PU300/PU500 INSTALLATION MANUAL
10232-10.doc
Polyamp AB, Sweden
www.polyamp.com
Page
6 (10)
Figure 3. Load regulation with voltage drop U
d
between output and load
3.3 Adjusting output voltage when units
are paralleled on the output
1.
Connect and start all converters according to
2
Installation on page 4. We recommend using the
series diode and separate cables as mentioned
above in
3.2 Connecting converters in parallel
on the
output.
2.
Measure the voltage at the load. Connect
voltmeters as showed in
Figure 4
. If you have
only access to one voltmeter you must move it
around to make the adjustments. This will take
time but is of course possible.
Figure 4. Adjusting output voltage
3.
To
increase
the output voltage.
i.
Increase the output voltage by turning
the potentiometer marked ”V.ADJ”
clockwise on the unit with the lowest
output voltage until you reach the desired
voltage at the load or until the output
voltage does not increase anymore (as
the unit is in current limit). To find the
unit with the lowest output voltage you
can measure the voltage difference
before the series diode, as in
Figure 4
.
ii.
Repeat from i. until you reach the desired
output voltage at the load.
4.
To
decrease
the output voltage.
i.
Decrease the output voltage by turning
the potentiometer marked ”V.ADJ”
counter clockwise on the unit with the
highest output voltage until you reach the
desired voltage at the load or until the
output voltage does not decrease
anymore (as the other units supply all
current). To find the unit with the highest
output voltage, measure the voltage
difference before the series diode, as in
Figure 4
.
ii.
Repeat from i. until you reach the desired
output voltage at the load.
5.
To achieve good current sharing, adjust all
converters so that the voltage difference before
the series diode is 0.00V between all units that
are connected in parallel and so that the voltage
at the load is still the desired.
4 Multiple loads at the output
If you are using several loads, we recommend
fusing them separately with fast acting fuses. Some
considerations regarding short-circuits should be
taken. See below.
4.1 Short-circuits
1.
If there is a short-circuit in one branch and the
total current in all branches
does not
exceed
105% of the nominal current of the converter
(see label on front panel), the output voltage
will not be affected. The time for the fuse to
blow can be calculated from the data sheet of
the fuse if you know the short-circuit current
trough the fuse.
2.
If there is a short-circuit in one branch and the
total current in all branches
does
exceed 105%
of the nominal current of the converter, the
output voltage will drop until the fuse is blown.
Depending on the impedance of the short-circuit
(whether it is abrupt or merely an overload) and
the resistance of the load cables, the effects of a
short-circuit will vary.
Long cables reduce short-circuit currents,
resulting in longer delay until the fuse is blown
and hence an increased voltage dip. Light
overload does not necessarily result in a blown
fuse.
To reduce the voltage drop at short-circuit and if
any branch has more than approximately 30% of
the total output current of the converter, a large
external capacitor is recommended. Such a
capacitor will supply the peak current needed to
blow the fuse, see
Figure 5
.
To calculate the
capacitor needed, use the following formula:
