Subject: Re: Welding with power supplies?

From: [email-masked] (Jonathan M. Elson)
Date: 25 Jun 1996 04:50:28 GMT

Frank Evan Perdicaro ([email-masked]) wrote:

: I have the chance to pick up a few very nice DC power supplies.
: These are Lambda 120A 5V supplies for DEC big iron of years ago.

: I should be able to put together a complete unit with iosolation
: transformer, circuit breakers and cooling fans, all in a roll-
: around box, for $0.

: Would this 240A, 5V power supply make a good welder of any sort?
: If so, how?  What voltage is DC welding typically done at, anyway?

The open-circuit voltage of a stick welder is often somewhere between
50 and 70 volts.  The O.C. voltage of a MIG or TIG welder is around
30 volts.

---

From: [email-masked] (Vrzal fla)
Date: 26 Jun 1996 01:52:48 -0400

In article <[email-masked]>, [email-masked]
(Frank Evan Perdicaro) writes:

>I have the chance to pick up a few very nice DC power supplies.
>These are Lambda 120A 5V supplies for DEC big iron of years ago.
>
>I should be able to put together a complete unit with iosolation
>transformer, circuit breakers and cooling fans, all in a roll-
>around box, for $0.
>
>Would this 240A, 5V power supply make a good welder of any sort?
>If so, how?  What voltage is DC welding typically done at, anyway?

The main problem would be getting the two supplies to track current and
voltage to support the same load. With a couple of amps thats not a big
problem. When your talking 200 amps the problem changes to voltage drop
over the cables from the supplies to the work, and cable heating. When I
worked as a test floor technician we ran supplies like that with 2/0
welding cables and still had to kick the voltage up to 6-7 volts at the
supply to get 4.80v at the load. The cables got real warm and every once
in the while one supply would short out and take the other with it.
Lambda's also don't like open circuits. You'll need to keep a load of at
least 20% to keep the regulator from toasting itself.
     IMHO if your getting the supplies for free, try the setup using one
supply. If it works be happy and keep the other around as a spare. Another
idea might be to use it as supply for EDM (Electic discharge machining).
Several articles (HSM) have described the process and construction of the
unit. A 120 amp would make one big spark.

Jim Vrzal

---

From: "Thomas A. Hively" <[email-masked]>
Date: 27 Jun 1996 00:38:06 GMT

Stick welders have open circuit voltages of around 80 volts and droop to 
about 25 Volts when the arc is lit. The large open circuit voltage is 
needed to help strike the arc and keep it stable. Also the stick welding 
supply is a " constant current" supply not a "constant woltage" supply 
like you have.

MIG welder use a "constant voltage" supply but they are adjustable from 
about 18 to 30 volts.

I guess your next hobby will be metal plating; just kidding!

tom

---

From: [email-masked] (James W. Swonger)
Date: 27 Jun 1996 15:03:20 GMT

Might make a decent spot welder. Too low a voltage for arc work. I 
guess you could control them with about anything, on the primary side.
-- 
##########################################################################
#Irresponsible rantings of the author alone. Any resemblance to persons  #
#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
#sify this effect. Pay no attention to the man behind the curtain. Billy!#