V=I*R

[robe_uk]

Am confused as to why you have attached resistors in series with the laser, I have one on my machine and it only needs 5volts applied directly and works no problem, the current draw from a laser diode like these is low enough for you to power directly from the computer usb as its the easiest source of 5v.

Good luck Rob

[IBBruin]

It won't light up at 5v. It says the operating range is 3.5~4.5v. When I first got it I hooked it to 3AAA batteries in series (4.5v) and the laser was real dim. I dropped back to 2 AAA batteries (3v) and it got real bright. I used as many resistors as I could find to cut the 5v phone charger down to get it as close to 3v as possible.

[Al_The_Man]

The specs show it normally consumes 5mw, with the set up you have it is consuming 8mw, so it would appear you are over driving it slightly?
If that is so, you increase the resistances accordingly?
Al.

[IBBruin]

I have a drawer full of old phone/cd player style chargers. If I can find one closer to 3 volts, I'll hook it up without any resistors and see what happens. That conglomeration of resistors was just to see approx what ohms I'd need to run it at 3v. I didn't plan on leaving them all in the final design. lol

[Al_The_Man]

What to watch for if you have the older style Wall-Warts is they were hardly ever regulated, they relied on the rated current to bring the voltage down, just about all now are regulated, maybe measure before hooking up!
Al.

[IBBruin]

Thanks for the heads up. I'll definitely check before I hook it up.

[JerryBurks]

The "5mW' spec is normally the rated OUTPUT power. Due to the low efficiency of laser diodes the input power requirement is much higher. I have seen 40mA@3V or 120mW for typical 5mW laser which is why the higher power ones get a bit warm. To be sure you should measure the actual current intake at normal 3V supply.

Also, the modules have an internal regulator that may not like series resistors because that increases the power source impedance and the circuit can become unstable. If this is the case it can probably be mitigated by adding a capacitor parallel to the laser module (e.g. 1microfarad to 10 microfarad Tantalum type with 10V rating, check polarity).

[Al_The_Man]

You could also try using three forward biased diodes on 5vdc, e.g. 1n4005, in series, they each drop .7v and are a constant voltage source, once forward biased the volt drop is the same regardless of current.
Al.

[Claytonc]

You could also try using three forward biased diodes on 5vdc, e.g. 1n4005, in series, they each drop .7v and are a constant voltage source, once forward biased the volt drop is the same regardless of current.
Al.

Thanks to IBBruin for bringing up this subject because I'm now adding the same functionality to my machine. I've been wanting this since I first built my machine.

And thank you Al_The_Man for the simple diode solution to the voltage difference. Now I sit and wait for my laser from China...

Heck, thank you all! Its great to have a place where I can just sit and learn about the stuff I love to do.

Knowledgeable, friendly, and experienced advice! And its all free right here on cncZone! What more could you ask for?

[ma1]

Here is some general info from a laser expert:

1- Lasers are diodes, they run at almost constant voltage
across varying current levels at lasing conditions. So, any
decent laser diode driver should be a constant current
regulated driver (not voltage). Laser diodes should not
be operated with higher voltage levels than
they are specified for.

2- Lasers have a turn-on current level for lasing operation.
For current levels higher than this level, they become really bright.
Anything below this current is not the lasing condition, it is called
spontaneous emission (dim output).

3- Many of those small red diode cans come with an
embedded, "fixed constant current/constant power" driver.
This driver usually runs with a linear LM317 type circuit
that can tolerate a range of input voltages. However, you
should operate to the lower range of these voltages to
reduce heat load.

**

Now , to the specific problem:

Here are some comparable lasers to what you have (albeit half the power claimed) that includes the diode driver:
VLM-635-04-LPA Quarton Inc | VLM-635-04-LPA-ND | DigiKey
VLM-635-11-LPA Quarton Inc | VLM-635-11-LPA-ND | DigiKey
The datasheets claim 3-5 volt wall plug operation with
the laser diode dropping ~2.7Volts and up to 60mA
current. The output is 2.5mW, but wall power consumption is up
to 300 mW (low efficiency).


I suggest you ask the seller to provide the datasheet for
your unit.Your laser may not have the constant current/power driver
built-in, as you are reporting ~2.7 volts drop across the
leads of the diode.

If you don't get the manual, I would assume no built-in
driver, and hook a maximum 3 volt, 100 mA limited supply to it
(no resistors).
If you only have the 5 volt wall-wart supply, and want
some simple operation, I would limit the current to 100 mA,
and drop the voltage to ~2.7 volts with the resistors (Similar
to what you are doing).

Assuming 5-2.7=2.3 Volt across the resistors, and
a maximum of 100 mA current, this gives:
2.3/0.1=23 ohms with a power rating of 2.3x0.1=0.23 watts

Therefore the resistor should be 23 ohms with a power
rating of 0.5 watts (for safety). Or you can use 10 pieces
of 230 ohms in parallel with a rating of 0.05 watts.

Hope this helps, feel free to ask questions.

[RomanLini]

In addition to that I would add NOT to touch the laser wires without being careful to ground yourself first, they can blow in an instant from static electricity. I have a couple fo dead laser pointers as proof.

These days I solder a cap across the laser wires, a cheap 0.1uF greencap is fine. That helps a lot with laser life. The cap goes after a resistor, so the cap is across the laser itself THEN power goes to that through the resistor.

Also 100mA will be painfully bright on most 1mW lasers so you can use a larger resistor, and reduce the current. Even at 25mA it should be quite visible. There's no point getting eye damage and reducing laser life when you just need to see an indicator dot or line on the workpiece.

[IBBruin]

I bought two, the first one has something screwey with the prism or something. The beam it emits is twice as thick on X as it is on Y and would flicker so I threw that one in a drawer for a backup. I've supplied so many different voltages to the second one from 1.5v to about 7 that it's on it's last leg and isn't very bright anyway. I figured I'd do all my experimenting with these two then order a couple more that I plan on using. I do appreciate everyones imput.