will turn them on and if the voltage is less than that they will not come on.

However, a lower voltage could be over the LED threshold but the fan may not run fast enough to keep the heat down?

That's kind of what I thought.  The fan on mine is small with a fair amount of heat sink.  I think it only radiates aprox. 30 watts of energy. Think I will hold on the headlight relay mod..  I do like the coil mod though !
George

[Pat Conlon]

Hooli, FYI, there are dimable 120v LEDs although they don't dim thru the full range like incandescent.

Using a conventional rheostat dimmer switch, they dim from 100% to 30%

[simi_ed]

Dimmable LEDs are available, but it is the power supply, not the LED that makes them dimmable.  They are dimmed by using a pulse width modulated signal to the LED.  The brightness of the LED is determined by the amount of time the pulse is on, from perhaps 5% to 95%.  But now you've added complex electronics and an electrical noise source.  How badly do you want this?  

[Charlie-brm]

Our traditional idea of a single clear plastic LED in a dome shape with two leads - anode and cathode - like the power light on your home stereo or TV, does have a threshold and should have a current limiter in its power path. It's either on or off.
e.g. building a home DIY circuit, you buy an LED, see on the package the current spec is 30 mA and the voltage threshold is 1.7 Volts, you do the math for a typical 9V or 12V battery or 4-AAA's and pick a resistor in series to limit current to 30 mA and you get the LED's full rated lumens output. Blah blah blah, it's been a long time since I had to do that.

But the LEDs for higher output light headlights are run from driver circuits that work from a large input range, eg. 5.5 Volts to 36 Volts DC and they deliver a constant output at a steady voltage and current. That's where a lot of the competition on technology is - making an efficient driver circuit to power the actual LED elements. Kind of like a voltage regulator in a vehicle takes care of the irregularities in alternator power so the ignition is running at a steady optimum, and as we know some VR's do it better and last longer than others.
A bike battery even putting out 8 Volts and a few Amps could run that driver at full design output.

Highly efficient, very powerful LEDs like the Cree XML2 are relatively inexpensive, and have lots of interesting uses.  According to Cree, they can "deliver an unprecedented 1198 lumens at 116 lumens-per-watt efficacy at 3 A," with a maximum forward voltage somewhere around 3.15V.

All that said, I replaced my car's interior door and map lights with the same LED arrays I put in my FJ's dash and the ones in the car slowly dim when I lock the car, just like the incandescent bulbs do. I'm still looking into that and won't share a half ass guess but I have my ideas.




Below: Center bulb OEM 194 incandescent. Outer, my new gauge lights.

[movenon]

A note for anyone converting to LED's in there cluster.  Because the led in that application is not dimable use the stock type bulb for the low fuel light.
Also before you bolt the cluster back in power it up to make sure all the LED's are installed correctly. The polarity has to be correct. Just notes along the way.
George

[Charlie-brm]

A note for anyone converting to LED's in there cluster.  Because the led in that application is not dimable use the stock type bulb for the low fuel light.
Also before you bolt the cluster back in power it up to make sure all the LED's are installed correctly. The polarity has to be correct. Just notes along the way.
George

Good points to know anytime.