12 | SAMLEX AMERICA INC.
SECTION 3 |
General description &
Principles of Operation
Models
The following models are covered in this manual:
G4-2012A -12 vDC Input, 120 vAC output, 2000vA
G4-2524A - 24 vDC Input, 120 vAC output, 2500vA
G4-3524A - 24 vDC Input, 120 vAC output, 3500vA
Features and benefits
benefit 1:
This unit is a Bi-directional Inverter / Charger with a Transfer
Relay that operates either as an inverter OR as a battery charger. It uses
a common Converter Section that can work in two directions – in one
direction it converts external AC power to DC power to charge the
batteries (Utility / Generator Mode) and in the other direction, it converts
the DC power from the battery to AC power (Inverter Mode). This allows
the same power components to be used in both directions resulting in
high-energy transfer efficiency with fewer components
benefit 2:
The waveform of the output voltage is a Pure Sine Wave like
the waveform of the Utility / Grid Power / Generator. In some inverters,
the output waveform is a stepped square wave (termed as Modified
Sine Wave). Modified Sine Wave has a number of limitations e.g. -
produces higher order harmonics leading to increased radio interference
that may affect audio and video devices, produces higher heating in
motors and transformers that may lead to their premature failure, is
not suitable for laser printers and other devices that are based on zero
crossing (clocks) or phase control (dimmers and transformer less battery
chargers using SCRs).
Please read white Paper titled "advantages
of Pure sine wave inverter over Modified sine wave inverter"
available online at www.samlexamerica.com (Home > support
> white Papers).
benefit 3:
It is a powerful, cost effective, micro-controller based Inverter
Charger with a Transfer Relay consisting of 3 devices in one unit -
Inverter, Battery Charger and Transfer Relay. When used as an AC Power
Back Up Unit in conjunction with an external AC power source,
it provides an un-interruptible AC output voltage that is stable in
voltage and in frequency despite interruptions, brownouts or sags in
the Utility / Generator.
benefit 4:
The AC input power can be fed to the G4 either from
utility or from generator. Normally, utility power has a stable frequency.
However, the frequency of the generator may vary appreciably based on
the value of the load and the sensitivity of engine speed governor.
When a load is transferred from a primary AC source of power to
another backup AC source of power through a Transfer Switch, there
will be a finite interruption of power to the load for the transfer to
take place. When AC power fed to a reactive load (consisting of circuit
inductances and capacitances) is interrupted, the voltage across the
load does not die instantaneously but dissipates in tens of milliseconds
due to residual power stored in its reactive components (combination
of its circuit inductances and capacitances). The voltage and phase of
the residual power in the load after interruption of the AC source are
the same as the voltage and phase of the AC source at the time of
interruption. A mismatch of phase and frequency of the primary AC
source and the backup AC source at the time of transfer is likely to
damage the backup AC source / load. For a smooth and safe transfer
to take place, the phase and frequency of the backup AC source that
is going to take over the load has to be synchronized with the phase
and frequency of the primary AC source that is being removed from the
load. A very fast transfer is desirable for sensitive loads like computers
etc because a longer transfer time may crash the computer if the power
supply of the computer does not have adequate “Hold Up Time” (“Hold
up Time” is the duration of power interruption that can be withstood by
the computer to prevent crashing. This time is usually > 20 millisecond).
In the G4 series, the phase and frequency of the internal Inverter
Section is always kept synchronized with the external input from
the utility / generator for fast and safe transfer.
benefit 5:
The high power maximum charging current of the Battery
Charger Section is adjustable. This allows selection of appropriate
charging current based on the Ah capacity of the battery (Normally, 10%
of the Ah capacity of the battery). very high charging current for lower
Ah capacity batteries will reduce the percentage of the returned capacity
and will damage the battery due to overheating.
benefit 6:
The Battery Charger Section of these units is a powerful,
micro-controller based, 4 Stage Charger - 80A for the 12v, 2000vA
version and 70A for the 24v, 2500vA and 3500vA versions. 4 Stage
Charging Algorithm is used – Bulk, Boost, Equalization and Float. (The
Equalization Stage is selectable). Equalization Stage is desirable for the
proper health of Wet Cell Batteries. Further, the charging voltages and
currents are programmable within the ranges given below to take care
of a wide range of battery types like flooded, AGM, Gel Cell, Lead
Calcium, etc.:
12V Version
24V Version
Boost (Absorption)
14 to 16v
28 to 32v
Float
13 to 15v
26 to 30v
Equalization
14 to 16v
28 to 32v
Charging current
10 to 80A
(in steps of 10A)
10 to 70A
(in steps of 10A)
An automatic Adaptive Charging Algorithm is used that ensures that the
battery is completely charged in a safe manner for longer battery life. In
this algorithm, the time the battery remains in Boost / Absorption and
Equalization Stages is proportional to the time the battery remains in the
Bulk Charge Stage. A battery that is deeply discharged will remain in Bulk
Stage for a longer duration and will require longer time in the Boost /
Absorption and Equalization Stages for complete charging. On the other
hand, a battery that is almost completely charged will remain in the
Bulk Stage for a shorter duration and consequently, will remain in Boost
/ Absorption and Equalization stages for a shorter duration. This will
prevent overcharging / boiling of the battery. In other inverter chargers
that execute Boost / Absorption and Equalization Stages for a fixed time
of 4 to 8 Hours, a nearly fully charged battery may overcharge / boil and
hence, will reduce battery life.
benefit 7:
A Battery Temperature Sensor BTS-G4 (Fig 2.4, page 8) has
been provided to ensure optimum charging by modifying the charging
voltages based on temperature if the battery sees very wide temperature
swings. Without temperature compensation, the battery life is likely to be
drastically reduced because the battery will be undercharged during
