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Thread: Project : Laser By Batteries

  1. #1
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    Default Project : Laser By Batteries



    Images here : http://photonlexicon.com/gallery/album46

    Right, this is a laser I pulled from a “Silverstar Longteng III”. It was a naff little laser system with servos as scanners.

    Only about 20 – 25mw but a nice little laser none the less.

    The laser will not work with under 38.8v, I used a bench power supply to test and this is the lowest you could go to keep the laser on. Any lower on the voltage and it would flash on and off.

    I have tested the head with 6XPP3 (9v) batteries in series. I was going to use five which is about 45v, this didn’t work as I only got a pulse. The only way I could get the laser to stay on was using a sixth battery. Which worked well, they were only naff cheap batteries so I think all 6 were outputting about 50v.

    They ran the laser fine for around 8 mins, then started flashing on and off. Ok so I thought it had killed the batteries already which I wouldn’t have been surprised at. But no, the voltage was still 49.9 – 50. So I gave it another go and found that the laser was fine again for around 2 – 3 mins before it started flashing. I kept repeating this process and the longer you leave the batteries to “recover” the longer you kept the beam going when you reconnected it. (Within reason, the “on-time” reduced slowly, IE it was hardly staying on for another 8 mins solid)

    So, why when I leave it off for a bit dose it happily carry on for a few more mins? Is there another way to get round this, maybe other batteries? Im open to suggestions as to how to go about the whole “power the laser by batteries” problem.

    The idea is “having a laser in the field” where you have no mains power. (And the fact I don’t want to buy a laser pointer when I can mount this kit in a project box and power it myself for A LOT less cost then a laser pointer.

    Any help is greatly appreciated.

    Thanks,
    Regards,

    Aidan

  2. #2
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    My guess would be either 1) the laser is pulling more current from those 9 volt batteries than they're designed to deliver, or 2) there is a thermal overload circuit built into the head that is shutting off the laser when it gets hot.

    To test theory # 1, measure the current draw. If you're trying to pull more than about 30 milliamps out of those 9 volt batteries, then you've found your problem. Replace them with a larger power source that can deliver more current. (7 or 8 of the large 6-volt lantern batteries in series should do the trick.)

    Theory # 2 is going to be more difficult to test. It could be that the driver module for this laser wants a specific voltage, and by feeding it too much voltage you are overheating the voltage regulator. A larger heat sink might help, but lowering the input voltage would work too. Then again, it may be that the head itself was mounted on a metal base that served as a heat sink. When you removed it from the projector, you lost the heat sink, and now the head may be overheating.

    But my money is on #1 being the problem. 9 volt batteries are just not designed to deliver high currents for a sustained period. They are capable of short bursts, but if you have a constant draw, the current falls off pretty fast. (But it will recover if you let the battery "rest" a bit.)

    Adam

  3. #3
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    Default

    The heatsink is still attached to the head itself. It doesn’t even get slightly hot.

    The laser doesn’t go off fully, it just pulsates / flash’s

    I think it is the current, though I cant get my multi meter to measure current! I think its broken.

    But I agree, I thought it was the current! I was hoping to fit it all into a small project box but I think that is wishful thinking.

    May have to have a separate box for the cells.

    On another thought, I expect it’s the ampage it wants rather than the voltage.

    So maybe it will run on a much lower voltage if the amps are there to for fill its needs?

    Those battries look more beefy. Gonna cost me around £25 for 8.

    How long do you think they would last? (PJ996) http://www.machinemart.co.uk/product...1&r=2100&g=114

    As PP3s are £4 for 12 hehe.

    Thanks,
    Regards,

    Aidan

  4. #4
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    Without knowing how much current your laser actually needs, it's hard to predict which battery will be the cheapest for you to use.

    I think the 6 volt lantern batteries will last quite a long while, even if you keep the laser on for several hours at a time. If you could get a set of rechargable lantern batteries, you'd be all set!

    "D" size batteries might also work, but they could be exhausted by a few hours of continuous use. Plus, you'd need like 25 of them, so that's not very practical. (And it won't be cheap either!)

    If you don't mind using it near your car, you could buy an AC power supply (a "wall wart" that runs off 110/220 volt power and gives you, say 40 volts of DC) and then buy a 12 volt to 110/220 volt inverter and plug that into your car... Or if you really want to have fun, you could build your own voltage doubling power supply from scratch and power it from your car. But all of these solutions are going to be more expensive and much more involved than just using the lantern batteries.

    As to the voltage requirement, didn't you already say that you tested the laser with a bench power supply, and it wouldn't lase at anything less than 38 volts? Assuming that your bench power supply was able to deliver an amp or more of current at that voltage, then you know that 38 volts is the minimum...

    If you multi-meter won't measure current, the internal fuse is probably blown. Check it. Also make sure you have the low current / high current switch set properly. Most meters have a low range of 0~200 milliamps and a high range of 0~10 amps. If you have the switch in the wrong position, or the test leads plugged into the wrong jack, you won't be able to read current.

    Adam

  5. #5
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    i think the best solution is to use a sealed lead acid battery (12v @ 6 or more Ah) and build a step-up with specialized integrated circuits like Maxim or National semiconductors.
    but this voltage (38v) is for the head on the picture or there is an electronic system before?
    because if there is a step down before you can make some modification on it to work at lower voltage.

  6. #6
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    Adam :

    Yes you must be right, i presume the bench PSU can provide whatever the laser needs thus 38v must be the smallest.

    If its going to last a few hours then £25 isnt that bad.

    And yes, the fuse has gone.

    Genesis :

    Im not realy that "advanced". hehe

    There is a board befor the head. Images here : http://photonlexicon.com/gallery/album46

    Thanks,
    Regards,

    Aidan

  7. #7
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    Adian;

    Once you replace that fuse, be sure to check the current draw of your laser when it's running off your bench power supply. That will give you a good idea of what you'll need in a portable power supply. Genesis has a good idea, but it will be even more involved than simply buying a "wall wart" transformer and an inverter for your car. Still, it is doable...

    It all depends on how portable you want this laser to be, and how long you need to be able to run it off batteries. If you are going to use it a lot out in the field, you may want to look into buying rechargable batteries.

    Adam

  8. #8
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    Its only really a bit of a challenge to get a laser powered by batteries so it can be used outside.

    Im not looking at operating it for hours on end, was just an intrusting project.

    Once I have the fuse at the weekend ill check the current draw and get back to you and then I can see what really is needed battery wise.

    Thanks for your help,
    Regards,

    Aidan

  9. #9
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    ok.
    the board on the picture is a switching PSU. the question now is if this PSU include the laser diode driver or not.
    the answer can be know with a multimeter and take a voltage measure between the laser wires in working condition (with PSU on)
    in mosts case this is only a step down with a 5v output. in this cas you can use your laser with a simple voltaga regulator like 7805 or simple switching regulator like lm2575.
    edit : i think the driver is on the board.
    can you take a macro shot of the top and bottom of the board? in good quality? because i need to know the parts of the chips.

  10. #10
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    Ahhh makes sense, i will take some high res images when im home.

    How easy is it to make \ get a voltage regulator?

    Thanks,
    Regards,

    Aidan

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