Inverter Basics: 115VAC at Your Fingertips

Inverters provide locksmith service vehicles, boats and recreational vehicles with house current (115VAC) required to remotely operate electrical devices. Unlike a generator, an inverter is an electrical power converter that changes 12 VDC (Direct Current) into 115VAC (Alternating Current) using the vehicle’s alternator and a 12VDC battery.

Inverters come in two basic types - the true (pure) sine wave inverters and modified sine wave inverters. A true sine inverter is a high efficiency converter of 12 VDC to 115 VAC. It will output pure sine wave current just like the electric current in your home or business, delivering high quality waveform with little harmonic distortion. True sine wave inverters have high surge capacity, as some electronic items require additional power to initially begin operation. True sine wave inverters are more expensive than modified sine wave inverters.

Locksmiths are investing in inverters to power tools, recharge the batteries for cordless tools or operate key machines, grinders and other types of machinery. Some devices require true sine wave output from the inverter or they will not operate properly. These include some variable speed motors, some key machine motors, some power tool battery packs and flashlights that are plugged directly into 115VAC.

Depending on the model, inverters can provide from 100 to several thousands of watts continuous duty. Every inverter also has a peak wattage output for surge requirements. For inverters with less than 300 watts peak (150 watts continuous), there are cigarette lighter plug-in models. For greater power demands, a 12VDC inverter must connect directly to a 12 VDC battery.

Inverters are sold by the amount of wattage that can be produced. Two terms are used to describe the output: peak wattage and continuous wattage. When purchasing an inverter, use the continuous wattage value.


Choosing The Right Inverter

Before choosing an inverter, determine the amount of power required and the output of the vehicle’s alternator. How many devices are going to be powered at the same time? This could include a laptop computer, a key machine and a battery charger. The more devices that must be operated at the same time, the more wattage required.

However, the wattage required and the amount of wattage a vehicle alternator and battery can output are usually not the same. Want is usually greater than available output.

Most van and pickup truck alternators will produce 100 to more than 200 Amps at full load. From this amount, about 30-50 Amps are required to operate the vehicle. A 110 Amp output alternator turning at full capacity (14.4 VDC) produces about 1500 Watts. However, when an alternator heats up to normal operating temperature, the output current diminishes. Continuous Amperage provided to the inverter can drop as much as 50 percent depending upon the variables. Determine the output of your service vehicle’s alternator. If it is not sufficient, high power alternators are available from most vans and trucks.

Important: Before installing an inverter, make sure the alternator is in good operating condition.

Read your vehicle owner’s manual or contact the parts department to determine how much amperage your vehicle’s alternator can deliver to an inverter. Providing the Vehicle Identification Number should get you the amount. This way, you can avoid spending too much on an inverter that your alternator is not able to power sufficiently. The cost of the inverter, both true sine wave and modified sine wave, increases with the greater the amount of wattage. In addition, check the optimum (peak) efficiency of the inverter. The lower the efficiency, the less wattage produced.

Always know the amount of wattage required by a piece of equipment before connecting it to an inverter. Do not overload the inverter by plugging in too many wattage-hungry devices at the same time. For example, the average drill motor requires approximately 400 watts. A circular saw requires approximately 1400 watts. A laptop computer requires approximately 10-60 watts. An average cordless battery pack requires approximately 70-120 watts.

When you determine the amount of watts that will be used at one time, add another 50 percent. This gives surge consideration and will ensure proper performance. For example, a drill motor requires approximately 400 watts. Add 50 percent of the wattage to be on the safe side. Thus watts should be provided to operate the drill motor using an inverter and an extension cord.

Note: If a very long extension cord is required to get from the vehicle to the jobsite, consider purchasing a heavier gauge (lower number) wire extension cord to compensate for the resistance.

If the electrical device requires more than the power available from the alternator and the battery, the device will operate for a short period of time until the voltage drops to an insufficient level. Some inverters have overload protection.

If the inverter is overpowered, when the device is activated, the power surge can overwhelm the conversion circuitry possibly causing a shutdown if fused or damage to the attached device(s), the inverter and/or the electrical wiring, etc. if not fused.

When installing a larger inverter, the inverter must be connected directly to a battery. The following chart provides suggestions for the wire gauge (AWG) when operating an inverter where the draw will be up to the specified amounts.

Using a dedicated battery will improve the performance. It will also allow you to operate the inverter for short periods of time without having to operating the engine.

Remember, no matter how sophisticated the power consuming device is, it cannot change the laws of physics. As Albert Einstein stated, “Energy can neither be created nor destroyed; it can only be changed from one form to another.”

For most installations, a second battery installed in parallel wiring will improve efficiency. Install a battery isolator between the positive terminals as a precautionary measure. Install circuit breakers or fuses at each end of the wiring to protect against damage or fire. Also, if the inverter drains the battery, the vehicle can still be started, which can then charge the second battery.


  • Inverters normally heat up when operating. Do not place the inverter next to heat sensitive materials. Place the inverter in an area that has cross ventilation.
  • Keep cable from battery to inverter as short as possible.
  • Install an inline circuit breaker at each end of the power cables.
  • Ground the inverter chassis to the vehicle body.
  • Twist the power cable one to three twist per foot to minimize radiated interference.

FYI: Depending upon the inverter, there may be a slight spark and beep when the unit is first connected.

Having 115VAC in your service vehicle makes life easier. Purchasing the right inverter and using the proper AWG wire to make the connections will provide years of satisfactory service.