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  #11  
Old 01-14-2017, 07:20 PM
yooper yooper is offline
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Default Diodes

If you haven't ordered the diodes already - these are a less expensive option than four separate stud diodes and you only need one heat sink and don't have to worry about isolating / insulating the heat sinks .

http://www.ebay.com/itm/US-Ship-MDQ-...wAAOSwiO9Xi5CB
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  #12  
Old 01-14-2017, 07:30 PM
Oscar Oscar is offline
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Originally Posted by Rufus View Post
This is based on Tesla's findings. If I am not mistaken, the old High Frequency Tig Welders are based on Tesla's principles. I do know that In a lot of old HF tig welders there is a spark gap in which a spark jumps across the gap and in turn fires a Hf transformer (if I am wrong, please feel free to correct me).

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Exactly. High-Frequency. By definition, if you have frequency, you have an AC waveform, not Direct-current. Skin-effect only applies to very very high frequency waveforms. This is covered in any undergraduate Electromagnetic Field Theory course worth its tuition cost.

With regards to cable size and amperage, keep in mind that even though the Lincoln table shows values that take into account thermal heating, it does not take into account voltage drop, which there will always be. Be sure to use a voltage drop calculator to see if the resultant voltage drop is acceptable.
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Last edited by Oscar; 01-14-2017 at 07:39 PM. Reason: Thought the quoted text was from someone else
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  #13  
Old 01-14-2017, 08:42 PM
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The old Lincoln table probably dates from the days when welding machines were capable of 30-40 arc volts at rated current. Old welders had balls.
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  #14  
Old 01-15-2017, 12:23 AM
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Quote:
Originally Posted by Oscar View Post
Exactly. High-Frequency. By definition, if you have frequency, you have an AC waveform, not Direct-current. Skin-effect only applies to very very high frequency waveforms. This is covered in any undergraduate Electromagnetic Field Theory course worth its tuition cost.

With regards to cable size and amperage, keep in mind that even though the Lincoln table shows values that take into account thermal heating, it does not take into account voltage drop, which there will always be. Be sure to use a voltage drop calculator to see if the resultant voltage drop is acceptable.
+1...

I design and build bus bars and shunts that carry 45k amps or more for the EW side of copper mining. The CDA book (Copper Development Association) states that the skin effect applies only to AC current. DC current requires a minimum of cross sectional area per amp to minimize heating.
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  #15  
Old 01-15-2017, 01:59 PM
Rufus Rufus is offline
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Quote:
Originally Posted by yooper View Post
If you haven't ordered the diodes already - these are a less expensive option than four separate stud diodes and you only need one heat sink and don't have to worry about isolating / insulating the heat sinks .

http://www.ebay.com/itm/US-Ship-MDQ-...wAAOSwiO9Xi5CB
I already ordered my diodes. It's amazing how someone on this website always comes up with a good alternative

Thanks
Tim
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  #16  
Old 01-17-2017, 07:13 AM
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As far as I know, when you convert the AC into DC using a full bridge rectifier the conversion will raise your output voltage up, something to do with RMS, so you will get approximately 1.414 x your original voltage. I am sure that the sparky's here will correct me if I am wrong. Which may result in getting a hotter arc when welding in DC. Adding a few large capacitors will smooth out the ripple effect and also improve the arc. Something to consider.
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  #17  
Old 01-17-2017, 07:29 AM
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An AC to DC rectification tutorial: http://www.bristolwatch.com/ele/basi...tification.htm
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  #18  
Old 01-17-2017, 08:21 AM
Lew Hartswick Lew Hartswick is offline
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Originally Posted by USMCPOP View Post
An AC to DC rectification tutorial: http://www.bristolwatch.com/ele/basi...tification.htm
:-) Well right here is the problem with using the internet for information:
The second sentence in the linked article; quote, A diode is a solid-state device
unquote , implies that all the other devices that permit current to flow in one direction are not diodes.
I would guess that was written by some young person that hasn't been taught electronics, just self, poorly, educated . :-)
Like asking your local barber or garage mechanic for a medical opinion.
Oh well I'll drop this and any other electronic threads that come along.
...lew...
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  #19  
Old 01-17-2017, 10:37 AM
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terry lingle terry lingle is offline
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Quote:
Originally Posted by Ed. View Post
As far as I know, when you convert the AC into DC using a full bridge rectifier the conversion will raise your output voltage up, something to do with RMS, so you will get approximately 1.414 x your original voltage. I am sure that the sparky's here will correct me if I am wrong. Which may result in getting a hotter arc when welding in DC. Adding a few large capacitors will smooth out the ripple effect and also improve the arc. Something to consider.
actually if all you do is rectify the ac into dc you will lose either .6 or 1.2 volts depending on if you use a two diode ,center tapped transformer or a fullwave bridge setup.
The lost voltage is the voltage required to turn on the diodes. The improvement in performance comes when you add reactive components inductors and/or capacitors that store energy during the high power part of the voltage cycle and return it to the circuit during the low power part resulting in higher average power to the load.
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  #20  
Old 01-17-2017, 04:24 PM
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My bad, I forgot about the capacitor I installed to smooth out the ripples on my step down transformer which is where the voltage kicked up.
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