Inverter / Charger Installation General Operations and AC and DC

Inverter / Charger Installation General Operations and AC and DC
Inverter / Charger Installation
General Operations and
AC and DC Connections
The Inverter is just one piece.
• Sometimes, a
tendency is to mount
the inverter and
batteries, and “make
it work”
• It is better if we pay
attention to the other
practices that make a
good, reliable
Elements of the Inverter / Charger
Elements of the Inverter / Charger
• DC to AC Inverter;
• AC to DC Battery Charger;
• Transfer Switch between using AC Incoming Power or Battery Power;
• Transfer Switch to choose between two different AC Sources;
• Relays to perform a variety of user selected functions; and
• Computer with LCD screen and user input for customizing most of the
This presentation is based on the Xantrex
Model SW inverter, observed most
frequently during field visits, and is
applicable to models SW 4048 and SW
5548, which were most prevalent. With
minor variations, this information can be
applied to Outback Power equipment and
other manufacturers’ equipment.
Modes of Operation:
AC IN Operational
• The SW can be connected into an electrical scheme in
many different ways. However, some common elements
remain unchanged from installation to installation.
• The over-riding purpose of the SW is to provide
continuous power to the loads (AC OUT). If there is
power (with the proper characteristics) at the AC IN
terminals, then the equipment will utilize this power to:
• Power the Loads (AC OUT); and
• Charge the Batteries – through the built-in Battery
• The following diagram shows the operation and power
flow when there is proper power supply at the AC IN
Modes of Operation:
AC IN Operational
When AC IN Power is lost
• When power is lost to AC IN, the on-board
computer switches the transfer switch so that the
AC OUT loads are fed from the battery through
the DC to AC Inverter, and the inverter is turned
on. This happens nearly instantaneously.
• When this situation occurs, the entire load is
powered by the battery bank. Of course, this can
not go on forever, and when the battery bank
reaches a programmed low state of charge
(depicted by low voltage) the system turns off.
(Alarms can be installed to warn operators of
impending cut-out, see section 10.2)
Modes of Operation:
AC IN Operational
AC IN 1 and AC IN 2
• The SW model inverter/charger includes
provisions for two AC Inputs. Field visits
did not reveal any field application where
both inputs were used. In many cases,
both inputs will not be needed, but there
are many applications where they would
be useful. The basic system diagram
changes only at the AC IN provisions:
AC IN 1 and AC IN 2
Connections to the Real World
The SW equipment is strictly the core equipment necessary to
monitor and switch power sources to feed the given load.
In order to become part of the entire wiring system, it is essential to
use proper wire sizes, and the proper fusing and disconnecting
means to (a) protect the wiring, (b) protect the equipment, and (c)
protect people.
In many cases, when improper auxiliary equipment is used (or not
used at all) not only is the result unsafe, but it also results in
improper operation, battery failure and un-powered loads. These
problems can be avoided by following some guidelines on
connecting the SW equipment to the rest of the electrical system.
In the next section, the manual will discuss AC OUT connections,
AC IN connections, and finally DC and battery connections.
Connections to the Real World
AC OUT Connections
• All of the AC terminal blocks inside the SW AC box (on
the left hand side of the unit) will accept up to #6 AWG
conductors (16mm2). It is advised that this #6, 10mm2,
or 16mm2 wire be used.
• The AC OUT terminals should be supplying only a predetermined set of loads. These loads should have been
the basis of the selection of the size of the battery bank
and the size of the inverter. These loads should be fed
from a separate, dedicated circuit breaker panelboard
connected to the AC OUT terminals. The conductors
carrying the load current from the SW to this panelboard
should land first in either a fused disconnect switch, or a
main circuit breaker on the panelboard.
AC OUT Connections
AC IN Connections
There are several options for AC IN connections:
• AC IN from a grid supply only
• AC IN from a generator supply only
• AC IN from both a grid supply and a generator
• AC IN from a combined grid / generator supply.
The following section discusses each option.
AC IN 1 – Grid Supply
AC IN 1 – Grid Supply
Even though the output of the inverter is limited to either 33 or 46
amps, it is important that the 60 amp circuit breaker is used and
conductors feed the AC IN terminals. This is because when the grid
power is on, it is performing two functions: First it is feeding the
loads, and secondly it is powering the battery charger. The battery
charger could draw up to as much as 30 amps depending on how
the settings are programmed.
If it is not possible to provide a 60 amp supply to the ACIN 1
terminals of the SW, then certain settings MUST be changed in the
programming, and the design needs to be studied to be sure that
the batteries will receive enough charging power. See the discussion
under “Programming” for more information on this subject.
AC IN 1 – Grid Supply
AC IN 2 - Generator
AC IN 2 - Generator
The amount of power that can be drawn from the generator needs to
be calculated (based on the size of the generator and other loads
the generator may have to supply). If, for example, a 6KW generator
is dedicated to this inverter, then the maximum power that can be
obtained from the 6KW generator (if it is single phase) is 6000w /
120V or 50Amps. In this case, a 40 amp breaker to feed the SW and
a therefore, 40A wire will be sufficient.
If the generator is designed to support other loads as well, then how
much of its power can be dedicated to the SW equipment needs to
be determined and the breaker and conductors needs to be sized
accordingly. The proper programming needs to be completed to
match this value.
The equipment needs to be programmed so that it does not try to
pull any more power than the circuit breaker feeding it (or any more
power than the generator feeding it.). This would trip the breaker
and/or overload the generator. See the section on “Programming”
for more information.
AC IN from both Generator and
AC IN from both Generator and
• When both grid power supply and generator
power supply are available, the above is the
preferred method for connecting to the system,
particularly when the generator size requires a
smaller circuit breaker and feeder that would be
allowed by the grid input power.
• However, in most cases with grid and generator
available, the two sources are combined in a
transfer switch, with one set of conductors going
into the SW, as shown below.
AC IN from both Generator and
AC IN from both Generator and
Discuss pros and cons of the combined
Generator / Grid AC IN wiring versus the
separate Generator and Grid AC wiring.
AC IN and OUT Connections
Summary of AC IN and AC OUT Connections
There are several different configurations possible for the AC IN and
AC OUT connections. Key factors to consider in planning the
installation are:
Sizing of the conductors for the greatest possible current that they
may experience;
Using dedicated, separate, AC OUT circuit breaker panelboards for
the loads decided to be powered by the SW;
Bringing separate AC IN 1 Grid conductors and AC IN 2 Gen
conductors to the SW equipment panel; and
Providing disconnecting means for the ACIN 1, AC IN 2, and AC
OUT conductors to be able to isolate the SW equipment from any
power wires.
Additionally, the SW Cabinet should be installed in a readily
accessible location (not in a storeroom), where ventilation from left
to right is unobstructed, to provide adequate cooling.
AC IN and OUT Connections
All of things cost money and take added
effort, but compare the cost of the
electrical work to the cost of the medical
equipment we are trying to protect.
DC Connections
DC Connections
Discussion topics here will include:
• Proper DC Cable connections to the SW
• Overcurrent / Disconnecting means in the
DC Input cables;
• Connecting Strings of Batteries; and
• Paralleling the Strings of Batteries.
Connecting the DC Cables to the
DC Cable – from Battery to Inverter
Battery Cable Sizing (use 4/0)
DC Cable – from Battery to Inverter
Current Limiting Fuses in
Positive Cables (4/0)
Positive and Negative
Cables kept together.
DC Circuit Breakers in
positive feed to individual
System shown is Outback
Series Connections
Sometimes the series connections are made with copper bus bars.
These are 2V batteries, in sets of 24 in series
Series Connections
More often, series connections are made with cables.
These are 12V Batteries – in sets of 4 in series
Connecting Batteries
Connecting Batteries
Paralleling Batteries
“ILSCO” common
bus terminal blocks
for 4/0 cables
4 Strings of 48VDC
batteries connected in
parallel, and 2 home
run cables back to
Keep the Battery Cables Together
We need to always keep the positive and negative battery cables
together, as long as possible. As battery cables are separated by a
distance, they have much more inductance than if they are close
together. This induction creates an induced current which opposes
the applied current. This leads directly to loss of inverter
performance and greatly reduced efficiency. With cables separated
by 48”, the inductance can be 3 times greater than the inductance
recognized if the cables are together.
The result can be as dramatic as the inverter failing to allow certain
loads to start, because it can not get the required current to flow in
the batteries. This has been seen in cases where installers have
done a very neat job in the installation but have grouped all positive
cables on one side of a wall, and the negative cables on the other
• We have Covered
• Elements of the Inverter / Battery System
• Connections to the Real World
– AC OUT Connections
– AC IN Connections
– DC Connections
• Still to come:
– Programming
– Operations and Maintenance
– Troubleshooting
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