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Petrol Generator Mod - Inverter AC Output

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WanaGo:
Thanks Johnny

Not sure how much of that is relevant for me or not.

This is a capacitor excited alternator, not AVR. Its a 4HP Honda GX120 engine with governor to control the engine RPM.
Running drills and angle grinders directly off the generator before I added the inverter, was no problem, it adjusts fine, no doubt the output blips, but it was hardly noticeable.
The aim ideally was to have the inverter also cope fine, and make it work with all loads I might plug in which are within rating.

Unsure what the discussion is about sensors, propane and dual fuel, fuel storage, electric starts and controllers etc - none of that seems relevant for what I am trying to get help on. I'm a bit confused with over half of your reply to be honest.

I do not want to buy a new generator.
I do not need the generator daily.
I do not suffer blackouts. I will not be powering the house with this.
I don't need propane or dual fuel or anything like that.

This is a project.
I wanted to try and build this for if I needed remote power when working on something away from the house. Maybe to charge a laptop, power a drill, small welder, small fridge, other power tools, battery chargers, etc. Its not for daily use. Sure, maybe in a natural disaster etc, so I can charge stuff up etc.
I wanted to try and put an inverter on it so if I ever had a load I wanted to run off it which was sensitive to rubbish AC outputs, it would work OK.
I wanted to try and see if I could make the inverter be as capable as the raw AC output of the alternator was before I started playing with things.

I hope its clear what I am trying to do.

This is a project I am trying to learn from, to figure out how this stuff works and to tap into knowledge that other people on this forum have that I dont, that might be helpful to what I am trying to do.

This is the first inverter I have ever played with, short of a 300W 12V to 220VAC one I have from about 10 years ago which I used in my car.
Speaking of which, that has a PTC in series with the phase output...

If you are able to help and provide some help, please do share and let me know what I could do or could try.

Thank you.

Johnny B Good:

--- Quote from: WanaGo on January 29, 2019, 11:04:45 pm ---Thanks Johnny

Not sure how much of that is relevant for me or not.

This is a capacitor excited alternator, not AVR. Its a 4HP Honda GX120 engine with governor to control the engine RPM.
Running drills and angle grinders directly off the generator before I added the inverter, was no problem, it adjusts fine, no doubt the output blips, but it was hardly noticeable.
The aim ideally was to have the inverter also cope fine, and make it work with all loads I might plug in which are within rating.

Unsure what the discussion is about sensors, propane and dual fuel, fuel storage, electric starts and controllers etc - none of that seems relevant for what I am trying to get help on. I'm a bit confused with over half of your reply to be honest.

I do not want to buy a new generator.
I do not need the generator daily.
I do not suffer blackouts. I will not be powering the house with this.
I don't need propane or dual fuel or anything like that.

This is a project.
I wanted to try and build this for if I needed remote power when working on something away from the house. Maybe to charge a laptop, power a drill, small welder, small fridge, other power tools, battery chargers, etc. Its not for daily use. Sure, maybe in a natural disaster etc, so I can charge stuff up etc.
I wanted to try and put an inverter on it so if I ever had a load I wanted to run off it which was sensitive to rubbish AC outputs, it would work OK.
I wanted to try and see if I could make the inverter be as capable as the raw AC output of the alternator was before I started playing with things.

I hope its clear what I am trying to do.

This is a project I am trying to learn from, to figure out how this stuff works and to tap into knowledge that other people on this forum have that I dont, that might be helpful to what I am trying to do.

This is the first inverter I have ever played with, short of a 300W 12V to 220VAC one I have from about 10 years ago which I used in my car.
Speaking of which, that has a PTC in series with the phase output...

If you are able to help and provide some help, please do share and let me know what I could do or could try.

Thank you.

--- End quote ---

 Ok WanaGo,

 I see where your coming from. Sorry for the information overload. I appreciate it's a lot to digest but you can never really have too much info. You can pick out the bits that seem relevant to your project and perhaps refer back to the other, seemingly not so relevant bits as you see fit.

 One thing I will say is that you'll never be able to match the raw output of your generator with the inverter module since this is yet another conversion stage with its own losses. These class D inverter modules are pretty efficient (circa 95% or better) but in your case, you also have the issue of PFC in the rectifier pack. Rectifying and smoothing a single phase supply voltage needs considerably more filtering compared to the three phase case. If you just slap a BFO capacitor across the bridge rectifier output, you'll be presenting your generator with very high current spikes which it won't take kindly to if you're trying to push for an output from the inverter that matches the original output you were getting directly.

 Even if you use a third order LPF with a series inductor between two smoothing capacitors to reduce the commutation spikes  to reduce the stress on the generator, you're unlikely to do better than 80% of the original rating with such an add on inverter module. However, this might be all you require anyway and you'll have solved the issue of poor quality power for your sensitive electronic kit so there is still merit in what you're trying to achieve. Just don't expect the impossible.  :)

Regards, Johnny B Good.

WanaGo:
Thanks, thats helpful information.

Yes I was never expecting to get the same output power from the inverter as I do from the generator itself, losses were expected. Getting it to work and not blow up is the part I am trying to work around.

Even contemplating at this stage to just have the inverter as an option, switch it in and out, using Raw output when required, or Inverted output when required, depending on what i'm powering.

So are you suggesting I need to look at doing filtering between the Rectifier and the Inverter input, some sort of 3rd order LPF with Inductor?
I still seem to have a problem with this inverter than it has no output protection.
Some of the other inverters I see on Aliexpress have a few extra bits, but none of them taken the HV DC input like this one did, so I had to rule them all out.

Some of them like this one (when you scroll down the page you see the image) has overload protection, short circuit, under voltage, input over voltage etc. Mine has none of that.
https://www.aliexpress.com/item/Free-shipping-1pcs-1800W-5500W-DC12V-24V-36V-48V-to-AC-220V-pure-sine-inverter-board/32637730780.html

I currently have the 2000W version of this which they sent in error, ordered the 3000W version, which is on its way to me now.
https://www.aliexpress.com/store/product/1pc-3000W-Pure-Sine-Wave-Inverter-Power-Board-Post-Sine-Wave-Amplifier-Board/627093_32657842137.html

as mentioned in a previous message

--- Quote ---Page 1 of this is essentially the circuit I seem to have in the Inverter, however, on mine there is a Toroid on the output stage which is not pictured, with a 0.2uF 375VAC capacitor directly across the output.
http://www.lz2gl.com/data/power-inverter-3kw/egs002_manual_en.pdf
--- End quote ---

So any suggestions on improvements that could be added on, would be a huge help. I can design a PCB and get it made, and build it etc, I just don't have knowledge of power electronics to this extent to know what is required.
Even if I was do to the initial suggestion above and switch inverter in and our depending on what i'm powering, having the inverter protected still seem to be quite an important thing, as if it's so easy to pop with something like an angle grinder, then that's not going to be much chop.

Thanks

schmitt trigger:
I believe that the AliExpress product will work, if you can make sense of the following Chinglish gibberish:

" First, after the correction of the inverter inverter power tube removed, and then look at the
correction of a few transformers transformer, look at the transformer secondary circuit is
connected in parallel or in series, and then add the transformer parameters, modified wave
transformer secondary is parallel , In each transformer secondary plus 16 laps.
The secondary of the modified transformer is a tandem type, plus 8 laps per transformer
secondary. Then in the correction transformer which transformer 1 empty foot plus a small
voltage parameter, the small voltage parameters using 0.6 copper wire, in the transformer
inside around: 5 laps, the small voltage is linked AC: 16V position."


Just be sure to fuse both the input and the output, and you'll be fine.

WanaGo:
Yeah that chinese detail is a shocker, makes no sense at all.

I have a feeling its to do with how normal people would be powering this board. You would get the 16VAC by winding a few laps around the primary transformer which might have otherwise been used to generate power for the 380VDC input.
In my case I just have the rectified output out of the generator, and the 16VAC I am just using the 12VDC output of the generator too, as that is somewhat like AC and more at 22V levels, so when this goes into the board its rectified also and then passed to a 15VDC regulator and a 5VDC regulator, which is used to power the EGS002 driver board. So that side of thing works fine.

If there is something else in that description of note, I have not clicked on to it however. Very poor translation.

Yesterday I managed to get hold of an english speeking engineer from EGMicro who makes the Driver Boards used in this inverter. While he wasnt familiar with this model specifically as its made by another company, we discussed various parts of it and I am a bit happier with the whole thing now.

So there is a feedback shunt, which is marked as 0.1ohm in the schematic example in the EGS002 datasheet, which is used to determine if the voltage goes over 0.5V over this resistor, so it can stop the output to save the FET's. It however is a little on a slow side, and in my case the Surge I enduced from the angle grinder would have happened too fast.
In my case, these shunts I believe are 0.02ohm each, and in my model there area 2 of them. So 0.5V/0.02ohm=25A and I have 2, so 50A. So in theory if the current passing gets to be 50A then the inverter will trip and save itself. But for surge it happens too fast, as the IFB pin sample time I believe is 600mS.
Anyway, I got talking with the engineer, and brought up these NTC's, and showed him another schematic I had found which uses these same driver boards, and features an NTC on the 220VAC output, and is used for exactly this - Surge protection.
You can see it near the top centre of this image


The engineer agreed, and said the NTC could solve the problem.
If I for example aimed for a 10ohm NTC, then at 25 degrees C, the NTC resistance will be 10ohm. As the Surge hits on startup, it will be like a 10ohm resistor, and block current over 220/10=22A approximately. As the current flows, the NTC resistance will drop down to almost nothing due to the NTC warming up, and then full current will then pass unhindered. The question is though how big should the NTC be. 10ohm, 10A steady current capable?
There is then the side of it which is the recovery time, how long it takes for the NTC to cool again to come back to 66% of the initial resistance or something, which in some of the larger NTC's could be over 100 seconds. SO I assume if I was to surge with an angle grinder, it saves that, then turn it off, and start the angle grinder again, would it save the next one... I dont know.

The FET's I have in it currently are rated 650V, 47A @ 25C, so I would hope that preventing surge over 22A would be enough to save the FET's. Some items like a fridge compressor etc might not like this 'soft start' approach, but for most things it should be OK, right?
Not looking for a rocket science solution here, but would something like this work for basic protection of the FET's?
After the Surge is taken care of, then the shunts with the IFB protection can work as normal.

Would love to know what people think.

10ohm 10A NTC's from Aliexpress are about $1 each. 10ohm 15A NTC's are about $7 each.

Thanks

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