12 replies to this topic

[headhunter23]

Hello, back again, been searching on how to power a 30W LED with a 12v power source, so far all options are kind of expensive. I'm curious as to whether there is a cheaper way to power em? The source is 12vdc but the voltage required for the LED is 15-18vdc. A simple transformer? Light would be a good option, I"m putting 2 o these on a scooter.

Ideas?

[W3FJW-Ron]

You're not running the scooter on 12V are you? What's the combined weight of the scooter & Operator?

[headhunter23]

Oh your thinking of an electric scooter, nah i picked up an 98 50cc model from a buddy for 500 bucks, got her all together but hate the halogen lighting. So was thinking put less strain and go LED. I think the batt is actually 12.5v not exactly sure how many volts it is running, I know it's not 13.5-14v like a car though, apparently these batteries don't like running like that.

What do you think?

[Kilrah]

Have you actually bought a "real" LED headlight, or are you making it yourself? (Question being, does it already have a constant current source for the LEDs?)

[headhunter23]

Ummm... I'm buying the LED itself and have to make everything else to get it to work. I just need to slap heat sink and make housing for scooter to pop it on, plus get a lens to focus the light as the viewing angle is high at 140 degrees.

Just planning it out at this point, no it doesn't have a constant source, that's what I'm trying to figure out. I wished it could connect directly to batt but need a little more voltage. There are LED drivers which can connect to a source and then up it to 16v but they are expensive, I was just curious if there was another way.
These are the 30W LED's that I'm going to buy;
http://cgi.ebay.ca/3...id=p3286.c0.m14

I have a 10W and a 12W already but they're for different applications(one was to replace flash light(I have to say these things are insanely bright!), the original was to mess with, didn't realize they needed to be attached directly to heat sink with heat paste and burned up 7 of the 9 LEDs on the board). The messed up one is still bright but no where near the original good condition.

So far the cheapest way I can think of is to buy a cheap LI-po charger from hobbyking, a cheap 4s lipo to the charger and connect the lights to the lipo. It would cost me 20-25 bucks that way versus... geez thought i found a couple the other day but pretty much everything I've come across is ac to dc!

The one from digikey which does specifically what I want is only 206 bucks.

[headhunter23]

Ah found one in my price range, btw IBM laptop dc power supplies can do 16v, 4.5a, $40 bucks. Pita.

[Kilrah]

OK, single LED. The point is, you can't just plug your LED to a 16V supply straight away, or you risk blowing it up. The LED needs regulated current (apparently 1.8A max from what they say). That's the use of the resistor we usually put in series with a LED, but here with that power a resistor would heat up way too much, hence those LEDs usually being used with active switching mode current regulators. It would be best to find a suitable one, maybe the seller of the LED has one.

[W3FJW-Ron]

Boy! He sure makes a good profit on shipping.
Must be coming from China. I'd try it on your battery first. Might be bright enough. BTW, Batt voltage & charging system should be same as a car. You can use one of those 3 terminal regulators hooked up as a constant current source.
I'd just get another pb cell or two & hook it up in series with the bike battery. Charge it seperatly from the bike battery.
You have to disconnect a lipoly charger when it's done charging. They're finicky about charging. I'd look more toward LifePo4 batteries or A123 if you go that route.

Edited by W3FJW-Ron, 09 September 2009 - 03:35 PM.

[Xygax]

The conventional way to run a series LED stack is a small switch mode (30w from 12v is a flyback) these are normally run in current mode with upper voltage limit about 0.3-0.5v above the upper led stack voltage. probably simplest with a 3842 and an irf530 and a quality 10 A shoktty diode would be about right for this type of application it would reject the varation in bike battery voltage completly and provide a constant current to the load from 9 - 16 v and they are 80+% efficent ...


Steve

[headhunter23]

Wow, just slightly above my head the last few posts. So just to confirm, that power supply hooked onto the scooter, should convert 12v to 16v so that the LEDs can run. But I would still need to have a resistor in series right Kilrah? I'm hoping to run both LEDs on at the same time and then lights off... so then should I run each LED as a separate circuit or put both LEDs in series with whatever resistor value is required?

Sorry Xygax, I totally didn't understand your reply, just a bit too technical(or at least the terms used) for me .

[Kilrah]

OK.... let's try a simplification.

What matters to a LED is current, not voltage. Your LED as shown on the seller's page needs 1.8A to run at full brightness, but voltage can have to be anywhere between 15 and 18V, and will be different for each LED. And a little change of voltage will induce a large change of current, so maybe yours will require 17.16V, and if you supply 17.1V it will run dim at 0.5A, while if you give it 17.2V it will burn up with 2.5A...

So, you need to buy or make a circuitry that will regulate the LED current, by automatically continuously adjusting the voltage so that the current in the LED is what it should, i.e 1.8A, which is what the previous 2 posts gave hints on how to make

[headhunter23]

Crappy, did not know that... thought just running the right voltage was all ya needed. Thanks, will look into it and try to understand what the other posts had mentioned then.

[W3FJW-Ron]

Look at the constant current charger on page two for an idea.

http://www.qsl.net/s...files/LB-35.pdf