300 Watt Inverter: The Ultimate Guide to Safe Usage and Appliances You Can Run

A 300-watt inverter can be the perfect device you need to power your low-wattage appliances when on the road, perhaps it in your car, RV, or Van.

But what appliances can you safely connect to it? What are its limitations?

This post outlines what appliances you can safely connect to most 300-watt inverters, importantly which ones you shouldn’t, and what side of batteries to use to run the appliances so that you enjoy the convenience and entertainment that your appliances provide wherever you are.

What Appliances a 300-Watt Inverter Can Run

A 300-watt inverter is best suited to powering one or more low-wattage appliances provided their combined continuous power consumption does not exceed 300 watts and the combined surge power draw is up to 600 watts (estimated).

Note, these power consumption figures may differ from one inverter to another so always consult your inverter manual.

If the power draw of the connected appliances exceeds the limits above then the inverter may be damaged and/or the appliances may not work properly.

When the inverter power limits are exceededthe Dangers

If the combined power draw of the connected appliances exceeds the inverter handling limits, the inverter usually shuts down and may show an overload alarm. Depending on the inverter model this may include a beeping sound accompanied by a red LED light.

Running the car battery down

When using the car battery to power the inverter, you need to periodically run the car engine to guard against deeply discharging the car battery!

Here is a sample list of appliances with their indicative power consumption (watts) that you can connect to a 300-watt inverter (The list is not exhaustive)

  • 42″ LED TV – 50 watts
  • LED lights – 10 watts
  • Phones and Tablets -10 watts
  • CPAP (pure sine wave inverter only) – 65 watts
  • DVD player – 30 watts
  • Laptop – 45 watts
  • Fan – 20 watts (pure sine wave inverter only)
  • Mini fridge (pure sine wave inverter only; surge power does not exceed 600 watts) – 65 watts
  • Air compressor – 120 watts
  • Car vacuum cleaner – 110 watts

Examples of appliances that should not be connected to a 300-watt inverter (List is not exhaustive)

  • Microwave
  • Electric kettle
  • washing machine
  • full-size fridge

and other appliances whose continuous and surge power draw exceeds 300 watts and 600 watts respectively.

300-watt inverter USB devices

Newer 300-watt inverters may include one or more USB ports where you can plug in:

  • iPad,
  • phone,
  • kindle or any other USB device to charge.

How Many amps a 300-watt Inverter Draws

Maximum Current draw

When supplying maximum power (300 watts), depending on the inverter efficiency, the inverter draws about 27-30 amps from a 12V battery.

Plugging a 300-watt inverter into the car cigarette lighter port

Many cigarette lighter ports only handle up to 10 – 15 amps or 120 – 180 watts of power – consult your car owner’s manual. Therefore, even with a 300-watt inverter plugged in, you can only safely power appliances with a combined power draw of up to 180 watts!

To draw up to 300 watts of power, you need to connect the inverter battery terminals to the battery directly typically using alligator clips.

300-watt inverter (no load current)

The inverter uses about 4 watts (300 mA at 12V) when no appliance is plugged in provided it is switched on.

That might not look much but it can drain a car battery in about 4 days even when no appliance is plugged in!

What Gauge of Wire for 300 watts Inverter

You can use up to 10ft (3 meters) of 10 AWG battery cables on the DC side to handle up to 30 amps from the battery for a voltage drop of up to 3%.

What Size of Battery for a 300-watt Inverter

There is no one answer. It depends on how long you’d want the connected appliances to run. When supplying maximum power (300 watts), the inverter will run for nearly 2 hours with a fully charged 100 Ah AGM or 50 Ah LiFeP04 battery before discharging it to 50% and 80% of its capacity.

How Many Batteries for a 300-watt Inverter

As an example, when running at maximum capacity, the inverter can power appliances with a total power consumption of 300 watts for nearly 2 hours, when using:

  • 1 x 100 Ah AGM battery or
  • 2 x 50 Ah AGM batteries connected in parallel

Assumes batteries are only discharged to 50% of their capacity.

Note: These are just 2 of the possible battery combinations you can use.

How Long the Inverter Lasts on Battery

At maximum capacity (300 watts), the inverter will run for nearly 2 hours when connected to a fully charged 100 Ah AGM or 50 Ah LiFeP04 battery before they’re discharged to 50% and 80% of its capacity.

How long it actually lasts will depend on:

  • the actual power draw of connected appliances – switch off non-essential appliances to extend how long it lasts
  • the battery capacity (Ah). Use a larger battery capacity for a longer runtime
  • the state of charge of the battery. A partially charged battery will not last as long.

Related Questions

1. Will a 300-watt Inverter run a CPAP?

Yes, a good quality 300-watt pure sine wave inverter should be able to run a CPAP. Several CPAPs do not consume more than 100 watts of AC which is within the capabilities of the 300-watt inverter.

2. Can a 300-watt inverter Power a Battery charger?

Yes, provided the battery charger does not draw more than 300 watts. Check the AC power draw of the battery charger. If it is under 300 watts, the charger should be able to work well.

A battery charger rated 100 watts AC (DC 8 amps, 12V or DC 4 amps, 24V) will work well.

3. What Causes an Inverter to Shut down?

If the inverter is shutting off, a few things you can check right away – check for error LEDs to direct you to what the fault might be.

Some of the common faults from experience that may make the inverter shut down are:

  • connected an appliance whose power draw is more than what the inverter can safely handle – switch off some appliances
  • the inverter is overheating ( make sure the inverter is well ventilated, there is no source of heat, and that the fan works well) or,
  • the battery cables have been interchanged.
  • it could also be that the inverter is faulty and should be repaired/ replaced!

4. What size of Inverter to run a TV and DVD?

A 300-watt inverter can comfortably power a TV (50-60 watts) and DVD (30-45 watts). The estimated power draw of 105 watts in only 30% of the maximum power it can supply.

Closing Thoughts

The 300-watt inverter is a low-power inverter. Consider only if you plan to run appliances whose power consumption does not exceed 300 watts. Remember to keep the engine running from time to time to guard against draining the car starter battery.

For sensitive medical equipment such as CPAP, use a pure sinewave inverter. How long the inverter lasts depends on the battery capacity and the power consumption of the connected appliances.

When supplying maximum power, the inverter will last for over an hour when connected to a fully charged 100 Ah AGM or 50 Ah LiFeP04 battery before they’re discharged to 50% and 80% of its capacity.

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