Author Topic: Petrol Generator Mod - Inverter AC Output  (Read 10653 times)

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Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #25 on: January 28, 2019, 08:01:17 pm »

Now, my two yen on this subject.
Power tools most likely utilize series-wound universal motors. They generate very significant amounts of noise, due to the brushes. Additionally and this is most important, they draw very large surge currents.

I would advise that you go to E-bay and purchase a bank of power resistors, such that you can do all sorts of troubleshooting without worrying -at first- about your load. Later, you can add in parallel some motor-run capacitors, to simulate a lagging power factor.

Yep lesson learned about the angle grinder, it was a poor choice, but I would have come to this position at some point, so better at the very start than when I actually needed to power something.
Thanks for the reply. I need to do some more reading on the subject.
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #26 on: January 28, 2019, 08:22:08 pm »
Take it from one who knows from bitter experience, you're wasting both time and good money.

That's unfortunate. However, that said, my time is free to me and this was a learning exercise more than anything. The inverter itself was not expensive, and the company that sold it to me actually offered it for free if I could make a video on the project after I have it working, but I don't think that's going to happen given the results so far.


With regard to your proposed conversion to inverter power, I'm afraid you're not going to see any benefit since what makes the inverter type genset more efficient and noticably quieter on no or quarter/half loadings is the use of a multi-pole (typically 6 or 7 pole pairs on the runner with 18 or 21 pole piece windings on the stator) three phase permanent magnet generator head feeding a full wave 6 diode three phase rectifier to generate the required low ripple 200 or 400 vdc used by the 60 or 50 Hz inverter (basically a pair of back to back high voltage class D amps in H bridge output configuration, driven from the required 50 or 60 Hz reference sine wave generator).

That makes sense, damn. I guess this 2 pole generator was never going to cut it. I was naively hoping that rectifying it to DC would remove a number of issues with the limited poles, and then inverting the DC back to AC would then just work. But obviously I have a lot to learn. Which I guess what the whole purpose of this.


Basically, I'm advising you to invest your money in an off the shelf inverter genset rather than wasting it on your folly of a project which can only succeed as an educational exercise in "Learning from your mistakes". There are surprisingly cheap inverter gensets available these days (long gone is that accursed Honda monopoly in such kit) but you still need to be wary of the Workzone shite (to name but one).

Yep but again that's not the purpose of this at all. I didn't just want to buy something. This isn't something I need to use, it was more of a learning project for me. Buying something teaches me nothing. I was trying to learn from this, and if failing is the way to do that then I guess I am succeeding. It would be nice though to get this working, but from what I am reading I may never get there. I guess I need to do more research on the subject and find out exactly what is going on.


As mentioned, I would have assumed that rectifying to DC and then inverting the DC back to AC would have solved limitations with the old generator. Maybe the DC doesnt have enough 'storage' to cope with surge, but maybe the inverter is just too simple to handle surge anyway. Maybe some power resistors would help limit surge current, but is that a good idea? I dont know.

This isn't something I want to keep throwing money at, and to date hasn't cost me very much at all, but if there is something more I can do to at least get something out of it, I can convert the generator back to how it was pretty easily, and have the traditional AC output for most things, and have a more limited inverted output for smaller more sensitive loads, then I guess that could be a comprimise. I don't know what the best solution is.
I just want to try and understand why this failed more than anything. If its rated to 2000W then in what situation would that actually be viable? A slowly ramping load, rather than anything with surge above this limit?

If anyone has any more ideas on what I could try, then I would love to hear.

This FPC stuff I really have no idea about, what it is, where it typically is in a system etc or what it does.

Thanks All
 

Offline Circlotron

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #27 on: January 28, 2019, 09:55:00 pm »
Somewhat off topic, but it would be cool if someone made a portable inverter generator with 3-phase VVVF output that you could use to drive a 3-phase induction motor.
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #28 on: January 28, 2019, 10:42:31 pm »
Just been googling and came across this youtube video, and just wanted to pick brains on the concept conveyed.



So this guy seems to improve PF by using a Run Capacitor on the AC output of the Inverter he has. It seems the Run Cap would change depending on the equipment being run, but I am curious if this concept could be put into practice as a general output capacitor of the inverter to help deliver surge currents to protect the FET's, along with maybe large current limiting power resistors.

So off the top of my head, he used something like a 20uF cap for his Freezer, and something like a 90uF cap for his drill press, and it improved the PF considerably.
If I was to say put a 25uF run capacitor (which I happen to have one sitting here) on the output of the inverter, would that in theory help deliver current for surge startup on some devices, and help limit the surge loading on the FET's?
Obviously it's not perfect as different devices will demand different caps, based on what he showed in the video, but could it help protect the inverter FET's?

As what suggested above, power resistors might also help...
If I was then to also put say a 5ohm power resistor of suitable sizing on the output of the inverter, before the capacitor (this is likely totally wrong math but say 220V / 40A = 5.5ohm), that might help limit the maximum current pulled out, right?

Is this thinking totally wrong, and all I end up making is a basic filter which does nothing useful and I will still blow FET's ?

Be nice :) Thanks
 

Offline WanaGoTopic starter

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Offline schmitt trigger

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #30 on: January 29, 2019, 01:41:00 am »

Now, my two yen on this subject.
Power tools most likely utilize series-wound universal motors. They generate very significant amounts of noise, due to the brushes. Additionally and this is most important, they draw very large surge currents.

I would advise that you go to E-bay and purchase a bank of power resistors, such that you can do all sorts of troubleshooting without worrying -at first- about your load. Later, you can add in parallel some motor-run capacitors, to simulate a lagging power factor.

Yep lesson learned about the angle grinder, it was a poor choice, but I would have come to this position at some point, so better at the very start than when I actually needed to power something.
Thanks for the reply. I need to do some more reading on the subject.

Please note.... I made a typo error. Connecting the capacitors in parallel with the resistors will produce a LEADING power factor.
If you want to obtain a LAGGING power factor, nothing beats an unloaded induction motor.
 

Offline Circlotron

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #31 on: January 29, 2019, 07:56:05 am »
If I was to say put a 25uF run capacitor (which I happen to have one sitting here) on the output of the inverter, would that in theory help deliver current for surge startup on some devices, and help limit the surge loading on the FET's?
For an induction motor load it would help ~somewhat~ because during the time an IM is running up to speed the power factor is presents is awful. You would need a larger capacitor for runup and a smaller one after it has reached full speed. For brush motor loads like for example an angle grinder, I don't expect a power factor cap is going to help at startup.
 

Offline coppercone2

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #32 on: January 29, 2019, 08:16:04 am »
i got a propane powered generator. Holy shit its a thing of beauty.


FUCK gasoline.  :'(

the things I have gone through because of small gasoline engines  :'(


strip engine at 1am during hurricane. run out of ether. all sorts of BULLSHIT.  :scared:

Do yourself a favor and get a propane compatible one.

I need to order a refurbish kit for the old gasoline one. And hopefully never use it again.
« Last Edit: January 29, 2019, 08:19:58 am by coppercone2 »
 
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Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #33 on: January 29, 2019, 08:34:21 pm »
Would having an NTC in series with the output help solve this surge current?
Would it help protect the FET's instead of blowing them up if the surge is too high?
Do inductive loads like NTC's, or are they a no-no ?

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

Any suggestions at all for improving this?

One thing I have spotted is bottom right of the schematic, there is a 0.1ohm resistor for the current sense feedback. On mine I don't seem to have this, however there are 2x M shape thick wire bridges which tie from the bottom of the 2 FET's back to the input -ve (GND), so potentially those do act like this. The Chinese comment states 'Kang Copper Wire' so maybe...

Would love to hear suggestions for improvement on this thing, if there are any.
 

Offline Johnny B Good

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #34 on: January 29, 2019, 10:20:02 pm »
 The PFC circuit is part of smpsus with ratings above the 75W limit, iirc. It's job in this case is to reduce distortion of the current drawn from the mains supply due to the narrow conduction angle of the basic rectifier and capacitor circuit used to generate the 165 or 330 volts DC supply to the high voltage switching circuit that drives the stepdown and safety isolating transformer in the smpsu. Without such a circuit, the rectifier only draws narrow spikes as the voltage waveform matches then exceeds the charge voltage stored by the smoothing capacitor(s).

 The PFC circuit draws these current spikes out over a much larger portion of the waveform to mimic the effect of a resistive load, a characteristic also shared by universal motors (albeit with an additional startup surge characteristic- they don't have the narrow conduction angle characteristic of a basic smpsu rectifier and capacitor pack). Induction motors have low PF but at least this is of the ordinary kind were it's essentially just a lagging of the phase of the current relative to the voltage waveform which can be largely corrected for (in the motor circuit) with a simple PFC capacitor.

 Incidentally, if you're trying to compensate for lagging current loads with additional capacitor across the genset's output, don't try this with the more fancy types that boast "AVR" unless you want to see the output voltage go north of the 140 or 280v mark (120 and 240 volt gensets respectively). You might get away with it using a homebrewed generator based on a suitably rated single phase induction motor using a bank of capacitors to induce excitation in the rotor (after flashing some residual magnetism into it with a 12v car battery before firing it up) but quite frankly any PFC has to be done at each load. There's no one size fits all as that generator capacitor mod implied.

 The traditional generator only suffers the overvolting effect with capacitive loadings. The inductive loading from motors doesn't create this effect but the excess 'wattless' current still has to be considered from the point of view of avoiding exceeding the generator's maximum current rating. If you run a 1KW motor with a PF of 50% on a 1KW rated generator, although the mechanical load on the genset's engine isn't increased by that factor of two increase in the current draw, you're likely to overheat and possibly burn out the generator windings if such a load is maintained for more than a minute or two at most if the circuit breaker doesn't trip out beforehand.

 Although the inverter type of genset is free of this troublesome overvolting effect, such additional 'wattless' current of either leading or lagging type still has to be allowed for. Incidentally, the generator inverter modules are surprisingly robust in regard of handling such overloads with the microprocessor providing superior overload shutdown control compared to the simple thermo-electromechanical circuit breakers used in traditional gensets.

 BTW, I do understand your desire to experiment in the hope of improving the genset and gain some useful experience to increase your understanding of generator technology but I thought it best to let you know what you were up against in this laudable enterprise of yours.

 Basically, it's a lot more complicated than just simply trying to fullwave rectify and smooth the existing generator's single phase 120 or 240 vac output to provide the necessary high voltage DC to power a 60 or 50 Hz 120 or 240 vac output inverter module. You'll also have to add a stepper motor drive to the carburettor or replace it with a stepper motor controlled one, making the basic mechanical speed governor redundant. If the engine is a four stroke unit, it should already incorporate a low oil level warning float switch which you may need to invert the sense of if you wish to wire it into the inverter/engine management module rather than have it directly disable the ignition to automatically protect the engine from impending loss of lubricant and the risk of seizure.

 Regarding the comment made by coppercone2 about the use of propane (or, for that matter, natural gas) instead of the ethanol polluted 'gasoline' foisted upon the American nation, I heartily agree with that advice, if only because the use of propane or natural gas removes the need to store quantities of gasoline (petroleum) with a limited shelf life (a year, perhaps two or three with the use of an additive). Also, it eliminates the more corrosive products of gasoline/petroelum combustion, leaving the engine and its lubricant in a much better condition after each run, considerably extending the service life of the engine. What's not to like about a dual or tri fuel genset option?  :)

 Obviously, preserving the facility of still being able to run off a petroleum based fuel with a dual / tri fuel engine maximises your chances of still being able to run the genset if your supply of propane or natural gas gets cut off - you may still be able to scavenge gasoline/petroleum to ride out any disasters severe enough to curtail those supplies.

 Here in the UK, the most likely disaster scenario for the majority of the populace will be either a very rare fault induced outage for those in the suburbs, or for those living in the countryside, outages from trees falling onto rural 11KV lines, in both cases, typically a matter of hours, rarely any longer than a day or three.

 However, the mismanagement by the UK government with regard to investment, particularly of the Nuclear Power station kind, in our National Grid has raised the spectre of rolling blackouts during particularly severe winters. The capacity margin to cover unplanned power station outages is extremely slim indeed, just a matter of a percent or so, afair. Thus far, we haven't experienced severe enough winters in recent years to put the system to the extreme test and it looks like we won't be experiencing one this year.

 However, it was this possibility in mind that gave me sufficient justification to invest the rather modest £99.90 in that Parkside inverter genset as a backup to my current 2KVA 1500W UPS setup. Initially, I didn't think it would provide for more than just the IT kit alone but the lighting upgrade to LED lamps over recent years has now made it possible to keep both the IT kit (and a TV set or two) and all the lights on through the next electrical outage. Although it's a little too marginal for my liking, it was a surprising result of my renewed assessment of just what this could keep running.

 The only downside with such cheap inverter gensets is the lack of an electric start option. However, I'm looking to add a bldc controller with, in my case, a 48v dc supply and fast acting isolator relays to use the PMG as a BLDC starter motor, neatly avoiding the need for gross mechanical modifications beyong that of adding a position sensor to provide the necessary "Hall Sensor" commutation signals to my BLDC controller.

 The sensorless option is only good with well defined mechanical loadings such as pumps or fans and prop blades, hence the need for such enhanced commutation signals. I've proved it will work in principle. With the spark plug removed I see 480rpm using a 48v test battery but even after it has started running just blocking the sparkplug hole with a thumb is all it takes to stall it.

 Sensorless operation just doesn't cut the mustard in this application. I know exactly how to fix this, I just haven't sprung for the Adapter Board for AS5047P just yet since I need to determine whether the PMG is a 6 or a 7 pole pair outrunner type. I've only recently acquired a 'scope that will let me determine this without the need to physically remove parts just to eyeball the inboard stator coils to get a count (I'm anticipating a count of 18 or 21 such salient poles). This is a project I've put on the back burner for now.

 What grieves me most about this (lack of) electric starter option in the cheaper inverter gensets (and which also drives my 'electric starter' project) is, well quite frankly, the very lack of such circuitry being integrated into the inverter/engine management modules used in these gensets.

 In mass production, the extra circuitry would literally only be a matter of a few cent's worth and a square millimetre or two of additional silicon. The more expensive 50vdc converter could be supplied as a luxury add on (a purchase option or after sales upgrade kit ). Even this would only add a few dollars to the BoM costs, far less than that of adding a starter ring gear to the engine and a klunky starter motor and associated mechanicals adding needless extra cost and weight to what is touted as a lightweight suitcase portable inverter genset. The heaviest item being a small starter battery which won't necessarily have to be the obligatory 7AH SLA, it could be replaced with a much lighter and more durable LiPo or L-ion battery pack to keep the weight down to little more than that of the original recoil starter only version.

 Anyhow, that's the level of my generator improvement project. Starting from where the OP was hoping to end up and finishing with a realisable goal of eliminating the faff of using a recoiling pull cord starting rope.  :)

Regards, Johnny B Good
John
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #35 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.
 

Offline Johnny B Good

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #36 on: January 30, 2019, 02:19:45 am »
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.

 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.
John
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #37 on: January 30, 2019, 02:33:39 am »
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

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
 

Offline schmitt trigger

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #38 on: January 30, 2019, 04:03:56 pm »
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.
« Last Edit: January 30, 2019, 05:08:28 pm by schmitt trigger »
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #39 on: January 30, 2019, 08:48:37 pm »
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
 

Offline Johnny B Good

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #40 on: January 30, 2019, 09:25:51 pm »
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.

 I landed up on a French Language page trying to make sense of the 'technical specification'. Typically, when it comes to tech specs, the language doesn't matter so much. However, after second visit, I managed to stumble upon the "Original English" description page, aka the Chinglish Description page as you've just quoted. Sheesh! I can't imagine what a nonsense a French translation of Chinglish would look like to a native Francophone!  :-//

 That seems to be describing an ancient digital switching sinewave synthesis technique based on a bunch of tapped transformers which that inverter module is most definitely not. The eight powerfets on the heatsink suggests the use of a pair of class D amplifiers in bridged output mode with sample filter inductors designed to filter the 5 or 8KHz sample rate typically used in these 50/60Hz inverters.

 I'm surprised if the absence of any form of overload protection is actually true. The Chinglish description could be hiding any number of 'standard features' by simple omission. However, the description seems to be one made up by the manufacturer and appears to be total and utter bollix. Personally 69 dollars is at least 60 dollars too much to take a punt on it being any use. It might  turn out to be perfectly fine but that's not something that can be discerned from its current description.

JBG
John
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #41 on: January 30, 2019, 09:37:34 pm »
Ignore the chinglish description, the circuit is much the same as that above, and what is posted in the reference schematic in the EGS002 datasheet which I have linked in previous posts.

The main difference is the one I have has an extra Toroid on the output which is used to help with EMI, so I am told by the engineer.
For 1000W and 2000W models, there are 4 FET's. For 3000W there are 8 FET's, to simply move more power.
On these models there is no actual protection circuitry other than the IFB pin which I have already mentioned, which is somewhat slow so would be for general current overload, and then there is temperature protection from a thermistor which is bonded into the heatsink, and then voltage feedback which is adjustable to modify the nominal output voltage too.

Some other inverter designs I have seen which are more for Battery inversion to 220VAC, but still using the EGS002 drivers, do have over current, over/under voltage etc protection, however I have not yet found any published schematic on these circuits.
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #42 on: January 30, 2019, 09:54:24 pm »
Here is a vid I found on Youtube, sadly it's in Portuguese, but Youtube auto translate to English subtitles gives somewhat useful information I guess.

 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #43 on: January 30, 2019, 09:58:08 pm »
Here is another one in Russian, but auto translate to English is also somewhat helpful

 

Offline Johnny B Good

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #44 on: January 30, 2019, 11:50:35 pm »
Ignore the chinglish description, the circuit is much the same as that above, and what is posted in the reference schematic in the EGS002 datasheet which I have linked in previous posts.

The main difference is the one I have has an extra Toroid on the output which is used to help with EMI, so I am told by the engineer.
For 1000W and 2000W models, there are 4 FET's. For 3000W there are 8 FET's, to simply move more power.
On these models there is no actual protection circuitry other than the IFB pin which I have already mentioned, which is somewhat slow so would be for general current overload, and then there is temperature protection from a thermistor which is bonded into the heatsink, and then voltage feedback which is adjustable to modify the nominal output voltage too.

Some other inverter designs I have seen which are more for Battery inversion to 220VAC, but still using the EGS002 drivers, do have over current, over/under voltage etc protection, however I have not yet found any published schematic on these circuits.

 I think you may be overthinking the overload protection aspect here. You have to remember that the 380v is not coming off a 100A battery supply but from the more limited capability of a 3 or 4 KVA genset. An overload is more likely to stall the engine before burning anything out. The slower speed of the built in overcurrent protection is there to deal with the edge case of sustained overload that's not quite sufficient to stall the engine or trip the genset's own breaker. These inverter modules are surprisingly robust.

 The more sophisticated inverter/engine management unit in that little Parkside PGI 1200-B2 is rated for a continuous 1KW output (or with my particular example, 980W - not a trimpot in sight so I'm waiting for Lidl to get some more back in stock so I can test and swap inverter modules if the next is set to a more reasonable 1020 to 1050W overload set point and return the donor machine for a refund). It has an overload capability of up to 1200W for 30 seconds duration (not the 5 seconds claimed in the user guide). If it's overloaded above the 1200W mark, it shuts down the inverter immediately as you'd expect. TBH, I was quite surprised at this half minute endurance against modest overload surges, especially after reading the 5 seconds overload spec given in the owner's manual.

JBG
John
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #45 on: January 31, 2019, 12:13:06 am »
As mentioned already though, I can run drills and angle grinders directly off the raw AC from the generator without issue, the engine hardly blinks an eye.
Yet when I ran the angle grinder off the inverter, it blew the FET's up.
So not quite sure what you are saying here, as the generator side of things seems to cope fine, and the inverter doesnt, so its the inverter I can trying to protect with the NTC idea, to try and stop the FET's blowing from surge loading from things like an angle grinder.
Yes the generator isn't a large battery, but at the same time it seems to handle the output required to start the angle grinder...

Thoughts on this...
 

Offline Johnny B Good

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #46 on: January 31, 2019, 03:45:02 pm »
As mentioned already though, I can run drills and angle grinders directly off the raw AC from the generator without issue, the engine hardly blinks an eye.
Yet when I ran the angle grinder off the inverter, it blew the FET's up.
So not quite sure what you are saying here, as the generator side of things seems to cope fine, and the inverter doesnt, so its the inverter I can trying to protect with the NTC idea, to try and stop the FET's blowing from surge loading from things like an angle grinder.
Yes the generator isn't a large battery, but at the same time it seems to handle the output required to start the angle grinder...

Thoughts on this...

 The only thought I have on this is that either the switching FETs are too underrated for the task or else there's a design flaw subjecting them to high voltage transients. If you're still waiting on the 3000W version to turn up, you might have better luck with that seeing as how they've doubled up the FETs in that design.

JBG
John
 

Offline schmitt trigger

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #47 on: January 31, 2019, 06:56:13 pm »
WanaGo;

I know for a fact, as stated earlier, that series wound motors as found on these types of tools, draw very significant inrush currents.

Do you have access to a current clamp meter? Otherwise, we are only speculating at the current surge levels.
 

Offline WanaGoTopic starter

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #48 on: January 31, 2019, 07:56:26 pm »
Yep I have a current clamp meter. Just not sure its fast enough to capture surge, but ill give it a try.
 

Offline Circlotron

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Re: Petrol Generator Mod - Inverter AC Output
« Reply #49 on: January 31, 2019, 08:37:43 pm »
Measure what it pulls with locked rotor and 24VAC applied. Then multiply by 10. Actually it might pull way more because presumably the magnetic would be saturated?
 


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