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CENTRIC 3x480, User Guide, rel. 1.7
2.7
Dc-to-dc voltage converter modules
The dc-to-dc converter modules are located below the UPS modules (see Figure 1 or Figure 2). Each dc-dc
converter module contains two dc-to-dc converter blocks. Each converter block is dedicated to a single
UPS module. For every two UPS modules there is one dc-to-dc voltage converter module.
The dc-dc converter modules and the UPS modules, and the relation between them, can be seen in Figure
1 (240 kVA model) and Figure 2 (120 kW model).
The lowest dc-dc shelf is shelf 1; the next shelf up is dc-dc shelf 2, and so on. Dc-dc shelf 1 supplies dc
power to UPS shelves 1 and 2. Dc-dc shelf 2 supplies power to UPS shelves 3 and 4, and so on up to dc-
dc shelf 4. Therefore, if you are operating a Centric 3x480 Vac system with less than its full complement of
modules, it is recommended that the UPS modules and the dc-dc modules be installed beginning from the
lowest shelf and moving upwards.
No harm is done if there are more dc-to-dc converter blocks than modules. The extra dc-dc blocks (that is,
those without a corresponding UPS module in place) will simply enter “sleep” mode.
If a UPS module doesn’t have a corresponding dc-dc block the UPS modules will still function normally,
except that in battery mode there will not be any dc current supplied to that module. There is no common
dc bus between the UPS modules.
2.7.1
What the dc-dc converters do
The dc-dc modules convert the battery voltage of 540 Vdc to the 840 Vdc required by the UPS modules.
The dc-dc modules make it possible to supply the UPS modules with 840 Vdc using fewer batteries than
would otherwise be required. The Centric 3x480 Vac system requires a total of 40 12-volt batteries. Without
the dc-dc modules, at least 70 12-volt batteries would be required in order to supply 840 volts to the UPS
modules. So the use of dc-dc voltage conversion modules enable the user to save on battery costs.
The dc-dc modules also increase safety by reducing the total battery voltage to which the technician is
potentially exposed when replacing batteries.
The dc-to-dc modules extend battery life by charging the batteries with minimal ripple current, and by
reducing the effects of varying load types (active vs. reactive loads) on the charging process.
