I believe some of the newer designs are actually a multiphase DC generator (like a car alternator) that doesn't run at a fixed frequency, and the output of that is fed to an inverter which then generates a very poor approximation of a sine wave. It's easier to generate a fixed frequency under varying load this way.
Without disassembling one, I don't understand why typical gasoline powered generators generate such low-quality AC power. Seems to me that an alternator rotating through a magnetic field should be the literal definition of a sine wave, yet their output is often bad enough to trigger UPS's and there's a whole subcategory of generators that rectify the AC just so they can synthesize a sine wave with less distortion!
I understand that the stability of the frequency could be poor in a gas-powered generator, especially under varying loads, but why would the shape of the output sine wave be poor?
They are, they're called "inverter generators" and it will be prominently displayed on the unit. The one I have is a Honda EU2000i and it's fantastic
Seems to me that an alternator rotating through a magnetic field should be the literal definition of a sine wave,
Yep, inverters I definitely understand. They use a multiphase alternator and are the "rectify the AC" style I mentioned in my original post. PWM gives good control over the output waveform. We actually have a smaller, 2KW portable inverter that we use for mobile stuff but it's not large enough to run the house. All of our heat sources are NatGas (no resistance heating) but we still have some larger loads that 2KW just won't handle.
The Honda units are indeed excellent but you really pay for the name. There's a new "hybrid" style of generator that goes with the less expensive open frame mechanical design but employs the multiphase-PWM inverter. I'm looking at a unit from Champion, their 100520, that is 8750/7000 watts and claims 3% THD for ~$1200: https://www.championpowerequipment.com/product/100520-8750-watt-open-frame-inverter/
It will be noiser than a Honda but given the savings I can live with it, and it would already be significantly quieter than the industrial-style generator I'm presently using.
Power outages seem to be more frequent lately, and tend to last longer. Our last one was three days and it was a PITA having my lab UPS's cutting in and out all the time. In a couple of cases their batteries eventually died because of what they deemed interrupted power (noisy power from the generator) so when the generator had an event my equipment cycled anyway, making work basically impossible. I knew an inverter was the way to go - just had to find one big enough to run the house - but it raised the question "Why are traditional spinning generators so noisy in the first place?". As I said, the comments and links herein have answered that.
Thanks again!
If I had more frequent outages I would consider the EU3000i, or parallel a couple of the smaller units.
Curious about the possible effect of the genset's slot noise ripple, I wired a spare 4.7uF fluorescent lamp ballast PFC capacitor across the genset's output in an attempt to attenuate the slot noise component only to be greeted with the 240vac output rocketing north of 270vac! It seems you don't need much capacitive loading on these AVR gensets to render the AVR completely helpless against the self excitation effect induced by this leading current loading.
Also, with virtually all of the lamps in the house now being LED types, the 1KW (995W actually) is actually quite sufficient to maintain the IT kit and keep every light in the house burning.
They run them without seeing how much power is being used.
I'm just the opposite. I have one of those little plug-in-the-wall power monitors that displays voltage and frequency. I plug that in whenever the generator is running. Granted I'm only monitoring one of the two phases but the frequency has to be the same and the voltage is likely close.
I'm reluctant to parallel them because it halves your reliability. If either unit goes down, human intervention is required because anything on that phase - or any 240VAC loads across both phases - becomes inoperative. Meanwhile, things on the OTHER phase stay alive. That could play some weird games in your house. As just one (non-fatal) example, many 240VAC appliances run their electronic front ends on just one phase... not sure if their designers considered the proper action if the other phase drops. Or if the non-intelligent phase is alive while the intelligence isn't alive to control it. I'm also not sure what a "center-tapped" (so to speak) load were to only have one phase energized.
Thus you're forced to scramble around to either kill the remaining generator, or rewire things so that the remaining generator attempts to power everything - in which case you're right back where you would have been with a single. This is why I've been watching the market for larger inverter-equipped units, and the Champion I mentioned fits that bill nicely: 7000 running watts in a single unit with clean power.
Perhaps paralleled units are smart enough to disable themselves if the other unit dies. But in any case you're now dependent upon everything running properly on TWO engines. I'd rather have a single larger system.
But you cannot run the house from it since it's only a single phase...
Sure you can. Just jumper the phases in the main panel.
Hint: Try to remember to pull the jumpers before restoring normal power.
Sure you can. Just jumper the phases in the main panel.
How would that work for 240VAC loads?
How would that work for 240VAC loads?It wouldn't. But at least you could have a lightbulb in every room no matter which phase it was on.
...when dealing with line voltages that can be a dangerous game.
Incidentally, I did toy around with the idea of installing an electric start circuit to drive the PM alternator as a BLDC starter. I even got so far as to invest 16 quid in a 60v rated 300W electric scooter BLDC control unit with both Hall effect sensor and sensorless control options. I could get it to spin at about 480rpm using a 48v battery pack but only by removing the spark plug. Even blocking the spark plug hole with my finger whilst it was running was sufficient to stall it, proving that sensorless operation wasn't up to the task of handling such erratic mechanical loading.
Sure you can. Just jumper the phases in the main panel.Wait, what? Surely you don't mean paralleling (jumpering) both phases so they act as a single phase?!? How would that work for 240VAC loads? At best they'd see a net 0VAC across their inputs.
I don't have any 240V loads on the portion of my panel that is on the transfer breaker and neither does he but it wouldn't cause any problems, they'd just get 0V just as you'd expect. ... I fail to see how it is dangerous to feed both legs of the panel from the same wire. There's a physical interlock on the breakers so the generator breaker cannot be turned on while the utility main is on, and the bridge is in the socket on the end of the cord that goes from the generator to the house.
Ah, camping, back to nature, peace and quiet.
For some Americans that apparently has no appeal.
No, this photo is not from a rock concert only a little camping site.
QuoteIncidentally, I did toy around with the idea of installing an electric start circuit to drive the PM alternator as a BLDC starter. I even got so far as to invest 16 quid in a 60v rated 300W electric scooter BLDC control unit with both Hall effect sensor and sensorless control options. I could get it to spin at about 480rpm using a 48v battery pack but only by removing the spark plug. Even blocking the spark plug hole with my finger whilst it was running was sufficient to stall it, proving that sensorless operation wasn't up to the task of handling such erratic mechanical loading.
I have a Honda EU2200i that I want to electric start so the lady can easily start with push of a button. Using the PM alternator as the starter motor is of particular interest. Any pointers you can share on this?
I would be interested in using a 12VDC lawn mower battery or Dewalt 20V max 9AH battery or Dewalt 60V 3AH battery(20v max 9ah)
First time post for me.
Johnny B Good
Thanks for the info. You've answered my questions. I think that's enough to help me decide it's a viable project.
Honda EU2200 3Q winding- 1.0 to 1.8 ohm acceptable resistance(according to Honda spec sheet)
During testing I've seen peak voltage of 286VAC L-L
Connecting a drill as a starter is something I do for other lawn & garden equipment but I've decided not to do that on EU2200 because it would require:
1. Removing/eliminating existing recoil start
2. Modifying flywheel mounted fan and mounting setup
3. Totally relocating the inverter
Well the EU2000i definitely uses a 3 phase permanent magnet alternator so it shouldn't be too hard to spin it with a BLDC controller. You don't need anywhere near the power level it is designed to generate in order to turn over the engine for starting so you might get away with a considerably lower voltage. Normally I think electric start is a pointless gimmick that adds considerable cost, bulk and weight and I actually quite like the elegant simplicity of a recoil starter, no battery to haul around or keep charged, no separate starting accessory to keep track of, just pull the self contained cord and it starts. In the case of a generator that already has most of the hardware present it makes a lot more sense though, just add a battery and a few extra parts and firmware on the inverter board. Hybrid cars have been using combined alternator/BLDC starter units for years.
For a DIY project, the cheap electric bike BLDC controller with isolating relays looks the most promising cost effective way to endow these inverter gensets with an electric start feature (provided some sort of hall effect sensor can be cobbled up - sensorless, fine as it is with propellor motors used by drones and RC controlled fixed and rotary wing models just doesn't work in this case).
TBH, I started losing motivation to continue my DIY electric start once I'd figured out a less painful technique to prime the carb float bowl by cranking not so energetically on the pull starter with the ignition off for about four pulls before finding the top of the next compression stroke and taking it just 'over the hump' before turning the kill switch to the run position and giving the starter cord a very firm yank with a very high probability that it will fire up "First go" rather than snatch back.
My problem had simply been a lack of finesse, wasting energy in priming the carb leaving me too little energy left to crank it fast enough to avoid the kickback risk by the time it was finally ready to start. A fuel lift pump priming lever would have made life so much easier for both me and the service life of the starter cord. Still, for just £99,95, I suppose I should be grateful they'd even equipped it with a recoiling starter cord.
I have built a number of alternator sets over the years mostly using stamford brand of alternator, now part of cummings power, I never had any trouble with noisey power from them and they use electronic AVR's or transformer type regulation on the smaller units. All the rotors have had a slight helical form to the windings which i understand helps with delivering a smoother waveform.
I couldn't figure whether these caps could be safely disconnected or not and their exact function remains a mystery... that SmartUPS is well over a quarter of a century old now
Have you ever tested the effect of connecting a 4.7uF PFC capacitor across the output? You might be shocked by the result. These generators can handle resistive and inductive loads ok but can end up overvolting due to the self excitation effect caused by the leading current produced by a capacitive load which in my case was the 9.4uF's worth of capacitance across the mains input of a SmartUPS2000 line interactive UPS which would be disconnected when it transferred to battery power due to the incoming generator voltage going north of the 240v mark by some 30 volts or more.
I wonder if that effect could be put to good use by allowing the generator to run a little slower while still delivering the correct voltage thus saving fuel if the full output rating is not required.
...before the voltage dropped to the cut out point at 40.4v.
...before the voltage dropped to the cut out point at 40.4v.Wow, you run the batteries hard, 10.1 V cutoff?
I used to see things pointing straight down as soon as I hit 11.5 V.
I guess that I'm a wimp, under 200 W load I like to keep them above 12 V.
Standard practice with LFP is to limit their charging to 90% of their maximum capacity (3.2v per cell) and their discharge to no less than 10% (around 2.25 to, preferably, 2.5 volt per cell), hence the typical 80% of their full capacity that's normally used to determine their optimal total WH's worth of autonomy.
I have built a number of alternator sets over the years mostly using stamford brand of alternator, now part of cummings power, I never had any trouble with noisey power from them and they use electronic AVR's or transformer type regulation on the smaller units. All the rotors have had a slight helical form to the windings which i understand helps with delivering a smoother waveform.
Have you ever tested the effect of connecting a 4.7uF PFC capacitor across the output? You might be shocked by the result. These generators can handle resistive and inductive loads ok but can end up overvolting due to the self excitation effect caused by the leading current produced by a capacitive load which in my case was the 9.4uF's worth of capacitance across the mains input of a SmartUPS2000 line interactive UPS which would be disconnected when it transferred to battery power due to the incoming generator voltage going north of the 240v mark by some 30 volts or more.
I couldn't figure whether these caps could be safely disconnected or not and their exact function remains a mystery. It's possible that modern line interactive UPSes may have eliminated the need for such a large amount of capacitance on their mains input circuit (that SmartUPS is well over a quarter of a century old now) so you might not see the overvolting issue I'd suffered with my own setup if you're feeding the generator's output into the mains in socket on a modern UPS.
As for my own thoughts on how to add a fuel priming bulb to that Parkside inverter genset, it has occurred to me that I could have saved on the T adapters and just plumbed it into the fuel line (before or after the pulse driven lift pump), assuming the one way valves don't create an excessive pressure drop. I'll test the simple series arrangement first but my original parallel arrangement might well prove to be the only viable alternative to the more usual arrangements.
Such arrangements being that it's plumbed into an extra hose nipple on the carb to let it suck the fuel through to prime it and send the excess back to the tank or else simply to squirt extra fuel into the inlet port to make up for a dry bowl and make it easier to start.
It seems I've come up with a third alternative that's never been mentioned in any of the youtube videos I've watched (the only source I could track down that offered even so much as a clue as to how these pulse driven fuel lift and priming bulb pumps work) in relation to priming such small engine kit relying on a (crank case pressure) pulse driven fuel lift pump. I'll report my results here in a week or two's time after I've had a chance to work on the generator.
As for that mysterious plastic pipe connection to the carb, I think it must be an atmospheric pressure equalisation vent tube but why such a plastic tube would be deemed necessary when the more usual system of pressure balancing with a small vent hole into the float chamber above the normal fuel level beats the hell out of me. Presumably there IS a good reason for this bit of extra plumbing. Maybe someone here knows the answer to that question?
I'm guessing they mounted it there to make use of the airflow from the engine cooling fan. Heat soak when shutting the unit off probably is an issue to some degree, although I'm guessing in most cases it will not exceed 100C.
I do love inverter generators, mine is only 2kW but has proven adequate since outages are fairly rare here and most of my appliances are gas.
If I have it in eco mode the UPS's will kick in for a moment most of the time when the refrigerator starts but that's a small price to pay.
I'm guessing they mounted it there to make use of the airflow from the engine cooling fan. Heat soak when shutting the unit off probably is an issue to some degree, although I'm guessing in most cases it will not exceed 100C.Yep, I thought of that but haven't checked the airflow direction yet. Seems like they could have easily mounted it as a "wall" on one side of this "open frame" unit but I wasn't on the design team, so who knows.QuoteI do love inverter generators, mine is only 2kW but has proven adequate since outages are fairly rare here and most of my appliances are gas.Ours too - everything that CAN be NatGas is. My motto is "if you want heat, burn something". Electricity is a terrible way to generate heat unless it needs to be very carefully controlled, like in aluminum smelting or soldering or welding. We have NatGas water heater, oven, cooktop, clothes dryer, whole-house furnace, the works.QuoteIf I have it in eco mode the UPS's will kick in for a moment most of the time when the refrigerator starts but that's a small price to pay.As noted earlier, that's why I transitioned to the large inverter. We too have a 2KW "suitcase" inverter but it's not sufficient to power the entire house in a worst case situation (both refrigerators running at the same time, a few lights on, maybe someone uses the microwave, etc.). Since I was buying a new unit anyway I wanted to go as big as possible because our previous 6KW unit would labor once in a while, though that may have just been due to transient startup loading. This is the largest inverter unit I have found, and "I've never wished for a smaller whole house generator" so the more margin the better - and ECO mode means the engine isn't running WOT all the time so it's likely more efficient than a smaller traditional generator anyway.
I've found a small oil leak in the valve cover, but haven't investigated in detail yet. It's maybe two drips per hour hitting the concrete, so it's not going to risk low oil level before I change it regularly anyway.
Does anybody make a VFD fridge???
And for that fridge, just use a nice Dometic water/ammonia/hydrogen thermal cycle fridge, nice and quiet.
I remember my grandparents had one in their old motorhome and it put out a ferocious amount of heat.
I remember my grandparents had one in their old motorhome and it put out a ferocious amount of heat.They have a chimney flue for the heat.
Unless you put your hand under the flue cap you can hardly notice the heat.
The flame is like a disposable cigarette lighter goosed up to about twice the flame.
It runs me about 7.5 US gallons of propane a month ~$30 with tax (in an expensive area).
You've got me thinking though.
It does have 120 VAC switchover, but no 12 VDC switchover
There are certainly times where my solar panels are throwing electrons to the wind.
I'll have to consider that.
Regarding VFD compressor fridges, when I checked what was available here in the UK about a year back, there wasn't a single one.
... mains as well ...
... to keep it working during towing, where you cannot use the gas.
FYI: The 120 VAC heater on my fridge is 180 Watts.
The run time on propane is somewhere around 50%.
I have a feeling that the 140W figure I'd quoted for our home fridge might have been the immediate reduction a second or so after the 1KW surge since I can't shake off the memory of figures of 72W and an 'average' figure of 36W.
It looks like I'll get a chance to measure the fridge's startup and running demands in the next day or two. The missus told me today that she's going to see her friend tomorrow or Thursday, probably landing up at their favourite garden centre or some such for lunch.
That'll give me a chance to set up the generator to test its capacity to handle the fridge compressor startup surge which might well be significantly higher than that almost 1KW peak reading I saw on the MetraWatt's 1000W scale (5A 200V settings). I might even try repeating these tests with the chest freezer if I have enough time. Hopefully, I'll be able to report the results of these tests in another day or two.
I have a feeling that the 140W figure I'd quoted for our home fridge might have been the immediate reduction a second or so after the 1KW surge since I can't shake off the memory of figures of 72W and an 'average' figure of 36W.
It looks like I'll get a chance to measure the fridge's startup and running demands in the next day or two. The missus told me today that she's going to see her friend tomorrow or Thursday, probably landing up at their favourite garden centre or some such for lunch.
That'll give me a chance to set up the generator to test its capacity to handle the fridge compressor startup surge which might well be significantly higher than that almost 1KW peak reading I saw on the MetraWatt's 1000W scale (5A 200V settings). I might even try repeating these tests with the chest freezer if I have enough time. Hopefully, I'll be able to report the results of these tests in another day or two.
I've measured my fridge before, once it starts up, the consumption increases steadily for a bit as the head pressure builds up, then it levels off at around 140W steady state until it shuts off. This varies ambient temperature, which doesn't really vary much inside my house. US fridges are typically quite a bit larger than UK fridges though.
It runs me about 7.5 US gallons of propane a month ~$30 with tax (in an expensive area).
It runs me about 7.5 US gallons of propane a month ~$30 with tax (in an expensive area).(25.3 MJ/L) * (7.5 US gallons per month) = 273 Watts.
Absorption fridges have their upsides, but efficiency is not one of them. I suppose it does compare favourably with a compressor fridge run from a propane fuelled generator.
Yes those 12VAC 2 phase fridge compressors are available off the shelf, and are a common way to convert the typical bar fridge to boat fridge, though they are rather less than stellar in the cooling department, as they cannot really get down to low temperatures due to the compression being lower. They are pretty expensive though, at least double the cost of the same size refrigerator compressor, plus then you need the inverter to drive them.
Yes those 12VAC 2 phase fridge compressors are available off the shelf, and are a common way to convert the typical bar fridge to boat fridge, though they are rather less than stellar in the cooling department, as they cannot really get down to low temperatures due to the compression being lower. They are pretty expensive though, at least double the cost of the same size refrigerator compressor, plus then you need the inverter to drive them.Or what about just drive the existing compressor as the 2 phase motor it really is? I'm aware of a proprietary/research implementation of such (Shannon Liu Quadrature Drive), but it should be possible to build one that's open source.
Or if all you need is to reduce the inrush, a single phase inverter that does V/Hz ramp up would probably do the trick without modifying the fridge at all. Perhaps at least some inverter generators have that feature?
I'm afraid using a separate VFD as you suggest just won't work. The starting capacitor will be the wrong value for the initial low ramp up frequency and won't do anything useful until you get within 10 to 15% of the compressor motor's nominal mains frequency rating.
As far as I know, VFD compressor motor systems driving an otherwise conventional pump use three phase BLDC motors which don't require any capacitor starter to be switched into the circuit, merely a three phase supply that can ramp both supply voltage and frequency together from a very low initial start condition, culminating in nominal voltage and frequency for full output (perhaps as high as 70Hz and 140vac for a compressor designed for 120v 60Hz mains supply).
I think his idea was to nix the capacitor all together. Most compressors use a PSC motor so the capacitor is not just a starting capacitor, it's a run capacitor that creates the phase shift necessary to produce a rotating field. I haven't tried, but it should be possible to drive a PSC motor with a 2 phase VFD without any capacitor at all, the phase shift would be produced electronically.
I think his idea was to nix the capacitor all together. Most compressors use a PSC motor so the capacitor is not just a starting capacitor, it's a run capacitor that creates the phase shift necessary to produce a rotating field. I haven't tried, but it should be possible to drive a PSC motor with a 2 phase VFD without any capacitor at all, the phase shift would be produced electronically.I've only had a couple of (older, UK) fridges apart, but they were all capacitorless motors with thermally controlled switching of a resistive start winding.
I've only had a couple of (older, UK) fridges apart, but they were all capacitorless motors with thermally controlled switching of a resistive start winding.
I didn't think they used the R/L phase shifting technique in domestic fridges (or even that it was "A Thing") hence my DDGing to find this description on the following page:-
https://www.theengineeringknowledge.com/starting-methods-of-single-phase-induction-motor/
It (described as a Split Phase Induction motor on that page) offers the lowest startup torque option second only to the shaded pole single phase induction motor typically use to drive zero torque startup fan loads. I'm surprised it's used at all with a potentially high start up compressor load. The more popular system is the switched start winding capacitor, with or without the smaller run capacitor.
I've only had a couple of (older, UK) fridges apart, but they were all capacitorless motors with thermally controlled switching of a resistive start winding.