Electronics > Projects, Designs, and Technical Stuff
Petrol Generator Mod - Inverter AC Output
schmitt trigger:
--- Quote from: WanaGo on January 28, 2019, 08:01:17 pm ---
--- Quote from: schmitt trigger on January 28, 2019, 04:40:17 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.
--- End quote ---
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.
--- End quote ---
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.
Circlotron:
--- Quote from: WanaGo on January 28, 2019, 10:42:31 pm ---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?
--- End quote ---
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.
coppercone2:
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.
WanaGo:
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.
Johnny B Good:
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
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