Anyone with experience fixing lab type psu

Discussion in 'Prius PHEV Plug-In Modifications' started by glyndwr, Jan 7, 2014.

  1. glyndwr

    glyndwr Member

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    not sure if this is in the right section, but here goes,

    I got a Tenma lab type switch mode power supply that i was using to manually balance my 76 cell lithium battery pack. The power supply is a tenma 72-2085, qnd its a 0-30v 0-5a power supply.

    It was working beutifully until i had a little accident with it.

    I have made a distibution board that has got 76 banana plug sockets fitted to it, i did this to make test access to each battery much easier, and not have to get any where near the 250v dc battery pack whilst doing any manual balancing, as i havent fitted a BMS, i use cell loggers and do cell monitoring instead.

    Anyhow, after i was topping up the charge in 1 cell, when i removed one of the banana plug leads from the socket whilst the other banan plug lead was still inserted in that cell socket, it unbeleivable rested and touched another cell banana socket over sending over 40 volts DC back into the power supply.
    Now, the lab supply powers up still works, but only on max voltage output, which is 48v, there is no adjustment possible.

    I have changed the motorolla voltage regulators shown in the pics 2n3055, there are 4 of these, but it made no difference.

    I have taken pics of the unit and the pcb, with the hope that someone may have knowledge on what may have to be changed to get it working properly again. I can solder components into the pcb ok, and can use a meter ok to check individual components if necessary.

    Any help is greatly appreciated.

    Many thanks, Anthony.
     

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  2. mrbigh

    mrbigh Prius Absolutum Dominium

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    the 2n3055 are the output power transistors, the voltage regulator circuit is a dedicated one before the output stage.
    I will look for an schematic, I remember seeing a similar one at work.
    Surely, there is a shorted diode or burnt resistor in withing the circuit, I will update tomorrow.
     
  3. glyndwr

    glyndwr Member

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    Thanks mrbigh,

    The components on the pcb look fine, no obvious burns or blown components,

    On the small pcb that holds the output banana sockets, there is a blown capacitor on that, there's not much else on that pcb, there is a diode on it I think, I'll check later.

    Many thanks for your help, it's much appreciated.

    Anthony
     
  4. glyndwr

    glyndwr Member

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    Hi mrbigh,

    Any luck sourcing a circuit diagram for the psu unit?

    I have eyeballed the pcb, all the components look fine, no obvious burnt or blown components.

    Would love to get it working again.

    Many thanks, anthony.
     
  5. mrbigh

    mrbigh Prius Absolutum Dominium

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    Word I received is that it was discarded a while ago due to unreliability.
    I asked the test equipment calibration dept if they have/kept an schematic for it; they are still looking ................not to promissory.
     
  6. glyndwr

    glyndwr Member

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    Thanks very much for trying your best, hopefully a diagram will appear from somewhere.

    If I was to take a close up pic of sections of the pcb, would you be able to advice any part I could test.
    I can a search u tube for ways to test ic and voltage regulators with a meter. At least I may be able to find something by way of elimination then.

    Many thanks. Anthony.
     
  7. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    Just a quick guess, if the output voltage is at maximum, then the feedback node is probably at a minimum. I.E. the feedback pin is saying "you have not raised the output voltage high enough to equal your reference voltage for regulation, therefore MORE POWER!!!!".

    You replaced the output power stage, but I think the problem is that you blew the controller. Generally the feedback pins are just resistor dividers off of the output. So at 30v ABS MAX output, the FB pin is probably close to ABS MAX as well. By taking it to 40v you probably overvoltaged the FB.
    The resistors themselves should have survived. Can you ohm out the feedback pin to ground? My guess is that it is shorted. Remove the IC, measure again, and my guess would be that it is OK. Unless there is a small cap on the FB bottom node resistor to keep the output more stable which was overvoltaged.
     
  8. glyndwr

    glyndwr Member

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    Thanks for that description.

    So basically, if I test the ohms on the voltage output pins, if they are shorts, trace back in the output lines for the 1st ic in the line and remove it and rest it for open circuit?

    I am not very good at electronics, I can trace a circuit, remove and test components by watching you tube video of testing components, I may need alittle more walking though it though.

    Any help greatly appreciated.

    Many thanks, anthony.
     
  9. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    There will more than likely be a resistor between the regulated voltage output and the feedback node. And then from the feedback node to ground, there will probably be another resistor and maybe a small capacitor. Or there can be feedback circuits that only require 1 resistor straight to the IC, or some have internal top side R's and you have just 1 resistor from the IC to ground outside, maybe with a parallel C as well.

    But I would trace back to the IC. Get that part number. Find the datasheet, see if you can find the feedback node. That's generally plan A.
     
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