Everything you need to know about inverters

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• How long will my batteries last?
• Each time I run my inverter, a high pitched alarm is sounding
• How much power will my inverter draw?
• I left my inverter on all night and now nothing works
• What size batteries do I need?
• What size inverter do I need?
• What happens if someone plugs an appliance in that they shouldn’t have?
• What inverter/size do I need to run my C-pap (respirator) machine?
• My inverter is running very hot, is this alright?
• When using my television off the inverter, there are a number of fuzzy lines across the screen
• Can I run my computer / laptop from an inverter?
• My electrician will not install my inverter because there is no earth from the 240 volts AC output. Will my RCD’s work, and can the inverter be installed safely?

How long will my batteries last? 

This is the most often asked question regarding power inverters, and is the most difficult to answer. The length of time that your batteries will last is proportionate to the size of the battery, the load of your inverter, what other loads are running from the battery and what charging sources are connected. Without knowing all of these factors no one can give a precise answer.

What we can however do is look at the power requirements of the appliances you need to run, how long do you intend to run them and what other DC appliances are going to use the batteries.

Each time I run my inverter a high pitched alarm is sounding?

The high pitched alarm being experience can come from two problems: Insufficient battery cables creating voltage drop, or, a depleting battery capacity. If the alarm keeps going off, even when your batteries are fully charged, have someone look at your battery cable set up for undersized cables, or loose connections powering the inverter.

How much power will my inverter draw?

The power required to run an inverter is approximately 8-10% more than the power load of the appliances being run. This is due to the efficiency of the inverter. These days, quality inverters are between 90-92% efficient. An easy formula to use to work out how much DC Amps you will use from your battery is, simply divide the AC wattage of your appliance by 12 (or 24 if a 24v system) and times this number by 1.1 to get a very close estimate of the DC draw.

Inverters(bn,pt,ja) will draw power from your batteries when not in use, and the unit is turned on. This can vary from around .02 amps right up to 2amps depending on the unit and design of their standby systems.

I left my inverter on all night and now nothing works?

If you leave your inverter turned on with no load attached, the average draw from your batteries will be 1 amp per hour; 24amps per day; or 168 amps over a week. The simplest solution to this is to just turn the inverter off when not required as the battery drain then becomes zero. Many of our inverters feature standard or optional remote on/off controls.

What size batteries do I need?

The simple method of working this out, is to find the largest constant AC load you plan to run from your inverter (in most cases a microwave is the largest appliance), and divide this wattage x 5 (20% of your load). This will give you a rough idea of how much battery capacity you require to sustain your loads. With the example above, the microwave draws around watts AC, so a battery bank of around 200amp hours would be required.

What size inverter do I need?

Sizing your inverter is a difficult task, and is not made any easier by different brands and manufacturers rating the power of their units at different temperature ratings. The power output of an inverter is dramatically decreased as its internal temperature rises, this is sometimes called its 5, 10 & 30 minute rating; but in reality if the inverter cannot remove the heat quick enough, then the output power will rapidly drop off. Many of the inverter brands on the market are rated to supply full output power up to 25°C and start to de-rate the output power from this point on. Some industrial models with supply full output upto a staggering 40°C.

Basically, add up all of the AC loads you want to run, then determine if you want to run all of these items at the same time. If not, choose the largest load in the system and size the inverter 50% more to cover peak surge loads.

What happens if someone plugs an appliance in that they shouldn’t have?

The great advantage of the power inverter is its ability to surge to power output levels well in excess of its normal continuous ratings. These levels are generally twice the normal output power for 1-2 seconds to allow for starting of larger, or inductive type loads. If the load is too large for the power output (e.g someone connects a hair dryer to a 500watt inverter), then the inverter simply shuts the power down. Depending on the inverter, an audible alarm will sound, or the inverter will simply restart to try the load again. Always keep in your mind that a power inverter has limitations, mainly its power size.

What inverter/size do I need to run my C-pap (respirator) machine?

For C-pap machines to function correctly they require a pure sine wave power output. These machines tend to draw around 200watts, which equates to 18amps per hour. For a normal night of sleep (7-8 hours), you would need a battery bank of around 200amp hours (and a suitable recharging system). The ePOWER 400watt inverter is perfect for basic C-pap machines, contact us for details if your machine has a heater inbuilt.

My inverter is running very hot, is this alright?

Power generation creates heat, so yes your inverter will get warm. For this reason it is important to keep your inverter in a location that is cool and dry, and installed in an orientation that will help assist with ventilation (e.g. you are not blocking the intake vents or fans with clothes or tools). If your inverter gets too warm, it will simply shut down until the unit cools down. As mentioned above, the hotter your inverter gets, the less AC power it will deliver (hence the new designs such as Prosine that allow for rapid removal of warm air from the inside workings).

When using my television off the inverter, there are a number of fuzzy lines across the screen.

Again a result of using a modified sine wave inverter. Many appliances react to this type of waveform (such as televisions generating lines across the screen, or radios having a hum through the speakers). There is not a great deal you can do to stop this except to upgrade pure sine wave inverter. Try twisting the battery cables together and then wrap them in alfoil, as well as moving the inverter as far away from the interfered appliance as possible (these are merely suggestions and may not work in every case).

Can I run my computer / laptop from an inverter?

The answer to this is very much the same as the Televisions above. Modified sine wave inverters can be used on either a computer or laptop, however if the laptop is to only ever be powered from the inverter then a pure sine wave inverter (such as the ePOWER or ePRO) should be used, as the modified sine wave inverters will actually destroy the laptop battery pack.

My electrician will not install my inverter because there is no earth from the 240 volts AC output. Will my RCD’s work, and can the inverter be installed safely?

Unlike mains power, the AC output of the majority of inverters do not have its neutral bonded to earth. Both the line and the neutral are isolated from earth, the chassis, and from the DC input. As a result of this isolation, the earth cannot become part of a current path returning current back to the output of the Inverter. To rectify this common installation problem, many installers are recommending a Mains Earth Neutral Connection (MEN), which bonds the Neutral to the Earth, thereby nominating the Neutral conductor. Enerdrive have overcome this problem with the RCD-GPO inverter kits (400/600//W) and the new ePOWER AC transfer inverter range (,W). The RCD-GPO kits are designed for the home handyman to install without the need for an AC electrician. The new AC transfer inverter range incorporates the M.E.N connection internally running via the in-built RCD safety switch and only active when operating in inverter mode. Both Enerdrive models meet the current Australian AC Electrical standards and registered with ERAC (Electrical Regulatory Authorities Council of Australia)

If you like what you’ve read, you can find even more helpful advice by joining our Enerdrive Unplugged Facebook group! The group is for sharing installations, errors in installations and best practice install guidelines utilising Enerdrive Products across Caravans, Campers and 4WDs. Acting as a space to leave feedback and comments, get inspired and learn from other veteran users along the way!

What is an Inverter?

A power inverter is a device that converts low-voltage DC (direct current) power from a battery to standard household AC (alternating current) power. An Inverter allows you to operate electronics, household appliances, tools and other electrical equipment using the power produced by a car, truck or boat battery or renewable energy source, such as solar panels or wind turbines. An inverter gives you power when you are "off the grid" so you have portable power, whenever and wherever you need it.

What is the difference between an inverter and inverter/charger?

An inverter simply converts DC (battery) power into AC power and then passes it along to connected equipment. An inverter/charger does the same thing, except it is an inverter with batteries attached. It remains connected to an AC power source to continuously charge the attached batteries when AC utility power – also known as shore power – is available.

An inverter/charger is a quiet alternative to gas generators, with no fumes, fuel or noise to deal with. During prolonged outages, you may need to run a generator occasionally to recharge the batteries, but the inverter/charger lets you run the generator less often, conserving fuel.

What is a Power Inverter Used For?

Simply put, a power inverter delivers AC power when there's no outlet available or plugging into one is impractical. This could be in a car, truck, motorhome or boat, at a construction site, in an ambulance or EMS vehicle, at a campground or on a mobile medical cart in a hospital. Inverters or inverter/chargers can provide power for your home during an outage to keep refrigerators, freezers and sump pumps operating. Inverters also play an essential part in renewable energy systems.

DC to AC Conversion: How Inverters Work

The direct current, or DC, power that comes from a battery flows in one direction from the battery's negative terminal, through the completed circuit and back to the positive terminal of the battery. However, typical 12-volt or 24-volt batteries provide only relatively low-voltage power. Depending on your location, appliances need to run on 120-volt or 230-volt AC power.

120V Power Inverters

230V Power Inverters

An inverter tackles this disparity by increasing the voltage and using transistors or semiconductors to reverse the polarity of the DC input back and forth rapidly, sending it one way through the circuit, then very quickly reversing it and sending it the other way. In most cases, it does this 60 times per second (60 Hz).

Frequently Asked Questions

What is the difference between an inverter and an Uninterrupted Power Supply (UPS)?

Inverters and UPS systems both provide power from batteries in the absence of AC power. A UPS typically includes the battery and battery charger in one standalone unit. Batteries for an inverter are generally user-supplied.

A UPS system also can have communication with the equipment that it is powering, letting the equipment know that it is operating on standby, giving it shutdown warnings or communicating with the human in the loop. Inverters typically don't have this capability.

Depending on the inverter, it will respond to a power outage in 4.2 to 16.7 milliseconds. A UPS responds in a fraction of that time, making the UPS a better choice for applications that must remain powered, such as computer networking equipment.

What is the difference between an inverter and a generator?

A generator runs on gasoline, diesel fuel or propane to produce electric power. An inverter converts DC power stored in batteries to AC power needed to run tools, electronics, appliances and other devices.

A generator may be a better choice when large amounts of power are needed for prolonged periods. However, an inverter/charger is a cleaner and greener choice. It is quiet and fume-free, making it preferable for residential areas or for use indoors.

An inverter/charger can work along with generator power when the generator is running, allowing you to turn the generator off for periods of time to save fuel without turning off your equipment.

Link to Jiwei

What is an inverter/charger?

An inverter/charger converts DC (battery) power into AC power and then passes it along to connected equipment. When it is connected to an AC power source, it continuously charges the attached batteries. During a power outage, the inverter/charger will automatically switch to battery power to provide power to connected equipment. The batteries will be recharged when the AC power source becomes available again.

How do I use an inverter for basic home emergency backup power?

Most often, emergency home backup power runs off a standard car battery, essentially turning your car into a generator. The car should be kept running while the inverter is in use to prevent the battery from becoming depleted. The inverter can still be used if the car is off, but this is not recommended for prolonged periods. If you do use the inverter without the engine running, start your car up every hour and let it run for about 10 minutes to recharge the battery.

To create an emergency backup system without a vehicle, you can hook up two 12V car batteries to one inverter. That will provide enough power to run the average household refrigerator for up to two days, depending on the size of the batteries and the size of your fridge. It's a smart idea to have a spare battery or two on hand in case the duration of the power failure exceeds your battery runtime.

Look for an inverter with a wattage capacity greater than the appliances you need to keep running. Refer to Table 2: Typical Wattage of Common Home Appliances below. Ready to buy? See our recommended inverter/chargers for emergency home backup power.

Can I power my home using my car and a power inverter?

Absolutely! First, know the total wattage of the appliances you need to keep running using the guidelines given below. This will help you buy the right inverter for your home emergency backup system.

An inverter is not waterproof, so keep it out of the rain, as well as away from dust and direct sunlight. Although you can connect the inverter to the vehicle's battery using jumper cables and alligator clips, the preferred method is with a ring terminal that fits securely over the inverter post. Then connect an extension cord no more than 200 ft. from the inverter to the appliance(s) you want to run. Beyond this distance, you are likely to experience signal loss.

To keep the battery charged, you should run your car for about 10 minutes every hour. The inverter will still work when the car is off, as long as you have not depleted the battery.

Does an inverter provide surge protection?

Yes. Because an inverter converts DC power to AC power, the AC output is conditioned before it reaches your equipment. The inverter provides stable output voltage and frequency to protect your equipment from power surges and line noise interference, allowing your equipment to perform at its peak.

Can an inverter power a refrigerator or freezer?

Yes, but there is an important point to keep in mind. When a refrigerator or freezer cycles on, it will draw a high start-up surge of power, several times the wattage it requires when running continuously. Make sure your inverter can handle the peak surge. As a rule of thumb, ensure your inverter can handle a peak surge of 500-750W for a refrigerator and 500-W for a chest freezer.

What kind of battery should I use with my inverter?

Most commonly, 12V batteries like the one in your car are used to power inverters. Heavy-duty inverter/chargers are available that use 24V, 36V or 48V batteries for applications requiring higher wattages. Make sure the batteries you choose match the input voltage capacity of your inverter.

Deep cycle batteries look like ordinary car batteries, but can provide sustained power over a longer period of time and run reliably until discharged up to 80%. They are ideal for inverter applications, especially in RVs, boats and off-the-grid renewable energy because of their ability to be almost completely discharged before they need to be recharged.

Along with batteries, you'll need a fuse and fuse holder. One of the easiest types of fuses to use is an "ANL" fuse that can be spliced into the positive wire coming from your battery pack.

What type of cable should I use to connect batteries?

Most inverters are sold without cables so the user can select the cable best for their application. In general, the distance between the battery and the inverter should as short as possible, ideally 10 ft. or less. Cables used for connecting inverters should be type SGX, which is the type of cable typically used to connect a battery to a car's electronic system and ground it.

The below recommended wire gauge table is a general rule of thumb. The actual size wire you need will vary based on the voltage of your battery, the total amps your equipment is drawing and the length of the cable. Our best advice is to stick to what is specified in your inverter's owner's manual.

Table 1: Recommend Wire Gauges

Inverter Continuous Wattage Recommended Wire Gauge < 500W8 AWG 500 - W4 AWG - W2 AWG - W1/0 AWG > W4/0 AWG

Is a pure sine wave inverter really important?

Depending on what equipment you're using the answer could be a resounding yes. A pure sine wave inverter produces a smooth, sinusoidal AC output with very low harmonic distortion. Sensitive electronics, variable-speed tools, medical equipment such as oxygen concentrators, TVs and A/V components, fluorescent lights with electronic ballasts and any appliances with microprocessor control will not run well under modified sine wave power.

What size power inverter do I need?

To know the right size inverter for your application, you need to total up the wattage of all the appliances, tools or electronics that will run off the inverter at the same time. Many appliances and power tools have their wattage rating indicated on a label on the product itself or in the item's owner's manual. If your devices indicate only amps, the wattage can be arrived at using this simple formula:

Volts x Amps = Watts

Example: You want to run a small mini fridge. You know from the product label it uses 0.7 amps. In the U.S., voltage is 120. Therefore:
120 x 0.7A = 84 Watts

Now factor in how long you want the device to run. This is its runtime. Assuming you are using 12V batteries, divide the total watts by 12.

In our mini fridge example:
84 ÷ 12 = 7 DC amps

This is the DC amp hours required to run the fridge for 1 hour, if it were to run continuously. You'll need to observe the fridge running for a period of time to determine how long it actively runs, so observe it for 15 minutes and record the length of time it runs.

Let's say you want the fridge to run for 12 hours before the batteries need to be recharged. Your observation shows the fridge runs for 5 minutes during the 15-minute observation period. Use this formula:

Active runtime required = Minutes Running ÷ Minutes Observed x Total Runtime Required
12 Hours = 5 Minutes ÷ 15 Minutes x 4 Hours

Next, multiply the DC amps required by the number of hours you estimate you can operate your fridge without charging the batteries.

7 DC Amps x 4 Hours = 28 Amp-Hours

Now you should factor in an adjustment for variable conditions that might affect how frequently the fridge runs, such as warmer weather, opening the fridge, etc. A good rough estimate is a factor of 1.2.

28 Amp-Hours x 1.2 = 33.6 Amp-Hours
This is the minimum amp-hours your batteries must supply.

How much wattage do common home appliances and tools use?

This table of common appliances, electronics and tools will help you estimate your needs. Be sure to check the product label for the actual wattage requirements, and remember that many tools and appliances have significantly higher peak surge requirements when they start up/cycle on.

Table 2: Typical Wattage of Common Home Appliances

Device/Appliance Typical Wattage Desktop Computer with Monitor200 - 400W Laptop Computer20 - 75W Inkjet Printer15 - 75W Laser Printer500 - W Satellite Dish75W Gaming Console125W LCD TV, 32"50 - 70W LCD TV, 42"90 - 250W DVD Player40 - 50W Table Lamp with Incandescent Bulb60W Table Lamp with CFL Bulb13 - 15W Table Lamp with LED Bulb6 - 9W Fluorescent Tube Light40W Blender300 - W Toaster800 - W Coffee Maker, Drip550 - W Coffee Maker, Keurig200 - W Microwave Oven - W Mini Fridge350W Refrigerator, 15 cu ft.240W Chest Freezer 15 cu ft.180 - 500W Vacuum Cleaner300 - W Tabletop or Box Fan50 - 120W CPAP Machine200W Hair Dryer - W Flat Iron800 - W Sump Pump850 - W Space Heater - W Furnace Fan75 - 400W Electric Drill700W Electric Screwdriver60 - 300W Circular SawW Jig Saw350W