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  1. #31
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    So did you get it working?

  2. #32
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    Jul 2010
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    Melbourne
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    Sorry for not updates. Haven't had a great deal of time.

    No not working yet.
    Been testing things when I get the chance.
    I bypassed the PCB(mainly so I didn't have to worry about blowing it up) and fitted a press button that actives the contactor.
    The contactor happily switches a 2400W resistive load with the same V drop on both sides of the contactor(so its in the line).
    With all the tap selection wiring disconnected at the transformer the contactor works fine(so no short in the switch/wiring)
    With everything disconnected from the secondary the fault is still there.
    Primary-secondary isolation seem fine.

    I need to drag the welder up to the house, which I should have done a week ago but I am not looking forward to it.
    Might be the primary winding(of course there is a chance its not)

  3. #33
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    Sep 2012
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    North Yorkshire UK
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    Hi Stuart,

    Its starting to look like the transformer has an earth leakage !

    Disconnect the transformer completely and use a 500 volt megger to check for earth (frame) to windings for leakage. Or less likely, winding to winding leakage.
    Best Regards:
    Baron J.

  4. #34
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    Quote Originally Posted by BaronJ View Post
    Its starting to look like the transformer has an earth leakage !
    Nope

    Quote Originally Posted by BaronJ View Post
    Disconnect the transformer completely and use a 500 volt megger to check for earth (frame) to windings for leakage. Or less likely, winding to winding leakage.
    Seems I left this out of my past post. I've megger tested primary to secondary and primary to earth and my megger tester says its great.... off scale great.... which does make me wonder that either my megger tester or myself isn't working correctly I plan to put it on a motor and see if it gives numbers that make sense.
    Pretty sure is isn't earth leakage, as it tripped a 10amp overload during testing.

    Tried measuring Ohms and Henrys between taps but I'm not sure I came up with any useful figures.

  5. #35
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    Sep 2012
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    North Yorkshire UK
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    Hi Stuart,

    If it is tripping a ten amp breaker without any load on the secondary of the transformer, I can only think of two reasons why ignoring earth leakages. One is shorted windings between turns, the other is the magnetising current at switch on. If the core has some residual magnetism, it shouldn't, but you have been using an Ohmmeter to test its winding resistance, so there may have been some magnetisation of the core. Its possible for the peak current draw on switch on to be very high. But this should disappear within a few mains cycles, so when switching it back on it would have cleared it. Its also possible to temporarily magnetise the core when the power is disconnected at a mains current peak, but this is quite rare, but does happen and can be the cause of very intermittent tripping.

    002a.jpg
    Disconnect everything inside the red circles. This will isolate the control board completely. I'm assuming that the diodes and large capacitor have been disconnected already. You will have to operate the contactor with a lolly stick, because there will not be any power to operate it, the fan or small transformer.

    Does it still trip the breaker ?
    Best Regards:
    Baron J.

  6. #36
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    Quote Originally Posted by BaronJ View Post
    Disconnect everything inside the red circles. This will isolate the control board completely. I'm assuming that the diodes and large capacitor have been disconnected already. You will have to operate the contactor with a lolly stick, because there will not be any power to operate it, the fan or small transformer.

    Does it still trip the breaker ?
    I found an easier way. Just pull the DB9 connector, which leaves me the pilot light(if it dims I know there is a problem, so I don't have to walk 100m to turn the breaker back on)

    I have tested the transformer with everything disconnected(including the inductor) and it still faults.
    The final test was going to be 240V direct to the transformer through a spare sub panel I have with a 16amp breaker. Just to remove everything(even the parts that seem to have tested ok)

  7. #37
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    Well that's sad

    The Inductor and 240V wiring have been disconnected since that picture was taken.

    If you number the terminals from the left 1 to 5.

    Terminals 1 to 4 match settings 1 to 4.
    5 being neutral.

    My LCR meter gives the following

    1-5= 1.0ohm 0.16mH
    2-5= 0.9ohm 0.10mH
    3-5= 0.7ohm 0.06mH
    4-5= 0.7ohm 0.07mH


    1-2= 0.4ohm 0.01mH
    2-3= 0.5ohm 0.01mH
    3-4= 0.4ohm 0.01mH

    The only reading I can get on my megger other than off scale high is between the the two secondary windings which is above 1000MOhm(I didn't bother to let it stabilise)

    240V wired straight to terminals 1 - 5 through a 10amp breaker and the breaker trips as you try and close it.

    I don't think I have space at the minute to try a rewind. Sadly it might just have to go into a corner until I do.
    Attached Images Attached Images

  8. #38
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    Hi Stuart,

    Quote Originally Posted by Stustoys View Post
    Well that's sad

    The Inductor and 240V wiring have been disconnected since that picture was taken.

    If you number the terminals from the left 1 to 5.

    Terminals 1 to 4 match settings 1 to 4.
    5 being neutral.

    My LCR meter gives the following

    1-5= 1.0ohm 0.16mH
    2-5= 0.9ohm 0.10mH
    3-5= 0.7ohm 0.06mH
    4-5= 0.7ohm 0.07mH


    1-2= 0.4ohm 0.01mH
    2-3= 0.5ohm 0.01mH
    3-4= 0.4ohm 0.01mH

    The only reading I can get on my megger other than off scale high is between the the two secondary windings which is above 1000MOhm(I didn't bother to let it stabilise)

    240V wired straight to terminals 1 - 5 through a 10amp breaker and the breaker trips as you try and close it.

    I don't think I have space at the minute to try a rewind. Sadly it might just have to go into a corner until I do.
    The first set of readings between 3-5 and 4-5 suggest shorted windings ! I would have expected 0.4 or 0.5 ohms there particularly looking at the inductance value going higher. Any damage around the transformer tap connections where the wires come out of the windings ?

    I hadn't realised that there was a D9 plug and socket to disconnect the control board ! Good idea that.

    I've seen welder transformers that buzzed quite badly and have caused winding damage, nearly always shorted turns. Trouble is that they are rarely worth attempting a repair, because the wire is often lacquer coated aluminium and isn't very durable. The older ones are usually copper wire wound and the scrap boys love those.
    Best Regards:
    Baron J.

  9. #39
    Join Date
    Oct 2015
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    melbourne
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    Quote Originally Posted by Stustoys View Post

    1-5= 1.0ohm 0.16mH
    2-5= 0.9ohm 0.10mH
    3-5= 0.7ohm 0.06mH
    4-5= 0.7ohm 0.07mH


    1-2= 0.4ohm 0.01mH
    2-3= 0.5ohm 0.01mH
    3-4= 0.4ohm 0.01mH


    .

    Something odd with those readings.. If 1-2 is 0.4
    Then 1-5 should be 0.4 more than 2-5, not 0.1 as the second set show.

    Its hard to measure low resistance. Test Leads and clips can have a disproportionate effect. If I remember, 4 wire test sets were preferred for this circumstance.

    Basically, one pair supplied a fixed current, while the other pair measure the voltage across the target. That pretty much eliminates the effect of the cables.
    Could be worth hacking something up if you have 2 meters available.

    -Russ

  10. #40
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    Hi Baron,

    No sign of damage, it all looks good and smells good. But I guess having another look wont hurt.

    This wasn't a "bad buzzer" by any means, but bad enough it seems. I assume you mean Alum secondary? I'm pretty certain its copper. The interesting winding lay out might make it possible to reuse the secondary. All of the primary appears to be in the top half of the bobbin, most of the secondary appears to be in the bottom half with just a single layer of secondary over the the primary windings. I'm sure there is a good reason for doing that. Fancy a guess at how many primary turns?

  11. #41
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    Hi Russ,
    Yes the readings are so low the LCR meter might be struggling.
    My multi meters did worse.(I should have mentioned that)

    I have two meters, are you saying I can use one as a source?

    Quote Originally Posted by russ57 View Post
    Something odd with those readings.. If 1-2 is 0.4
    Then 1-5 should be 0.4 more than 2-5, not 0.1 as the second set show.

    Its hard to measure low resistance. Test Leads and clips can have a disproportionate effect. If I remember, 4 wire test sets were preferred for this circumstance.

    Basically, one pair supplied a fixed current, while the other pair measure the voltage across the target. That pretty much eliminates the effect of the cables.
    Could be worth hacking something up if you have 2 meters available.

    -Russ

  12. #42
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    Sep 2012
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    Hi Stuart, Russ, Guys,

    Quote Originally Posted by Stustoys View Post
    Hi Baron,

    No sign of damage, it all looks good and smells good. But I guess having another look wont hurt.

    This wasn't a "bad buzzer" by any means, but bad enough it seems. I assume you mean Alum secondary? I'm pretty certain its copper. The interesting winding lay out might make it possible to reuse the secondary. All of the primary appears to be in the top half of the bobbin, most of the secondary appears to be in the bottom half with just a single layer of secondary over the the primary windings. I'm sure there is a good reason for doing that. Fancy a guess at how many primary turns?
    No ! The transformers that I mentioned, all the windings were aluminium, just lacquer coated the same as copper would be. I've been had several times trying to solder what I thought was lacquered copper wire.

    No I wouldn't like to take a guess ! Though I suspect that it may not be too large a number from the resistance readings.

    Russ:
    Four wire measurements are done to eliminate the effects of meter loading during measurement.

    220px-Four-point.png
    Essentially a known current is passed through the resistance to be measured and the voltage is then measured. Using Ohms law the resistance can be accurately calculated.

    Ohms-Wheel.png
    Here is an "DC Ohms Wheel" that I've had for a good number of years, as an aid memoir showing all 12 calculations.
    Best Regards:
    Baron J.

  13. #43
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    Hi Stuart,

    Its me again I've been thinking ! (A dangerous thing, thinking)...

    You could test just the transformer by running it backwards ! What I mean is feed a low AC voltage into the secondary, say 5 or 6 volts, and then measuring the AC voltage out on the primary side. This will immediately show any discrepancy between taps.
    Best Regards:
    Baron J.

  14. #44
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    Hi Baron,
    Quote Originally Posted by BaronJ View Post
    No ! The transformers that I mentioned, all the windings were aluminium, just lacquer coated the same as copper would be. I've been had several times trying to solder what I thought was lacquered copper wire.
    Ok. Well as I said I'm pretty sure the secondary is copper. So I guess the primary is as well?(again guessing that there is far more weight in the secondary so you would start there if it was a cost thing)

    Quote Originally Posted by BaronJ View Post
    No I wouldn't like to take a guess ! Though I suspect that it may not be too large a number from the resistance readings.
    Chicken (again guessing, the first tap 4-5 should have a much higher resistance then the other three, but the numbers are so iffy ATM that its anyones guess)
    I'm hoping it will be closer to 200 than 2000

    Quote Originally Posted by BaronJ View Post
    Russ:
    Four wire measurements are done to eliminate the effects of meter loading during measurement.

    220px-Four-point.png
    Essentially a known current is passed through the resistance to be measured and the voltage is then measured. Using Ohms law the resistance can be accurately calculated.
    Ok now I see why Russ wanted two meters.


    Quote Originally Posted by BaronJ View Post
    You could test just the transformer by running it backwards ! What I mean is feed a low AC voltage into the secondary, say 5 or 6 volts, and then measuring the AC voltage out on the primary side. This will immediately show any discrepancy between taps.
    I'll have a think about what I have handy. I do have a variac that would seem a pretty good place to start.

  15. #45
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    Quote Originally Posted by Stustoys View Post
    I do have a variac that would seem a pretty good place to start.
    Do I need to limit current?

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