12 Volt LED Lamp on 24V

I do advise you to have a look at Boylestad's book "Introductory Circuit Analysis"...There are some ANSWERED problems matching your question!!

a 12V LED? interesting

LED Car Bulbs.

Everything is a guess based on the pitiful lack of information provided by the OP.

In any case, LEDs don't like AC power. Do they?

LED's will work with either A/C or D/C , it's the voltage and/or current direction that must be maintained....and as was already stated, some LED's have a wide range of voltages that will work...and some come with a blocking diode built in....

http://www.instructables.com/id/Using-AC-with-LEDs-Part-1/

http://www.ledlight.com/12-volt-led-lightbulbs.aspx

The assembly may be rated at 12v, but the LED/LEDs in the assembly are not, and I expect that was Fredski's point.

Almost all LEDs have a maximum forward voltage of about 3.5 volts, most are lower.

They all have to have current limiting of some sort, and this will obviously limit the voltage across them.

I have never heard of one as high as 12v, perhaps someone might enlighten me.

12 volt LEDS have been available for around 25 years in my limited experience. That is, just the LED, no other components across the 12- 14 volts DC.

Example, search online for this data sheet:- BR-B21V1-12V Datasheet

You will find one here, select the "BL-R213P":-

BRIGHT/BR-B21V1-12V

That's not a 12 LED Andy..

That link is for a 12v assembly which uses an LED with a forward voltage of less than 3 volts (check the graphs). The first page when you bring up the link tells you that it has an 800 ohm series resistor in the package.

Here is the text

"BR-B21V1-12V : GaP/GaP Green Internal For DC and pulse operation. Resistor 800Ω
BRIGHT LED ELECTRONICS CORP "

Here is part of the data sheet, note items 5. and 8.
1. Chip material: GaP/GaP 2. Emitted color : Green 3. Lens Appearance : Green Diffused 4. For DC and pulse operation. 5. With current limiting resistor for 12V 6. TTL & CMOS compatible. 7. 3mm diameter package. 8. Internal Resistor 800Ω

It is a 12 volt LED, NOT what you wrote which was "That's not a 12 LED Andy" whatever that is ?????

Even if internally its more than one LED, what difference does that make, in appearance it looks like a single LED and it uses an internal resistor to drop the voltage.....did you even look at the first page of the datasheet? Probably not.

Sorry its not bigger, I am using Ubuntu and chrome, which appears not to be able to resize the jpg....but I think its clear enough but small. If you need a better picture, just ask and I will try another browser and OS for you.

I have resized with Firefox, but its still not very clear, so I will try and add a second copy below....

Here it is:-

I think its quite obvious that appearance is of a normal LED......and its 12 Volts and it has an internal resistor, demonstrated by the small schematic.....

Its no better sadly.....you need to find it yourself!!

QED

I missed the v in 12v...So what Andy...any fool would have known what was meant.

As for the rest of your diatribe.... I reprinted some of the data...so obviously I did read it... and it clearly states that the device incorporates a current limiting resistor...Which, after all, is the subject of this debate.

As I am sure you know..LED is an acronym for Light Emitting Diode.. Not Light emitting Diode plus Resistor.

I repeat that the device may be 12v (see I got the v right for you that time) but the LED itself is not.

Maybe a reprint of your slogan is in order

"For those who understand, no explanation is necessary, for those who don't, no explanation is possible!"

unsubscibe not worth it.

You are an unfriendly troll.

You made multiple errors of fact.

Then you lost your temper.....simply because the information I supplied was correct, in a single case of an LED, with no other external components, was a LED that needed 12 volts. They have been around probably longer than you have been around, judging by your temper!!!

If you stay around here, you will learn how to behave.....but probably very slowly I feel.

Or you will leave......

Prove me wrong either way......

Your choice!

"Wer nicht weiß, glaubt viel!"

see http://en.wikipedia.org/wiki/Voltage_divider

You need to be concerned with the voltage and the wattage.....What watt bulb? What watt supply?

Depends if you want an LED light and a nice resistive heater. What's the rating of the LED light?

look up the max current spec for the led, use the formula E=IR to determine a series resistance that keeps the current below that value for the E you are using.

That would work if correctly calculated, Gerald has already mentioned that.

"Is it just a case of putting a resistor (same resitance as LED) in series?"

The LED is a diode, megohms in one direction, ohms in the other, using this approach to an R value would result in malfunction in either case.

It isn't a 12 volt LED, it's an LED with a built in voltage (and/or current) regulator circuit. Check the specs. Many of these so called 12 volt units have a wide range of input voltage, some up to 30 volts.

I get your point! You about poked my eye out with that one!

Or OP could take his two 12V LED (bulbs) and put them in series (as other contributors have suggested) on his 24 VDC supply. There is no way he means on a 24 VAC supply, although stranger things have probably happened.

OP has jumped ship - so this is my last word on this thread.

If you measure the current, you can pick out a 12 volt zener diode of the appropriate wattage and us it as a constant voltage shunt in series with your 12 volt product.

Simple, cheap, exact, and reliable.

But it would not work much different than a resistor would.....the resistor would drop 12 volts if correctly calculated.....and be cheaper....

What am I missing?

Thanks.

In any case a Zener diode requires a dropping resistor in order to regulate the voltage, and in this case of reducing 24v down to 12v, the resistors would be the same value so - apart from providing a more stable voltage - nothing saved.

No it dosen't. The load gets what ever the zener diode drops out of the loop. It also allows the current to fluxuate while maintaining the voltage to the load.

Whatever!

Application will help. Are you intending to use car bulbs in a truck? Do you want an indicator LEd on a power wheelchair? Is it a panel containing electronics that needs an On indicator? Different solutions for each.Jim

Hey Jack! Put two LED (12 volt) in parallel on a 24 VDC supply, and then you can burn out two at once! First the weak one hogs the current and burns really bright for a short time, then the other one pulls too much current and burns brightly for a short time.

Think: Flash! Flash! Aw crap!

The lamp current draw is probably stated. If it is 12V/Ilamp=needed R.