Problem with HF 90 amp AC conversion

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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.
Reply: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/B00G5GIIQ6However, 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.
Reply:The rectifier without a capacitor drops a volt or two.A volt is a lot.Even a 60,000uf capacitor would help.
Reply:

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=1-2I'll have to reconsider the capacitor.  Without a cap, the voltage will dip close to 0 many times per second.
Reply: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.
Reply:

Originally Posted by tweake

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.
Reply:

Originally Posted by tweake

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.
Reply: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  

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

Originally Posted by rlitman

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
Reply: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.

Last edited by rscapri2600; 10-07-2019 at 03:52 PM.
Reply:For around 90A .023 wire would be the right size.
Reply:

Originally Posted by rlitman

Flux core is a CV process.  You need a capacitor.Stick is a CC process that needs an inductor.