Re: [CAD_CAM_EDM_DRO] Re: welding machine as a power supply

Ordinary old style AC welders have two principle components, a transformer
and
an inductor. The transformer works in a conventional manner. The purpose
of the inductor is to limit the current. When there is no load there will
be
no voltage drop across the inductor. As the load goes up the voltage
drops.
That is the essential principle of electric welding.

A welder will take a dead short for a few seconds and not overload the
system. This commonly happens when a welding rod gets stuck. The
current setting of conventional AC welders is determined
by varying the inductance of the inductor. This can be done with taps
on the coil or by a sliding iron slug in the inductors magnetic circuit.

This is not ideal for a power supply. It will act like a very unregulated
voltage source. However, the transformer alone is useful for a supply. I
would
recommend that you tap into the circuit between the inductor and the
transformer.
That should give you the best results for an unregulated supply.

Pete.

----- Original Message -----
From: "Bob McKnight" <bobmcknight@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, March 21, 2004 11:19 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: welding machine as a power supply


> To: CAD_CAM_EDM_DRO@yahoogroups.com
> From: "caudlet" <info@...>
> Date sent: Sun, 21 Mar 2004 16:00:19 -0000
> Subject: [CAD_CAM_EDM_DRO] Re: welding machine
> as a power supply
> Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
>
>
> One feature of a welding transformer, and the more expensive
> the machine the more it has this feature.
> At low/no current they have a high secondary voltage to make
> it easy to strike the are, Then as the current increases, the
> voltage goes down. A good ransformer welder will have
> and have a 'open circuit secondary voltage rating'. It seems
> like the old/new Lincoln adjustable 250 amp welders had
> an open circuit voltage of 70 volts which went down to about
> 23 when the arc was struck. Some of the cheap 'cracker box'
> welders were not near that wide range and were hard to start
> an arc. So, you might want to look at a cheap, small, cracker
> box welder for you power supply.
>
> Bob McKnight
> [ Double-click this line for list subscription options ]
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "ftomazz"
> <filipetomaz@p...>
> wrote: > Hello. I need about 65V to feed 3 motors that take 10Amp
> each
> (max > ratings). > > There is any good reason not to use a welding
> machine (or more than > one) in a serial configuration to reach the
> 65V@30Amp? I can get old > (not inverter welding machines). > >
> Probably a bad ideia...
>
> Actually a 65V 30A supply IS a welding machine! If the 10A ratings
> are peak then you probably don't need to design using that number.
> Most servo's average power consumption is 50% of peak. I suspect
> that
> a 65V 15A design with a 30A bridge rectifier would do fine. While I
> don't see anything wrong with using parts from a surplus Welder
> provided you can get the correct AC secondary voltages, it sure would
> be a big hummer! Magnetic and most passive components can live
> long
> productive lives if you stay within their ratings on average. Example:
> You can hit a 10W wirewound power resistor with 100W for one
> second
> every 11 seconds and it will get warm but not burn up. Semiconductors
> are less tolerant of short peaks over their ratings. While they will
> let you pulse them with higher currents over short duty cycles they
> will create blue smoke if you exceed max voltages ratings for even
> short durations.
>
> What kind of machine is this going on and what are the motors? What
> are the secondary voltages of the transformers in question? You might
> be able to get a lower secondary voltage if it has a dual or tapped
> primary that would allow you to use the 230v configuration but run it
> at 120VAC. That would make the secondary voltage 1/2 of the full
> rating. You might have to derate the transformer if they use two
> separate windings for the primary and expect them to be in parallel
> for 120V operation. The wiresize of the primary winding becomes the
> limiting factor. I doubt this would be a factor for something like a
> 100A or larger welder transformer.
>
> There might well be other components in the welder that you can use
> as
> well. They might have some large diodes you could use but they would
> probably need to be rewired to form a full wave rectifier circuit. If
> it is a wirefeed it will have a variable speed gearhead motor. While
> it's not much use in CNC it does make a dandy variable speed power
> drive for a manual mill! My first mill/drill still has the motor,
> gearbox and original motor controller from an old miller wirefeed as
> the X axis power feed. Saved a whole lot of hand cranking.
>
>
>
>
>
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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