Help with repair of industrial multi voltage PSU?

Discussion in 'Technical Repair' started by viper1234, Jan 2, 2019.

  1. viper1234

    Thread Starter New Member

    Oct 9, 2018
    4
    1
    Just going to see who might be lurking here or possibly a contact to someone that could offer a little advice on test and repair of this PSU. Long story short, we are trying to repair an industrial VFD that 'did' power up except when estop was cleared, which should charge the DC buss, it failed to close a contactor to charge the buss. While messing with the drive a while, the PSU decided to take a nap. It was previously tested and all voltages were present, stable, and clean. Then they all went south for a while and the control board display went blank.

    The PSU is provided unregulated DC 280-350VDC from another board and it kicks out regulated 5V/15V/24V. I have it on the bench now and it is providing stable voltage but I need to test it further as I suspect it is not providing the amperage it should. Schematics are NOT available and the OEM won't even tell me how much power it should provide so I am left to figure that out.
     
  2. Reloadron

    Distinguished Member

    Jan 15, 2015
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    Not knowing how much power it should supply makes testing difficult. My best guess is find some resistive loads and see if it delivers. For example 5 Volt buss 1 Amp load would be a 5 Ohm resistor of about 10 watts minimum. 0.5 Amp would be a 10 Ohm load. I would justtry some light loads on the 5V/15V/24V buss lines and see how it does.

    Ron
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    5,878
    Generally the 24vdc on a VFD is for the PLC unit (I/O) so I would imagine you could concentrate on the 5v for the logic first, this normally would be a fixed load without any external interference.
    Even the 24v I/O is generally has isolated outputs via opto isolators.
    I much prefer the types that have transformer for low voltage rather than the SMPS variety.
    Max.
     
    atferrari likes this.
  4. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,543
    1,198
    The power MOSFET should have a current sensing source resistor - usually reliable unless the MOSFET punches through, but try a replacement if you run out of other ideas.

    Any smarts are probably in the thick film module - always worth a nosey for dry joints around it.

    The electrolytics don't look stressed out - but if it powers up, load it and see if any run hot.

    High value resistors have a habit of going even higher - but they usually cause non starting or too much starting all at once.
     
  5. viper1234

    Thread Starter New Member

    Oct 9, 2018
    4
    1
    Thanks for the replies guys and figured I would update. I hate when people just vanish after helping them. Anywho, I determined the 5V was the voltage with the feedback loop for the driver. The 15v and 24v are just on linear regs and don't have much current. Actually nothing does. 24v is 500mA. I replaced the two small caps near the driver hybrid only because I removed them from the board for testing and had new ones. I found a couple solder joints that had started to crack so I touched those up and wouldn't you know it, the thing runs in the VFD and the VFD has not missed a beat yet. If it does, I guess I have some records on it now.

    And I learned a bit more on SMPS. I am really surprised they went through all that for such little power! I might have kicked that voltage down to close with a transformer, rectified, filtered, regulators, etc. Who knows but Yaskawas are generally reliable so.....
     
    MaxHeadRoom likes this.
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
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    Some do kick the voltage down first - the Optimate lead acid maintenance chargers have a regular transformer, somewhere around 40V secondary AFAIK. A very early thorn Consumer Electronics CTV had a crude, inefficient and unreliable SMPSU which probably had about 60V input. Samsung did it on various VGA mono displays.
     
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