PU300/PU500 INSTALLATION MANUAL
10232-10.doc
Polyamp AB, Sweden
www.polyamp.com
Page
5 (10)
cable will not bridge the insulation barrier in
case of coming lose.
4.
Start the converter with your external input
disconnection device.
Beware of hazardous voltages!
The output voltage can be ad10% to
-5% of nominal output voltage with the
potentiometer marked V.ADJ on the front
panel. Clockwise turn increases the output
voltage. The potentiometer has 15 turns. If
you have connected units in parallel on the
output, the procedure of adjusting the output
voltage is described in
3.3
Adjusting output voltage when
units are
paralleled on the output
on page 6.
4.
When the converter is disconnected, switch-off
the input voltage with the disconnecting unit.
Disconnect the input cables first, then output
and last the protective case connection.
3 Parallel connection
If a redundant power supply system is requested,
two or more converters can be connected in
parallel. To achieve redundancy the number of
converters must be dimensioned to carry the whole
load even if one converter is faulty. Connect your
load to the + output after the series diode (cathode),
see
Figure 1
.
Another reason for connecting two or more
converters in parallel is to get more power. Use the
output with series diode, see
Figure 1
.
Figure 1. The series diod output marked with an
arrow (option on PU500).
3.1 Series diode on the output
The series diode protects the converter output from
external voltage sources. A series diode is
necessary if the output is connected in parallel with
another power supply or if you require redundant
operation. If a converter breaks down with an
internal short-circuit on the output and other
converters are connected in parallel on the output,
the broken unit will short-circuit the others if the
series diode is not used. This might cause excessive
heat or even fire in the faulty unit.
If the series diode is used, the alarm relay will
switch to ”ALARM” on the faulty unit if one
converter breaks down in a redundant power supply
system. Otherwise there will be no alarm indication
from a faulty converter unless all units are in
current limit and the output voltage drops 10%
below nominal output voltage.
Max. output current may have to be derated when
using series diode. See data sheet.
Do not forget to fuse the inputs separately to
achieve redundancy.
3.2 Connecting converters in parallel on
the output
The expected life of the converter is dependant on
converter temperature. It is therefore important for
paralleled unit to share the load as equal as possible
to reduce the converter temperature. To achieve
good current sharing the converters must have
separate cables to the load. The cables should be
dimensioned to have a voltage drop, U
d
, between
the converter and the load at maximum current
capacity, see
Figure 2
and
Figure 3
.
Figure 2. Voltage drop U
d
= U
out
- U
load
When the series diode
is used, which we
recommend, the voltage drop should be
approximately 1.0% of nominal output voltage
(to also compensate for the negative
temperature coefficient of the diode).
When the series diode is
not
used
, this is not
recommended,
the voltage drop should be
approximately 0.5% of nominal output voltage.
Note that the voltage drop affects the load
regulation (the voltage at the load), see
Figure 3
.
