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  1. #181
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    Did you measure the volts accross the diodes both ways. AC or DC?

    Do you have a clamp on ammeter?
    Can it read DC current?

    A good diode should block current in one direction(showing full volts), and pass current in the other(showing low volts). But with 60hz AC you will have both happening.

    Could you put a battery on the AC side of the diode bridge, with the transfomer disconnected?

    Add a small load an check the diodes again. And then reverse the battery connections an check again.

    I'm sure your problem is in the diodes. Just not sure witch ones.
    Are they expensive? If not, I would just replace them all.
    Dan H.

  2. #182
    Super Member California's Avatar
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    Default Re: Thoughts on this used welder?

    Seems like there are welding theory gurus lurking in this thread. ...
    Would there be a simple way to put an external rectifier/choke/capacitor module in the ground lead of Harbor Freight's AC flux welders to convert to DC and make them weld better?

    I'll start a new thread if this is worth discussing.

  3. #183
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    Default Re: Thoughts on this used welder?

    Quote Originally Posted by CNC Dan View Post
    A good diode should block current in one direction(showing full volts), and pass current in the other(showing low volts).
    Could you put a battery on the AC side of the diode bridge, with the transfomer disconnected? Add a small load an check the diodes again. And then reverse the battery connections an check again.
    Earlier in the test procedure, I did a full diode check with a 12 volt battery and a tail light as a load, and all diodes checked out, but at your prompting and due to the high likelihood that a bad diode is the cause, I went and did it again tonight. Sure enough, I found a problem with the same diode that had the 80 mV reading in my voltage tests. Once I disconnected its post from the plate it was bolted to, I noticed that it had a bad internal connection to its own lead. If I held it just right, I could get the bulb to light and the meter to read a good values in the diode test function. But if I wiggled it another way, it would show open both directions. Also, I can twist it 360 degrees while the soldered lead just sits there and doesn't twist at all, so that's clearly not right. It must have been marginally connected, and I must have finished breaking it internally when I did this second round of diode tests.

    I'm sure your problem is in the diodes. Just not sure witch ones.
    Are they expensive? If not, I would just replace them all.
    Yup. That is now the plan. I have read that if one diode goes bad, the other three will usually take damage as a result, and so they should all be replaced as a set. Woo hoo! I'm glad to have finally tracked down a definitive fault. All this time, I have been saying to myself, "Look. It's got to be the diodes." I just wasn't willing to commit money to replacing them without some evidence. Now I've got some.

  4. #184
    Super Star Member k0ua's Avatar
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    Default Re: Thoughts on this used welder?

    Some thoughts..I could not make out anything useful in your cap check.. You cannot really check a cap that way with a digital voltmeter, and it needs to be out of the circuit. Also the measurements across the diodes.. I have never tried to do that..You have an AC voltage on one side and a DC (pulsating DC) on the other..what were you on AC or DC? when you measured... I just dont know what you would get. I have never had any luck testing Caps with a digital meter. You check diodes with an ohms function. Again digital meters are lousy choices for checking diodes too. You can do it, and some have a diode check setting, but an analog meter is much better for this type of trouble shooting. A digital is best for precise measurements, of voltage current and resistance and very poor for troubleshooting. The substitution of the secondary winding of the transformer with a battery is a good idea, to check the diodes with your digital meter and would let you easily know if they were good or not.. put one lead on the battery, put the other battery post on one side of a diode to check and measure the voltage on the other side of the diode with the other lead of the meter.. If it is in forward conduction the voltage on the other side of the diode will be about .7 volts less than the source voltage of the battery.. If you reverse the battery, you should measure 0 volts. No conduction thru the diode at all. The .7 volt drop is the normal drop of a given voltage thru the silicon diode that is forward biased. Check all four diodes by applying the battery voltage and reversing the polarity of the battery.. you could get an idea if the cap is storing charge by placing the battery across the cap.. after you disconnect it from the circuit. (at least one leg) and checking to see if it is a polarized cap. in other words does it have a positive and negative end, or is it non polarized. Then connect the battery to the positive end if polarized, or to either end if non polarized, then the other battery lead to the other cap lead. It should charge up to the battery voltage in a fraction of a second. put your meter across the cap also. and note the battery voltage, now remove the battery, and the voltage on the cap should bleed down slowly from the impedance of the meter. But I would imagine your digital meter impedance to be very high therefore drawing little current from the cap, and if it is not too leaky it should draw down rather slowly. ..Remember inside this welder, is 240VAC high current, and 62VAC even higher current.. so if you screw up, and become part of the circuit, we will not be hearing from you for the rest of your life. The test's we are talking about here with a battery are relatively safe and I would suggest using a 9 volt transistor battery. But unplug the welder, and do not get the 9 volt battery across the secondary winding. (in other words disconnect it) or when you remove the battery or the back EMF will knock the PI$$ out of you.. That's right a 9 volt battery across a large transformer winding will really rattle your teeth when you remove it. from the magnetic flux collapsing back into you as a load. Good Luck and stay safe, and think out each move beforehand.

    James K0UA
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  5. #185
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    Default Re: Thoughts on this used welder?

    Quote Originally Posted by California View Post
    Seems like there are welding theory gurus lurking in this thread. ...
    Would there be a simple way to put an external rectifier/choke/capacitor module in the ground lead of Harbor Freight's AC flux welders to convert to DC and make them weld better?
    Not a welding guru, but I have seen instructions for adding a rectifier bridge to an AC-only welder to make it output DC. A little google searching can get you started down that road.

    https://www.google.com/search?q=conv...hrome&ie=UTF-8

  6. #186
    Super Star Member k0ua's Avatar
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    Default Re: Thoughts on this used welder?

    Aha I just read you have a defective diode now for sure... OK. one other thing.. you show a resistor in your schematic as a load.. not sure what that is, unless this represents your light bulb, but the voltage across that cap should be a heck of a lot more than 27 volts, unless that is one heck of a low impedence load like the arc! if you have 62 AC volts on the secondary, and you put that into a bridge the Open circuit voltage without any load should be about 1.414 or the square root of 2 times the AC voltage or about 87 volts Open Circuit..It might not be quite that, and any load will drop it quick, but not to 27. This is Peak Voltage, Not RMS. anyway to sum up the 27 volts on the cap does not seem right for a no load situation, but you have apparently found a problem. hope you get it fixed .

    James K0UA
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    Kioti DK35se hydrostat with 2 QA buckets, 48 inch. King Kutter Rotary Cutter. 750 lbs ballast box. Loaded tires, Construction Attachments SSQA Lightweight Pallet forks. EA 50 inch single lid "wicked" Grapple. Satisfied Everlast PA160 welder owner How to add a link to a post . Best way to search TBN


  7. #187
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    Default Re: Thoughts on this used welder?

    James: I think you probably posted before you saw my latest post about the bad diode I found, so much of the info you very-helpfully supplied is now moot, but thanks regardless.

    Interesting, your suggestion about putting a battery in instead of the transformer. When I have been testing the diodes, I have had the welder entirely unplugged, and have simply been using alligator clips to connect it in at the required parts of the circuit. When measuring voltage, I had the welder plugged in, but I had welding gloves on the whole time and restricted myself to the rectifier circuitry, staying away from the main transformer. Fortunately, the rectifier bridge is very accessible from the side of the unit. I think that welding gloves should be a good choice for working inside the rectifier, since they're designed specifically to protect from the voltages that the welder puts out.

    Your point about the current is well taken. It's a good reminder. At times, I reassured myself that the voltage down in the rectifier section was "only" 60 volts or so, but because it's going through a transformer, the available current is proportionally increased, and as we all know, it's current that will mess you up, not voltage.

    Anyway, now that I found the dead diode, I shouldn't have to futz around in there any more, I hope. When I get around to it (i.e. when I have the money) I'll replace the diodes and then hopefully everything will work as it should. Here's looking forward to some lovely DC welding! In the mean time, I'll keep practicing on AC.

  8. #188
    Super Star Member k0ua's Avatar
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    Default Re: Thoughts on this used welder?

    Joshua just for fun sometime if you want the snot knocked out of you, take a 9 volt battery, and if you can find an old AC/DC transistor radio, you know the kind you can run on AC plug or they have a battery holder inside.. and hold the power plug in you left hand with your thumb and forfinger on the metal of the power plug, then put the 9 volt battery terminals on the AC power plug for just a second, and then when you remove the battery the back EMF will flow out of the power plug and across your finger and thumb.. for an extra surprise be sure to wet your fingers.. you will be surprised, and not pleasantly. This will work with any decent sized transformer winding also. The DC voltage creates a magnetic field in the core of the transformer, and when you remove it the magnetic field collapses, and comes out of the transformer as a rather high voltage pulse right into any load that might be across it, like your fingers. This doesnt get your welder fixed, but though I would mention it for fun

    James K0UA
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  9. #189
    Super Member California's Avatar
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    Default Re: Thoughts on this used welder?

    Quote Originally Posted by joshuabardwell View Post
    Quote Originally Posted by California View Post
    simple way to put an external rectifier/choke/capacitor module in the ground lead of Harbor Freight's AC flux welders to convert to DC?
    I have seen instructions for adding a rectifier bridge to an AC-only welder to make it output DC. A little google searching can get you started

    https://www.google.com/search?q=conv...hrome&ie=UTF-8
    Thanks! I think you'll laugh, the second link went to a WeldingWeb thread where someone had built a DC converter by trial and error, and I had asked a few questions in that thread. So far I haven't seen any such threads over there where I thought the project turned out well.

    I don't have the diagnostic tools or knowledge to design the choke/capacitor circuit that would be needed for this. I should be more specific - is such a DC converter available as a completed external 'black box'?

    Thanks!

  10. #190
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    Default Re: Thoughts on this used welder?

    https://www.galco.com/shop/70HF-Vish...ecovery-Diodes

    I have found what appear to be replacement diodes for my welder. One question: when they refer to "stud cathode" or "stud anode," which part of the diode is the "stud"? Is it the threaded post or is it the little tab that the wire lead gets welded to?

    I have read that you can find the anode and the cathode of a diode by seeing which way the meter shows open vs. short. Only problem is that, according to the site I read, not all meters put out their test current on the red lead, and you can't know for sure unless you have two multimeters and test one with the other (which, currently, I don't). So if I was to take a 12 volt battery and a light bulb and put it across the diode, would I be correct that, when the light bulb lit up, the positive lead is touching the anode?

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