Parallel wiring problem

Discussion in 'General Electronics Chat' started by chris311, Mar 15, 2009.

  1. chris311

    Thread Starter New Member

    Mar 15, 2009
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    I'm new to this forum and my knowledge of wiring circuits is pretty basic. I have wired together 80 laser diodes (not Led's). Each laser has the following specs: 3.2 voltage drop, draws 30ma, with an output power of 3.5-4.5 mw. I wired them in parallel and am using a 2400ma power supply that can be adjusted to both 3v and 3.5 volt. The wiring is also tiered meaning I connect in parallel the lasers in groups of 8 and connect an individual wire to each group, then connect those individuals wires to the power supply (still in parallel).

    I have been using the device about 3x week now for a month and recently after each use, a diode burns out, now totally 4 burned out diodes. I don't have to be a genius to realize something is wrong with my wiring scheme. I lowered the power supply to 3v after one burned out so I'm guessing that the modules are drawing vastly different amounts of amperage but they all appear the same brightness though.

    Should I incorporate resistors (even running at 3 volts)? Also, could I keep the groups of 8 together and use a resistor for each group (10 total resistors) or would that not fix the problem of varying amperage draws. Am I way off base in my wiring in general??? Any help is much appreciated.

    Also, I have wired Led's in the past with success and revisited some of those Led calculator websites for this but I notice that Led's dissipate far more mw (around 80mw) than these laser modules are supposed to (3.5-4.5mw). Does that play into my problem at all? Again, many thanks to any input from someone more knowledgeable than me.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    Do you have a link to the datasheet or specs of the diodes ?
    Do the diodes have to be current limited ?

    Greetings,
    Bertus
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. chris311

    Thread Starter New Member

    Mar 15, 2009
    8
    0
    Hi Bertus,

    I just emailed the manufacturer I bought them from asking for more specs because there website info is somewhat scant (not a good sign to begin with! yikes)

    Thanks for the great link beenthere, that's going to take some time to digest but looks very promising.

    More to come...

    Chris
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You get what you pay for.
    Cheap price, cheap junk.

    LEDs and laser diodes need regulated current, not a regulated voltage. They limit their own voltage. Your circuit must limit their current or they blow up.

    A cheap laser pointer uses the internal resistance of the button battery cells to limit the current. My son bought a cheap white LED small flashlight. It burned out its LED in two days. No current limiting resistor.
     
  6. chris311

    Thread Starter New Member

    Mar 15, 2009
    8
    0
    I got some more info via email from the owner of the company. He says the lasers have built-in automatic current control circuitry, operating range is 2-8VDC and he also said the lasers 'are positive ground when assembling a device which makes them sensitive'. I've never heard of positive ground, does that require a particular type of wiring or additional component? He also said he will warranty any defective units. He gave me his phone number to call which I am going to do (after St. Patty's of course). Would there be any further helpful info I could get from him besides just more detailed specs?

    Would there be any suggested testing I could do with a multimeter also while the device is running to measure current variances. I have limited experience with multimeters, can I just touch the probes to the respective + and - points while device is running to measure current or will that damage something? Thanks for putting up with my very limited knowledge!
     
  7. chris311

    Thread Starter New Member

    Mar 15, 2009
    8
    0
    I'm taking a new approach to my problem and am going to rewire the device into 11 strings wired in parallel with 7 lasers wired in series in each string. Since I've never actually done this with lasers, only LEDS, can anyone tell me, can I treat these like LEDS in figuring resistors and power supplies?

    I figure a 24 volt 1 amp power supply is good. Each laser has 3.2 forward voltage (7x3.2=22.4) and each laser draws 30ma (11x30=330ma) Based on LED resistor calculations I should use a 56ohm 1/4 watt resistor per string. Since these are not LEDs but lasers, can anyone verify my thoughts so far as to whether this wiring scheme is correct? Do lasers behave differently and this scheme might do harm them? One final thought, all long as the power supply meets these specs (24v 1amp) would it be appropriate to use. I've found one that looks like it charges something small like a phone but the specs match what I need. I was planning on stripping the wire and attaching postive and negative sides. I've already experienced too many diode burnouts so I'm looking for the best way to limit current and I figure this is it, even though the lasers supposedly have current limiting circuitry built in.

    Thanks for any input you have!

    Best,
    Chris
     
  8. chris311

    Thread Starter New Member

    Mar 15, 2009
    8
    0
    I decided to change the wiring to 11 strings wired in parallel of 7 lasers per string wired in series. If my thinking is right, a 24 volt 1 amp power supply would work well. Each laser has 3.2 forward voltage and draws 30ma (7x3.2=22.4vdc, 11x30=330ma). Based on LED resistor calculations, I would use a 56ohm 1/4 watt resistor per string.

    Here is my real question though: can I treat laser modules like LEDs in my figuring for resistors, power supplies and wiring schemes? I think I read they are more sensitive. I found a 24vdc 1 amp power supply (looks like it is designed to charge a phone, maybe a bit bigger) and was planning on stripping the wire and connecting to the + and -. Can someone please give me a vote of confidence or, if I'm wrong, prevent me from ruining the rest of my diodes. It's getting frustrating losing a diode every time I use the device. Thanks for your valued input

    Best,
    Chris
     
  9. chris311

    Thread Starter New Member

    Mar 15, 2009
    8
    0
    Can anyone tell me if this will work for lasers: I would like to rewire 11 strings in parallel with each string having 7 lasers wired in series. I have used this scheme when wiring LEDs and had success but I've heard how laser can be much more sensitive. Each laser has 3.2 forward voltage and draws 30ma so a 24 volt 1 amp power supply was what I was thinking would be appropriate. Also, b/c my reason for rewiring is to avoid current spikes, I was going to use a 56ohm 1/4 watt resistor for each string making 11 total.

    Is my thinking correct and could anyone confirm that wiring lasers in this way would be ok and not potentially do harm? As for the power supply, I've found a few with the right specs of 24 volt 1 amp and they look like they are for a cell phone or some small device, they plug straight into the wall. Would this be ok to use as long as the specs are correct? Could someone please advice, thank you for your valued input!

    Best,
    Chris
     
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