Building a Low-Voltage Inverter: A DIY Project with Unexpected Challenges

The AC output terminal and its corresponding DC voltage to the inputs are crucial components in building a low-voltage inverter. By observing the voltage across the resistor, we can notice the modified square wave shape that is produced. The precise frequency of 50 Hertz and an AC RMS voltage of around nine point seven seven volts create the same power through the resistor as if producing the same value as a DC voltage source. This results in an input current of 661 milliamps at the inverter inputs, with a current draw of 648 milliamps when connected to a pure DC voltage source.

The efficiency of the inverter is around 80% in this setup, which may seem acceptable but highlights potential issues that arise from using inductive loads. In fact, connecting loads with more inductive properties like a transformer can lead to alarming voltage spikes right when the MOSFETs turn off. The collapsing magnetic field of the inductor creates a current through the circuits, but since all MOSFETs are already closed, this results in voltage spikes that must be addressed.

To mitigate these issues, four diodes can be added anti-parallel to the MOSFETs, offering an exit route for currents that may occur. Additionally, incorporating a capacitor serves as an energy bank, allowing the reflowing electrical energy to be stored after adding these five additional components to the perf boards. Following these modifications, the low-voltage inverter is complete and works fine with inductive loads.

However, it becomes apparent when attempting to utilize a higher frequency switch that another voltage pulse appears during operation. This issue arises because even though all MOSFETs are closed, current still flows through the diodes, as previously described. The loads act like a voltage source and exhibit inverted voltage drops compared to the previous setup where it exits through the loads.

To simplify this problem, one could short the lower two MOSFETs to avoid the voltage spikes and achieve a perfect modified square wave shape. Nevertheless, this would not be an efficient solution. Instead, exploring alternative solutions is necessary to address these unexpected voltage spikes when stepping up the voltage to mains voltage levels.

A toroidal transformer from an old lab bench power supply can be used to converge 230 volts AC down to fifteen point five volts AC and eight point nine volts AC. The idea behind most DIY inverter circuits involves simply flipping the energy flow through the transformer, which implies that applying the low-voltage AC signal to the secondary side of the transformer should result in the desired high voltage AC signal on the primary side.

When decreasing the AC RMS voltage of the inverter to eight point nine volts and connecting it to the fitting secondary sites, a loud humming noise is initially noticed. However, this first negative impression does not last long as the multimeter measures an AC RMS voltage of around 230 volts on the primary side, which aligns with expectations.

Furthermore, the shape displayed on the oscilloscope is also not as terrible as initially thought but still features voltage peaks of around 450 volts, whereas mains voltage peak values are only around 330 volts. Hooking up a small 10-watt load to the primary power source reveals that it can be powered without issues and decreases the humming sound significantly.

Measuring the inputs and output currents and voltages yields an efficiency of around 84%, which is respectable but may not be sufficient depending on the loads attached to the transformer. The overall shape, voltage spikes, and changes in the AC RMS value are also influenced by the absence of feedback circuits in this setup.

In light of these findings, it becomes apparent that utilizing a low-voltage inverter without proper safety features can indeed be hazardous. Moreover, DIY inverter projects that incorporate transformers often face similar challenges due to the inherent properties of transformers. As such, investing in a proper inverter with more robust safety features is highly recommended.

In conclusion, building a low-voltage inverter as a DIY project offers opportunities for learning and growth but also poses unexpected challenges. By understanding these issues and exploring alternative solutions, it becomes possible to create an efficient and safe inverter system that can handle various loads.

WEBVTTKind: captionsLanguage: enwhen you got a photovoltaic off-grid system like I do then you usually get such a device like this installed as well it is called an inverter whose job is to take the DC voltage of the system's battery and convert it into an AC voltage that is suitable to power most of your ordinary mains AC voltage appliances I say most of them because that generally exists two types of inverters the first type is what I'm using aka the cheap type whose output is a so called modified square wave which is basically an AC square wave with pauses between their pulses while thus modified square wave does somehow resemble the sinusoidal mains AC voltage there can be problems if you try to power AC appliances with the Tri control like for example a coffee machine on the other hand though the modified square wave works for ohmic loads motors and even transformers but of course due to the sharp edges of the voltage in comparison to the sinusoidal voltage there are lot more problems with humming but anyway what matters is that my inverter works fine when it comes to charging up my boombox which ironically steps the high voltage down again to charge up two letters at batteries whose voltage levels we started with and the other kind of inverter is the expensive kind which outputs a pure sine wave and thus can be used for all AC appliances now I've been getting requests to create an inverter on my own underneath almost every video I posted so far and honestly speaking I think it is not a good idea to build an inverter on your own that is why in this video for educational purposes only I will show you how you can create a modified square wave inverter but also what kind of problems come with such a cheap DIY design let's get started this video is sponsored by jl CPCB from quick turn prototypes to production supports there are four great quality and service you can test a PCB quality and fast delivery time for only 2 dollars for 10 PCBs when doing a google image search for inverter circuits then you get a ton of variations of pretty much the same circuits it basically combines an astable multivibrator which creates a square wave with a transistor push-pull configuration that like the name implies pulls and pushes current through a transformer in order to create a changing magnetic flux through its core which creates a higher square wave voltage only transformers outputs not only does this output voltage not feature a pause between its pulses it also comes with a handful of other problems but feel free to watch a fro tech mots video about the subjects if you want to learn more so for my inverter circuits I had a different idea I will be using two P channel and two N channel MOSFET in an h-bridge configuration like it shown here if I turn on the top right one and the lower left one current will flow from right to left and if I turn on the top left bond and the lower right one current will flow from left to right that means we created an AC current and voltage at the load in the middle but of course we can also turn off all the MOSFETs in order to create the required pause to complete this H bridge I added 10 kilo ohm pull-up resistors to the P channel MOSFET gates and pulldown resistors to the N channel MOSFET gates so that they're normally all stay off next I added 10 ohm gate resistance to limit the gate currents which all connects two different outputs of 2 TCU 4 4 to 7 MOSFET arises those will either pull the gates of the MOSFETs high although in order to activate slash deactivates the MOSFETs but keep in mind that the turn-on voltage for the p-channel and Angela MOSFETs isn't Verdes last but not least the inputs of the mosfet drivers connect to four digital pins of the Arduino which will later create the precisely timed voltage signals and after choosing suitable MOSFET types the prototype schematic was completes which means it was time to solder all dimension components onto a piece of per port and connecting them to one another through solder bridges and virus as soon as the MOSFET driver Isis were then inserted it was time for the programming which for this circuits was very easy to do first off I created three functions that either turn all MOSFETs off turn 2 on to create the current flow from left to right or turn the other two on to create a current flow from right to left then all I had to do was to set up the timer one of the microcontroller which starts off by turning on MOSFETs off and then after 3 milliseconds either activates the Heian although on function depending on whether the last executed function was high on or low on after another 7 milliseconds the timer starts over again with the OL MOSFET our function and repeats the cycle endlessly to create the AC voltage control signal after uploading the codes i powered Solia d12 outside of the circuits in order to check the gate voltage of the MOSFET on the oscilloscope which seemed to be correct in case you're wondering where I got the information from on how long the path should be or the pulses then let me tell you that I simply measured the times of my commercial inverter which hopefully follow standards to finish off our low voltage inverter I added a resistive loads to the AC output terminal and it's volts DC voltage to the inputs and by having a look at the voltage across the resistor we can observe the modified square wave Weaver precise frequency of 50 Hertz and an AC RMS voltage of around nine point seven seven volts this AC RMS voltage value basically creates the same power through the resistor as if we produce the same value as a DC voltage and since we got an input current of 661 milliamps at the inverter inputs and the current draw of 648 milliamps with a pure DC voltage source at the same level the efficiency of the inverter is around 80% not too shabby but there are still a problem which can be seen if we connect the loads with more inductive properties like the transformer we will sooner or later needs the loads still powers like usual but we can see a couple of alarming voltage spikes right when the MOSFETs turn off the problem is that the collapsing magnetic field of the inductor wants to press a current through the circuits but all MOSFETs are already closed which creates the voltage spike to get rid of that we can add four diodes anti parallel to the MOSFETs in order to offer an exit route for the currents which can occur in two different ways also we should add a capacitor as an energy bar farm in which the reflowing electrical energy can be stored after adding those five additional components to the perf boards according to my finalized schematic this low voltage inverter is basically completes and also works fine with inductive loads I have to say when it comes to low voltage AC devices this circuit is not off pants even without a feedback circuits but once I tried to utilize a higher frequency R there appeared another voltage pulse during the pause the reason for that is that once the MOSFETs all closed current still flows through the diodes like I described it's a minute ago this time though the loads acts like voltage source and thus features an inverted voltage drop in comparison to before where it exits like loads which explains the inverted voltage poles of course we could simply short the lower two MOSFETs in order to avoid this voltage poles and get a perfect modified square wave shape but that would not be as efficient so let's see whether the unexpected voltage poles option is a problem when stepping up the voltage to mains voltage levels to try that out I grabbed myself a toroidal transformer from an old lab bench power supply that can converge 230 volts ac down to fifteen point five volts ac and eight point nine volts ac the idea of most DIY inverter circuits I found is simply flipping the energy flow through the transformer which means that by applying the low voltage AC signal to the secondary side of the transformer we should get the desired high voltage AC signal on the primary sites so I decreased the AC RMS voltage of my inverter to eight point nine volts and hooked it up to the fitting secondary sites what I immediately noticed was the loud humming of the transformer just listen but this first negative impression did not lasted that long because my multimeter measured an AC RMS voltage of around 230 volts on the primary basically it just what we want devoted shape on the oscilloscope was also not as terrible as I thought but still featured voltage peaks of around 450 volts while the mains voltage Peaks are only around 330 volts next I hooked up a small 10 watt loads to the primary which was powered without a problem and this load also decreased the humming sound significantly and by measuring the inputs and output currents and voltages I calculated an efficiency of around 84% which once again is not that bad at this points you might be thinking great this design works good enough which is definitely not the case depending on what kind of loads you attach to the transformer the overall shape and voltage spikes of the primary sights voltage changes as well as the AC RMS value since this circuit still features no feedback it can truly be dangerous to utilize my inverter and generally most DIY inverter circuits who have a transformer so why not forget about the transformer parts have fun with a low voltage inverter and invest a bit of money into a proper one that offers a lot more safety features and with that being said I hope you enjoyed this video if so don't forget to like share and subscribe stay creative and I will see you next timewhen you got a photovoltaic off-grid system like I do then you usually get such a device like this installed as well it is called an inverter whose job is to take the DC voltage of the system's battery and convert it into an AC voltage that is suitable to power most of your ordinary mains AC voltage appliances I say most of them because that generally exists two types of inverters the first type is what I'm using aka the cheap type whose output is a so called modified square wave which is basically an AC square wave with pauses between their pulses while thus modified square wave does somehow resemble the sinusoidal mains AC voltage there can be problems if you try to power AC appliances with the Tri control like for example a coffee machine on the other hand though the modified square wave works for ohmic loads motors and even transformers but of course due to the sharp edges of the voltage in comparison to the sinusoidal voltage there are lot more problems with humming but anyway what matters is that my inverter works fine when it comes to charging up my boombox which ironically steps the high voltage down again to charge up two letters at batteries whose voltage levels we started with and the other kind of inverter is the expensive kind which outputs a pure sine wave and thus can be used for all AC appliances now I've been getting requests to create an inverter on my own underneath almost every video I posted so far and honestly speaking I think it is not a good idea to build an inverter on your own that is why in this video for educational purposes only I will show you how you can create a modified square wave inverter but also what kind of problems come with such a cheap DIY design let's get started this video is sponsored by jl CPCB from quick turn prototypes to production supports there are four great quality and service you can test a PCB quality and fast delivery time for only 2 dollars for 10 PCBs when doing a google image search for inverter circuits then you get a ton of variations of pretty much the same circuits it basically combines an astable multivibrator which creates a square wave with a transistor push-pull configuration that like the name implies pulls and pushes current through a transformer in order to create a changing magnetic flux through its core which creates a higher square wave voltage only transformers outputs not only does this output voltage not feature a pause between its pulses it also comes with a handful of other problems but feel free to watch a fro tech mots video about the subjects if you want to learn more so for my inverter circuits I had a different idea I will be using two P channel and two N channel MOSFET in an h-bridge configuration like it shown here if I turn on the top right one and the lower left one current will flow from right to left and if I turn on the top left bond and the lower right one current will flow from left to right that means we created an AC current and voltage at the load in the middle but of course we can also turn off all the MOSFETs in order to create the required pause to complete this H bridge I added 10 kilo ohm pull-up resistors to the P channel MOSFET gates and pulldown resistors to the N channel MOSFET gates so that they're normally all stay off next I added 10 ohm gate resistance to limit the gate currents which all connects two different outputs of 2 TCU 4 4 to 7 MOSFET arises those will either pull the gates of the MOSFETs high although in order to activate slash deactivates the MOSFETs but keep in mind that the turn-on voltage for the p-channel and Angela MOSFETs isn't Verdes last but not least the inputs of the mosfet drivers connect to four digital pins of the Arduino which will later create the precisely timed voltage signals and after choosing suitable MOSFET types the prototype schematic was completes which means it was time to solder all dimension components onto a piece of per port and connecting them to one another through solder bridges and virus as soon as the MOSFET driver Isis were then inserted it was time for the programming which for this circuits was very easy to do first off I created three functions that either turn all MOSFETs off turn 2 on to create the current flow from left to right or turn the other two on to create a current flow from right to left then all I had to do was to set up the timer one of the microcontroller which starts off by turning on MOSFETs off and then after 3 milliseconds either activates the Heian although on function depending on whether the last executed function was high on or low on after another 7 milliseconds the timer starts over again with the OL MOSFET our function and repeats the cycle endlessly to create the AC voltage control signal after uploading the codes i powered Solia d12 outside of the circuits in order to check the gate voltage of the MOSFET on the oscilloscope which seemed to be correct in case you're wondering where I got the information from on how long the path should be or the pulses then let me tell you that I simply measured the times of my commercial inverter which hopefully follow standards to finish off our low voltage inverter I added a resistive loads to the AC output terminal and it's volts DC voltage to the inputs and by having a look at the voltage across the resistor we can observe the modified square wave Weaver precise frequency of 50 Hertz and an AC RMS voltage of around nine point seven seven volts this AC RMS voltage value basically creates the same power through the resistor as if we produce the same value as a DC voltage and since we got an input current of 661 milliamps at the inverter inputs and the current draw of 648 milliamps with a pure DC voltage source at the same level the efficiency of the inverter is around 80% not too shabby but there are still a problem which can be seen if we connect the loads with more inductive properties like the transformer we will sooner or later needs the loads still powers like usual but we can see a couple of alarming voltage spikes right when the MOSFETs turn off the problem is that the collapsing magnetic field of the inductor wants to press a current through the circuits but all MOSFETs are already closed which creates the voltage spike to get rid of that we can add four diodes anti parallel to the MOSFETs in order to offer an exit route for the currents which can occur in two different ways also we should add a capacitor as an energy bar farm in which the reflowing electrical energy can be stored after adding those five additional components to the perf boards according to my finalized schematic this low voltage inverter is basically completes and also works fine with inductive loads I have to say when it comes to low voltage AC devices this circuit is not off pants even without a feedback circuits but once I tried to utilize a higher frequency R there appeared another voltage pulse during the pause the reason for that is that once the MOSFETs all closed current still flows through the diodes like I described it's a minute ago this time though the loads acts like voltage source and thus features an inverted voltage drop in comparison to before where it exits like loads which explains the inverted voltage poles of course we could simply short the lower two MOSFETs in order to avoid this voltage poles and get a perfect modified square wave shape but that would not be as efficient so let's see whether the unexpected voltage poles option is a problem when stepping up the voltage to mains voltage levels to try that out I grabbed myself a toroidal transformer from an old lab bench power supply that can converge 230 volts ac down to fifteen point five volts ac and eight point nine volts ac the idea of most DIY inverter circuits I found is simply flipping the energy flow through the transformer which means that by applying the low voltage AC signal to the secondary side of the transformer we should get the desired high voltage AC signal on the primary sites so I decreased the AC RMS voltage of my inverter to eight point nine volts and hooked it up to the fitting secondary sites what I immediately noticed was the loud humming of the transformer just listen but this first negative impression did not lasted that long because my multimeter measured an AC RMS voltage of around 230 volts on the primary basically it just what we want devoted shape on the oscilloscope was also not as terrible as I thought but still featured voltage peaks of around 450 volts while the mains voltage Peaks are only around 330 volts next I hooked up a small 10 watt loads to the primary which was powered without a problem and this load also decreased the humming sound significantly and by measuring the inputs and output currents and voltages I calculated an efficiency of around 84% which once again is not that bad at this points you might be thinking great this design works good enough which is definitely not the case depending on what kind of loads you attach to the transformer the overall shape and voltage spikes of the primary sights voltage changes as well as the AC RMS value since this circuit still features no feedback it can truly be dangerous to utilize my inverter and generally most DIY inverter circuits who have a transformer so why not forget about the transformer parts have fun with a low voltage inverter and invest a bit of money into a proper one that offers a lot more safety features and with that being said I hope you enjoyed this video if so don't forget to like share and subscribe stay creative and I will see you next time