How to Determine Battery Sizes when using Pure Sine Wave Inverters
How do you power all your electronics with no outlets available? Batteries are the answer! They can store plenty of energy depending on their capacity, and by utilizing DC-to-AC inverters, you can take that DC energy out of the battery and transform it into AC energy.
BatteryStuff.com sells modified and pure sine wave inverters and inverter/charge combo units.
Modified sine wave inverters are economical for running basic non-microprocessor devices like heaters, pumps, or power tools. These types of inverters are often installed on commercial vehicles, buses, and other applications that are just running simple devices.
Pure sine inverters, also known as true sine wave inverters, are a little more expensive than modified sine wave inverters, but they create a cleaner form of power that closely mimics your home's household plug. Today most modern-day devices, such as TVs, computers, and other household electronics, need a pure sine wave inverter in order to operate properly.
We often get calls asking, “What size battery do I need to power my Pure Sine Wave Inverter?” And, I admit that is a fair question to the beginner, so we’re here to educate our customers so they know exactly what size battery to buy.
When using true sine wave inverters, you’re powering the sine wave inverter by connecting it to a battery or battery pack. Once the pure sine inverter is turned on, it starts to invert the DC energy to AC regardless if a load is applied or not (I’ll talk about this parasitic draw later). When a load is applied, electricity is pulled out of the battery, energy is inverted, and you can now run your device. So while the beginner’s question seems right, what you really need to ask is, “What size battery do I need to power my 120 VAC device run through a battery inverter?”
Now, I know that seems like a mouthful, but that is really what we need to know in order to size your battery correctly. It isn’t so much about powering the inverter, as it is more about what your device is actually pulling out of a battery through an inverter. This may be a great place to mention that changing electrical form from DC to AC is called “inverting,” while changing from AC to DC is “converting.”
Sine Power Wave Inverter Sizing
Sine wave inverters come in all sizes, from a small micro sine wave inverter, to larger kilowatt pure sine wave power inverters. When choosing your sine waveform inverters, you need to make sure you are selecting an inverter that covers your total watt draw. Also be sure to account for a possible surge draw. Most devices such as laser printers, pumps and compressors take a lot more energy to get started, and it isn’t always listed on the device. It’s a good idea to ask the manufacturer to verify if there is a surge amp rating for the item you are trying to run. As a general rule you will need to oversize your inverter to load by as much as 75%. Meaning, if you have a 200 watt load, you should start looking at a 300 watt-sized inverter.
Now let’s talk about inefficiencies and that parasite draw. By just simply powering up the inverter, there is a no-load-draw, or what’s commonly referred to as a parasitic draw coming off the battery pack. It is a good idea to power down the pure sine wave power inverter if you are not going to be using it. Depending on the inverter, you could be losing around ½ an amp an hour if it comes with a power save mode; up to 3 amps or more if it does not. You can get an idea of how much parasitic load your inverter has by looking at the efficiency rating in the specifications.
Determining Load and Battery Pack Size
So can your inverter run your appliances, a small cabin or an entire household? Yes, they can, if the inverter rating matches your total load, but often times you want to weigh the cost. Pure sine power inverters can really run anything as long as the device falls within its specification. However, what you need to remember is the battery pack needs to be suited for the device you plan to run. This means you’re going to have to gather some specifications before you even try to size the battery pack.
Now that we’ve covered some of the basic information, you can start to size your inverter. First, you need to know what wattage inverter to select. Some devices are labeled with a wattage, but many are just listed with their voltage and amperage rating. Remember, all inverters are simply pass-thru devices, meaning your inverter rating is simply the MAX power (in watts) that it can invert at any one time. Stated again, you cannot use a 100 watt inverter to power a 200 watt load because the inverter is not capable of inverting that much energy without causing harm! Use the following formula to calculate the wattage:
Volts x Amps = Watts
Once you have the wattage figured out, it’s a good idea to figure out what size battery pack you will need. In general, higher voltage inverters are more efficient and consume less energy during the inverting process. In the end you need to determine a battery or battery pack that is capable of running your load for as long as you anticipate.
First, our DC to AC Amperage Conversion Calculator takes into account the inefficiencies of inverters, and the amperage they consume just by inverting DC energy to AC. It will tell you the hourly DC Amp draw your devices will consume. Once you know the hourly DC Amp draw you can size the battery using our calculator for sizing a 12v battery to a load.
We hope this information will help you in selecting the proper inverter and battery pack for your next project. We are always open to tech questions, so feel free to comment below if you have a question that we didn’t cover here. Or, if you would rather email us directly, you can fill out our tech question form on our Contact Us page.