Rick's Free Auto Repair Advice

Power inverter for your car

Power inverter for your car — What to look for in a power inverter

Before you jump at the cheapest power inverter for your car, there are some things you need to know, like:

How much can your power port handle
How many watts of power does your device need
Does your device need “pure sine wave” power or can it accept “modified sine wave” power.
How long do you intend to use the inverter?

How much power can your power port handle?

The “power ports” in older vehicles were just cigarette/cigar lighters. They were usually fused at around 8 amps. But in newer vehicles, the accessory port is often fused at 12 or 15 amps.

Let’s convert that to watts. Amps x volts = watts. With the engine running and battery voltage at 13-volts, you get a potential of 104 watts on an 8 amp circuit, 156 watts on a 12 amp circuit and 195 watts on a 15 amp circuit.

Generally speaking, watts are watts. However, it takes power to convert DC power into AC power. So you can’t conclude that your 15 amp power port will give you 195 watts of AC power. You’ll lose between 10% to 20% of power from doing the conversion. That’s the power to run the circuitry to reverse the polarity of the electronics and the loss due to heat.

In reality, purchase a power inverter for your car that is rated at 20% more watts than you’ll need.

How many watts of power does your device need?

This is easy to find. Just look on the label of your laptop charger, drill or other device. If the current draw is listed in amps, here’s the conversion

Amps X volts = watts.

Let’s take a look at this Lenovo laptop power supply. It needs 3.5 amps at 120 volts (3.5 X 120= 420 watts) from the power inverter in order to convert the power into the 230 watts @ 20 volts the laptop needs.

laptop power supply
Now let’s assume that you bought this Maxpart 1000 water power inverter for your car. I mean, it says 1000 watts, right? But will it work with your 15 amp power port? Nope. Why? Because your 15 amp power port can only supply up to 195 watts. You’d need at least 33 amps to make this work. To get that, you’re going to have to connect this power inverter to your car battery or tap into an used fuse slot in your fuse box.
Maxpart 1000W power inverter

What’s the difference between a pure sine wave and a modified sine wave inverter?

Your car’s alternator produces AC power that’s converted into DC power using diode (one-way electrically “valves). In generating AC current the alternator spins an electromagnet (the alternator rotor) past a coil of wire (stator). As the North/South poles rotate, you get a smooth transition of electrons moving back and forth from a positive to negative direction (see AC sine wave below). Once the AC to DC conversion is complete the electrons only flow in one direction (negative to positive if you believe in the negative flow theory or positive to negative if you were taught conventional electrical theory).

AC sine wave

The power inverter’s job is to take that unidirectional DC power and make it mimic an alternating current. To do that, the inverter literally reverses the direction of the electrons. The inexpensive power inverters do that by creating an all positive then all negative electron flow. Since it can’t produce a gentle curve up and down like a normal sine wave, it tries to imitate the curve by increasing and decreasing the amplitude in steps (see the modified sine wave below).

Modified sine wave from power inverter

What devices can use a modified sine wave?

Simple electrical devices like plug-in power tools, light bulbs (non LED) can use modified sine wave power. However, though a modified sine wave will power a drill it will run hotter than if the same drill were powered by a pure sine wave inverter. Most modern electronic devices can’t. They need a pure sine wave.

Don’t use a modified sine wave power inverter for your car with laptop computers, audio/video players, power tool battery chargers, or any sophisticated electronic devices.

What is a pure sine wave power inverter?

Pure sine wave power inverters produce extremely clean and reliable power, just like you’d get by plugging the device into a power outlet in your home. If you want to power your laptop, power tool battery charger, or any sophisticated electronic device from a power inverter in your car, it must be a pure sine wave inverter.

Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN