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DC Polarity reversed. PDB fried? — Parallax Forums

DC Polarity reversed. PDB fried?

mapimapi Posts: 5
edited 2011-04-04 18:34 in General Discussion
Hi,

yesterday i unpacked my Basic Stamp experiment Kit and was eager to do some programming. Unfortunately the power converter was also a kit, and i assembled it wrong...

After powering on the PDB and wondering why my PC did not see the basic stamp suddenly smoke was coming from the board!! Arrgh!

This morning it occurred to me that the power might be reversed, and yes, it was. After reassembling the power converter the right way and turning on the PDB it showed the blue "i am alive!" light.

Now i wonder what is broken on the board, the smoke came from one of the orange "thingies" (i'm just a software guy...) next to the power input. Does it need fixing? When will I get into trouble?

thanks.

Comments

  • LeonLeon Posts: 7,620
    edited 2011-04-04 02:57
    It's probably damaged beyond repair. You could try contacting Parallax about it.
  • mapimapi Posts: 5
    edited 2011-04-04 03:41
    i am continuing with the experiments now, and experiment #1: Flash an Led is working.

    So i guess/hope nothing really important broke. :smile:

    Would be nice if someone knows for sure though.. I have already send an email to the parallax support.

    thanks.
  • Zap-oZap-o Posts: 452
    edited 2011-04-04 06:10
    Electrolytic capacitors are great for blowing smoke in the air when they are hooked up backwards.

    You got lucky and it sounds like the caps only need replacing.

    Your unit may still work but I would replace the caps and possibly the LDO.
  • kwinnkwinn Posts: 8,697
    edited 2011-04-04 06:34
    As Zap-o said, you got lucky. I would replace the polarized capacitors on the power supply as well as the regulators. For sure something was damaged if there was smoke, and sooner or later it will die, and might do a lot more damage when it does. Question is......Do you feel lucky?
  • LeonLeon Posts: 7,620
    edited 2011-04-04 07:21
    I would have thought that it would have a protective diode. I'd include one on anything like that which was aimed at beginners.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-04-04 07:31
    I agree Leon .


    * note to self . add one to my PDB*

    Peter
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-04-04 07:58
    If it was mustard colored then it was probably a Tantalum cap that went up in smoke. They hate reverse polarity! If it took the hit and protected the rest of the part's you're lucky.

    If you have surface mount soldering experience (or want to try) then you can replace that part. It is there to help filter the power.

    Robert
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-04-04 08:05
    Leon wrote: »
    I would have thought that it would have a protective diode. I'd include one on anything like that which was aimed at beginners.

    Or, better than that add a full bridge rectifier so it is polarity inpendant! I've done that for a piece of test gear that is meant to be powered by an external battery. Since the user connects the leads I wanted to be sure it worked no matter which way they connected them.....

    Robert
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-04-04 08:15
    Robot ..

    good and a bad Idea AS it can be a huge V drop isue

    1.4 V total . so if your device Needs 12V from a 12V car batt you may have issues after losses in the diode stack .

    but for idiot proofness its great !

    In my stuff I use a parllal diode and aPTC ot fuse or breaker so it blocks the wrong DC . no loss .
    but it needs a 10A diode that will take the surge of a batt hooked up backwards long enough to pop the fuse ( half a second )

    If PTC or breaker is used I add a LED accross it so it wil light If its poped .

    Peter
  • mapimapi Posts: 5
    edited 2011-04-04 08:28
    RobotWorkshop wrote: »
    If it was mustard colored then it was probably a Tantalum cap that went up in smoke. They hate reverse polarity! If it took the hit and protected the rest of the part's you're lucky.

    If you have surface mount soldering experience (or want to try) then you can replace that part. It is there to help filter the power.

    Robert

    Yes, there are 2 mustard colored parts there.. one of them is now a bit darker though.

    I never did serious soldering, but i know some collegues who can, so i'll ask them for support.

    Thanks for your reply.
  • mapimapi Posts: 5
    edited 2011-04-04 08:36
    Leon wrote: »
    I would have thought that it would have a protective diode. I'd include one on anything like that which was aimed at beginners.

    The "Professional Development Board" is obviously not aimed at beginners. ;-) The main problem was the configurable power converter..

    Well, lesson learned, measure before connecting...
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-04-04 09:02
    Peter KG6LSE wrote: »
    Robot ..

    good and a bad Idea AS it can be a huge V drop isue

    1.4 V total . so if your device Needs 12V from a 12V car batt you may have issues after losses in the diode stack .

    but for idiot proofness its great !

    Peter

    You are absolutely correct about the voltage drop and that needs to be a consideration before going that route. I'm aware of the voltage drop but as long as you account for that then it can be an excellent solution! If the voltage drop is an issue then other methods like the PTC, singe diode, of fuse may be a better option. I like that idea of adding an LED/lamp across the fuse/breaker that will light if blown.

    Whatever route you take depends on the device you want to protect, the input voltage, and the voltage your circuit expects to power it. I don't add that often but for power connections used by others where it may easily be connected backwards it is cheap insurance if the voltage drop isn't a problem.

    In my case the tester was meant to be connected to a 12V battery but the motors that were being test didn't care about the voltage drop across the two diodes. I think the 7805 regulator onboard ran a bit cooler with the drop in voltage. For me there was no downside to the voltage drop and the huge benefit was that the device would work whatever polarity you connected the leads. Also if I want to use a wall wart I the polarity on the plug didn't matter either. Before I did the mod to add the bridge on the input I had two testers sent in because of fried 7805 regulators (from reverse polarity) After the mod was made I haven't had a bad one yet!

    I suppose if you wanted to add a couple extra caps on the output you could even get by with using an AC adapter too. This can make you device very flexible in case the power adapter is misplaced and people start trying spares they may already have on hand. If I was designing something for use in a classroom then I would add this to the design to help protect it from the students.

    Robert
  • ctwardellctwardell Posts: 1,716
    edited 2011-04-04 11:07
    RobotWorkshop wrote: »
    If I was designing something for use in a classroom then I would add this to the design to help protect it from the students.

    In the classroom case the parallel diode with fuse version would seem best to me, that way they will at least see some consequence to not paying attention and being careful. Having no consequence to incorrect hookup could lead to expensive mistake in the less forgiving "real" world.

    C.W.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2011-04-04 11:47
    ctwardell wrote: »
    In the classroom case the parallel diode with fuse version would seem best to me, that way they will at least see some consequence to not paying attention and being careful. Having no consequence to incorrect hookup could lead to expensive mistake in the less forgiving "real" world.

    C.W.

    That is a good point. However, building the power adapter may not be part of the course and there will probably be lots of other opportunities for them to learn. They could just as easily use this as an example on how something can be designed to be more resiliant and keep on working with a different adapter vs a board with no protection or one-way protection. Also thinking ahead for when they lose a power adapter (which they probably will) and someone finds out that the polarity on the connector is reversed. It just works.

    I think it is probably more important on some of test gear I've made. You just want it to work so you can use it to help track down issues with something else. As long as I have an adapter with the appropriate voltage/current rating I perfer it be able to accept either polarity so it just works. I've only found a few places where I've really felt it was appropriate to use and will definitely keep it in mind and use it again for similar projects. Saves time on support..................

    Robert
  • mapimapi Posts: 5
    edited 2011-04-04 13:22
    hi,

    i've contacted parallax support and they said i could just use the board as it is now, nothing else should be damaged.

    thanks for your replies. (and i'll be more careful from now on, ofcourse.)
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-04-04 18:34
    Requiem for An Orange "Thingie".

    Orangimandias
    I might a traveller from an antique land who said,
    "Two vast and trunkless orange thingies stand in the desert."
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