Question concerning a DIY laby

Hi, I want yo make a red laser labby using a red closed can long die laser diode from a GGW sled. It will be air cooled using a fan and the module will be set in a custom aluminium heatsink from Jayrob.

Now the first question is :
All of the fans I found work on 12v, now, I need 6v for the module. How can I fix that without using two power supplies, and also, will a regular transformer (the one that has a plastic box were you connect it in the wall) work for such a laser? And do I need to regulate the current for my fan?

And finally, is it possible to set a pot between a DDL driver and a power supply to have a variable current output to the DDL?

I've already have a found a great host at my local surplus store, and guess what? They used it for lasers!

BuildAbluraylaser said:

All of the fans I found work on 12v

Click to expand...

Where have you looked?

At my local surplus store and my parts bin
Also took a look at digikey, but the shipping is too expansive just to buy that

BuildAbluraylaser said:

And finally, is it possible to set a pot between a DDL driver and a power supply to have a variable current output to the DDL?

Click to expand...

No. You vary the current by changing the resistor in the DDL circuit (the one connected between the Vout and Adj pins). Input current into the driver will always equal the output current.

So, what do I do than since over turning the pot will blow up my laser?

you can get a fan like this.

http://cgi.ebay.com/NEW-5v-fan-40mm...6|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

good, but I want to know if there's a way to use a 12v fan since I have one perfect for the job.
Nice halo pic

You can run the fan and DDL off the same 12V supply voltage (in parallel). One drawback, the DDL will have to "burn off" a lot of excess voltage at ~400mA, so it will run hot. Make sure to cool it as well.

Another option is to run the fan at less than 12V. It will turn slower, but it will be more silent and your laser and driver don't produce that much heat. At 8V & 400mA for example, you'd get 3W of heat and 200mW of laser light.

If you want to vary the current through your LD, you have to vary the current sense resistor. Use a fixed resistor with a value resulting in the max current (that's 3 Ohms for 420mA) in series with a pot with a value such that the sum of pot+resistor determines your min current. Using a logarithmic pot instead of a linear one should result in easier current setting for the full range.

A common wall-plug power supply might or might not work. It depends on whether the output is not only rectified, but also smoothed - it does not have to be regulated. If necessary, add a big capacitor on the driver input.

Ok, first, I tested my potentiometer idea, it works perfectly, now for the fan, I don't want to run it slower, but could you add a resistor before the DDL, mabye 40ohms 2W to drop the voltage? Or I could built a converter that does 6v to 12v. I can't give you the link, I'm on my ipod, but you can find it at www.aaroncake.net, in electronics, in the circuits, in the power supply section, called 6v to 12v converter.
The only problem is I don't know how to build the L1 component that needs to be custom made. Else, the circuit is very simple for what I've already built and the components can be found easly. As for the cap you said to add to smooth the output, how do I set it? Parallel? In series? How many Farads? 15volts?

Essentially a linear driver like the DDL contains a transistor that serves as a variable resistor (transistor=transfer resistor), converting current and voltage drop into heat. By adding a resistor before it, you offload some of this heat generation onto the resistor. Depending on the package type of your LM317, and the heatsinking you give it, that may or may not be necessary (check the datasheets for the rating).

If you use 40Ohms@400mA, you'd get a voltage drop of 16V - won't work. The DDL needs some headroom to work, so I'd suggest around 10 Ohms for a 4V drop (however, it's preferable to NOT use a series resistor - the LM317 does the job better, if it doesn't get too hot).

The capacitor goes over the input of the DDL (from + to Gnd). How many Farads depends on how good your power supply is and how much space you have - generally more is better. If your power supply just provides rectified current, 15V won't be enough, better get 20V or more.

Getting a 6V-to-12V-converter just for powering a fan is a massive overkill...

I have some small 12VDC to 6VDC voltage converters (also outputs 3VDC).

They deliver 800 ma of current.

You can find them at a large electronics dealer.

I have $5 in the ones I have, if you can't find one.

You should be able to buy a 5 VDC fan for that, and use it at 6 VDC.

LarryDFW

The converter is very simple, just take a look

http://www.aaroncake.net/circuits/6-12conv.asp
I still don't understand how to install the cap lol.
Is it like that :
+ input of the DDL, + lead of the cap
- input of the DDL, - lead of the cap

??

LarryDFW said:

I have some small 12VDC to 6VDC voltage converters for the fan.

They deliver 800 ma of current.

You can find them at a large electronics dealer.

I have $5 in the ones I have, if you can't find one.

LarryDFW

Click to expand...

I need 6 volts to 12 volts, not 12v to 6v.

You really only need ~3 VDC for the Red LD and 5VDC for a fan.

A 115 VAC plug-in 5VDC supply will furnish that easily.

One resistor will drop the 5 VDC down to 2.9 VDC.

Don't make this more complex, than it needs to be.

LarryDFW

I like complex!
I'll wait for the Dr. advice (dr-ebert), the thing is I don't want to buy another fan, I would prefer using the 12 volt one, and building the converter to power it. It's not very complex...

you can reverse feed the 12v-6v supply. it just won't be as efficeint so you would need one with a higher output rating.