Since the
voltage across the arc will vary from zero to fifty volts, this machine
will save from zero up to seventy per cent of the power that the machine
delivers. The rest of the power, of course, has to be dissipated in the
resistance used in series with the arc.
A motor generator set which can be purchased from any electrical company,
with a long piece of fence wire wound around a piece of asbestos, gives
results equally as good and at a very small part of the first cost.
It is possible to construct a machine which will eliminate all losses in
the resistance; in other words, eliminate all resistance in series with the
arc. A machine of this kind will save its cost within a very short time,
providing the welder is used to any extent.
Putting it in figures, the results are as follows for average conditions.
Current at 2c per kilowatt hour, metallic electrode arc of 150 amperes,
carbon arc 500 amperes; voltage across the metallic electrode arc 20,
voltage across the carbon arc 35. Supply current 220 volts, direct. In the
case of the metallic electrode, if resistance is used, the cost of running
this arc is sixty-six cents per hour. With the carbon electrode, $2.20 per
hour. If a motor generator set with a seventy volt constant potential
machine is used for a welder, the cost will be as follows:
Metallic electrode 25.2c. Carbon electrode 84c per hour. With a machine
which will deliver the required voltage at the arc and eliminate all the
resistance in series with the arc, the cost will be as follows: Metallic
electrode 7.
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