The still unanswered question is why use the welder at minimum reactance
(shorted) rather than at maximum reactance (open)?
On Wed, Jun 6, 2018, 10:14 AM Dave Leddon <dave@xxxxxxxxxx> wrote:
> I purchased an inexpensive arc welder from Sears
> which had a retractable transformer core to
> adjust the current. With the welder output
> shorted I could adjust the pole pig current from 18 to 60 amps.
>
> Dave
>
> At 07:21 PM 6/5/2018, you wrote:
> >Content-Transfer-Encoding: base64Dan,
> >
> >A shorted welding transformer stores energy in
> >an expanding magnetic field which is then
> >returned to the power circuit as the sine wave
> >of the input power waveform decays, kinda like
> >compressing a spring. When you relieve the
> >pressure on the spring, the spring pushes the energy back into your
> system.
> >
> >If you use a resistor, the resistor converts the
> >energy to heat, which is lost, and not returned
> >to the system. This is much less efficient. It
> >would provide ballasting, at the expense of a
> >lot of waste heat. Any resistance in the
> >ballast components will generate waste heat, so
> >you want to minimize that as much as possible.
> >
> >If you want an easily and infinitely adjustable
> >ballast, you would use a saturable
> >reactor. This is a special transformer which
> >would perform the same function as a shorted
> >welder, but in which the permitted current is
> >controllable by a small low voltage DC current
> >applied to a special set of control windings.
> >
> >Saturable reactors provide nice control for TC
> >systems, but ones big enough to effectively
> >control a pole pig can easily weigh half a ton,
> >and are usually very expensive, unless you can find a surplus unit for
> cheap.
> >
> >Last spring, I bought an assembly nearly
> >identical to the following one for $130 for the
> >copper scrap value, but it cost me $580 in
> >shipping fees to get it to my friend's factory
> >shipping dock. "Some day" I hope to build a coil
> >big enough to put it to effective use.
> >
> >
> https://www.ebay.com/itm/40-KVA-20-AMP-460-VOLT-HUNTERDON-SATURABLE-CORE-REACTOR-TRANSFORMER-S-1207-1/292572873068
> >
> >The reactor that was in it looks just like the
> >following one, but is mine "only" 52 KVA
> >rated. I think there is a typo in the
> >listing. The rating should be more like 60 KVA,
> >not 600. I would speculate that a 600 KVA core
> >would likely weigh several tons.
> >
> >
> https://www.ebay.com/itm/NEW-Hunterdon-Saturable-Core-Reactor-Transformer-600KVA-60Hz-WE-1097-R-C98R2/282780054079
> >
> >(I have no connection to either seller.)
> >
> >You can buy a lot of welders to short out for $4,800 plus shipping.
> >
> >To understand saturable reactors, look up "magnetic amplifiers" in
> Wikipedia.
> >
> >Dave
> >
> >
> >On 6/5/2018 11:22 AM, Daniel Kunkel wrote:
> >>As already pointed out, for a current limiting ballast transformer, the
> >>secondary coil will be shorted out, and the primary will be in series
> with
> >HØY‚€£â†÷vWfW"Â’†fR&VVâvöæFW ing what would happen if you put a (variable)
> >>resistor on the secondary side of the ballast transformer (instead of a
> >>dead short). I wonder if this would give you some degree of variable
> >Ý\œ™[ [Z][™Âg&öÒÆÂ×’&VF ng, it seems like the best current
> >[Z][™È\Ù\È“Õ@nductance and resistance...so I wonder if resistance
> >Àcated in this location would work.
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