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Replacing a faulty SMPS

Discussion in 'Troubleshooting and Repair' started by HellasTechn, Feb 13, 2016.

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  1. Alec_t

    Alec_t

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    It's because voltage is always a potential difference. In this case Vcc is tied to the mains line, but the GND point is floating 5V (or whatever) below Vcc.
     
  2. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Got it !
    You reset my head from thinking that common is 0V. :p
     
  3. Alec_t

    Alec_t

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    If it were me I'd probably buy a couple of generic off-the-shelf SMPS supplies (one +5V, one +12V) and wire them like this :-
    SMPSreplacement.PNG
     
  4. HellasTechn

    HellasTechn

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    I already have the transformers and the regulators so why order smps and wait a month to get them.

    I have no idea how this circuit works. I have never seen a power supply using mains voltage at the output as reverence voltage.

    Are you sure it is safe to wire it like that ?
    Practically there is no difference as far as voltages are concerned if i use your circuit "with smps" or mine "with linear transformers and regulators" right ?
     
  5. Alec_t

    Alec_t

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    The linear regs should do the job. Good luck.
     
  6. HellasTechn

    HellasTechn

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    I am still a little afraid of what will happen when i i connect the +5v rail to the mains line !!!
    It may just be due to the fact that i am too ignorant to understand how it works.
     
  7. Alec_t

    Alec_t

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    When it comes to mounting your components in the machine, remember that ALL parts of your added circuit should be treated as HOT/LIVE and housed in an insulated, ventilated enclosure accordingly.
     
  8. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    .



    Sir Constantine . . . . . . . .


    If this was my problem to solve my primary researching would be to initially see what potential power demands are being made on those two supplys.
    To get a stable 12 VDC I would be using 8 C or D cells for that supply source, which would be creating a completly " floating " 12 VDC supply.

    For the" floating " 5VDC supply, use 4 separate cells with an end connected . . . .2 series connected 1n400X series diodes for corrrecting for that excess
    voltage , by voltage loss thru their junctions.
    Initially read the 5V supplys resultant end voltage with the machine powered up and if too low, eliminate that one extra diode.
    The reason being, that this would be a bit "iffy" in not initially knowing the current that the diodes will be passing thru them.
    (I'm not expecting much of a current need on that supply.)

    The 12 VDC supply will typically be needing one relay and potentially another relay in use, along with an occassional use of yet a third relay . . .like the initial
    water fill solenoids.

    Once you know the typical power neeed of those two supplies, then there is the option of your drawn circuitry, or use already UL/CSA approved wall wart types of supplies
    of twice or three times the rated power usage for some cooling threshold safety.
    The manufactured units will be providing a secondary supply voltage , completely isolated from the Mains hot line.

    Observations:

    Omron G2RL-1A-E-HA
    12VDC @ 33 ma coil consumption

    Omron G5LB-1-HA
    12VDC @ 33 ma coil consumption
    (Looks like this relay is obsolete and they are recommending
    using a G5LA or G5LE series, with its heftier contacts)

    The BLUE relay is the heftiest of the relays, and is probably the
    motor switching function.
    However . . . . it is assuredly being a Solid State Relay, with that
    mere 10 ma at 5 V spec for its power.

    Overall now . . . in looking at the magnetic core footprint of the original
    SMPS transformer and the combined relay coil utilization's.
    There may be only the need of 1/4 amp from those supplies.

    Do you need that machines main schematic ?

    ( You had better hurry in getting that machine going again, as Mamma's getting tired of hand washing your clothes.)

    Aside:
    Sir Alec t . . .in your Post #23 . . I am seeing need of the labeling of the LINE and NEUTRAL being switched.
    As it is drawn that then puts the sub power supplies at 220 VAC potential.

    Referencing after changing that, then has the neutral at ground potential, with the secondary supplies having reference to that same ground neutral also.
    So nothing is at an AC shock hazard as regarded to touching the secondary power supplies.
    A ground is a ground is a ground on the AC line as it is also a ground being common on the small power supplies.

    Now the only thing left weird, is the person who drew /designed this schematic/circuitry and his assignment of - 5 and - 12 to the supplies . . . . . . .he is being a drummer . . .with his own beat.


    73's de Edd.



    .
     
    Last edited: Feb 17, 2016
  9. HellasTechn

    HellasTechn

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    That is for sure !!! never play with things like that.
    Sir 73's de Edd.

    Please forgive me but i am having trouble understanding what you say in the above post.
    Could you please draw a schematic of what you think would be safe to work ?

    I will make a schematic as i think it might work and you can make comments on that also !

    Thank you so much for detailed answer.
     
  10. Alec_t

    Alec_t

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    That's precisely what the original Whirlpool circuit does, and why the TS is concerned ;).
     
  11. HellasTechn

    HellasTechn

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    Apr 14, 2013
    So do you think that my design in post #1 picture #1 is correct and will work if i connect :
    +5v to VCC(tp146), transformets middle rail to GND(tp31) and -12 to -12(tp48) ?
     
  12. HellasTechn

    HellasTechn

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    judging by the size of the original transformer 1/4 watt is about right, maybe even a little more.

    Yes please the full schematic might help more.

    Mamma needs it up and running soon, dont want to keep her waiting !
     
    Last edited: Feb 17, 2016
  13. Alec_t

    Alec_t

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    Jul 7, 2015
    Well, you won't need four regulators: two will suffice. I think you could go with the +5 and the -12 wired as you're suggesting. Alternatively, if you choose to go with the +12 and +5 you should be ok if they're wired similarly to the diagram in post #23. Fingers crossed!
     
  14. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I shall run a test by friday.
    May god be with us !
     
  15. HellasTechn

    HellasTechn

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    Apr 14, 2013
    First test Failed.

    When i pluged the power cord i noticed the led's on the board where not steady lit but kind of blinking. I started the wash cycle and everything was ok untill the motor begun to run. It made a weird noise and smoke came out of the board.
    I removed power and checked. the weird noise was indeed from the motor and two relays on the board where burned.

    I suspect that the psu didn't have enough power to drive the circuit and the relays and that made them click on and off fast and that is what caused the burn.
     
    Last edited: Feb 18, 2016
  16. Alec_t

    Alec_t

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    Jul 7, 2015
    Hmmm, that's a shame :(. Presumably it was/is something taking excessive current that caused the original SMPS to fail. When you say "two relays on the board where burned" do you know if the relay coils are still intact?
     
  17. HellasTechn

    HellasTechn

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    One of the relays still works but the other is dead. Both relay coils read about 500 Ohm resistance meaning the coils are still good.

    The relays where clicking on and off fast, that is why the motor was making this weird noise, it was starting and stoping at very fast rate. That could explain the motor draining too much current and killing the relays, even arcing within the relays contacts due to fast switching rate could have done the damage.

    I know for sure that with the original psu on even after it got damaged the motor worked smoothly.
     
  18. 73's de Edd

    73's de Edd

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    Sir Constantine . . . . . . . .


    Test your power supplies with load resistors to see how much current they can put out.
    Monitor the 12 and 5V supplies to see if that fluctuation that was showing , is also being confirmed on the meter monitoring.

    Herewith is a Magged up . . to help on its clarity . . . . and marked up schema:.

    [​IMG]



    73's de Edd
     
  19. HellasTechn

    HellasTechn

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    Apr 14, 2013
    Finally i dropped the project. I used SMPS and board came live but never got to execute a program correctly so there must be a problem with microcontroller also.
     
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