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Inverter FAQs

Inverter Frequently Asked Questions (FAQ)

There are two stages involved in transforming 12-volt DC (or battery) power into 110V AC (household voltage):

STAGE 1: A power inverter uses a DC to DC transformer to increase the 12-volt DC input voltage from the power source to 145-volts DC.

STAGE 2: The inverter then converts the 145-volts DC into 110-volts AC (household voltage) using advanced MOSFET transistors in a full bridge configuration. A “modified sine wave” waveform is generated by this conversion.

Inverters, in their most basic form, operate similar to battery chargers in reverse: they take 12vDC power from a battery and run it through modern circuitry to change it into 120vAC current.

It depends on the model of the inverter and what you intend to run with it. For electrical loads up to 200 watts, the power-inverter can be plugged into the car’s cigarette lighter. This allows you to power laptop computers, small power tools, most small appliances, and even a small (13″) TV directly through the cigarette lighter. If you want to power larger equipment, or if you want to run more than one item at a time, a direct connection to your car battery is necessary. Generally, if you intend to power loads of more than 200 watts, your inverter should be direct-wired to the battery to ensure safe operation.

When using a power inverter, it is always a good idea to turn on the car’s engine every 30 minutes to help maintain your battery’s charge. Assuming your battery is fully charged and in good condition, it is possible to use a 400W power inverter for about an hour (not starting you car) without fully discharging your battery.

To find how long your battery’s charge will last with any given inverter, use this formula:

Take the wattage being used (400W) divided by the battery voltage (12 Volts) to see how many amps are being drawn from the inverter : 400 Watts/12 Volts = 33.33 Amps. Inverters only convert power at around 90% efficiency, so that means the inverter is really drawing around 37 amps (33.33 Amps / .90 = 37 Amps). A typical car battery has a reserve capacity of about 80 minutes (80 minutes @ 25 Amps). So if you are drawing 37 Amps with the 400W inverter it will completely discharge the battery in 54 minutes ((80 minutes * 25 Amps) / 37 amps = 54 minutes).

  1. Poor contact at terminals. Unhook and re-hook the 12-volt connections, and try again.
  2. Using incorrect type of voltmeter to test output voltage. Use a true RMS reading meter.

Your Schumacher power inverter is fitted with 25-amp spade type fuses, which should not have to be replaced under normal operating circumstances. A blown fuse is usually caused by reverse polarity or a short circuit within the appliance or equipment being operated.

If the fuse does blow:

  1. Disconnect the appliance or equipment immediately.
  2. Find the source of the problem, and repair it.
  3. Install the new fuse (supplied with your power inverter.)

Attention: Do not install a fuse higher than 25-amps, as this may damage the inverter. Make sure to correct the cause of the blown fuse before using the inverter again.

  1. The Battery voltage is below 11 volts. You need to recharge or replace battery.
  2. The equipment being operated is drawing too much power. Use a higher capacity inverter or do not use this equipment.
  3. The Inverter is too hot (thermal shut down mode). Allow inverter to cool. Check for adequate ventilation. Reduce the load on the inverter to rated continuous power output.
  4. Unit may be defective. See warranty and call customer service.
  1. The input voltage is below 11 volts. Recharge or replace battery to maintain adequate power input.
  2. Poor or weak battery condition. Recharge or replace battery.
  3. Inadequate power being delivered to the inverter or excessive voltage drop. Check the condition of your cigarette lighter socket. Clean or replace if necessary.

Try turning the inverter ON, then OFF, then ON again. Contact TV manufacture for start up surge and/or if the TV is compatible with a modified sine wave. An inverter producing a larger power output may be required.

When you turn on an appliance or a tool that runs on a motor, the appliance basically goes through two stages:

  1. Start up – requiring an initial surge of power (commonly known as the “starting load” or “peak load”).
  2. Continuous operation – power consumption drops (commonly known as the “continuous load”).

Before using your power inverter, you need to calculate these loads, i.e.:

  1. Starting load (at start up).
  2. Continuous load (on continuous operation).

The formula for power consumption (measured in either WATTS (wattage) or AMPS (amperes)) is: AMPS x 110 (AC voltage) = WATTS. The wattage (WATTS) or amperes (AMPS) can normally be found stamped or printed on most appliances and equipment, or in the user’s manual. Otherwise, contact the manufacturer to find out whether the device you are using is compatible with a modified sine wave.

To calculate the starting load: Starting Load = 2 x WATTS. In general, the start up load of the appliance or power tool determines whether your inverter has the capability to power it.

To calculate the continuous load: Starting Load = 2 x WATTS. In general, the start up load of the appliance or power tool determines whether your inverter has the capability to power it.

Attention: Always run a test to establish whether the inverter will operate a particular piece of equipment or appliance.

In the event of a power overload, the inverter is designed to automatically shut down. This safety feature prevents damaging the inverter while testing appliances and within your power inverter’s range.

If an appliance will not operate properly when first connected to the inverter, turn the inverter rocker switch ON (I), OFF (0), and ON (I) again in quick succession. If this procedure is not successful, it is likely that the Schumacher power inverter does not have the required capacity to operate the appliance in question.

Make sure the ON/OFF rocker switch is in the OFF (0) position. (If connecting in a vehicle, remove the cigarette lighter from its outlet.) Push the 12-volt power plug firmly into the outlet. Switch the inverter rocker switch to the ON (I) position. The LED indicator light should glow GREEN verifying the inverter is receiving power. Turn the inverter rocker switch to the OFF (0) position. (The GREEN LED power indicator light may flash briefly and/or the internal speaker may make a brief “beep.” This is normal). Make sure that the appliance to be operated is turned OFF. Plug the appliance into one of the two AC outlets. Turn the inverter rocker switch to the ON (I) position. Turn the appliance on.

Attention: The internal speaker may also make a brief “beep” when the inverter is being connected to or disconnected from the 12-volt power source.

You can use an extension cord from the inverter to the appliance without significantly decreasing the power being generated by the inverter. For best operating results, the extension cord should be no longer than 50 feet.

The LED Indicator briefly flashing when you first turn the inverter ON, is a sign if that there is a short circuit within the power supply. Turn the inverter OFF. Remove the 12-volt plug from the cigarette lighter socket. Firmly re-insert the plug. Turn the inverter ON again. If this does not remedy the problem try using a different 12-volt power source.

The inverter is shielded and filtered to minimize signal interference. Despite this, some interference may occur with your television picture, especially with weak signals. Below are some suggestions to try and improve reception.

Make sure the television antenna produces a clear signal under normal operating conditions (i.e., at home plugged into a standard 110 AC wall outlet). Also, ensure that the antenna cable is adequately shielded and of good quality

Try altering the positions of the inverter, antenna cables, and television power cord. Add an extension cord from the inverter to the TV so as to isolate its power cord and antenna cables from the 12-volt power source.
Try coiling the television power cord and the input cables running from the 12 -volt power source to the inverter. Affix one or several “Ferrite Data Line Filters” to the television power cord. Ferrite Data Line Filters can be purchased at most electronic supply stores including Radio Shack – Part Number 273-105. Try grounding the inverter with an 18 AWG (minimum) wire, using as short a length as possible.

Attention: You may hear a “buzzing” sound being emitted from inexpensive sound systems when operated with the inverter. This is due to ineffective filters in the sound system. Unfortunately, this problem can only be resolved by purchasing a sound system with a higher quality power supply.

The LED Indicator light will turn from GREEN to RED and the inverter will automatically turn itself off when:

  1. The power input from the battery drops to approximately10 volts. (When the power input drops to approximately 10.5 volts, an alarm will sound for an extended period).
  2. The power input from the battery exceeds 15 volts.
  3. The continuous load demand from the equipment or appliance being operated exceeds the inverter’s power capability.
  4. The case temperature exceeds 145 ºF.

Attention: The Schumacher power inverter is fitted with a cooling fan that runs as needed while the inverter is operating. If the cooling fan is unable to maintain a cool enough temperature for safe operation, the inverter will automatically shut down. If the inverter automatically shuts down or a continuous audible alarm is heard:

  1. Turn the inverter rocker switch to the OFF (O).
  2. Determine the source of the problem, and resolve it before continuing to use the inverter.
  • For the most effective use, place the power inverter on a flat surface.
  • Keep the inverter dry.
  • Do not allow it to come into contact with rain or moisture.
  • Do not operate the inverter if you, the inverter, the device being operated or any other surfaces that may come in contact with any power source are wet. Water and many other liquids can conduct electricity, which may lead to serious injury or death.
  • Do not place the inverter on or near heating vents, radiators or other sources of heat.
  • Do not place the inverter in direct sunlight. The ideal air temperature for operation is between 50º and 80ºF.
  • Keep the inverter well ventilated in order to properly disperse heat generated while it is in use.
  • While in use, make sure there are several inches of clearance around the top and sides of the inverter.
  • Do not use the inverter near inflammable materials.
  • Do not place the inverter in areas such as battery compartments where fumes or gases may accumulate.
  • Only connect the power inverter to a 12-volt battery.
  • Only connect the power inverter to a 12-volt battery with the supplied 12- volt power cords. Make sure the cord connections to the inverter are tight.
  • Do not modify the power cord or plug in any way.
  • Make sure the inverter is not close to any potential source of inflammable fumes or gases before connecting the inverter to the power source.
  • Make sure the power consumption of the appliance or equipment you want to operate is compatible with the capacity of the inverter
  • If you are using the power inverter to operate battery charger, monitor the temperature of the battery charger for about 10 minutes. If the battery charger becomes abnormally warm, disconnect it from the inverter immediately.
  • Use only 25-amp spade type fuses.
  • If you are powering the inverter with an automobile or marine battery, start the engine every 30 to 45 minutes and let it run for about 10 minutes to recharge the battery.
  • If you hear a continuous alarm or automatic shut down, turn the inverter OFF immediately. Do not restart the inverter until the source of the problem has been identified and corrected.
  • Disconnect the inverter when not in use, in order to avoid battery drain.

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