What is and what does an inverter do?

Initially I wasn't really convinced whether to do an article strictly about inverters but I had two discussions recently where it seems that the information was a bit misunderstood, of course an important contribution here being made by the seller. So today we continue our series of educational articles about electricity in the campgrounds with a topic that is ... electrifying ... namely automotive inverters. This is the fifth episode in a series of educational videos about offcamping electricity, so if you haven't seen how to size a system, what batteries to choose and what solar panels to choose, I recommend seeing those first. It'll make a lot more sense. We started this series after many interesting discussions in our facebook community CamperVan Romania, where we learn of course how to build campers and all kinds of expedition cars. And, since these questions often come up in other RV or motorhome communities, we thought it would be easier to make an easy-to-follow educational series

Generically, an inverter will convert current from 12/24 or 48v DC to 230 or 110 for Americans, AC. That is, from what we use in our car or USB sockets to what we use in our home sockets. There are inverters that are also chargers, i.e. they can take 230v from the grid and convert to 12/24/48v to charge the batteries. We'll talk about those towards the end.

There are a few aspects of inverters to pay attention to: power in W, which includes peak power in w, own consumption, efficiency and pure sine. With all these aspects the producers are quite generous in their interpretation, not to say that they lie directly or lie by omission. And we need to discuss them one by one, to see what they mean, why they are important and how the sellers manipulate them, because it kind of annoys me and is basically a kind of deception. Sorry, it's not a kind of, it's outright cheating.

First of all we have the power in W at normal consumption but also at peak These numbers tell us how much the inverter can sustain as constant consumption and maximum consumption, over extremely short periods, i.e. seconds or in generous cases tens of seconds. In general the peak is twice the normal current.

Let's look at a case study: you go to an online shop and see a 1000w inverter. You know you have a small espresso machine that consumes 850w and, you do a simple calculation like 850 is less than 1000, and you say ready, that's it for me. Add to cart. The next day, the FAN guy knocks on the door with the package, you unpack it, mount it and want to do the first test. Surprise of the show ... the inverter goes into protection and that is instant, knock out in 2 seconds, and you are left with an empty wallet and an empty soul and you wonder what the hell is going on? Few people know that Chinese wats are not the same as European quality ones. They are smaller, much much smaller, about 60-70% of normal. So essentially, the first problem with power is that the watts stated on the box are not those in the inverter. This problem has existed for years with low end inverters. I know because I have a 600w one that was plugged into my Pajero and it squeaks if I put two Macbooks and a cooler in it, although theoretically it should work fine. Chinese inverter from Well that doesn't do what it promises, case in point with me. Plus case in point with the espresso machine, from a friend. I was actually there when it happened.

But that's not the worst thing as the watts are a little lower than on the box. People have got used to this samsarella. More recently, however, a completely new thing has appeared in inverters, namely, instead of passing the rated power per description, peak power is passed. So our 2000w inverter actually only knows 2000w for 15 seconds, or what we call peak power, before it goes into protection, as in reality it is a 1000w inverter. That's not ok at all and I see it as a kind of cheating. I've seen it on several large sales sites, it's not an isolated case. The convention, since time and earth, is to pass rated power, not peak. It's like me saying I can run 3 minutes a mile like a world champion. But I forget to mention that I can run 3 minutes per kilometre for about 100 metres until I stop in the first bushes and give up the ghost. But I'm coaxing the information to put me in a good light and it's essentially completely untrue.

The market is starting to get flooded with this kind of stuff and the result, in the short term, will be broken electronic equipment and fried inverters. I'm not defending big sites or marketplaces, because partners post all kinds of stuff. At first it's the fault of the manufacturers, because it's misleading information done with good knowledge and then of the importers who want to sell anything after they give it a little polish and say it's professional or premium or whatever sad marketing words they use in their descriptions. So, you always look at the power rating and ... unfortunately ... 2000-3000w pure sine inverters at 100 euros only exist in dreams. What you find on websites or, worse, on OLX, often have false specifications that are not true.

The next important criterion for me is pure sinus / modified sinus. As the name implies, a pure sine inverter will deliver a very stable and high quality current, which resembles the graph of the sine function in mathematics. Whereas the modified sinus will look like a series of stairs going up and down. Essentially, the current comes with gallons and is of inferior quality to the modified sinus. It is quite possible that some electric motors will not start at the modified sine, although the inverter power would correspond to their starting. Also some electrical and electronic appliances are sensitive to interference created by the modified sinus. This includes refrigerators and microwaves, but not only.

Also, many battery-operated appliances such as phones, tablets or laptops can have their life shortened or their chargers damaged by the poor quality of current produced by a cheap inverter with a modified sine wave. The reality on the ground is that at least 5 out of 10 inverters that say pure sine are not pure sine, and the manufacturers and sellers know this. But it relies on the fact that no one is demented enough to put the oscilloscope on the inverter to see what the wave actually looks like. Likewise, almost no one makes the connection between how much phones or laptop chargers heat up when sitting in the inverter, an effect that is also caused by the poor quality, gated current that passes through them. So, as with power, and pure sine is often in pen. To have a benchmark, a 1000w pure sine inverter, with 2000w peak and real efficiency over 90%, is not likely to be under 1300-1400 lei except on Black Friday, maybe. At 300-400 lei, we're getting a relatively power-hungry inverter, most likely with a modified sine, which will noticeably affect the rest of our electronics, but will do so slowly, slowly, arduously, in the long run. So you, as a user, will never make the connection between cause and effect. And, again, this is what manufacturers and sellers rely on: nothing blows up immediately, but degrades over time, and so it becomes hard to argue that it was the inverter at fault. Although physics doesn't lie much. Oh, and there's another important point to remember. Apart from very high quality inverters, in general the power will be shared between the outlets in the inverter and will not exceed 1500W per output. Regardless of what manufacturers promise, for sustained consumption (and we're not talking one-minute tests here) and larger consumers, it's best to look for an inverter that has terminals not sockets, to which you can build a 230v socket system. I repeat, it depends from case to case, but this is where the generic approach is.

This brings us to a less debated aspect, namely the inverter's own consumption and efficiency. Here I won't even bother looking at the versions made on the boat, because if they lied to me on sinus and power, I think we're all wasting our time on these finesses. Let's start on the right foot and take three big brands that are market leaders: Mastervolt AC Master 1000, Dometic SinePower 1012 and Victron Phoenix 1200, three quality inverters that come with data sheets you can rely on. At Mastervolt, the standby power consumption is reported to be less than 0.1A and when switched on but without consumers it is less than 1.5A with a 92% efficiency of conversion from 12 to 230v. We add here a total harmonic distortion or THD of 3% and ±0.5 hertz, so super good values for a pure sine quality. As an aside, that pure sine line isn't perfect either. It has small variations which are called harmonic distortions and the lower the value, the better. We won't get into the subject as we're going straight to Narnia, but it was important to know what THD is. Moving on, for the Dometic SinePower 1012 we have 350mA standby consumption, 1 amp on and over 90% efficiency, but it doesn't tell us exactly how much over 90. It can be 90.5 or 99%. My impression is that it's over 90 but up to 91, as all marketing calls it. We have a THD of 5% and ±0.5 hertz, so marginally weaker than the Mastervolt in this respect. The latest is the Victron Phoenix 1200 which in the data sheet states an efficiency of 92%, a consumption in zero load of 8w or 0.6A approximately and in standby of 2w or 0.15A approximately. As for the current we have a THD of 2% and the same half hertz variation.

By comparison, all these inverters give an infinitely better current than what you get at home from the grid from Enel, Engie or whoever you have a contract with. I've seen the specs, let's see some indicative prices: the Mastervolt AC Master 1000 is about 2500 RON, the Dometic SinePower 1012 is just over 2000 RON and the Victron Phoenix 1200 is around 2200 RON, of course depending on where you look. Now, seeing these specifications for what we can call 3 units in the top range, let's ask ourselves... what are the chances that an inverter of a few hundred lei will have 2-3000w Nominal (as it says 6000-7000w on it, it looks like it holds a block staircase), 95% - 96% efficiency, i.e. above Victron, Mastervolt or Dometic and pure sine. But of course, without any data sheet, i.e. we go on trust. Well, we determine that the odds are zero, hold a moment of mourning for sellers and importers and get on with it.

Let's be clear, I'm not saying that a cheap inverter with a modified sine doesn't do some work nor that there isn't pure sine a more affordable idea at the price, but with savings elsewhere, such as build quality, real power or so on. You want to stick a camping light in the socket, a peeler box or a mosquito zapper is Super ok, you do your job with it. But it will have an extremely poor yield and a huge own consumption. Going back to my Chinese inverter bought in 2014, the efficiency measured in the pajero was 68% real, with a 2.1A own consumption without consumers, summer. I mean, for 10 amps consumed, I was getting about half, which is not great. As you've seen, electrical systems lose everywhere, from the loss in the solar panel to the batteries, then to the 12-230 conversion, then possibly more loss if you have a laptop that converts 230 to 18-19v or whatever its operating voltage is. And that makes cheap inverters extremely inefficient.

It's simply burnt out power for nothing, going nowhere but into an inverter fired up with fans on full blast to try to cope. That's actually the argument I'm trying to make about the quality of an inverter. A good unit helps you enjoy your equipment and power from the offgrid system. A bad one leaves you in the dark quickly and you have the chance of ruining some electronics in your camper. I too used this Well in my Pajero, because I didn't have room to put anything bigger in it at the time. But I have used it always knowing its disadvantages and the problems that can occur. I mean, other than charging the iphone and very rarely the laptop, he didn't have much work to do. Oh yes and I used the Peltier box from Campingaz in this episode about camping fridges.

Finally, there's an inverter-charger like the one we have installed in the Gloria. Ours is called Victron Multiplus 2000, but most of the big manufacturers have a version. At Mastervolt it's called CombiMaster and at Dometic it's also called SinePower but has a different product code, of course. Ours retains the same specifications as the Phoenix, with 92% efficiency but 2kw power (nominal, not peak). What makes it different is that it can draw from the grid when you're out in the field or when you put the car in the yard, and it can charge 2kwh batteries. The Multiplus saved us from needing another device to perform this task, because in terms of speed, nothing compares to this method of charging batteries. In an hour or so it's a full bank, considering we don't get below 30% most of the time.

Of course, there are other things to discuss about inverters but I wanted to review the most important things. It came out a longer episode with more hate because it's probably the most commonly bought product and, naturally, there are most sellers who try to sell inferior stuff and offer misleading specifications. For anyone who wants to dispute what I'm saying, we can always sit down with the product and test it for both efficiency, as we see everything through the Victron SmartShunt in my Sprinter and keep the data on the server for public viewing, and also put it on an oscilloscope so we can see that 3-4-7 kw pure sine at 400 lei. But seriously, it's easy to relax. I tested a few and the results were more than disappointing.

Now that we've cleared up this mystery of good and bad inverters, we've completed the part of must have components in the camper. In the next episode we'll go over nice-to-have components, 5g system communication, miscellaneous monitoring, charging from the alternator and all sorts of little auxiliary units that can make an electrical system better and help you conserve your resources.