I have a LED lamp with (you guessed it) 20 LEDs. It runs off three AAA batteries. I was changing them out and noticing that with a little cutting and wiring I could set it up to run a 9v. My questions are these:

1. Would that fry the LEDs?

2. Would switching to 9 volt make them burn brighter, or just longer, or both?

I don't need it to be brighter, it's only use is a headlight on my scooter and I only use the scooter on well lit streets. It's there so that cars can see me and the police won't hassle me (if they did, it'd only be for concern over my safety).

Anybody know much about LEDs and how they work? Whatever info y'all have will be useful.

LEDs are just glass capsules with wires leading to electrodes which excite the encapsulated super special pixie dust. If you know any pixies electricians i'd ask one of them.


BTW only dirty pixies have dust and i think the dirtier they are the brighter it burns so be carefull.

Is there anything parker doesnt know?

i dont know how they actually get the dust off the above mentioned pixies.

By running an LED by a higher voltage than rated WILL cause them to burn brighter and shorter. Some LED's have a voltage range they will operate on.

3 AAA batteries in series = 4.5VDC
A 9 volt battery is just that...9 VDC

So... you would need to build a voltage divider, sending 1/2 the battery voltage out on two different legs. ( or we could get into using two strips of the LEDs in parallel, but then you may not have enough current, depending upon how much they are drawing)

To sum it up. PITA and not worth the trouble.

If you want to take a chance, stick a 100K resistor in series with it...But since I havent measured the resistance of your string, nor done the ( simple) math, it'll probably blow your LEDS.

short answer is NO, don't do it or you will have the chance to buy some that will burn on 9 volts.
go ahead and ask me how I know this I double dog dare ya to.

You can use a dropping resistor to make it work. I think something in the neighborhood of 100 ohms rated one watt would do it..........maybe BOOM.

Also, I think.........I think.

You can wire two strings of these leds in series and make them work.

Strings are usually wired in parallel so they don't drop voltage from one to the other. If you split the string and wire them (2X10 leds) in series they should see half the voltage.

Wrong? Someone please correct me.

I wouldn't mess with anything with the label "Super Special Pixie Dust". That's all kinda wrong.

you ride a scooter?

The issue you're going to have is that you will send too much current to the LEDs and blow them up.

You can drop any amount of voltage over an LED, but you must limit the current to ~20mA.

If you wanted to do a little more modification, you could make it work.

Assuming the LEDs are wired in parallel (that's how I would do it), you can figure right now there is 4.5/.02= 225 ohm resistor in series with each. If you stick a 9V battery in there, you will supply 9/225= 40mA to each, and probably blow the LEDs up.

You can put another resistor in series with the 9V battery to limit this current. From the negative side of the resistor, you will see twenty 250 ohm resistors in parallel, which is the equivalent of R/N=250/20=12.5 ohms. You want 400mA total, so you need R=V/I=9/.4=22.5ohm. Throw a 10ohm resistor in there.

I think I did that right. You should drop ~4-4.5V over that 10ohm resistor, so the LED array will see roughly the same voltage as before. P=V^2/R=16/10=1.6W so get you a good 2W resistor.

Keep in mind, if you do this... The circuit could currently be setup to provide anywhere from 10-30mA to each LED, so the initial "250ohm" estimate could be off a little... Experiment with resistors from 30ohms to 10ohms and it should work... The more resistance, the better at first. Stop lowering the resistance when the LEDs are bright as you want them.

OF gave me the easy way. The issue is that the three AAA batteries don't hold charge as long as I'd like. Well, I can just put three D cells in line and BLAMMO! Done deed.

Thanks again OF.