Simple DIY 12V to 220V AC Inverter Project Using 4 Transistors. Does it work?

This video is kindly sponsored by PCBWAY.COM : For All Your PCB needs: free $5 discount coupon www.pcbway.com...
Find the original project on PCBWay here
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I decided to build this simple project from PCBWay and the results were... interesting. To find out what happened you just gotta press PLAY
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Thank you
Richard

[@twithheldmwithheld8938]

Love these videos. And I can't help but be very impressed with your transistor tray. Something I struggle with is organizing items like this. Maybe a video someday on how you organize your shop, as I am sure you have a ton more than I do, and it all seems in 'place'. 😁

[@alexyurchenko3569]

Please show how you organize your parts. The transistor bags are really nice.

[@karlsangree]

"It didn't blow up, that's a good sign." The words of many an intrepid experimenter. 😃

[@danblankenship5744]

I reverse engineered the PCB and the pins for the small signal transistors don't match the Toshiba datasheet for a 2SC1815. The transistor pins closest to the output Mosfet transistors are correct, these are the Emitter pins (GND connection). The other two are reversed, the center pins is wired as the Base pins, but the datasheet shows these are the collector pins (see 4:56). I believe the board layout might be correct, and the schematic has the Base and Collector pins reversed (the schematic appears a bit off to me).

[@steves8083]

That was my conclusion too (collectors and bases reversed) although I didn't go as far as reverse-engineering the board. It's likely that the circuit was redrawn at some point when this error crept in. Normally in a multivibrator using bipolar transistors, the collector resistors are a magnitude lower in value than the base resistors. 220R base resistors are too low for 12V. The electrolytics are also reverse polarised in the schematic as further confirmation.

[@LearnElectronicsRepair]

We can play with this on the next live stream 6th Oct 5pm UK time. Come and join us if you can make it

[@ralphj4012]

You may be able to create something akin to a sine wave (from that square wave astable) by using RC filters (1k and 0.1uF or something) in the base drives, perhaps between the junctions of the 220Rs and 330Rs.

[@Dutch_off_grid_homesteading]

Heya, that is a nice DIY pcb project. but I really miss is the polaritie protection on the 12 Volts

[@gendragongfly]

I think you should try with a lower wattage lightbulb. If this super basic inverter can provide 50 watts I'll be very impressed. Maybe start at 10 watts and work your way up while checking if the output voltage doesn't drop below 220v 🙂

[@LearnElectronicsRepair]

I think that 72W is the lowest power bulb I have. I'll have a look to see if I can find some at the car boot sale, I have seen them from time to time

[@analoghardwaretops3976]

Have you thought of improving this ....just a little bit.... driving the 1815's with additional Darlington tx. their base current would reduce drastically.. So the 220 ohm base resistance could be a up by a factor of 100-500..,consequently the two electrolytics value would reduce to some " nF" value, in order to maintain the same freq... ...using a zener..of around (6v2-6v8) in series with each mosfet gate would provide some "low batt" protection for the mosfets. A (12- 15)k res.in each g-s may be for better for improved turn off.

[@Dutch-linux]

juice it up!!! and you can put more voltage in that transformer it wont hurt it... and maybe make it like a 400 watts or so

[@steves8083]

Hi Richard, Looking at the schematic alone, it very much seems as if the circuit is illogical and badly designed. Does the schematic match the PCB? Q3 and Q4 appear to have their collector and base connections REVERSED! With the circuit as shown, the MOSFET gate drives come from the multivibrator transistors' base connections. This means two things: Firstly, the base voltage pulses cannot exceed around 0.6V to 0.7V above ground and secondly, the base current pulses for Q3 and Q4 (2SC1815), exceed the manufacturer's absolute maximum rating of 50mA. The peak base current is calculated as (VCC - 0.6) / 220 ohms. So, for a maximum base current of 50mA,the supply voltage must not exceed 11.6VDC! I would change the circuit by reversing the base and collector connections to Q3 and Q4. R1 and R5 (now the base pull-up resistors), I would increase from 1K to 2.2K each. This will result in a higher gate drive voltage. Then reduce the capacitor values to set the desired frequency which will be somewhat lower with these changes. Check that the capacitors, if electrolytics, have their positive sides connected to the transistor collectors. If it is necessary to use trimpots for fine frequency adjustment, place these in series with R1 and R5 each at around 2K. Ensure they are adjusted for waveform symmetry on the MOSFET gates. Once the correct frequency has been established, the MOSFETS are much more likely to saturate because their gates are being driven by larger pulses, which is necessary to get a good switching current in the transformer primary (12V side). This improves efficiency and reduces dissipation in the MOSFETS. It could also be useful to place an electrolytic of around 100uF / 25V between Vcc and ground on the PCB especially if long wires are used to connect to a PSU. Once working properly, this will be a useful project! Regards Steve in UK.

[@LearnElectronicsRepair]

Hi Steve, I did not actually check if the schematic matches the PCB. Obviously the PCB does work, if it is a little quirky, As mentioned at the end of ther video we can play with this on the next live stream Sunday 6th October 5pm UK time. Feel free to join us

[@CaseVerrijst]

I was wundering. To test the capabilities of the transformer on 50Hz. Can’t you take a 230 to 12 or 15V ac transformer, with sufficient amps available and then check wat the output wil be. So you know wether it is the circuit or the transformer causing the voltage drop from 240 to 120v

[@maks886]

I never could understand why is there such huge demand for these 220V inverter projects online. Most of them shown by people in some 3rd world countries. Not to judge, but is it really so much harder to get mains power than to get a battery, mosfets, resistors, pcb, a transformer etc? These basic inverters have so much flaws, they never give a stable 50Hz output, never deliver on the promised power rating, the efficiency is horrible, the ripples on the output are HUGE and dangerous to you and to most electronic equipment. To give 100W at the output from a 12V battery, the current through the primary would have to be like 20 A or more, which will never happen with 0 cooling. This circuit is only good for one thing, and it's powering a light bulb very inefficiently. So popular though, I don't get it! The only scenario I see it useful is the one presented here - for education and out of curiosity.

[@viniciusvbf22]

It depends on your needs. I've actually needed one of these to get 220VAC from a solar panel+battery setup as a backup (fallback) for my NVR and security cameras. I ended up buying a simple, 100W inverter from AliExpress. Of course, I could use an UPS, but I already had the solar panel and a 45Ah lead-acid battery. I was very determined to use that as my power source. I'd like very much to build my own inverter, but getting the correct/useful transformers is always a pain for me. Not very easy to find them. When I finally find them, they are more expensive than the entire inverter from some Chinese manufacturer.

[@LearnElectronicsRepair]

@maks866 Same applies here as per other reply. There are a lot of people here (Canary Islands) living off grid and they need to generate power one way or another, solar (it's always sunny here) and wind powered (we get a fair bit of that too) seem the most popular but of course you need batteries and inverters. Somewhat off topic but is there some reason why off grid living is popular in some places and not in others? Everywhere has poor people yeah, and we have people technically 'homeless' here, quite possibly employed in minimum wage jobs as some have cars, smart phones etc, but living in underpasses, caves and unofficial shanty towns and they seem to know how to provide for themselves... You can build a shack anywhere but need power? Does that make sense?

[@opera5714]

I make PV power point efficient hot water heating systems out of them which make an ideal power diverter.

[@Foobar_The_Fat_Penguin]

Can it not be used in a repair setting as well? If you need mains power (120/230V) with isolation, an inverter might be able to provide that. Isolation transformers (controlled or with an additional variac) can be quite expensive. "Normal" transformers, OTOH, can often be salvaged from old appliances. Add a few components from the parts bin, and you can probe and poke inside a mains powered device in a safe-ish way. If you're poor, or just starting out, or a hobbyist who only once in a blue moon has to repair mains devices, it might be a suitable stop-gap solution. I remember getting my control isolation transformer used for ~40 Euro, but I had to search for few years to finally find that good an offer. I might have used something like this in the meantime, had the need arisen.

[@LearnElectronicsRepair]

@@Foobar_The_Fat_Penguin I don't see why not. We could try connecting something like a SMPS to the output of the inverter and see how it reacts. Have you thought of using an old UPS to give isolated mains output (just unplug it from the mains first) those will run a PC for a while so they must be pretty good. You can find those UPS cheap second hand, usually the battery is no good but they will work with an old car battery instead, I've tried that before.

[@gorky_vk]

That's rip-off of old Chinese car inverters back in the time when every mobile phone had different charger connector so it was easier to have one of these so everyone can plug their own charger into it. Output power is low, even sellers from ebay back then didn't claimed more than 10-20W and product had much smaller transformer of course.

[@naeemhaq3504]

100 years old circuit

[@chrishartley1210]

9:00 Prediction, input=15VDC, output=140VAC. Let's see how close I am. Edit: wasn't a bad guess, you didn't allow for the fact that since the 15V output was AC, the peak would be about 26V. Reversing that, your peak input needs to be 26V not 15V.

[@LearnElectronicsRepair]

Spot on. Let's play with this on the next live stream and see what we can get out of it 🙂

[@chrishartley1210]

@@LearnElectronicsRepair I also considered why you appeared to have an output of 240V with no load. Probably because transformer theory of ratio of turns assumes a sine wave and your actual waveform is nothing like it. As soon as a load is applied the theory asserts itself. I hope I can make the next live stream (6 October?), I was busy for the last one.