Ambrell 3542, Manual

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Technical Information 63
A
MBRELL
801-9526-00.doc
Precision Induction Heating
The load may be thought of as being in series with the coil. At any fixed tap, the EASYHEAT is
presented with higher impedances corresponding to better coupling. Alternatively, an open coil
or a very lightly loaded coil presents the EASYHEAT with a lower impedance. The lower the
impedance, the more closely the application resembles a shorted coil with corresponding shorter
run intervals.
Tapping the EASYHEAT workhead transformer is done to match an application’s load
impedance to the EASYHEAT’s output impedance and is done at the transformer primary.
Higher taps can generate higher secondary currents but at the expense of lower compliance
voltage. Increasing the transformer tap causes a particular load to look like a higher impedance to
the EASYHEAT. In contrast, lowering the tap will generate less current than higher taps, but it
does so at a higher compliance voltage and causes the same load to look like a lower impedance.
Correct tapping is critical , assuring proper regulation and eliminating excessive peak currents
(hence, voltages) from being generated at the coil and resonating capacitor.
When an EASYHEAT’s workhead transformer tap has been incorrectly set to too low a tap for a
particular load (worst case would be an open coil), the run interval is kept very brief as this
condition is seen as approaching a shorted coil. While the generator may be able to maintain
regulation at low levels and meet application requirements, the short run time is less efficient and
the heat sink will run hotter than it needs to when at high levels, increasing mains current draw.
Additionally, even when in regulation, short run times can require very high peak currents to
meet the average current setpoint. These higher current peaks will correspond to a higher voltage
peaks across the resonating capacitor and coil.
Current peaks are hardware limited to protect the power module and to protect the resonating
capacitor against excessive voltage peaks as determined by the capacitor rating set at the
workhead menu. An incorrectly-tapped workhead transformer can make the generator unable to
achieve setpoint due to the proper action of one of these protection circuits.
In contrast, a heavily loaded coil is a poor fit for a high tap because the available voltage may not
be enough to generate the desired current level, even with a continuous run interval. While
operation remains efficient, output current would be unregulated and seen as not matching the
setpoint.
Importantly, EASYHEAT LI limits the maximum continuous coil current to 600A. This is to
keep the internal workhead buss and capacitor temperature within an acceptable level. While
more current is allowed to be generated, it is only for a limited duty cycle.