Problem with HF 90 amp AC conversion
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  1. #1

    Problem with HF 90 amp AC conversion

    I converted a HF 90 buzz box to DC using a 150 amp bridge rectifier without smoothing capacitor and added 75/25 C02/Ar gas with gun set to DCEP and using solid .030 E70S-6 wire. I really wanted to use .023 but waiting for the appropriate drive wheel.

    It works, but the power seems way down. I tested it in AC mode with no improvement other than increased spatter. I'm wondering if the problem is that the .030 wire is just too big for this little welder. I could put the flux core back in and test it as DCEN (.030 flux).

    It hums like it is under load but I'm not getting much penetration and have to run the feed at the 3 to 4 setting on high power for optimal burn.

    Any ideas?
    Last edited by rscapri2600; 10-04-2019 at 12:25 PM.

  2. #2
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    Re: Problem with HF 90 amp AC conversion

    A 150A bridge rectifier is potentially undersized. Did you perhaps burn out a diode.
    I went with a 400A bridge, simply because I didn't want to have to worry about not having a good enough heat sink, but a 200A should still leave a safe margin.

    As for wire, I'm using this .030 and it works great.https://www.amazon.com/gp/product/B00G5GIIQ6

    However, the capacitor makes a big difference. I'm using a 150000MFD monster that I had from work, and it welds great with this. Don't forget that with a large cap, you also need a high wattage bleeder resistor.

  3. #3
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    Re: Problem with HF 90 amp AC conversion

    The rectifier without a capacitor drops a volt or two.
    A volt is a lot.
    Even a 60,000uf capacitor would help.

  4. #4

    Re: Problem with HF 90 amp AC conversion

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    The 150 amp rectifier is mounted with heat sink paste directly to this aluminum plate mounted to the bottom of the welder. So far, I feel the aluminum get warm but never has gotten too hot to touch.

    I converted the welder to be a true MIG or Metal Inert Gas welder so using .030 solid core at this link https://www.amazon.com/Hobart-H30540...31&s=hi&sr=1-2

    I'll have to reconsider the capacitor. Without a cap, the voltage will dip close to 0 many times per second.

  5. #5
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    Re: Problem with HF 90 amp AC conversion

    i think you actually need an inductor to smooth the power rather than the cap. however i would use both.
    keep in mind that even just the rectifier will loose some voltage. how much depends on the specs of the rectifier.

  6. #6

    Re: Problem with HF 90 amp AC conversion

    Quote Originally Posted by tweake View Post
    i think you actually need an inductor to smooth the power rather than the cap. however i would use both.
    keep in mind that even just the rectifier will loose some voltage. how much depends on the specs of the rectifier.
    I was doing some research and I think you are right, inductor is my next addition. I notice my HF 170 which welds pretty good has an inductor but no caps. However, cap mods do improve total power output at the risk of diode failure.

  7. #7
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    Re: Problem with HF 90 amp AC conversion

    Quote Originally Posted by tweake View Post
    i think you actually need an inductor to smooth the power rather than the cap. however i would use both.
    keep in mind that even just the rectifier will loose some voltage. how much depends on the specs of the rectifier.
    Flux core is a CV process. You need a capacitor.

    Stick is a CC process that needs an inductor.

  8. #8

    Re: Problem with HF 90 amp AC conversion

    I did some testing this morning. Open Voltage DC showed 27 VDC with polarity DCEP which should be correct for gas. I put on my clamp on DC ammeter which registered 80 to 90 amps while welding on high power when continuously feeding into a molten ball. However, I saw about 40 amps when starting the weld ... looking at the meter ran than the weld so maybe I'm only getting approx 40 amps when actually welding? Everything looks about right. I laid a bead on some 3/32 steel with the following image but not sure how to interpret the resulting weld . There does appear to be some oxidation but I'm running the Ar./CO2 near maximum at approx 28 liters per minute. The welding tip is flush with the nozzle. I might have cut too much off but originally it was way inset into the nozzle. Any ideas if this welder is working fine? Is there some perceived power loss going from DCEN (flux Electrode negative) to DCEP

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    I looked at it from the side and took another picture. Penetration appears pretty poor. I just watched a youtube video and now I'm wondering if the wire speed is too high.

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    Attached Images Attached Images  
    Last edited by rscapri2600; 10-07-2019 at 12:06 PM.

  9. #9
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    Re: Problem with HF 90 amp AC conversion

    OCV is fixed by the transformer ratio. That's already correct. The weld looks WAY cold to me, but could be a problem with settings.
    Forget clamp meter readings. Flux core is a CV process. Just read arc voltages.

    And why do you even have a nozzle? You don't have gas. Lose the nozzle entirely, and better yet, get a plastic tip:
    https://www.homedepot.com/p/Lincoln-...H726/100341068

  10. #10

    Re: Problem with HF 90 amp AC conversion

    Quote Originally Posted by rlitman View Post
    OCV is fixed by the transformer ratio. That's already correct. The weld looks WAY cold to me, but could be a problem with settings.
    Forget clamp meter readings. Flux core is a CV process. Just read arc voltages.

    And why do you even have a nozzle? You don't have gas. Lose the nozzle entirely, and better yet, get a plastic tip:
    https://www.homedepot.com/p/Lincoln-...H726/100341068
    Yes, original problem is that the welder seems to be welding too cold. The voltage and current readings provide information to determine if the bridge rectifier is still working and not partially blown. This HF 90 amp welder has a gas shield.

    I just tried welding with slower feed and results were the same. Welder is generating enough amps to melt the ground clamp which obviously needs replacing now. I'm going to try some different wire... crossing my fingers.

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    Last edited by rscapri2600; 10-07-2019 at 02:04 PM.

  11. #11

    Re: Problem with HF 90 amp AC conversion

    OK, switched the wiring to DCEN and converted to .030 flux core (HF brand) and the welder works great again. So much better than AC, here is a photo of the weld and spatter which is much reduced from original AC design. I'll try .023 solid wire on gas when I receive the appropriate drive wheel.

    From what it is worth, I tried the original ER70S-6 .030 solid wire with gas on DCEN and it welded like crap again, maybe worse than with DCEP. Only theory I can come up with is that the .030 solid wire is just way too big and reduces the power that is available to fuse and melt with the welded objects. I'll try again when .023 is available.

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    Last edited by rscapri2600; 10-07-2019 at 03:52 PM.

  12. #12
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    Re: Problem with HF 90 amp AC conversion

    For around 90A .023 wire would be the right size.

  13. #13

    Re: Problem with HF 90 amp AC conversion

    Quote Originally Posted by rlitman View Post
    Flux core is a CV process. You need a capacitor.

    Stick is a CC process that needs an inductor.
    It appears to me that both an inductor and capacitor can bring a power supply to CV under certain conditions. I see that most of the capacitors that people have been adding have ripple currents of approx 30 amps which is to say they will supply approx 30 amps max current. Since a fully rectified single phase power source will approach zero 120 times per second and my clamp on meter states that the power supply which delivers approx 90 amps but really don't know the wave form to know how much that current is varying during welding as all these meters are averaging which is why I see 90 amps even if it may be varying between 30 and 100 amps. I would think one would need more than 1 capacitor's 30 amp of ripple current to keep a constant voltage or the power supply's voltage will sag. The inductor will force current to keep flowing which requires voltage... thus also keeping voltage from going to zero and helping the power supply toward CV. The main transformer has inductance which keeps the current from going to zero anyways.

    There is probably a sweet spot of inductance and capacitance that allows the better welders (Miller, Lincoln) to stay at CV which is why I would expect they would have both an inductor and capacitor(s) in their welding circuits.
    Last edited by rscapri2600; 10-08-2019 at 02:58 PM.

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