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John Stevenson
01-06-2011, 05:11 PM
Got some of these LED's.

http://www.dealextreme.com/details.dx/sku.11621

I have one that runs on a 4.5 volt wall wart and gives out a good light without getting hot. These will run from 3.7v to 18 volt but at the higher voltages they get hot according to the feedback.

I'm fed up with these machine lamps on stays as fitted the the Bridgy [ hawk - spit - ding ] no matter how you place them they get in the way of the hight precision quill fed lever [ laugh ] or the job.

What I want to do is scrap these and fit a couple of these under the ram to shine down and another one or two on magnetic bases and plugs to go where needed, not always the same for different jobs.

The lamps fitted ar 25 V AC Edison screw, another reason to get rid as the bulbs are expensive here, UK default are bayonet fitting, get hot and don't last long.

The Bridgy has provision for 12v AC and 24v AC.

Now the question?
What resistance would I need to drop the 12v down to say 6v to handle 3 or 4 of these ?

I know I'll need a bridge rectifier to get DC but it should still be at 12v when rectified.

rohart
01-06-2011, 06:15 PM
I don't think LEDs are made that take 18V. I think those already some voltage dropper circuitry in there.

With LEDs it's a question of feeding the required current, controlled. If you can check the current taken by the one you currently use (pun intended), then just choose a resistor to feed the same current from your new voltage, and go from there. I've had no problem running many LEDs in parallel from a well controlled voltage source. Just mess with a resistor in parallel with a pot and tinker till the brightness is about right.

If you buy LEDs from someone like RS, Maplin or Farnell, they tell you the brightness at certain currents, and the voltage you have to cover before anything happens. You don't get that with these made up units. You just have to experiment.

John Stevenson
01-06-2011, 06:20 PM
Yes these LED's are self contained with their own on board regulator hence the 3.7 to 18 volts, at 5v they work well and don't get hot and this is what I want to drop down to

bborr01
01-06-2011, 06:27 PM
I looked at the link and saw that someone calling themselves "junkmeister" posted pictures of Evans "ray of death" flashlight.

I thought Evan was the "Crapmeister".

Brian

lazlo
01-06-2011, 06:35 PM
John, I'm guessing you mean you have 12V DC? A simple way would be to use an LM317, which is a 3 terminal adjustable voltage regulator. Depending on the variant, takes up to 27V input, and outputs 1.2 - 37V @ 1.5A.

$2 at Radio Shack, I'm sure you have some equivalent.

KEJR
01-06-2011, 06:42 PM
I have a datasheet for these chip LEDs at work, but basically they are something like 3.5V LEDs. They get real hot at full power so the fact that you say they get hot is not all too surprising. The fact that it takes from 3.7-18VDC means there is most likely a current controller in the module, not just the resistor. Is the bulb a constant brightness, or does it vary with input voltage?

I would try just using a bridge rectifier and a capacitor across it to give some filtering if needed (This is all that is usually in a non regulated "DC" walwart power unit). While we are at it, why not just use a 300-500mA walwart in the 5-12V range? Are you trying to package everything nicely onto the machine or something?

To answer directly, to drop 6V, assuming the drawn current is 300mA (typical for these type of LED units) you would need a 20 ohm resistor. You would then need a 2 Watt power resistor:

6V/0.3A = 20 ohm
V^2/R = 36V/20ohm = 1.8Watts

Also keep in mind that 12VAC is really 12*sqrt(2) in peak voltage, or about 16.8V. If the description is right you should be OK since it is under 18V.


Let me know how your experiments go. It might be of help if you could put a current meter on it to see what it draws at different voltages.

KEJR

aboard_epsilon
01-06-2011, 06:47 PM
Go to any car boot sale ..there you will find hundreds of power supllies at lots of different voltages ..all mostly 50 pence each .

BTW Home and Bargain were doing a 75 led array for 4.00..they work well ..equal to a 60 watt lamp

all the best.markj

John Stevenson
01-06-2011, 06:55 PM
Update,
I have 12v and 24 volt from an internal transformer, this machine is supplied 440 volt 3 phase only, no neutral so I can't fit an internal wall wart and I don't want miles of cable going to outside sockets.

Lazlo, good idea about the LM XX05's we have here, feed 12v DC in and get 5v DC out.
I can make a simple board up with 3 or 4 of these, one per light and a bridge rectifier to turn the Ac to DC.

I'll look for the bits tomorrow.

KEJR
01-06-2011, 07:03 PM
I think the LM7805s will take a watt or two (check the datasheet) but if you use them I'd hook them up to a heatsink of some sort.

The voltage regulator isn't doing much more for you than a dropping resistor though (the LED is a constant load), so if you really do need to drop the voltage it might be simpler with the resistors.

KEJR

danlb
01-06-2011, 07:50 PM
Those are regulated dropins. If you add an lm-XX05 voltage regulator you will simply be buring off the excess volatage in a resistor at a different spot.

I'd run it straight from the 12 volt supply ( with filters to depress ripple).

Dan

KEJR
01-06-2011, 08:09 PM
Those are regulated dropins. If you add an lm-XX05 voltage regulator you will simply be buring off the excess volatage in a resistor at a different spot.

I'd run it straight from the 12 volt supply ( with filters to depress ripple).

Dan


Agreed, but OP stated he wanted to have the LED module run cooler. Hence the suggestion to use dropping resistors or external regulators.

KEJR

Evan
01-06-2011, 09:02 PM
A dropping resistor will work fine and moves the heat out of the module. Unless you use a switching regulator that extra power must be dissipated somewhere and outside the module is the best place.

The Q5 is about a 3 watt LED so it needs around 850 milliamps to run. Use a 10 ohm resistor in series with the 12 volt supply. The resistor should be wirewound and at least 10 watts. It will get hot enough to burn your fingers so keep that in mind. The resistor can be mounted on a heat sink with a clip to help it run cooler.

darryl
01-06-2011, 09:04 PM
Wire three in series, then drive the string directly from your rectified 12vac. For the least flicker, put a capacitor on the output of the bridge rectifier, anything over about 470 uf and with a 25 volt rating will do. The on-board regulators will divide the voltage equally as they regulate the current to each led. If you want more light, add another string of three in parallel with the first string.

Each module will get about 5 volts or so- no need to add any regulator or dropping resistor. Everything will run cool.

dp
01-06-2011, 09:22 PM
This will handle every contingency:

http://www.electronics-lab.com/blog/?p=1955

Peter.
01-06-2011, 11:25 PM
Wire three in series, then drive the string directly from your rectified 12vac. For the least flicker, put a capacitor on the output of the bridge rectifier, anything over about 470 uf and with a 25 volt rating will do. The on-board regulators will divide the voltage equally as they regulate the current to each led. If you want more light, add another string of three in parallel with the first string.

Each module will get about 5 volts or so- no need to add any regulator or dropping resistor. Everything will run cool.

I thought there was some reason why you couldn't run these in series like that. I'm sure I recall Evan explaining why, unless I'm remembering wrong.

darryl
01-06-2011, 11:50 PM
I would be surprised if it didn't work, but I'll defer to someone who knows for fact. My reasoning goes that the module with the lowest regulated current will set the maximum current for the string. The other modules would try to turn on harder to increase the current through their respective leds, but that will just drop the voltage across those modules. That drop should stabilize at the point where the led dims just slightly, only to the point where the current passing matches the string current. The three modules might have differing voltages across them, but none will get less than about 4 volts, which means that in the worst case, one module could have about 8 volts across it- still within reasonable limits for generated heat. I doubt whether the voltage differences would be that much, however.

I could be wrong- it has happened once before- :) I may stand to learn something with this-

ironmonger
01-07-2011, 12:29 AM
I have purchased this:

http://cgi.ebay.com/3w-LED-Driver-MBI6651-based-Luxeon-White-Green-Blue-/250751836966?pt=UK_BOI_Electrical_Components_Suppl ies_ET&hash=item3a61f96326

and this:

http://cgi.ebay.com/High-Brightness-3W-80-lm-White-Lumen-LED-1-pcs-/230570136091?pt=LH_DefaultDomain_0&hash=item35af0d121b

The power modual accepts from 9 to 35 volts, and will drive up to 8 - 3 watt led's.
The 'star' configuration led's have an isolated aluminum heat sink that really should be attached to a larger heat sink.

Like this:
http://www.fun-led-light.com/heat-sinks.html

or:
http://cgi.ebay.com/10pcs-Aluminium-Heatsinks-1W-3W-LUXEON-LED-Cooling-/360333380676?pt=LH_DefaultDomain_0&hash=item53e58b0c44

I have not purchased any of the heat sinks, I listed them for information only. I have used old heat sinks form computers CPU's, but you need to do something.
They sure are bright...
paul

John Stevenson
01-07-2011, 04:41 AM
Thanks guys, loads of ideas so I need to raid the bit box, see what's in there and work from that.

I'll post the final results later, I'm going to try do this later today but just had 22 new electric motors dumped on me for modification and they need to go out today - bloody customers they just won't accept that Friday is play day.

Main reason I wanted to run at 5 volts is that the first one I did that is fitted to my CNC router had a holder / head made of nylon so it's insulated from the machine and I want to do this with these.
At 5 volts they don't get hot so the nylon isn't a problem.

hojpoj
01-07-2011, 08:30 AM
John, just as a suggestion that I didn't see mentioned-

Why not just scavenge one of the cheap Automotive 12VDC adapters that puts out a 5VDC or so line? Hell, hookup would be fairly simple, could probably even just use one that provides a USB port to keep some of the wiring modular. Enclose it all to keep the chips out and you'd be good to go. You can probably find them at a thrift store locally, or order them from DealExtreme for a pittance.

lazlo
01-07-2011, 08:44 AM
What I want to do is scrap these and fit a couple of these under the ram to shine down and another one or two on magnetic bases and plugs to go where needed.

John, have you found a hood/receptacle that fits these lights, or are you talking about making them from scratch?

Deja Vu
01-07-2011, 10:05 AM
Thanks guys, just had 22 new electric motors dumped on me for modification and they need to go out today - bloody customers they just won't accept that Friday is play day.


You can get a little play in.....taking pictures of the modifications for future thread here with explanations.:)

John Stevenson
01-07-2011, 02:44 PM
You can get a little play in.....taking pictures of the modifications for future thread here with explanations.:)


No that's boring, don't mind taking pics of something interesting or broken as it gives others idea but these are all the same mod, turn the rotor down to the next smaller frame size, 28mm to 24mm and deepen the keyway.
The end cover has 4 extra holes drilled and the original holes are cut back so they can get a spanner in to reach the new bolts on a conversion plate.

They collected tonight and dropped another 10 off - sigh............

Robert I was making the whole lot up, I'll get a picture later of two I have done already, on on the CNC router and a free standing one with a flex head.

lazlo
01-07-2011, 03:05 PM
Robert I was making the whole lot up, I'll get a picture later of two I have done already, on on the CNC router and a free standing one with a flex head.

Interested in selling a couple? :)