Green Laser draws 280mA, overheats?

[emdeex]

Hi All,

I've got a 10mW green laser module, its a 3VDC model, and I'm running it with 2x 1.5v D Cell batteries. I'm using it to generate a line to guide a saw blade. That part works well.

The multimeter says its drawing 280mA, which seems about right from reading these forums.

What's happening is:

Especially first thing in the morning, when its cooler in the workshop, it takes about 5 minutes to become bright. Firstly, is that a function of the battery not outputting enough current when cool, or it something more to do with the laser module?

Also, after being bright for some time, say 5-10mins, it fades down again. Switching it off, leaving it for a minute, and turning it on, restores the brightness, for a while until it fades again, I can repeat this over and over. Again, is that from the battery slumping, or from the laser perhaps overheating and powering down?

To get it to start-up faster, and to run longer, I'd consider either lowering the current (it doesn't need to be as bright as it is), or running it on mains power where I can supply a regulated current. What do you think, can I even restrict the current it draws?

Thanks for any and all help!

 

[chimo]

There are crystals in the laser that convert the IR light to green. They expand and contract with temperature. Their length is critical due to the frequency they operate at - too cool -> low output. Too hot -> low output. You should consider switching to a red laser diode based system and avoid those problems.

Hi All,

I've got a 10mW green laser module, its a 3VDC model, and I'm running it with 2x 1.5v D Cell batteries. I'm using it to generate a line to guide a saw blade. That part works well.

The multimeter says its drawing 280mA, which seems about right from reading these forums.

What's happening is:

Especially first thing in the morning, when its cooler in the workshop, it takes about 5 minutes to become bright. Firstly, is that a function of the battery not outputting enough current when cool, or it something more to do with the laser module?

Also, after being bright for some time, say 5-10mins, it fades down again. Switching it off, leaving it for a minute, and turning it on, restores the brightness, for a while until it fades again, I can repeat this over and over. Again, is that from the battery slumping, or from the laser perhaps overheating and powering down?

To get it to start-up faster, and to run longer, I'd consider either lowering the current (it doesn't need to be as bright as it is), or running it on mains power where I can supply a regulated current. What do you think, can I even restrict the current it draws?

Thanks for any and all help!

 

[emdeex]

There are crystals in the laser that convert the IR light to green. They expand and contract with temperature. Their length is critical due to the frequency they operate at - too cool -> low output. Too hot -> low output. You should consider switching to a red laser diode based system and avoid those problems.

OK, so you'd say its the crystals reacting to the ambient temperature, not a power supply problem. Thanks!

We used to use a red laser, but the green line is SO much more visible than the red, especially when working with dark/black material.

Do you think the 280mA draw is high, and could it be restricted to allow the laser to stay cooler?

 

[chimo]

OK, so you'd say its the crystals reacting to the ambient temperature, not a power supply problem. Thanks!

We used to use a red laser, but the green line is SO much more visible than the red, especially when working with dark/black material.

Do you think the 280mA draw is high, and could it be restricted to allow the laser to stay cooler?

If it's adjustable, you could try cranking down the current a bit (say drop by abouit 50mA or so).

Options:
1. You could also try improving the heatsinking on the module. Perhaps installing a small fan to cool it. Does it also get heat from the equipment it is mounted to? Although it's more complicated, you could try picking up a small Thermo Electric Cooler (TEC) and use that to help cool the laser.

2. Pick up a higher quality module. Larger crystal, better heatsinking...

3. Try a lower frequency red (635nm). They are more visible (and expensice) than the more common 650/660nm reds.

Good luck.

 

[emdeex]

Thanks for the replies Chimo,

The unit doesn't get hot from the environment or equipment, it's well ventilated and it's not hot.

How could I take the current down 50mA, what would I need to put into the circuit?

I'll look at one of those 635nm reds as well.

 

[chimo]

Thanks for the replies Chimo,

The unit doesn't get hot from the environment or equipment, it's well ventilated and it's not hot.

How could I take the current down 50mA, what would I need to put into the circuit?

I'll look at one of those 635nm reds as well.

Do you have access to the driver board? If so, does it have a potentiometer? If there is an accessible pot, adjusting it *may* have an effect on the current.

 

[emdeex]

Do you have access to the driver board? If so, does it have a potentiometer? If there is an accessible pot, adjusting it *may* have an effect on the current.

Thanks Chimo, I dont have access to the board, as its encased in a metal tube and glued/siliconed up.

A friendly person on another forum suggested that its probably the batteries voltage dropping under load thats causing the light to fade. They suggest using a LM317 IC and a 6VDC AC power adaptor to provide a steady current. What do you think?

 

[The_LED_Museum]

I'll throw in my 2¢ here that I suspect the MCA (multiple crystal assembly) as well; *NOT* the batteries. Especially not D cells.
I'd venture to guess that the laser diode is heating, causing subsequent heating of the MCA, which then leads to the drop in laser output.

To drop the current to the laser diode by 50mA if you cannot access the potentiometer, inserting a low-resistance, high-powered (2 watts or so) resistor in series with either of the power leads. Let's see if I can figure out a value in ohms that will accomplish this task...BBS... looks like a 4.7

2 watt resistor ought to do the trick here.

I figured this by having an input voltage of 3.0 volts, the laser module uses 2.0 volts, and the desired current is 230mA.

 

[emdeex]

I'll throw in my 2¢ here that I suspect the MCA (multiple crystal assembly) as well; *NOT* the batteries. Especially not D cells.

Thanks for the reply! That would correlate with my previous experience using a 5mW DPSS green with the same battery pack, it drew the same current (I think), but would not fade like the 10mW one does. Overheating of the MCA sounds like the best explanation so far.

Would a small fan, like a CPU cooler, actually cool it enough to be effective in reducing the MCA distortion?

Thanks again for the replies, I'm learning a lot and enjoying the project.

 

[The_LED_Museum]

...Would a small fan, like a CPU cooler, actually cool it enough to be effective in reducing the MCA distortion?...

If you can get active airflow through the laser body (not just through the barrel and stopping before it gets to the other side, but *COMPLETE* airflow through it so that moving air passes through/over the laser diode & optical train), then this approach may very well be viable.

I cannot guarantee with absolute, positive, 100% certainty that this WILL work, but it has a very high chance of working.

 

[emdeex]

If you can get active airflow through the laser body (not just through the barrel and stopping before it gets to the other side, but *COMPLETE* airflow through it so that moving air passes through/over the laser diode & optical train)

Nope, unfortunately, the laser is encased already in a metal tube and glued shut. I could at best blow air onto the head :naughty: !

 

[emdeex]

If you can get active airflow through the laser body (not just through the barrel and stopping before it gets to the other side, but *COMPLETE* airflow through it so that moving air passes through/over the laser diode & optical train), then this approach may very well be viable.

I cannot guarantee with absolute, positive, 100% certainty that this WILL work, but it has a very high chance of working.

Hi LED Museum,

I've got the 10mW Green laser on a steady regulated power supply, with adequate heat-sink, it supplies a steady 280mA. The laser still dims after 5mins or so. So I guess its the MCA overheating (I dont have a IR thermometer yet). I think I can access the potentiometer if I apply the multigrips to the casing, I'll try that.

Are there any green lasers you have tested that dont overheat the MCA? I've read your recent review of the 200mW red module from Aixiz that was very cool over long periods.

Thanks