What's new

Power Inverters in a Nutshell

Daway

Super Heavyweight
Joined
Jan 30, 2019
Messages
468
Likes Received
450
Location
Maritimes
The topic of MOSFETs and power delivery came up in another thread so I thought I would start a discussion on power inverters, the different kinds and their pros and cons, and places to get gear if you're interested in experimenting. Note that even though I do have some ECE courses from "back in the day" this is a HOBBY for me. There's a ton of handwaving in some areas and its fairly high level just to get some concepts across. Absolutely welcome clarifications/corrections/additions.

Now then...

Inverters convert DC power into AC power. They are popular because many energy production/storage options that the average person can access such as solar panels and batteries store and release energy as DC. The problem is most household appliances use AC and this is where the inverter comes in..

(An aside while I'm thinking of it- I did find a source for a PC power supply that runs off of 24v worth of batteries. Useful if you want to run a cryptocurrency miner because you save on the efficiency losses that comes with inverting DC to AC).

The AC power that runs your home is in the form of a sine wave and the difficulty comes in how to replicate the sine wave. Lower cost inverters will use use a square wave in place of a sine wave. Other low cost inverters will modify the square wave to have it better approximate the sine wave. The more desirable inverters are, of course, those that can reproduce a clean, pure sine wave. Here's a graphic that shows the differenet wave forms courtesy of https://www.rvworldstore.co.nz/guides-advice/pure-sine-wave-vs-modified-sine-wave-inverters/

modified sine wave vs pure sine wave.jpg

The most popular way to reconstruct the sine wave is through a technique called pulse width modulation. This is where we take an average value across a period of time based on the voltage applied in a pulse of a given duration (width). For example, let's say the period of time we are looking at is one second. If we apply one volt for 1/2 second that is the equivalent of applying 1/2 a volt for one second. Here's another example driving a car. Let's say you drive 100km/h for 15 minutes and then park it for 45 minutes. The distance you travelled is the same as if you drove 25km/h for the entire hour. Your "pulse" of 100km/h for a "width" of 15 minutes is considered equivalent to 25km/h for an hour. This "pulse width modulation" is the first step and a fundamental building block of constructing a sinewave from a DC source.

Since your house power is at 60Hz, we complete one complete cycle every 1/60th of a second. This means in order to reconstruct the sine wave we have to use VERY small time divisions. Here's a graphic of how pulse width modulated DC approximates a sine wave extremely well:

pwnsine.png

(source: https://www.google.com/url?sa=i&url=https://electronics.stackexchange.com/questions/191742/how-is-a-pwm-signal-converted-to-sine-using-a-transformer&psig=AOvVaw3V7rwSWFuwCAX9yXoKPUiS&ust=1581639084847000&source=images&cd=vfe&ved=0CAMQjB1qFwoTCNCY5vKezecCFQAAAAAdAAAAABAO)

You can see when the sine wave is near zero, the pulse width is extremely narrow (zero) and as the wave approaches maximum the pulse width is rather wide. The combination of a sufficiently high enough frequency of pulses combined with some low pass filtering is what gives us the nice, clean sinewave that we want.

When it comes to sine wave inverters there are two types that you will see: "high frequency" and "low frequency". The biggest difference between the two is the voltage that is passed across the MOSFETs (a type of electronic switch or a specialized transistor - the acronym stands for Metal Oxide Semiconductor Field Effect Transistor). In low frequency inverters the sinewave's peak value is roughly 1/sqrt(2) of your DC voltage through the MOSFETs. In high frequency inverters the sinewave's peak through the MOSFETs is already at 120V. The only way I can describe why is because in high frequency inverters, several smaller lightweight transformers step the voltage up as the sinewave is constructed but in low frequency inverters the step up happens after the sinewave is constructed using a much larger transformer. Each type of inverter has its advantages and disadvantages. High frequency inverters tend to be lighter (my 2000w high frequency inverter probably only weighs a couple of pounds) and more efficient. I've seen claims of 94% efficiency of high frequency inverters. Their main drawback is they don't handle surges as well as their low frequency counterparts. This is mostly due to the size of the transformer in a low frequency inverter. They are HUGE (the transformer in a 2000w low frequency inverter is probably twice the weight, if not more, of my entire 2000w high frequency inverter). Think of the transformer as the flywheel in a car. It is able to store energy and release it if there is a load to get the car moving. This is why you will often see surge ratings of high frequency inverters being about 50% above their nominal rating (e.g. 2000w inverter will have a 3000w surge rating) whereas a low frequency inverter can surge triple its rated power and for a longer period of time. Their simple design and surge advantage comes at an efficiency cost, however. Most low frequency inverters have an efficiency rating somewhere in the mid to upper 80s%.

Both types of inverters have their place. It all depends on your application. Loads that are resistive in nature (toasters, air fryers, portable space heaters, TVs, etc) do just fine with high frequency inverters and you can run them fairly close to their rated capabilities. Loads that are inductive in nature (motors, induction hot plates, blowers, water pumps, etc) do better with low frequency inverters because of their ability to deliver the surge current these loads need on startup without breaking a sweat.

Here's a funny youtube video that shows different inverters in the 600-2000w range and how the succeed (or fail, sometimes with comical results) to start a water pump. When he tests his DIY 600w inverter, note the size of the transformer on his gear. Definitely a low frequency inverter setup:

(for you ADD folks, the money shot where he starts the motor with his DIY inverter is at the 6:06 mark)

Coincidentally, his DIY inverter uses the EGS002 board for generating the sine wave, which bring me to my next topic.

If you're interested in experimenting with low frequency inverters, there are a plethora of them on Aliexpress that are based on using the EGS002 board. This small board generates a sine wave from pulse width modulation to which you can add the necessary MOSFET circuity and some other do-dads to make a complete inverter. I'll attach the data sheet which includes some examples of how to hook it up. The cool thing about the data sheet is that you can find examples of finished boards that use the reference design in the data sheet. Here's one example from Aliexpress that uses the EGS002 board and its reference design with H-bridge MOSFET setup:


the data sheet for the board is too big to attach, so here's a link to the PDF:

And a link to the data sheet for the 8010 chip (the main chip on the board):


To use the AliExpress board you do need to source a suitable transformer. If anyone wants information on how to that let me know and I'll write an update on that regarding core sourcing, how to wind, etc.

Or, if you can't be arsed and just want a basic inverter that will give you emergency power from a 12v marine battery, here's a 1500w high frequency inverter for a little more than half what Canadian Tire Wants for their 1000 watt and comes with a remote:

(I do not own this, just pointing it out as an example of what's available and prices have dropped since I bought my 2kW inverter 6 years ago).

Hope this helps, and happy inverting!
 

NG_F

Super Heavyweight
Joined
Oct 28, 2011
Messages
466
Likes Received
410
Location
The Great Lakes
Very interesting and I studied much of this in High school, electronic technology.

However in the last 7 years, I've been using mostly Corsair or Seasonic Power supply units which converts wall socket AC to Low voltage DC for the 5V rail which serpentines through the Motherboard . It provides this signal to the motherboard to instruct it when DC voltaqes are in spec, so that the computer can safely power-up and Boot.
Distribution is via a 12 or 14 phase motherboard which the VRM's ( Voltage regulator module) are you used to control and/or lower the voltages to various components. Most notably the gpu or cpu . VRM's are especially necessary for overclocking the CPU and GPU.
The mosfets help make up the VRM's and are also used in power supplies. Energy is pulled from an AC socket before its broken down into small packets with the mosfets acting as switchers. Those packets are then carried by capacitors, inductors and more electric components capable of storing energy. Ultimately, the packets merge into one for a single, and steady, output.

We use PWM( post width modulation) fans to be able to switch on and off once certain temperatures are reached.

The D5 and DDC liquid cooling pumps which are mostly used for water cooling CPU's GPU's , Monoblocks and some RAM modules are also PWM regulated by temperature thresholds and are DC as well.

Would be Happy to build a PC or hackintosh computer for any of the Monsters here. I have a friend who owns an autobody shop and I can custom create and paint any choices of Chasis colors
 

CurtisP

Unofficial Porn Section Moderator
Joined
Apr 20, 2019
Messages
1,093
Likes Received
1,841
Very informative - I usually go the other way (I convert AC to DC voltage) for the means of ignition
Thanks for the post and links ! I will do some more reading tonight on it
 

Daway

Super Heavyweight
Joined
Jan 30, 2019
Messages
468
Likes Received
450
Location
Maritimes
@NG_F you brought back some fond memories when you mentioned "overclocking" :)

@CurtisP the only thing I know about rectification is a bridge to some capacitors and there's a magic formula that shows how much ripple will be left in the DC lol.
 
Top