The Workhorse
Improvements Over Older SCR-based Inverter Welding Products.
Background:
The first lightweight inverter-based arc welder
was designed in 1976. This new machine's power conversion was
based on highly reliable SCR semiconductor components (thyristors).
This design has been proven successful in heavy industry for
thirty years. ARCON has made several improvements over time,
but has taken great care to retain all of the best features
and time-provencomponents of the original design. The total
production of the SCR-based inverter welder has now exceeded
100,000 units worldwide, and brand new units continue to be
placed in harsh work environments daily.
The design
of The Workhorse is based on this original design
with significant improvements in function and reliability. The
improvements stem from extensive experience and the feedback
from the market place, especially the repair shops from around
the United States and Europe.
This white-paper
outlines the improvements in function and reliability that has
been implemented in The Workhorse compared to
what here will be called "the old design".
The decision
by ARCON Welding to choose the SCR-based design for its new
series of welders, instead of the now more common IGBT elements,
is based on feedback from the field, indicating an up to 100
times higher failure rate of IGBT components compared to the
SCR elements. (See ARCON Welding's Frequently Asked Questions)
Welding
performance:
The Workhorse
has a smooth, stable and spatter free arc achieved by a new
output circuit
The smoothness
of The Workhorse arc has been dramatically improved
over the old design by optimizing the output circuits to give
a smooth arc at both low and high currents.
The comparison
was made by Kurt Ewy, Training coordinator, Earlbeck Corporation
in Baltimore MD - " The Workhorse makes the inexperienced
welder a good welder".
Other
industry and distributor comments: "The Workhorse
has the smoothest arc on the market, especially at very low
currents." "The Workhorse arc is as smooth as
silk".
Arc gouging
is now allowed for all currents.
The old
design was not designed for arc gouging. The voltage stress
on the output capacitors was so large that they were destroyed.
The
Workhorse has a built in circuit which protects the
output capacitors when arc gouging, which *allows it to be used
for all arc gouging at all current levels.
*POWCON®
is a registered trademark of Cyclomatic Industries, Inc. ARCON
Welding LLC is not associated or affiliated with Cyclomatic
Industries, Inc. and its products are not sponsored or approved
by Cyclomatic Industries, Inc.
The Workhorse reliability
improvements
Input
capacitors can sustain long time of high current welding on
single phase.
When welding
with maximum current on single phase, especially if connected
to 480 V or 380/400 V and a phase is lost or not connected,
the input capacitors maximum rated ripple current may be exceeded.
If so, the capacitor can be permanently destroyed if not protected
by a temperature sensing circuit. The Workhorse has
a vastly improved control circuit that will much faster and
more accurately detect over-temperature in the capacitor ensuring
that the capacitor design life of 10,000 hours of welding is
maintained. If an over-temperature is reached, The Workhorse
is automatically shut off for a few minutes and the panel light
blinks indicating over-temperature.
Output
capacitors can sustain long time low current welding on high-current
range.
The output
capacitors rated ripple current may be exceeded when welding
with low current on the high-current range. The Workhorse
has a temperature sensing control circuit, which ensures that
the internal capacitor temperature never exceeds the rated maximum
temperature where the capacitor is designed to operate for 10,000
Hours of welding. When this temperature is reached, The
Workhorse welder is shut off for a few minutes and the
panel light blinks indicating over- temperature.
Vastly
improved suppression of transients on the input power lines
The old
design has varistors from phase to ground only, The Workhorse
has in addition varistors between phases improving the suppression
of the voltage surges on the input power lines. These additional
devices limit the voltage surge between phases to a voltage
lower than the maximum rated voltage for the input diodes.
In the
old design varistors in parallel are used to protect the rectified
DC supply voltage. Varistors vary very much in clamping voltage
from device to device, which makes it non-effective to use varistors
in parallel. The Workhorse has a single varistor
with 7 times higher surge current capability (40,000 Amps.)
Increased
SCR overvoltage protection
The overvoltage
diodes in The Workhorse have increased from 16
A to 75 A, using the input diodes.
Auxiliary
transformer
The auxiliary
transformer of the old design is designed for 50/60 Hz. The
welder is often connected to generators at remote work sites.
When a generator is overloaded, its frequency drops and may
stay at a low frequency of as low as 40 Hz. This causes the
transformer to saturate if it is designed for 50 Hz and a dangerous
over-temperature may occur. The Workhorse auxiliary
transformer is designed to survive abnormal conditions and high
temperatures without being destroyed.
Enhanced
surge protection circuit for voltage spikes (Optional)
If desired,
we can increase the surge protection when connected to power
with "dirty" and powerful voltage spikes, such as mines and
certain generators.
Mechanical improvements
Skates
underneath The Workhorse.
The welders
are often dragged by the primary cable. Even if that is not
a recommended practice, that is a fact. The bottom of The
Workhorse is designed with heavy duty molded upturned
skates to make dragging easier and safer.
The
Workhorse can be nested.
The upper
case has mating indentations in the top, making nesting of two
units possible for storage purposes or, strapped together, for
welding purposes in the field.
Handles
are recessed
On the old
design the fixed upright handles were sometimes pushed down
with such a force that they were punched through the top case.
In addition, the upright handles made the units impossible to
stack on top of each other. The Workhorse has rugged, foldable
handles which recess into the top of the unit.
The corners
of the case of The Workhorse are dimensioned for abuse.
A study
of the old design indicates that sometimes the corners were
crushed from daily wear and tear. We have now greatly reinforced
The Workhorse corners to prevent this from happening.
Steel
louvers make the air intake screen safer, more efficient and
rain resistant.
The old
design had an air intake grill made from injection molded plastic
which was susceptible to being pierced by a forklift tine, thereby
exposing the 700 volt heat sinks. The heat sink voltage with
its 700 volt AC at 5000 Hz is many times more lethal than 480
Volts AC at 60 Hz.
When it
rained, the horizontal grill louvers could cause raindrops to
bounce into the inside of the welder. The Workhorse
has a steel grill with louvers sloping 45 degrees downwards,
making both piercing and the introduction of raindrops through
the grill practically impossible.
Changing
to strong steel louvers enables The Workhorse to
pass IEC-60974-1/14 which is necessary to pass the CE certification
.
Circuit
Improvements
The EMI
(radio noise emissions) filtering circuit is changed. The neutral
to ground capacitor is a type Y capacitor necessary for CE marking
The input
diodes have been upgraded to 1600 V
The single
volt design has enabled us to redesign the main transformer.
The voltage between each turn on the primary winding is now
reduced from 350 V to 12 V. This will drastically reduce the
arc-over risk in corrosive and humid atmospheres.
All screw
terminals are coated with silicone varnish to protect against
corrosion and prevent them from coming loose.
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