Bosch PLN-24CH12, PRS-48CH12 User Manual

Page 1 of 6

Security Systems

Addendum to manual

PLN-24CH12 / PRS-48CH12

7

1 General

This addendum to the manual of the PLN-24CH12 and PRS-48CH12
chargers contains important information for proper installation and
operation.

2 R

The PLN-24CH12 and PRS-48CH12 battery chargers have built-in Ri
monitoring. This is important and mandatory for compliance to EN54-4.
It means that the charger monitors the summed resistance of the
wiring, fuse, electrical connections and the Ri of the battery. It warns
the user when the battery has aged and must be replaced. The Ri
supervision threshold has been selected such that when the Ri of the
battery has increased to the maximum allowed value the backup power
system can still power the VACIE.

Because the resistance of the wiring and the connections is
incorporated into the measured Ri, it is important that these resistances
are very low, otherwise even good batteries will generate a fault. This
makes sense because a VACIE can take up to 150 A from the battery
and then every 10 mohm will already cause a voltage drop of 1.5 V,
limiting the maximum available output power from the VACIE.

-monitoring

i

Bosch Security Systems B.V.
PO Box 80002
5600JB Eindhoven
The Netherlands
www.boschsecurity.com
15-Jan-2021

Page 2 of 6

Security Systems

Addendum to manual

PLN-24CH12 / PRS-48CH12

7

3 Wire gauge selection

As installer, you should take into consideration all major contributors to
the total resistance, being:

• Battery R

• Cables – very dependent on length and gauge.

• Battery fuse – typically 1 to 2 mohms.

• Connections – typically 1 mohm.

The actual values need to be checked with the battery supplier and
fuse supplier. Also be aware of possible influences of connections, e.g.
pay attention to screw-tightening of connections.

Keep some margin to avoid false positive faults. Stay at least 20%
below the selected Ri-limit, because there is some tolerance on the
measurement accuracy.
To help you selecting the right cable gauge, two tables are provided
with maximum cable lengths per wire gauge for a number of battery
types. Use this guideline to determine the needed gauge.

The first table is for 24 V battery systems and the second table is for
48V battery systems. The maximum length is given in cm and depicts
the total cable length, i.e. all the wire length from charger to battery, the
bridges to connect the batteries in series and the length back to the
charger. Five different cable gauges are shown with cross-sectional
areas of 6 mm2 to 35 mm2. Then two different jumper settings can be
selected for the threshold of the Ri-supervision of the charger, the
setting ‘50’ is intended for loads up to 100 A, the setting ‘75’ for loads
up to 150 A.
Allow for up to 5 hours for the unit to report a battery fault.

In some cases the maximum resistance is already exceeded, even for
zero length cables. This is not allowed and indicated as n.a. (not
allowed).

i

and make.

Bosch Security Systems B.V.
PO Box 80002
5600JB Eindhoven
The Netherlands
www.boschsecurity.com
15-Jan-2021

– typically 2 to 6 mohm per battery, depending on size