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Misc Electronic Questions

Discussion in 'General Electronics Chat' started by Billy Mayo, Apr 4, 2013.

  1. Billy Mayo

    Billy Mayo Member

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    The unit is a UPS system
    1.) The UPS unit , takes the AC 120 outlet and converts it to DC and then converts it back to 120 VAC
    2.) The inputs and outputs are isolated because of the higher frequency switcher circuit

    No sure how the high frequency switcher circuit works? do you? I can't even see the high frequency on my oscilloscope because the frequency are so high, it just looks very messy on my oscilloscope

    3.) There is a phase shift between the UPS outputs and the AC Mains input
    4.) The Phase Lock circuit , locks the UPS output AC 120 with the AC mains input 120 VAC

    why does the input and output of an UPS system need to be in phase?

    To try and display the UPS output at the same time as the AC mains input, to see the phase difference, requires more than two channels

    How do you set up the oscilloscope to measure the UPS output at the same time as the AC mains input?
     
  2. Billy Mayo

    Billy Mayo Member

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    5.) When you turn off the AC mains breaker on the UPS unit, it's in DC mode which is called " inverter mode"
    The inverter circuit converts DC into AC

    I'm not sure how the Invert circuit converts DC back to AC 120 Volts , but it uses a High frequency switcher circuit which is a PWM signal which controls IGBT driver chips & IGBT transistors

    When you turn off the AC mains breaker on the unit, It's in DC mode which is in the Inverter mode

    **The UPS input and UPS output is not "Phased locked" anymore, It's only Phase locked when the AC breaker is turn on apply AC mains 120 VAC from the wall outlet into the UPS unit.

    I'm not sure why the UPS unit's output needs to be In phase and Phased locked with the UPS input?
     
  3. Billy Mayo

    Billy Mayo Member

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    In Inverter Mode, It's just running on DC batteries

    So It's called Free Running because on the oscilloscope the output waveform is Free Running and the phase shift gets longer as the output waveform keeps running away from the input waveform on a 2 channel oscilloscope
     
  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    waveforms: http://www.minutemanups.com/support/pwr_un10.php

    So, your probably pure sine, My guess is your unit is a big Class D amplifier: http://www.maximintegrated.com/app-notes/index.mvp/id/3977

    Phase lock: Seemless transfer to battery power. See: http://www.electro-tech-online.com/custompdfs/2013/04/3_Phase_UPS_Manual_rev_6_6.pdf

    Can you post the model or a link to the instruction manual for your scope?
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    If your UPS output is totally isolated as you say, I think what you can do is find any transformer and isolate you mains signal. At that point, you would have an attenuated 120 V line signal in phase or out of phase. Now the UPS neutral can be tied to one end of the secondary.

    Now, I really have to ask where is ground and where is ground relative to the output N of the UPS? I would expect the ouput of the UPS N to be tied to ground through the building ground.

    Earlier, I did suggest using an isolation transformer on the equipment your servicing.
     
  7. kubeek

    kubeek Well-Known Member

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    Do you mean between phase and neutral? That would produce a nice 48W of heat in that resistor on a 220V system, so I would hazard a guess that the value would be much higher.
     
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  9. Billy Mayo

    Billy Mayo Member

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    I think you found the term , This sounds like it, it's call Ghost voltages

    What are ghost voltages and where are they encountered?
    Ghost voltages occur from having energized circuits and non-energized wiring located in close proximity to each other, such as in the same conduit or raceway. This condition forms a capacitor and allows capacitive coupling between the energized wiring and the adjacent unused wiring.
    When you place your multimeter leads between the open circuit and the neutral conductor, you effectively complete the circuit through the input of the multimeter. The capacitance between the connected, hot conductor and the floating conductor forms a voltage divider in conjunction with the multimeter input impedance. The multimeter then measures and displays the resulting voltage value.
    Most digital multimeters available today have an input impedance that's high enough to show the capacitively coupled voltage, giving a false impression of a live conductor. The meter is actually measuring voltage coupled into the disconnected conductor. However, these voltages, at times, can be 80-85 % of what the "hard" voltage should be. If not recognized as a ghost voltage, additional time, effort and money will be lost troubleshooting circuit problems.
    The most common places to encounter ghost voltages are blown fuses in distribution panels, unused cable runs or electrical wiring in existing conduit, open ground or neutral on a 120 V branch circuit or in card cages where 120 V control circuits are used to control assembly line or conveyor functions. Some amount of ghost voltage can be coupled from the hot side to the open side across the blown fuse. When facilities or buildings are built and wired, it's very common for electricians to pull extra wire through the conduit for future use. These wires are typically left unconnected until needed, but are subject to capacitive coupling. In the case of the control circuits, these circuits are typically located adjacent to unused control lines, thereby creating a potential for a ghost voltage measurement.
     
  10. Billy Mayo

    Billy Mayo Member

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    Here is pictures of one of the load box we use at work

    There is light bulbs, But I don't know what the other things are called? my manager calls them resistor cones

    Look at the two different shapes of the resistor cones , what are they called ?

    Resistor Cones#1.jpg
    Resistor Cones#2.jpg
    Resistor Cones#3.jpg
     
  11. kubeek

    kubeek Well-Known Member

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    You could probably call them heat elemnts if you wanted to, but also load resistors.
     
  12. Billy Mayo

    Billy Mayo Member

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    yes but load resistors look difference, these screw into a light bulb socket

    Are they called something else since they screw into a light bulb socket?
     
  13. Billy Mayo

    Billy Mayo Member

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    How do you put a PCB board circuit vertically to do through hole Desoldering?

    I'm trying to put my soldering iron on one side of the board and the other side of the board is my solder sucker ,

    What can I use to place the PCB board circuit vertically so i'm able to desolder throughhole components?
     
  14. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Search for "panavise PCB holder"
     
  15. Billy Mayo

    Billy Mayo Member

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    Ya I have one of those, It's 80 dollars , plus i had to be the extended 30" inches crossbar

    The problem is there is components on the edges of the PCB, and it's hard for it to grip the PCB because of the components

    Also another problem is the board length and width of the PCB is bigger than 30" inches

    Here is the picture of what I have :
    http://www.amazon.com/PanaVise-333-...372047&sr=8-4&keywords=panavise+circuit+board


    What else can I use to make the PCB board stand up vertically?

    I will ask my manager about your questions and see what he says about the neutral wire being grounded
     
  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    So, get creative. For a fixed size board, I'm sure you can make a wooden stand. You might loose something, but say you used steel spacers, so you could use holes already on the board. 30" IS WAY TOO BIG. I friend made a board that's about 18" x 14" and that's big. There is 3 to 5 screw holes to attach to on all sides.

    Standoffs with thumbscrews ought to work for you. Also make something that you can change the vertical or horizontal appendages using T-nuts and thumbscrews.
     
  17. Billy Mayo

    Billy Mayo Member

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    I have been hanging the PCB board half way off my bench and using the solder sucking underneath and the soldering iron on top so suck out through hole
     
  18. Billy Mayo

    Billy Mayo Member

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    The UPS unit's input and output is Isolated, that's why there is a potential difference

    Since there is a potential difference that the reason why they use a phase lock circuit to keep the phases of the input and output of the UPS IN phase so there is no voltage or potential difference

    When there is a phase difference between input and the output , there is a potential difference which can cause a short circuit when the UPS goes into "static bypass switching"

    The reason why they have a phase lock circuit is because of a static bypass switching circuit

    I'm not sure what is does or how it work as of yet

    Another reason why the have a phase lock circuit or to keep the input and output of the UPS in phase, is because if a load is a motor it needs to be in sync with the AC Main's input

    If the output of the UPS is free running and not phase locked, the motor ( a load ) will start to shutter and cause problems because it's not in sync with the AC main's

    When the output of the UPS is free running, there is a potential difference between the input and output because of the phase difference which will cause a short circuit when it goes into a static bypass switching
     
  19. Billy Mayo

    Billy Mayo Member

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    This is what my manager said to me , but I think he is wrong

    The Phase lock circuit can go up to 2.5 milliseconds which is good, anything after 2.5 milliseconds is considers bad

    The Phase of the input to the output phase can not be over 2.5 milliseconds

    120 AC Mains Input is at 60hz at 2.5 milliseconds = a phase of 54 degrees

    I think 54 degrees is a big time interval and distance from the input and output phase to be Good right?
     
  20. Billy Mayo

    Billy Mayo Member

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    3 Reasons why the phase lock circuit is used to lock the UPS input and output together

    1.) Synchronization (Phase Lock or Sync.): Generally refers to synchronizing the output of
    the Inverter to the Utility mains, in order to allow smooth transfer of load from mains to Inverter
    and vice versa.

    2.) Frequency stability: Deviation of output frequency from nominal value when the UPS is not
    synchronized to mains power (at mains outage). The stability is generally +/- 0.5%, with RC
    oscillator and +/- 0.05% with crystal oscillator

    3.) Parallel Operation: Operation of two or more systems with outputs connected to a common
    Load Buss for Redundancy or power enhancement purpose. To enable parallel operation the UPS
    systems should have equal output voltages, operate synchronously (same frequency and same
    phase), and have load-sharing capabilities.


    Linear Load: load comprised of linear (non switching) components, such as, resistors,
    capacitors, inductors, motors, lamps, transformers etc.

    Non-Linear Load: Load comprised of switching components, such as diodes, rectifiers,
    Thyristors, Switching or Pulse modulating systems or circuits. Non-linear loads generate
    current and voltage harmonics with integral multiple frequencies of fundamental source
    frequency.
     
  21. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    It looks like you have a PCB holder for the most part.

    ---

    I agree 100% with items #1, #2 and #3.

    You need to find yourself a transformer, any transformer with a 120 V primary. Let's assume that it's 24 VAC.

    I'm also assuming that you should get a waveform when the scope is connected to ground, or the output or the input. You may not have that when the UPS is operating stand-alone. Not sure.

    Connect the transformer to line in and take on of the secondaries and connect it to output N of the UPS.

    Connect your scope to the free secondary wire and trigger on that channel. (Usually Cha2). You should be able to trigger on zero. Don't use auto-trigger.

    Connect Channel 1 to the output L1 of the inverter.

    They will roughly be in phase or roughly 180 deg out of phase. If out of phase, reverse the primary or secondary windings - not both.

    I'd probably use CHOP mode vs ALT sweep if you have them.

    I think now, you should be able to see both waveforms.

    ---

    Meters don;t care about the phase. They know NOTHING about it. If it's the same meter, then integration times should be identical, but it still knows NOTHING about the phase. Waveform should be the reason for the discrepancy.
     

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