Thread-topic: Welding Transformer As Ballast or Choke
Dan,
Another alternative, which I use, is to build your own ballast with an adjustable air gap. The maximum current is set by using a spacer of appropriate thickness to establish a gap between the E and I sections of the ballast. The spacer thickness is quite low. For my design the air gap thickness for a 20 amp maximum current is only 0.03 inches. My ballast will easily accommodate a maximum current of up to 40 amps without saturation by using appropriate spacers. My ballast is similar in construction to the one shown on Richie Burnette's web site, although I think I like mine better. The weight of my ballast is about 70 pounds. The hardest part about building one is to find E and I sections which are large enough and plentiful enough. I got my E and I sections from a discarded 120/240/480 volt transformer rated at 25 KVA. I delaminated all of the E and I sections and then reassembled an appropriate number of them to make my ballast. This type of ballast is extremely efficient. The core exhibits no discernible heating even after many minutes of operation. The design equations are fairly simple and can be found in any transformer design textbook. If you want to duplicate my design, I can supply the specs if you want.
Steve
----- Original Message -----
From: "David Speck" <Dave@xxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, June 5, 2018 9:21:52 PM
Subject: Re: [TCML] Welding Transformer As Ballast or Choke
Dan,
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
> the load.
>
> However, I have been wondering 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
> current limiting? From all my reading, it seems like the best current
> limiting uses BOTH inductance and resistance...so I wonder if resistance
> located in this location would work.
> ~Dan
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla