Re: Convert an AC to a DC Welder


"GregS" <zekfrivo@xxxxxxxxxxxxxxxx> wrote in message
news:fnv9c9$o3k$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <fnsiav$5fg$2@xxxxxxxxxxxxxxxxxxxxxxxxx>,
zekfrivo@xxxxxxxxxxxxxxxx (GregS) wrote:
In article <fnrpah$ab5$1@xxxxxxxx>, someguy@xxxxxxxxxxx wrote:

On Wed, 30 Jan 2008 09:34:24 GMT, "Arfa Daily"
<arfa.daily@xxxxxxxxxxxx> wrote:


<someguy@xxxxxxxxxxx> wrote in message news:fnpbr9$319$1@xxxxxxxxxxx

I recently read that an AC welder can be converted to a DC welder, and
all thats needed are either two or four very high amp diodes. The
welder puts out up to 240amps. I never measured the voltage, but I
think it's around 25 to 30. (I'll have to check). Two diodes will
make a half wave rectifier, but if my memory is right, I'll only get
half the voltage, whereas using 4 diodes as a bridge rect. I will get
the full voltage output.

Now, my question is this. How do I figure the amperage of the diodes
that I would need (for both methods), so I have at least 250amp
capacity. I'd guess 300 would be better to cope with heating. Of all
the years I puttered with electronics, I was never good at math. My
guess is that each diode should be 150A to achieve 300A. But I might
be wrong.
Can someone please help.

Also, where could I get something like this?

Thanks


I made a converter using a bridge made up of diodes of 1/2 the required
amperage,
and a series coil made out of a 2KW variac core with a cut going all the
way
through the torroid. I used parallel winding for the output through the
indictor.

greg

Before I did the mod, I just asked around like you did. The slotted
inductor makes
the current more constant. I don't imagine it would work well without it.
It seems like you have the same basic figuring as I in making a bridge.
If a bridge is outputting 150 amps, then each diode average current is 75
amps.

greg


If what I learnt nearly 40 years ago is correct, then that isn't true. With
a single untapped winding, at any given instant, one diode from the upper
arm of the bridge is conducting, and one from the lower. When the phase at
the winding ends reverses, during the following half cycle, the other two
diodes will conuct instead. The two diodes are in series in the circuit, not
parallel, so it's winding end - diode - load - diode - other winding end.
Thus any current in the load will be the same current as in either of the
diodes. If there is 150 amps in the load, then there will be 150 amps in
both the diodes, not 75 amps in each.

Arfa


.

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