8. Choose the Battery
Battery type and battery size strongly affect the performance of the power inverter. Therefore,
you need to identify the type of loads your inverter will be powering and how much you will be
using them between charges. To determine the minimum battery size that you need to operate
appliances, please follow these steps:
1. Determine the wattage of each appliance and/or tool you will need to simultaneously operate
from the inverter. To do this, read the labels on the equipment to be operated. Usually, power
consumption is shown in watts. If it is shown in amps, multiply by 110V/230V to determine the
◆ Battery Requirements
When possible, recharge your batteries when they are approximately 50% discharged, or sooner.
This gives the batteries a much longer life cycle than recharging when they are more deeply
discharged.
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POWER INVERTER
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INTERFERENCE WITH SOME EQUIPMENT
◆ Buzz in Audio Equipment
Some inexpensive stereo systems may emit a buzzing noise from their loudspeakers when
operated from the inverter. This occurs because the power supply in the audio System does not
adequately filter the modified sine wave produced by the inverter.
The only solution is to use a sound system that has a high quality power supply.
◆ Television Reception
When the inverter is operating, it can interfere with television reception on some channels.
If interference occurs, try the following:
1. Make sure that the chassis ground screw on the rear of the inverter is solidly connected to the
ground system of your vehicle or home.
2. Make sure that the television antenna provides an adequate (“snow-free”) signal and that
you are using good quality cable between the antenna and the television.
3. Keep the cables between the battery and the inverter as short as possible, and twist them
together with two to three twists per foot.( this minimizes radiated interference from the cables.)
4. Move the television as far away from the inverter as possible.
5. Do not operate high power loads with the inverter which the television is on.
The modified sine wave has an RMS (Root mean square) voltage of 110/230volts, which is the
same as standard household power. Most AC voltmeters (both digital and analog) are sensitive to
the average value of 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 20 to
30 volts low when measuring the output of the inverter. For accurate measurement of the output
voltage of this unit, use a true RMS reading voltmeter such as Fluke 87III, Fluke 8060A, Fluke
77/99 series or Beckman 4410.
wattage.
2. Estimate the number of hours the equipment will be in use between battery recharges.
3. Determine the total watt-hours of energy by multiplying the wattage of your appliance by the
time it will be working (in hours). For example, 60W laptop working for 5 hours will require
60W*5h = 300Wh (watt-hours) of energy. 250W TV working for 30 min will require 250W*0.5h =
125Wh.
4. Calculate the approximate amp-hours (Ah) which the battery bank will have to supply to your
appliance to enable it to work for a certain amount of watt-hours, by dividing watt-hours by 10
(for 12V battery bank), or 20 (for 24V battery bank) or 40 (48V battery bank). E.g. 300Wh for
laptop from a 12V inverter will require 300Wh / 10 = 30Ah of battery energy.
5. Add all the amp-hours (Ah) for each appliance to get the total battery capacity required for
your system.
Note: Some appliances required high surge power to start, then consume less power. And some
appliances are not operating for long periods of time. For example, a typical home-use coffee
maker draws 500watts during its brew time of 5minutes, but it maintains the temperature of the
pot at about 100watts. Typical use of a microwave is only a few minutes, sometimes at lower
power. Some exceptions to brief operating times are lamps, TVs and computers.
Important: The power inverter must be connected only to batteries with a normal output
voltage of 12 volts when you use a 12V inverter. The unit will not operate from a 6 volt battery,
and will sustain permanent damage if connected to a 24 volt battery.
Caution: Loose connectors may cause overheated wires and melted insulation. Check to make
sure you have not reversed the polarity. Reverse polarity connection will result in a blown fuse
and may cause permanent damage to the inverter.
◆ Recharging Batteries
The battery's back up depends on the battery capacity (Ah) and your appliances power (Watt)
The method to calculate the backup time:
Battery capacity (Ah) * Input voltage (Volt)/Loads power (Watt)
For example:
Battery capacity = 150Ah
Input voltage = 12Volt
Loading power = 600Watt
So:
(150Ah*12V)/600Watt=3 Hours
Note: this calculation of back-up time produces a theoretical value, and doesn't take into
account the self-consumption of the inverter. The actual back-up time may be significantly shorter
than this value, particularly for larger loads, old and partially discharged batteries.
◆ The Calculation of the Battery’s Back Up Time
