LED Electronics guys out there?

[fretsman]

Hi fellas, I've been putting together a new spindle light for my Taig Mill and I'd like it to be much brighter than before. In the enclosure, I have enough room to house 23 (yes, 23 lol!) LED's but I'm not positive about the best way to go about wiring them.

Some info:

23 white LED's
- forw. voltage 3.4
- forw. current 25 mA

Source will be a 9.5 volt Apple printer Power supply with 1.5 amps available

I've used the online calculators and I come up with 23pcs. 270 ohm 1/2 w resistors, but that's an aweful lot more parts to stuff in there. I bought one of those $5 puck lights that has 24 LEDs in it and they don't have hardly anything like that inside. They use those tiny little surface mount resistors, but there's like only 2 of them in there? Is there a cleaner way to do this with a lot less parts? I honestly don't mind soldering all that, but it just seems to be too much for what I'm trying to do.

Obviously I'm not an electronics guy, I just know enough to be dangerous -

Thanks for the help and your time-
Dave

[Al_The_Man]

I think I would look at higher intensity LED's, ones already in a known base e.g. MES or similar, or better still, I would look at the types you can buy now to replace automotive incandescent, these are clusters of high intensity lamps all in one, you just need a 12v supply.
Al.

[fretsman]

Thanks Al, but I already have these setup and ready to go in the housing.

As for the automotive, I'd have to tear that part and who knows what I'd have left after doing so...

Thanks,
Dave

[Curley]

Have you tried 3 in series. You would not need a resistor then if they really drop 3.4V each. Is the power supply unregulated Too bad 23 is not divisible by 3.

[Jay C]

http://led.linear1.org/led.wiz

I used 12V, 3.2V forward voltage, 20mA, and 23 LEDs.

-Jay

[thebodger@roger]

Thanks for the link Jay, that will come in handy at times. Fretsman, you can use resistor arrays that come in 16 or 18 pin DIP packages ( I.C. style ), that way your setup can be more compact. Just remember to not exceed to total power dissapation of the device.

[Curley]

Nice calculator link. Got me to search for LED characteristic. Found another link to a calculator discussing various series conections: http://www.ledtuning.nl/index_site.p...e=ledtechnical

[fretsman]

Thanks for the info and the help all. Definitely some food for thought here and the link posted by Curley is a fantastic link, thank you-

As for the power supply, it is not marked if it's unregulated or not as it's just one of those larger wall wart types.

Dave

[Al_The_Man]

Originally Posted by fretsman As for the power supply, it is not marked if it's unregulated or not as it's just one of those larger wall wart types. Dave

Most are not, an easy way to tell is check the off load voltage, if it is as stated on the label, then it is regulated, if quite a bit higher, then unregulated.
Al.

[fretsman]

Thanks Al, just did a quick check and it's 13.03V

How much can it fluctuate and is it a bad idea to use a wall wart type PS?

Dave

[Al_The_Man]

They normally go down to the rated voltage when run at the rated current, so anything in between is a guess.
If you want a guaranteed voltage, either make or buy a regulated one or stick a regulator on the output, the down side is the regulator will consume some of the rated current.
If you are drawing that low of a current total, why not use one of the PC 12vdc supply connectors?
Al.

[fretsman]

I actually played with the idea of doing that but I just hate to rob any power coming from the machine PC.

One of those "anal" things I guess. It's not like I'm using anything else, like any of the drives, so I'd probably be fine. If it's going to quit on me, it's not like it'll be the spindle lamp's fault

Thanks again-
Dave