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The Magic Smoke got out. — Parallax Forums

The Magic Smoke got out.

Martin_HMartin_H Posts: 4,051
edited 2011-01-25 05:47 in General Discussion
I point to point wire most circuits (I know I need to make printed circuit boards). Not often, but every once in a while I'll solder a circuit and mess up. There's a short and I fry something, which is really annoying because it's pretty much instantaneous.

Well yesterday was one of those days and I smoked a $6 IC. I was pretty careful with the continuity tester looking for shorts, but I missed something. This explains why I procrastinate about turning on the power to a circuit. It's not as forgiving as software.

Comments

  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2011-01-22 17:12
    I have done before too But most of the time I fry one or more input pins on a chip
  • Zap-oZap-o Posts: 452
    edited 2011-01-22 18:06
    I can defiantly agree that is, a bit of a nail biter, when I fire up a new circuit. I have blew up my fair share of ICs and its almost always because of a stupid mistake. Now I am very careful, and yet still flinch on a new fire up. I guess its always going to be this way.
  • TtailspinTtailspin Posts: 1,326
    edited 2011-01-22 19:51
    All of this can be avoided of course, it's simple really, just stop making mistakes, and assemble everything perfectly..
    Barring that, try using this for Your new Motto...
    "I can build it, tear it apart, and then build it right, faster then most people can build it right the first time.":smile:
    It's got me where I am today, that and, "Buy high, Sell low.":thumb:


    seriously, I am sorry for Your loss,
    Just what exactly did Your $6 doller IC chip do?, It would be good to know, so as we could write the eulogy.
    And People won't feel awkward at the wake...
  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2011-01-23 05:58
    The last parts I fried did not make any smoke, I wish they had made some smoke so
    I could have noticed my mistake sooner. They were tiny dc-dc power converter blocks
    that took 28v in one side and put out 5v on the other at 35 amps. I had the input cable
    wired up wrong and every time I plugged in a new converter it killed it dead. They were
    very expensive and nobody was happy with me.
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-01-23 07:13
    I hate giving advice "AFTER" and I can only guess what kind of circuit it was, but for low power stuff:

    Use a variable current power supply. Since I've been using one, the smoke has stayed inside everything(?). If you have a micro and five LEDs, set the current to 50ma + 5*20ma..... throw the power and see if it works. If the current needle pegs and nothing happens, you have a problem. Variable power supplies are pretty expensive, but the analog meter ones can found fairly cheap ~$60 - $100. Sometimes you get lucky and find one less.

    I can't vouch for the brand, but it looks like a decent supply for $60. 0-18V and 0-3A..... Fine / Coarse knobs are really nice to have (this one doesn't have them)
    http://www.mpja.com/prodinfo.asp?number=9600+PS



    Ah, one example this didn't work on :)

    I wired an H-bridge with a second high power source..... melted my protoboard :(
  • Martin_HMartin_H Posts: 4,051
    edited 2011-01-23 07:26
    @Ttailspin, it was a Peter H. Anderson 117 serial LCD chip. I've used it many times in bread board circuits and was finally installing it in something permanent that was Erco inspired. I ordered two more so I could have one for that circuit and one to bread board again. I'm actually more bummed out about the time set back than the $6.

    @HollyMinkowski , the IC itself didn't smoke, but a resistor that was part of the short did. The IC then got 5V to a ground pin which seems to have toasted it.

    @Spiral_72, advice is alway welcome as there will be a next time.
  • ercoerco Posts: 20,260
    edited 2011-01-23 17:06
    I have most of a box of Duracell 9V batteries dated 2005. Still ~8.5 volts and useful for some Stamp work. Curiously, they "blow up" just sitting on my desk, not connected or short circuited or anything. One blows about every 2 weeks. They make a loud pop like a capgun and the cardboard/fiber bottom blows out. No fire, and not much danger, but a curious phenomenon. People come from around the corner asking "what was THAT"?
  • ctwardellctwardell Posts: 1,716
    edited 2011-01-23 17:13
    Erco,

    I have had similar experience with 9V alkaline batteries in the smoke alarms in my house.
    I thought maybe it was bad design, they are the ones that run from the mains and use the battery as a backup, I assumed there may have been some leakage back into the battery, but after hearing your story it may just be a failure mode for typical 9V alkalines...

    C.W.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-01-24 08:10
    I have a power supply just like the one Spiral_72 linked to (I think it's the exact same model). I agree it is very nice to limit the current before turning on a new circuit. There is not a display that shows the cut off current (it does display the current being used). You kind of have to get a feel for it. You could preset it by using a potentiometer and watching for the cut off as you decrease the resistance. (I'm going to have to start doing that myself.)

    I use my power supply everyday. I think it's a good one for the price (I've had it a couple of years). I still check the voltage with a multimeter if I'm working with something sensitive (the display can be a little bit off sometimes).

    Duane

    Edit: For the record I have a slightly different model (14600PS). It has a data sheet available. I think it's an older version of the one Spiral_72 linked to.
  • GadgetmanGadgetman Posts: 2,436
    edited 2011-01-24 09:29
    I remember when I was a kid and had one of those 50-in-1 electronics experimenter kits...

    After a while I got pretty decent at removing and soldering in new transistors on the small PCBs they were mounted on.
    And when I got into the habit of buying more than one transistor at a time, I also found that I saved quite a bit on bus fare every month...
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-01-24 09:56
    Duane Degn wrote: »
    I have a power supply just like the one Spiral_72 linked to (I think it's the exact same model). I agree it is very nice to limit the current before turning on a new circuit. There is not a display that shows the cut off current (it does display the current being used). You kind of have to get a feel for it. You could preset it by using a potentiometer and watching for the cut off as you decrease the resistance. (I'm going to have to start doing that myself.)

    I use my power supply everyday. I think it's a good one for the price (I've had it a couple of years). I still check the voltage with a multimeter if I'm working with something sensitive (the display can be a little bit off sometimes).

    Duane

    Edit: For the record I have a slightly different model (14600PS). It has a data sheet available. I think it's an older version of the one Spiral_72 linked to.


    Cool, so you like the supply then?? No problems?? I've been looking at this one for some time. The PS I have now is 0-30V and 0-200mA, so this 3A supply would be nice.

    You probably already know, but set your voltage on the supply, turn your current all the way OFF. Short the positive and negative of the supply together. Now turn your current knob up until it reads the your desired current..... then power your circuit off that. This gives you a controlled current limit for your circuit instead of guessing.

    Some power supplies are not constant current (there may be other terms) meaning that at the current limit you select, it'll shut off.... With this one, you select 750mA and it'll drive 750mA.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-01-24 10:41
    Spiral_72,

    No, I didn't know about shorting the positive and negative leads. I just tried it and it works great. It does seem strange to purposefully short something like that. Thanks for the tip, it should help me a lot.

    Yes, I like the supply. No problems so far. I've had it for about two years. As I said before, I use it just about every day. I usually use it set to around 7V and I rarely use over 1 Amp of current. I'm generally powering Propeller Proto Boards with it. I like being able to see how much current different modifications use.

    This one does seem to be constant current. I just set the current to 0.09A while shorted with a voltage setting of 7.1V. I then put the leads across a 51 ohm resistor and both the supply and my multi meter read 4.7V which is just right. This is cool. I can make much better use of this supply now.

    Let me know if you have any tests you'd like me to try out on this supply.

    Duane
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-01-24 12:37
    Yes actually, at the risk of hijacking the OP's thread:

    With your meter set to AC, what is the voltage measured across the supply at ~7V under maybe a 50 or 150mA load?

    How are the knobs? My supply the knobs are very sensitive and too easy to move. I can brush the knob and move 2V easily while 2 degrees of movement is 250mV. Petty I know, but it's annoying. Coarse and fine control knobs would be nice.
  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2011-01-24 13:38
    I've fried 2 Propeller chips in ~4 years, (one was $12 and one was $8) and I have to say, that for the first time when I only had 1, waiting for a new one to get here was worse then simply losing $12. Second one burst more recently and gave off the telltale "failure" smell of burning electronics that gave away the state of the micro. No "magic smoke", though. More like Spiral_72's signature. :-)
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-01-24 16:37
    Spiral_72,

    The resistance to turning of the knobs seems about right to me. I can lightly tap against the knob without it changing.

    But when the knobs do move the voltage jumps quickly. It takes a bit of fiddling to get the voltage set to 7.0. It would be nice to have fine control.

    I set the supply to 7.0V and connected to a 51 ohm (3W) resistor. The displayed current was 0.14A. My multimeter (it's a decent Fluke) read 0.7mV in AC voltage mode.

    Anything else?

    Duane
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-01-24 20:14
    Duane,

    No sir, that's all good news to me! Thank you very much. I expect the "fiddling" as most / all I've used were the same way. Maybe I could change it to a ten turn pot or something, but I'm sure it's fine. The ripple sure seems reasonable for what I want to do.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-01-24 20:34
    Spiral_72 wrote: »
    Maybe I could change it to a ten turn pot or something.

    I had a old bench supply I modded with somw 10T pots with the little dial , worked like a charm!!!
    but now I have a new NON SMPS digital readout one .BK 1635.
  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2011-01-25 05:47
    To me the best power supply are the ones that have course and fine adjustment on the voltage and current
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