Marine or land vehicle, ProMariner is one of the leading brands out there. They’ve been in the battery and power supply industry for over 35 years and own almost a dozen brands that cover a variety of battery and electrical applications. Their brands include Ancor, BEP, Blue Sea Systems, CZone, Lenco Marine, Marinco, Marinco Power Products, Mastervolt, ParkerPower, Progressive Industries, and ProMariner. They specialize in both marine and RV electrical systems.
For a marine application you need an inverter that is not only shock resistant but can also stand up to the moisture around it. ProMariner’s TruePower Plus Power Inverters are the ideal choice. This model comes in 1000W Pure Sine, 1200W Modified Sine, 1500W Modified Sine, and a 2000W Pure Sine options.
Each model has all the safety mechanisms built right in including protection from circuit overload, overheating, short circuit, and reverse polarity. There is an audible alarm and automatic shut down for too low or too high of DC voltage. An on/off remote is included with the 9 foot cable and DC covers are included to protect the connections from the elements.
Additionally a on-unit dual color display provides immediate feedback on the DC to AC output, DC input and system status message area. This model is the perfect setup for a boat or even RV.
It’s tough to go wrong with a trusted brand like Energizer. With all the cheap Chinese models available online, going with a name you can trust is a must. Energizer offers a 100W, 500W, 1100W, 1500W, 2000W, 3000W and all the way up to a 4000W for your car, truck or SUV.
These energizer power inverters are modified sine wave inverters, but as mentioned earlier, should be fine for most applications. The 1100W model should suffice for most car and truck drivers, although the higher rated models are also available. Just be sure to check your car or truck’s electrical system beforehand to see if it can handle the power that the inverter will draw.
ProMariner power inverters are listed as the best brand, but Magnum Energy comes in close second. Their power inverters are incredibly reliable, offer versatile mounting positions, and are overall just well made products. For a RV, you probably won’t need a marine grade inverter, however you’re more likely to have a greater power need.
For a RV our pick is the Magnum Energy MSH3012M 3000W Pure Sine Inverter Charger Hybrid. This inverter is everything you’ll need and then some. It has all the typical protection points you’ll need and has a 5-stage charging capability. If you plan on being on the road a lot, this is the best option. Even if you don’t have a use for 2000W-3000W you can rest easy in the future knowing your system can handle the extra TV, the kids’ gaming system, or whatever unplanned item finds its way onto your RV.
Simply said, a power inverter allows you to use nearly any device, that requires your standard home wall outlet, in your boat, car, or RV. The current that runs through your typical wall outlet runs is called an Alternating Current or AC. Cars, Boats, RVs, Trucks and other vehicles use what’s called Direct Current, or DC power.
In a metaphorical sense, AC power speaks one language, say Spanish, and DC power speakers another, say English. An inverter is the translator between Spanish and English and allows one current to be converted to the other. For most applications, DC power is being converted into AC so people can watch TV, charge their phones, run refrigerators, and use other items that require an alternating current.
Your standard inverter is called a ‘standalone inverter’, or simply a ‘power inverter.’ This takes the direct current and converts it into an alternating current.
An inverter-charger combo is different from a regular power inverter in that it has 2 modes. The first being the regular inverter mode in which it converts DC power to AC power. The second, differing mode is standby or charging mode. In this mode, the inverter converts incoming AC power to charge the DC source, or use the incoming AC power to power the AC devices.
Think of it as a two-way street vs. a one-way street. A standalone inverter can only move electricity one way, from DC to AC. While an inverter-charger can convert DC to AC, and AC to DC.
You’ll notice in the title or description inverters are labeled as ‘true / pure sine’ or ‘modified sine’ inverters. Without getting too technical, pure sine is essentially a more accurate AC current. It’s truer than a modified one and many electronics require a true sine inverter to function.
The main difference between the two is price and performance. Modified sine inverters are significantly cheaper than pure sine inverters, however their performance suffers in certain electronics. Radios or speakers may sound worse due to interference and damage may be caused by the additional heat caused by slight inefficiencies in a modified sine inverter.
So, which should you buy?
If you ask me, it all comes down to use-case. A lot of electronics will work just fine with a modified sine inverter. However, if you plan on powering sensitive medical equipment, like a CPAP machine (especially one with a humidifier), a radio or other item where sound quality matters, or a device or appliance that uses a brushless motor or rectifier, buy a pure sine inverter. Otherwise, a modified sine inverter will usually work just fine.
A word of caution – be sure to pay attention to the wording used in listings online or on a package. “1000 Watts Peak Power!” is much different from “1000 Watts Continuous Power!” Peak power is what the inverter is able to handle in short bursts for a very short period of time. Continuous power is what the inverter can handle for a longer, sustained period of time.
The only time peak power will be relevant is on start up of some devices where there is a larger wattage or amp pull. Although, there would have to be a significant gap in the peak handling power vs. the continuous
Watts, Amps, and Volts are all essentially ways of expressing energy in electrical form. This post isn’t meant to be a science lesson, so here’s the practical information you’ll need to understand how they interact with each other.
WATT = (AMP) x (VOLT)
Yup, that’s it. Watts is equal to amps times volts. Most boats, cars, trucks and RVs run on a 12 volt system, so we’ll use that to calculate the your power needs down below.
Inverters are sold based on their wattage size. They typically range from a few hundred watts, all the way up to several thousand watts. If you only need to power a few small electronics like a phone, toaster, or charge a laptop, a 700 or so watt inverter will be more than enough, and your current battery will support it most likely. However, for larger applications, you will want to make specific calculations, which you can find help with below.
You need to make sure your current system can support the size of inverter you purchase. Other factors besides the posted rating will affect your current system’s output like age of battery, temperature, condition, etc. A general rule of thumb for 12V systems is you need a 1:10 ratio of DC input to AC output. So, for a 1000 watt inverter, you’ll need at least 100amps from the battery source.
Devices have different have different initial pulls and continuous use. What you’ll want to do is create a list of all the electronics you plan on running off the inverter. Add up the wattage and amperage displayed on those devices.
For example, let’s assume you plan on hooking up a microwave, 32” television, portable refrigerator, and your laptop charger. Open up Excel and create something like the setup below.
Note: When looking at any electronic that has some sort of heating element, look at the input power. The input power is what the device actually draws from the power source. A microwave labeled as 900W is likely pulling 1300W or more. You can find this in the item’s manual.
Note 2: Some electronics won’t provide the ampere pull, so you’ll have to do a little math to figure that out with the Watts=Amp(Volts) formula.
Note 3: Items that have motors or compressors will usually have higher ratings than what is printed on them. For example, in the case of a refrigerator with a compressor, it will have a higher pull (sometimes called a ‘surge’) rating each time it has to kick on vs. the average or continuous rating it may indicate. You will want to contact the manufacturer to obtain the startup wattage and amp pull. This is sometimes also referred to as “surge.” It’s common in vacuums, power tools, and other items with a brushless motor.
Microwave (FARBERWARE FMO07ABTBKQ): 1050W / 8.75A / 120V
32” TV (TCL 32D100): 45W / 2.67A / 120V
Portable Refrigerator (Whynter FM-45G): 65W / .75A / 115V
Laptop Charger (Dell Replacement HK65NM130): 65W / 3.33A / 19.5V
Total: 1225W / 15.5A
Now that we have our total, 1225W and 15.5A. This is assuming all electronics are running at exactly the same time. The microwave is heating something, the TV is on, the fridge’s compressor is running, and a laptop is charging – not recommended to run all at once unless your system can handle it, but not unlikely. The big thing to pay attention to here, is what is drawing the most and how much.
Looking at the numbers, the microwave is drawing the most amount of electricity and this item will not be running the entire time. Likely, only a few minutes at a time, if that. Furthermore, you probably won’t want to run the microwave until the generator/alternator is running or you’re connected to shore power.
We don’t notice it on land or at home, but microwaves draw a ton of power relative to other appliances.
For practical purposes, let’s just assume you’ll only be using the microwave while the engine is running. All other items are running from the power inverter.
Removing the microwave, that puts the total at 175W and 6.75A. A very reasonable number and one that is easy to work with.
So you only need a 200W inverter right?
Inverters need power to operate themselves, and 100% efficiency isn’t available just yet. You’ll need to account for these factors along with electronics you may want to plug in and use apart from those just mentioned. A good rule of thumb is to purchase an inverter that is at least double what your planned usage is.
A 400W inverter would be a good choice here, although 500W would probably be better.
What about the microwave?
Microwaves pull a lot of power and if you’re not connected to shore power or running a generator, then that bag of popcorn can drain your batteries very quickly. At minimum, a 3000W inverter would be ideal for the setup mentioned here. It’ll be ideal to have a small battery bank of sorts, which I’ve covered more in depth here.
But wait, why do the amps matter?
Amps matter as they will provide info to how long your battery (or battery bank) will last without it being charged, or while being used by the inverter. There has to be an external source recharging the power source, like an alternator for power to be harvested and that has to be equal to or above what is being drawn from the battery if using without a generator or recharging on shore power when low.
To put it in simpler terms, if you have $10 in the bank and work deposits $10 in your checking account every week and you pull $11 out every week, you’re pulling money at a -$1 deficit and will eventually run out of money. The same goes for the battery, it has to be continually replenished or very full, in order for power to be drawn from it.
In order to continually run your electronics, you will need to have a generator replenishing that electricity, such as a high output alternator, recharging at shore power when low, solar panels, wind generators, etc.
Now you need to estimate how much time each of your electronics will last before the next charge. Insert your estimated time usage in column H in the excel file. Now use the following formula to calculate the amp hours you will be pulling from the battery supply.
(Total Watts/12)(1.1)(Hours) = Amp Hours
Let’s not forget – there are other factors that will also play into this calculation. For one, it’s not good for the overall life of the battery to run it completely down to zero. Instead, only 80% or less of the battery’s total life should be used. Furthermore, different types of batteries (lead acid, zinc-air, carbon zinc, etc.) have different rates of discharge. I will be covering those in this article.
In our example, without the microwave, we’d use 288.75 amp hours if using each device for 6 hours total before another charge. As already mentioned, it’s not good for a battery to be completely drained of its reserve, then quickly recharged. Nor is it good for a battery to be drained below roughly 20% of its total power. There are batteries specifically built for these purposes called, ‘deep-cycle batteries,’ but those are covered in another article.
Instead, you should double the total amp hours you have calculated, (288.75)(2) = 577.5, and then add another 20%, (577.5)(1.20) = 693. This will help to ensure your batteries last long and do not fall short of their intended lifespan.
In an absolutely optimal scenario, you will need roughly 700Ah of power to run those 3 items at those specs for 6 hours before needing to turn on a generator 0or the motor. You can have a smaller bank of power, but keep in mind they will need to be charged more frequently in order to run all of the electronics accounted for at the 6 hour time frame indicated.
Learn more about types of batteries click here.
You’ve done the calculations and now know how much power you’re going to need. What additional features should you be looking for on top of just having an inverter?
As mentioned earlier, pure sine is preferred, but if you’re working on a budget a modified sine inverter will work fine for most applications.
Being able to know current usage is incredibly important with any sort of electrical system. Some inverters will have a built-in display while others, like Magnum’s Magna Sine inverter, have a remote display that can be attached just about anywhere on the boat. This is a wired remote, not a wireless one.
EMI stands for electromagnetic interference which can cause problems with all sorts of important equipment on your vessel. While I won’t get into the specifics of what an inverter can cause problems with, most new high-end inverters have little to no interference. Some cheaper, Chinese made inverters can cause electrical interference problems.
Having too high of voltage or too low of voltage can cause damage to your system. An inverter with a built-in voltage detector can shut off the inverter before it causes damage to the entire unit.
During regular usage some may forget how many items are actually running off of the inverter. All it takes is one electronic that has a startup spike or surge, to cause a fuse to blow in the inverter, rendering it useless until replaced. An overload warning helps to notify you there is a spike and you need to lessen the load, or it will shut down automatically to protect itself from damage.
Depending on what kind of system you have, having 120V or 240V capabilities offers you some flexibility.
Not as common on mid to lower end models, but just as important. While the name sounds confusing, it really just means protection against accidentally misconnecting wires. The positive and negative ends of a battery indicate the polarity, and if accidentally mixed up, can essentially fry the power inverter, rendering it useless.
Going back to high school trigonometry, AC and DC currents can be expressed as waveforms. If you recall, which I didn’t until entering it into my old but trusty graphing calculator, sin(x) is a perfectly sloping wave going up and down at a regular interval.
Notice how, in the image, the current alternates up and down (or in a diagram, forward and backward) . Your electronics are fed a constant supply of electricity that alternates back and forth. This probably doesn’t make a whole of sense by that sentence, so I highly recommend checking out water analogy, shown by Spark Fun Electronics (opens in a new tab).
In that example it becomes much clearer how electricity flows. You can see that it moves forward and backwards relative to the power supply.
On the other hand, car battery systems use a current system that supplies a direct and consistent level of voltage. Again using a water analogy, imagine a bucket of water with a hole on the bottom connected to a hose. If you fill this with water, the water will flow out of the bottom of the hose until it’s empty. This is essentially how DC power works. There’s a power supply that will feed whatever device it’s connected to until it’s empty.
This is why cars, RVs, trucks, and boats need to have some sort of charger in their system. In most cases, this is what is called the alternator. The alternator runs off energy produced by the gas and engine to charge the battery while the system is running, since your car’s electrical system is continually pulling power from the battery. Think of the alternator as a person that helps to refill that bucket and keep it from going empty.
For anyone that has ever worked on cars, finding the alternator is an easy job, but what about a boat? Most boats nowadays have an alternator or some other sort of charger built into the motor, especially for outboard ones.
A few final recommendations. As with everything, safety first. If you are unsure of what you are doing, heck even if you are sure, have a professional nearby for instruction and supervision. Electricity isn’t anything to mess around with.
Secondly, always buy at least a couple hundred volts up from what’s planned. You never know when you’ll have a guest, or extra electronic that makes its way onto your boat or RV that could end up overloading your system. Additionally the calculations made in this article do not take into account other factors that will affect your system such as wire length, current battery health, etc.
Third, document everything! Be sure to draw diagrams, keep manuals, and have all this information close by in the case of a breakdown or emergency. Proper documentation now, will save you frustration and time in the future.
Lastly, while there may be nothing wrong with the no-name brands on Amazon, Ebay, or elsewhere online, keep in mind you will likely not have a warranty with any of them. In the event the no-name inverter fails, fries your current system, or damages your electronics, you probably won’t be able to receive any customer service let alone compensation for damaged goods. Buy from a trusted brand in the first place so you don’t run into bigger issues down the line by trying to save a few hundred dollars.