Couple of things I'd add. Beware - there are LM317s out there with metal tabs which are internally connected to pin 2.

I don't really know what you mean there. pin 2 = ADJ ? how can I know which is which ?

 

X8 10Ω ¼W resistors in parallel creates exactly the value you need (1.25Ω at 2W), is much cheaper, and also meets the wattage requirements. It would work better with the PCB I recommended, which is the only disadvantage.

Look at the drawing I gave you on post #8, it was defined. There isn't a pin 2 with TO220 cases, this was an arbitrary designation.

As far as I know all the metal tabs on a TO220 case are connected to the output pin, this is pretty well universal. I use kapton tape and nylon shoulder washers, or you can buy mounting kits for that package style that have the same parts to keep the metal case isolated from the heat sink.

I asked SgtWookie about the fans in series, he thinks it is a bad idea, and I value his opinion very highly.

We need the specs on on those fans before I can guarantee we can use the same power supply for one or both fans.

Here is how to use a LM317 as a voltage regulator. One regulator will power both fans. There are better schemes though, since the voltage drop across the regulator is so high.

If you want to build a bit of circuitry I can help you make a switching mode regulator that will reduce the current requirements a lot for the fans.

 

Pin 2 = center pin

Not a T version but for example:

http://focus.ti.com/lit/ds/symlink/lm317.pdf
http://www.fairchildsemi.com/ds/LM/LM317.pdf
http://www.onsemi.com/pub_link/Collateral/LM317M-D.PDF

 

The "T" version is irrelevant, you are still talking about TO220 packages.

Not one on the TI version marks pin numbers, mainly because TO220 package don't have pin numbers. It is why I put the packages on my illustrations.

LM317 are available from Radio Shack, though at a marked up price. I get mine from a Mom&Pop electronics store for a bit over a $1.

 

The "T" version is irrelevant, you are still talking about TO220 packages.

Not one on the TI version marks pin numbers, mainly because TO220 package don't have pin numbers. It is why I put the packages on my illustrations.

Note all the way to the bottom of the TI data sheet. They may not be "pin numbers" so to speak, just reference numbers in the data sheets, but most TO-220 package data sheets still use the same ones.
http://www.fairchildsemi.com/ds/MJ/MJE3055T.pdf

I will however agree that it makes far more sense to use an illustration.

 

I take note of the resistors values and how to connect them for the LEd part of the circuit.

As far as I know all the metal tabs on a TO220 case are connected to the output pin, this is pretty well universal. I use kapton tape and nylon shoulder washers, or you can buy mounting kits for that package style that have the same parts to keep the metal case isolated from the heat sink.

Again, not too sure I understand what you say here. What is the metal tab ? is it the metal part at the top of the component ? Is this not to be mounted onto the heat sink for better cooling ?

Now about the fans and the LCD. I was thinking, rather than going into making a voltage regulator, about going back to my first idea and have a second transformer that would provide me with 12v to run the 2/3 fans and the LCD screen.
Would this be ok ? I found those two (which are actually LED drivers):
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180557685134
and
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110584450972

The fans would then be in parallel, but how do I go choosing a fan ?
Anyone in particular from this list for example :
http://www.maplin.co.uk/Search.aspx?criteria=fan ?

If you want to build a bit of circuitry I can help you make a switching mode regulator that will reduce the current requirements a lot for the fans.

I'm not sure I would be able to do this correctly and efficiently so I'd rather use and already made transformer and regulator.

Cheers,
R.

 

One fan should be matched to the LED heat sink. The second is less critical, and is for the current regulator. It might be convienent if it were matched to the heat sink too.

It is obvious you are in the UK, just like the gentleman in the other post I pointed you too. Your projects are virtually identical. You might look through his rather long thread to pick up ideas.

You'll note most of the old timers put their location as part of the profile. This assists in part location most of the time.

 

Does matchin the fan to the heat sink mean anything more than orientating it well so the fan cools the heatsink fins ?
I will also get a second one for the current regulator, just to be on the safe side !
Is there any theory as to how to mount and orient them so the air flows correctly in the box ?

I am in the UK indeed, and had a look through this thread you were mentioning to get some ideas.

Coming back to my previous post, is it fine to put a second transformer from the mains, for the 12v part of the circuit ? Anything to consider when connecting both transformers to the mains ?

Thanks for showing me the light !

 

Coming back to my previous post, is it fine to put a second transformer from the mains, for the 12v part of the circuit ? Anything to consider when connecting both transformers to the mains ?

Probably. The thing to be careful of is pay attention to the fans current rating. Remember, the power supply must exceed the total current rating by a comfortable margin. That and either a power strip or an extension cord with two outlets that can take both transformers. The big advantage is the design work for the power supply has been done.

If you use the 8 resistors don't bundle them tight, set it up where air can circulate around each resistor so they can all cool down.

The only reason to make sure the fans match the heatsink mechanically. If you get them as a matched set there is a very good change they will be smaller as a unit. I suspect you need something fairly thin and small.

 

OK, thanks for all your help, I think I'm on good tracks now.
I will be busy this week with other things, but will come back to this thread later if I run into any problems.

Thanks again,
Ronan