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Example
If, for example, the secondary rms voltage is 40 Vac, the peak
bus voltage will be 1.414 * 40 - 1.5 = 55 volts. A transformer
with 115 Vac primary and 40 Vac secondary would produce 55
volts peak bus voltage under nominal line conditions and at rated
loading.
However, if the line voltage increases 10% the peak bus voltage
increases to:
at rated transformer loading.
Load regulation must also be accounted for when selecting the
transformer. Transformers are designed to produce their specified
secondary voltage when loaded by their rated current. For
currents less than rated, the secondary voltage will increase.
Signal Transformer gives the following load regulation data for
its line of rectifier transformers:
This means that the secondary voltage of a 100 VA transformer
will increase 10% over the specified voltage if the load current is
reduced from rated current to zero. Since the stepper drive(s)
might sometimes be disabled, the full regulation effect as well as
maximum line voltage should be considered when selecting the
transformer.
1
The VA product is obtained by multiplying the specified secondary voltage (Volts rms) by the
rated secondary current (Amps rms). For example, a 24 Vac transformer with a rated secondary
current of 1 Amp has a VA of 24.
6415 Installation & Hardware Reference Manual - Rev E
(1.414 * 1.1 * 40) - 1.5 = 60.7 volts
VA Rating
1 - 100
100 - 350
> 500
Load Regulation
10%
8%
5% or less
C - 3
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