Your new PROwatt 250 power inverter is a member of the most
advanced line of DC to AC inverters available today. It will
give you years of dependable service in your vehicle, boat, RV,
or remote home.
To get the most out of your PROwatt 250, it must be installed
and used properly. Please read the installation and operating
instructions in this manual carefully before installing and using
your PROwatt 250. Pay special attention to the CAUTION and
WARNING statements in this manual and on the PROwatt 250.
CAUTION statements identify conditions or practices which
could result in damage to your PROwatt 250 or to other equipment. WARNING statements identify conditions or practices
that could result in personal injury or loss of life.
2. How Your PROwatt 250 Works
An inverter is an electronic device that converts low voltage DC
(direct current) electricity from a battery or other power source
to standard 115 volts AC (alternating current) household power.
In designing the PROwatt 250, Statpower has used design techniques previously employed in computer power supplies to give
you an inverter that is smaller, lighter, and easier to use than any
other inverter with a similar power rating.
2.1 Principle of operation
The PROwatt 250 converts power in two stages. The first stage
is a DC-to-DC converter that raises the low voltage DC at the
inverter input to 145 volts DC. The second stage is the actual in-
1
verter stage. It converts the high voltage DC into 115 volts, 60
Hz or 50 Hz AC.
The DC-to-DC converter stage uses modern high frequency
power conversion techniques that eliminate the bulky transformers found in inverters based on older technology. The inverter stage uses advanced power MOSFET transistors in a full
bridge configuration. This gives you excellent overload capability and the ability to operate tough reactive loads like lamp
ballasts and small induction motors.
INVERTER SECTION
145 VDC
+
INPUT
-
DC-DC CONVERTERDC
CHASSIS GND
+
GNDNEUTLINE
AC OUTPUT
115 VAC
POWER
MOSFET
Figure 1. PROwatt 250 - Principle of Operation
2.2 PROwatt 250 output waveform
The AC output waveform of the PROwatt 250 is called a
“quasi-sine wave” or a “modified sine wave.” It is a stepped
waveform that is designed to have characteristics similar to the
2
sine wave shape of utility power. A waveform of this type is
suitable for most AC loads, including linear and switching
power supplies used in electronic equipment, transformers, and
motors. This waveform is much superior to the square wave
produced by many other DC to AC inverters.
The modified sine wave produced by the PROwatt 250 is designed to have a RMS (root mean square) voltage of 115 volts,
the same as standard household power. Most AC voltmeters
(both digital and analog) are sensitive to the
the waveform rather than the RMS value. They are calibrated
for RMS voltage under the assumption that the waveform measured will be a pure sine wave. These meters will not read the
RMS voltage of a modified sine wave correctly. They will read
about 2 to 20 volts low (i.e. about 100V) when measuring the
output of the PROwatt 250. For accurate measurement of the
output voltage of the PROwatt 250, a true RMS reading voltmeter such as a Fluke 87, Fluke 8060A, Beckman 4410, or
Triplett 4200 must be used.
average value of
3
145 Volts peak
115 Volts RMS
8.3 milliseconds
Figure 2. PROwatt 250 Modified Sine Wave
3. Installation
3.1 Power source
For optimum performance, the power source must provide between 11 and 14.5 volts (22-30 volts for PROwatt 250/24V)
and must be able to supply sufficient current to operate the load.
The power source may be a battery or a
power supply. As a rough guideline, divide the power consumption of the load (in watts) by 10 (by 20 for PROwatt
250/24V) to obtain the current (in amperes) the power source
must deliver.
well-regulated DC
Example: Load is rated at 120 watts. Power source must be
able to deliver:
CAUTION: The PROwatt 250 must be connected only to batteries with a nominal output voltage of 12 volts (24 volts for
PROwatt 250/24V). The PROwatt 250 will not operate from a
6 volt battery (12 volt for PROwatt 250/24V) and will be damaged if connected to a voltage source above 16 volts (32 volts
for PROwatt 250/24V).
3.2 Connecting to power source
The PROwatt 250 is equipped with a cigarette lighter plug for
connection to the power source. The tip of th e plug is positive
and the side contact is negative. Connect the plug to the cigarette lighter socket in a vehicle or to the cigarette lighter socket
on a battery pack.
CAUTION: CONNECT THE 12V PROwatt 250
DIRECTLY TO POWER SOURCE WHEN OPERATING
ABOVE 150 WATTS
The cigarette lighter plug is suitable for operating the 12V inverter at power outputs of up to 150 watts. If the PROwatt
250/12V power inverter is to be used for extended periods at
power levels above 150 watts, direct connection to the power
source is recommended. Removal of the lighter plug is not necessary for the PROwatt 250/24V.
To make a direct connection, follow these steps:
1) Cut the cigarette lighter plug from the PROwatt 250 cord.
One conductor on the PROwatt cord is marked with a red or
white stripe. This is the positive conductor.
5
2) Connect additional wire to the cord if required to reach the
power source. Use wire with a conductor area of at least 12
AWG (3.3mm
cord and insulate them with good quality electrical tape or
shrink wrap tubing. Total length of cable to the power
source should be limited to a maximum of 2 meters (6 feet).
3) Make a good connection to the power source terminals. For
temporary use, heavy duty battery clips such as Radio Shack
part #270-341 are suitable. For permanent installation, use
heavy-duty ring tongue or locking fork/spade terminals.
4) Power to the PROwatt 250 can be controlled by a switch inserted in the circuit between the power source and the PROwatt 250. Use a switch rated at a minimum of 12V/25A continuous current, such as Radio Shack #275-704 for the 12V
PROwatt 250. Use a switch rated at a minimum of 24V/15A
continuous current, such as Radio Shack #275-701 for the
24V PROwatt 250. Alternatively, you can use a lighting relay in the power circuit and control th e relay with a low current switch.
CAUTION: If the power source is not overload protected,
use a fuse (30A for PROwatt 250/12V or 15A for the PROwatt 250/24V) to protect the wiring between the PROwatt
and the power source.
2
), solder the connections to the PROwatt 250
CAUTION: REVERSE POLARITY CONNECTION WILL
DAMAGE THE INVERTER
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