Another LED question

[24vdc]

I have another beginner question for you experts. If i purchase one of those cheesy strobing/flashing etc. 12v LED kits at Pep Boys (for cars) what type of resistor would i add to run it off my 24v system?

[Malc C]

I don't think you could do that, as the device probably has a designated supply voltage and contains the resistors for the LED built in. You would simply need to drop the 24Vdc to the supply voltage the device needs (probably 12v) and then you should be OK

[24vdc]

I don't think you could do that, as the device probably has a designated supply voltage and contains the resistors for the LED built in. You would simply need to drop the 24Vdc to the supply voltage the device needs (probably 12v) and then you should be OK

Yeah, i guess what i meant to ask was, how do i drop the 24v to 12v to supply the voltage for the device but still use the 24v as the power source (since the whole system is using the 24v)?

[Tomapowa]

If you are using two 12v batteries in series (like you were for your other project), you can simply run/power this light assembly from one of the 12V batteries vice both.... no?

[24vdc]

If you are using two 12v batteries in series (like you were for your other project), you can simply run/power this light assembly from one of the 12V batteries vice both.... no?
hahaha. oops. i really wish i would have thought have that. thanks.

[HFG]

Easy, 12V zener.

[24vdc]

Easy, 12V zener.
How would the 12v zener diode work? would it sort of "dissipate" 12v?

[HFG]

Diodes have more or less fixed voltage drops across them, just buy a 12V zener diode (12V forward conduction) with a current rating greater than what the switching circuit will ever use.

[BushmanLA]

LM7812

http://www.radioshack.com/product/index.jsp?productId=2062600

This thing is good for 1 Amp draw which should be fine for you. You can probably get away with 200mA with no heatsink, but get one just in case.

You will be wasting a good bit of energy though by stepping down from 24 to 12.

[Tomapowa]

How would the 12v zener diode work? would it sort of "dissipate" 12v?
Zeners are very inefficient regulators and are only recommended when you need to regulate an input voltage that is slightly greater than the intended output voltage (going from 24v to 12v is not good use of a zener reg... beware). A series resistor is also needed and would dissapate the extra 12v*current... More here:

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm
or
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c2

[Malc C]

The main issue is that to drop 12v an any sort of amperage results in heat, so even using a 12v Regulator ideally requires a heatsink to be on the safe side. I've not followed your post enough, but why do you need 24V to drive the LEDs. 12V should be ample to run whatever circuit you want and drive the LEDs

[Tomapowa]

The main issue is that to drop 12v an any sort of amperage results in heat, so even using a 12v Regulator ideally requires a heatsink to be on the safe side. I've not followed your post enough, but why do you need 24V to drive the LEDs. 12V should be ample to run whatever circuit you want and drive the LEDs

I think he got his answer here, several posts prior...:
http://www.rcgroups.com/forums/showpost.php?p=11090610&postcount=5

[Comatose]

If you want to do this efficiently and you don't have an intermediate 12v tap, a switch-mode dc-dc converter would be appropriate. http://www.dimensionengineering.com/DE-SWADJ.htm for example. (yeah, shameless plug)

[BushmanLA]

If you want to do this efficiently and you don't have an intermediate 12v tap, a switch-mode dc-dc converter would be appropriate. http://www.dimensionengineering.com/DE-SWADJ.htm for example. (yeah, shameless plug)


Hah!

I was gonna link to your little gems but I got too lazy and figured it was overkill anyway. :)

[Tomapowa]

...(yeah, shameless plug)
I'd say, especially since he already got his answer as I mentioned.
He forgot he was using two 12v batteries in series for his source, hence, he only needs to connect across one of his batteries. Sometimes the obvious escapes us...

[HFG]

Considering a LED circuit will most likely only draw 20-50mA i wouldn't even bother to consider a regulator as the power dissipated by a zener would be small.. If this thing is mounted to an electric heli/plane that will be drawing power in the hundreds of watts what is a 0.5W being wasted. I'm willing to bet the extra weight of the regulator having to be lifted starts to get close to the power dissipated by the zener :)

[I_Gotts_Ta_Fly]

Get 2 and run them in series (as in headlights for example).