Here's a table for wire size vs load limits: http://www.powerstream.com/Wire_Size.htm
They are conservative, which I like. AWG 24 wire (which is what you were looking at) is OK for up to 3.5A when used as chassis wiring (which is what you are doing).

"maximum working voltage is 1000V rms"
That means the insulation is good for up to 1000VAC.

 

ok, not sure where you go the 24 agw from. I think the 24 on that site refers to 24 copper strands. But I think judging by thickness it probably is around 24 agw by that table you gave me.
So this wire is perfectly suitable for my 1.5-2 amp circuit, right?

 

I'll go with Wookie on this one, it looks good.

The gauge is the total thickness, stranded or not. Stranded wire takes repeated bending better and is easier to bend.

 

brill, I'll get this stuff then. I'll let you know when everything has arrived.

 

Right, I'm still waiting for the resistors, I don't know whats taking so long with them...

But in the mean time I've drawn an extremely technical diagram of the circuit. I'm sure there's some mistakes in there so some advice would be great:
http://i760.photobucket.com/albums/xx243/i84cookie/CircuitDiagram_01.jpg

thanks

 

Didn't you mention something about fans?

 

Just a minor point, but I usually like to put a power switch in the +V supply "rail".

The reason for that, is the return line is frequently connected to chassis ground. If you switch the return line, then everything on the +V side of the switch will still be "live" or "hot"; and if you then start to work on it and accidentally cause a short between the components and chassis, you may burn something up.

Remember that you must not permit the power dissipation of the LED to exceed 20 Watts, as that is it's maximum rating.
Power in Watts is a function of Voltage x Current.

So, if you are supplying 1.5 Amperes of current to the LED, the forward voltage drop of the LED must not exceed 20W/1.5A = 13.333...Volts, or you will burn up the LED very quickly.

You will be much better off if you start with less than 12 of those 10 Ohm resistors connected between the OUT and ADJ terminals. That way you can start off slowly and cautiously, and build up to the correct current to keep your LED from melting into a little blob of dead plastic.

9 of those 10 Ohm resistors in parallel will give you 1.111... Ohms, and about 1.12 Amperes output.

Keep the wiring between the OUT, resistors, and ADJ terminals as short as possible.

 

FINALLY! Everything has come, I had problems with the place where I bought the resistors, they basically stole my £5, so I got them off ebay, for a lot cheaper too. Let me just say:

Do NOT buy parts from des-parts.co.uk they take your money and you don't get your stuff. (for anyone googling about that site)

Anyway, I put everything together exactly like in my diagram, minus the switch for now, and 9 resistors instead of 12... and to my surprise it works!! And works really well! All I have to do now is mount the stuff inside the projector, and see if it works well as a projector bulb (the film colours won't be as nice as the traditional incandescent bulb as the LED is very white, but I guess we'll see!).

The LED gets pretty hot after a while, but everything else seems ok, the LM317 doesn't get too hot, the LED heats up much quicker. So I'll have to make sure the fan in the projector is flowing across the LED heatsink as well as possible.

Just like to thank everyone who helped me out on this little project, especially SgtWookie and Bill_Marsden.

I'll post some pics of the finished projector when it's done.

 

So far, so good

Sorry about your experience with that vendor. I tend to stay with major suppliers, as they are much less likely to run off with your money or give you bad parts.

With your nine 10 Ohm resistors in parallel, they should measure approximately 1.111... Ohms.
The formula for the LM317 regulator when used as a current regulator is:
CurrentOut = 1.25/R1
and conversely:
R1 = 1.25/DesiredCurrent

Since your R1 is 1.111...Ohms, you should be getting 1.25/1.111.. = 1.125 Amperes current flow through your LED.

Before you assemble it, you should connect your voltage meter across the anode and cathode of the LED, set to read on the 20v scale, and then turn on the power just long enough to read the voltage across the LED. Please record and report this value.

Then move the positive meter probe to the input terminal of the LM317, and apply power just long enough to read the total voltage across the regulator and the LED. Please record and report this value.

Multiply the current (1.125) by the voltage across the LED to determine its' power dissipation in Watts. This is important; otherwise we will not know how much actual power you are dissipating in the LED or the LM317 regulator. You want this project to work for a good long time; telling us what your readings are will help us to help you make that a reality.

Also, when you are mounting your project inside the projector, make certain that the air will flow over all of the resistors as well as the heat sink for the LED. Otherwise, the resistors may get pretty warm.

 

I dont have a voltage meter at the moment. I suppose I should get one. This is turning out to be roughly 5 times the cost of a bulb! This LED better last longer than 6 times the life span of a bulb otherwise its not worth it!

will this be sufficient?
http://cgi.ebay.co.uk/Digital-volta...emQQptZLH_DefaultDomain_3?hash=item35a55a695b

 

It should. That and the next time (if there is one) the LED costs will be substantially down.

Electronics design (which is what you're doing) has high start up, but once you pin down the vendors and get the basic tools it goes down.

 

I dont have a voltage meter at the moment. I suppose I should get one. This is turning out to be roughly 5 times the cost of a bulb! This LED better last longer than 6 times the life span of a bulb otherwise its not worth it!

will this be sufficient?
http://cgi.ebay.co.uk/Digital-volta...emQQptZLH_DefaultDomain_3?hash=item35a55a695b

I would not get that one.
Note that near the bottom the vendor has stated that the image is "for illustrative purposes only". You might wind up with just an LED and resistor attached to some wire.

You should invest in an inexpensive digital multimeter, one that can measure: DC Volts in ranges from 200mV to 200V
AC Volts up to perhaps 500 or so
Ohms with ranges from 200 to 2 Megohms
DC current in ranges from perhaps 2mA to 10A
Here in the States, we can find inexpensive DMMS for as little as $4 USD or even less on sale. You might find one costing £10-£20 in the UK; I know things are a lot more expensive there.

 

ok, well too late on that one. It's ok, only cost me £2 including p&p. If it's crap, it's no big loss.

oh BTW, I couldn't resist but hold my LED inside the projector to see if it will work, and it works absolutely fantastically! The colours look great and it's a bit brighter and dare I say the image is sharper than its ever been!

 

Sorry, I missed that post. You can get DVMs extremely cheap (as you have seen). A slightly higher quality unit would have an ohm meter and current meter, both good thinks to have.

 

ok I got the volt meter. It was the one from the picture, seems pretty basic. Not sure if i'm using it correctly, but I touched it to the 'In' side of my LED and the read out said '123655'. There is a little 'v' above every second digit. Does this mean anything to you guys?

 

This is with the LED lite up? Sounds like it is not working. Might be a battery issue, what does this DVM take?

Touch the DVM to the battery terminals (or DC power supply), it should measure the power supply voltage.

 

That was with the LED on.
When I touch it to the power supply it says 12v36v55v110v. If I touch it to my radiator it says 12v, and to the av port on my TV reads 12v36v.

Looks like it just has 5 readings, i bet the next one up from 110 is 250. I suspect this is a piece of rubbish, or I'm not using it correctly?

 

Without knowing your meter I can only guess, but it sounds like garbage. Do you have two wires touching the circuit, one to negative, the other the point on the meter? You must have two wires connected to make measurements, this is universal.

 

actually I think this is just a 'voltage tester'. It's a screwdriver and you put your finger on it to see if there is a current... ok i'm an idiot, I'll admit it, but it's only £2 down the drain... plus it looks a little like a pregnancy tester. I'll try again. I've just ordered this:

http://www.maplin.co.uk/Module.aspx?ModuleNo=37279

 

That's what I was afraid you were getting.

The meter you've ordered will work just fine. I have several of them that are very similar. The test leads are a bit dicey, but you can't expect a lot for that little money.

It's always a good check to start with the meter set to measure on the 200 Ohm scale, and short the test leads together. If your reading is higher than a fraction of an Ohm, you need to check your test leads' connections.

Then change to the highest voltage setting before taking measurements. (don't try to measure Ohms or current when you meant to measure voltage!)