DC Welding

[Casey1]

That may be it, RMS ac amps = 225 x .707 = 159

That is, the ac amps are not quite real, but the dc ones are!

Mike

So that means you have near the same welding power with 150 amps DC as 220 amps AC?

 

[Soundguy]

"standard" utility electrical service - are the voltages Peak to Peak, or RMS? I've always assumed RMS, but never really had any reason to find out for sure.

yup...120v like a standard american outlet is an RMS reading..

Soundguy

 

[shaley]

I have a welding question, I am looking of information on 9013 (also called SAE9) welding rod has anyone here used this rod and if so where can it be purchased?

See page 4 of this PDF.

 

[patrick_g]

That may be it, RMS ac amps = 225 x .707 = 159

That is, the ac amps are not quite real, but the dc ones are!

Mike

Oh, AC amps are real enough but vary with the variation in the AC sine wave. RMS (Root Mean Square) can be though of as the DC equivalent current. That is, what AC current is equal to what DC current in heating power, Watts?

120VAC or 240 VAC as we usually describe it and see it mentioned in specs is actually RMS and if you hook a light bulb to 120VAC or to 120 VDC it would burn with the same brightness. The actual peak voltage is first 1.414 times the RMS in one polarity (say positive) and then it goes down through zero to 1.414 times 120 volts negative. The peak voltage of a 120VAC (RMS) sine wave is nearly 170 volts +/- and alternates between these values at the 60 Hz rate.

To add confusion, the peak to peak value of the sine wave is twice the peak value, i.e. if you used a 'scope to show you a picture of the voltage vs time waveform from the bottom of the negative peaks to the top of the positive peaks in 120 VAC is about 340 volts.

The amps of the DC rating on a welder is already given in RMS and it is incorrect to devalue it by 0.707 which is the factor for converting peak to RMS.

I haven't torn up a buzz box to see the circuit or to measure forward voltage drop of the rectifiers (can be considerable) but if they use 1/2 wave rectification (and I don't know that they do) then the RMS or the pulsating DC current would be 1/2 of the AC rating even if the rectifiers were perfect and had no loss.

I defer to anyone who has ACTUAL knowledge of the internals of an AC/DC buzz box. If no one here has then we can pass the hat, buy me a root beer float, and I will peek inside mine.

Oh, and I don't recall seeing where anyone posted regarding switching CD polarity to reverse vice straight. There are reasons to do that and it is something impossible with AC only.

Pat

 

[bucmeister]

I have one of the Miller 225/150 Ac/DC units, and for me once I went DC I never wanted to go back. All the things others have said, easier, smoother, more stable, and with my favorite rod (7018) I can just lay in on the and burn baby burn. Now have a MM210 wire unit and don't use the stick as much cause I have not been doing any heavy or high up welding. The 60' electrode and 50' ground cables give me room to move that the wire unit can't unless I go to a spool gun. There are many times I would love to have a 25-30' push/pull type gun on the wire unit.

 

[Farwell]

See page 4 of this PDF.

Shaley,
Thank you very much for the information.

 

[Casey1]

So the drop from 225 amps AC to 150 amps DC is due to the cost of conversion? Seems awfully inefficient.

 

[Soundguy]

One point. i think the other poster took the ac rated amps.. then hit them with the rms calc .707 and got nearly the DC amp rating. If that is correct.. seems that the manufacturer is rating the AC side as 'peak' rating.. etc. ( I don't know that this is true.. etc.. but I'm just saying what i think the poster said..etc.. )

As for the rectifier.. I was hoping that perhaps it was a center tapped xformer with 2 diodes to give full wave output.. or i guess simple a full wave bridge.. etc.

If anyone has one open.. all they gotta do is count the silicon.. 1=1/2 2=full, 4= full.. etc

Soundguy

The amps of the DC rating on a welder is already given in RMS and it is incorrect to devalue it by 0.707 which is the factor for converting peak to RMS.

I haven't torn up a buzz box to see the circuit or to measure forward voltage drop of the rectifiers (can be considerable) but if they use 1/2 wave rectification (and I don't know that they do) then the RMS or the pulsating DC current would be 1/2 of the AC rating even if the rectifiers were perfect and had no loss.


Pat

 

[patrick_g]

Sound Guy, Only audio amp manufacturers are brazen enough to list the power of an amp as peak output or for some really unprincipled, the max it draws from the wall!

There may be one somewhere but I have never seen a welding power supply rated peak, or peak to peak. RMS is a fair method with little confusion. One source of confusion for some is that the 0.707 and 1.414 numbers thrown around when discussing RMS vs peak is that they are only valid for a pure undistorted sine wave. RMS is still valid to rate welding current which is hardly a pure DC or pure sine but the math gets harder since the numeric values mentioned above assume pure sine. Calculus anyone?

Pat

 

[Soundguy]

I dunno.. I see chinese electric motors.. and other electric motor products all over the place that alre listing pek power on their UL tags, if you read the fine print. I wouldn't assume -anything- before I read the tag.. And it's not just foreign equipment.

My night job takes me to bars and venues to run sound.. I usually lurk around the kitchen during breaks.. and entertainmyself reading labels... for instance.. a 'Bun' industrial beverage brewer had it's wattage listed in peak power ratings on the UL tag... go figure..

As I said.. I've seen it on electric motors before..

soundguy