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.
Power supplies often perform switching functions, monitor and report their own status, and automatically compensate for changing site conditions such as brown outs, power interruptions, power surges...