Overpowered Laser Diode from eBay Laser Cutter?

Discussion in 'The Projects Forum' started by Shanjaq, Nov 30, 2015.

  1. Shanjaq

    Thread Starter Member

    Dec 6, 2010
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    I ordered a cheap laser cutter on ebay that said it uses a 405nm 500mW laser diode. It appears to cut through paper going around 100mm/Min. I bypassed the laser with an analogue current meter and measured 2A being sent to the laser!
    http://www.ebay.com/itm/500Mw-Deskt...ng-Logo-Picture-Marking-Printer-/252004276014

    I've looked up similar 405nm 500mW laser diodes sold separately through eBay, and they call for ~400mA typical. This either means that the diode was being overdriven by >4x, or that I was actually shipped a 2000mW laser diode??

    Curiously, when I hook the diode up to a FlexMod P3 set to deliver 400mA, it won't cut paper like it does with the original driver. So I guess my question would be, just how far above the "typical/recommended" current can these diodes be driven? Was I shipped a laser cutter that would have self-destructed after some hours/days of use?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    There is your proplem. To measure current, you put the ammeter in-series with the load; not in parallel with it.
    You effectively measured the short-circuit capacity of the power supply. Wonder you didn't blow it up???
     
  3. Shanjaq

    Thread Starter Member

    Dec 6, 2010
    12
    0
    Because the stock driver is a current-limiting laser driver? Maybe "bypass" wasn't the best word.. I put the current meter where the laser diode should be, while removing the laser diode from the picture. I basically wanted to test what current the laser driver was set to deliver, and it looks like it was delivering 2 amps! This seems like way too much for a 500mW laser diode as advertised on the assembled product.

    Does this clarify my original questions?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Measure the current with the laser in series with the meter and power supply.
    The current limit may just be just a resistor in series with the supply.
     
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  5. Papabravo

    Expert

    Feb 24, 2006
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    The ammeter is basically a dead short in either direction whereas the diode is not. The reading you got was totally bogus. In particular as the current through the diode increases, the forward voltage drop also increases up to the power handling capability of the diode, at which time the magic smoke that makes it work is released in a blinding PUFF! See the laser diode is part of the limiting mechanism which you completely defeated.
     
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  6. Shanjaq

    Thread Starter Member

    Dec 6, 2010
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    Ah, so you're describing this particular manufacturer's "quick-and-dirty" current-limiting setup that uses the intrinsic properties of the load as part of its control feedback, which explains why I can't just replace the diode with a current meter? Here's the driver that shipped with the cutter, it's labeled "d-sun" but doesn't have a trim pot, only fixed resistor:
    http://www.da-share.com/misc/dc-dc-converters/

    Hopefully this is not the case for the FlexMod P3 that I'm now using, which has its own self-contained current-sensing feedback which *should* pass the user-specified current across a wide range of load impedance & voltage drop:
    https://innolasers.com/shop/index.php?id_product=11&controller=product

    On a side note, everyone seems so delighted and anxious to see people's investments go boom.. EE forums have got to be the most sardonic communities on the interwebs :)
     
  7. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Have you considered asking your question on a philosophy forum? I doubt the responses would be any kinder. Though, perhaps, more enlightening.
     
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  8. crutschow

    Expert

    Mar 14, 2008
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    A true current source would deliver a fixed current independent of whether the laser diode load was in the circuit or it was a short.
    The measurement is bogus if the supply is not a true constant-current source (which I suspect is the case here).
     
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  9. Papabravo

    Expert

    Feb 24, 2006
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    I was suggesting that with the diode in the circuit, it might measure the forward voltage drop on the diode to limit the current (actually the power) to a safe level. With just the ammeter, such a circuit would never detect a measurable Vf and thus rely on the supply limit, which was certainly not what the TS/OP might have had in mind.
     
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  10. Shanjaq

    Thread Starter Member

    Dec 6, 2010
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    Ok! I've got the FlexMod P3 tuned so it's cutting paper again. It's looking like they definitely were overdriving the LED with the stock driver (~510mA) and it might not have lasted long.. Now to start engraving photos and exposing photoresist PCB's! Thanks all for the guidance in this precarious transition :)
     
  11. crutschow

    Expert

    Mar 14, 2008
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    That would not be a good way to regulate current since the diode forward drop varies from unit to unit and significantly with temperature.
     
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