Noisy power from typical backup generators

[IDEngineer]

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?

[Stray Electron]

 IIRC they pulse modulate the field coil to regulate the output voltage and that causes a pulsating DC output instead of a true sine wave.  I've wondered if running the output through an isolation transformer would help.

[amyk]

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.

[james_s]

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.

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, I can leave mine running at night during an extended outage and it will idle down and keep the refrigerator, clocks, internet router and phone chargers going for around 12 hours on a gallon of fuel. It uses a 3 phase brushless permanent magnet alternator which is built into the flywheel. The other side of the engine where the output shaft would normally be is blanked off with a plate.

Conventional generators are far less efficient at light load which is what most domestic generators spend most of their time doing. As far as the noisy power, I started a thread about the same thing probably a couple years ago. I don't remember whether there was ever a solid answer but I know there are multiple types of conventional generator. Some have an automatic voltage regulator feature which is an electronic module that regulates the field current. Others are simpler and have a self exciting rotor that just has a rectifier mounted on it. 

[floobydust]

I'm used to standby generators with rotating diodes in the (brushless) rotor and a "voltage regulating capacitor" or "capacitor excitation":

"A separate excitation winding in the stator has a capacitor connected directly across its output as shown in Fig. 5.19. The rotor is usually of salient-pole construction as described previously, but in this case the rotor winding is shorted through a diode. On starting, the residual flux in the rotor body induces a small voltage in the stator excitation winding and a current flows through the capacitor. This current produces two waves of magnetic flux around the air gap of the generator. One wave travels in the same direction as the rotor, to create the armature reaction described in section 5.3.2. The second wave travels in a direction opposite to the rotor, and induces a voltage in the rotor windings at twice the output frequency. The current circulated in the rotor windings by this induced voltage is rectified by the diode to produce a dc current. This dc current increases the magnetic flux in the machine, which in turn drives more current through the stator excitation winding, which in turn produces more rotor current. This self-excitation process continues until the flux reaches a point at which the magnetic circuit is saturated, and a stable voltage results. The process also produces an inherent AVR action, since any load current in the output stator winding induces more rotor current to offset the armature reaction effect."

I think it's just old tech. I've never really figured out how they work as far as regulation and harmonics.
http://machineryequipmentonline.com/electrical-power-generation/generatorsbrushless-excitation/

[bdunham7]

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?

What sort of noise are you referring to?

A single wire moving in a uniform field in an textbook does indeed produce a mathematical sine wave.  However real-life generators, even big ones, don't have uniform fields.  Mains power generally has a significant 5th harmonic and a detectable 7th, while the 3rd cancels out in a three-phase system, so any 3rd harmonic you see is caused by loads.  I'm not an expert in generator design, but I in medium-sized generators I see references to 2/3 and 4/5 pitch, which refers to how wide the coil windings are relative to the poles.  Apparently 4/5 pitch is better for three-phase generators and 2/3 is better for single-phase because it has less third harmonics--but more 5th and 7th.  Typical cheap gasoline generators will have 10% or more distortion just due to their geometry, as opposed to the supposed 5% limit for the power company.

https://r5.ieee.org/houston/wp-content/uploads/sites/32/2016/10/2016-09-27-3-Generator-Advanced-Concepts-1.pdf

Then you have to consider the field coil system and load regulation.  On the small models, that's usually a mess and not pretty under any kind of varying load.

Inverter gensets do a much nicer job.  I just picked up a Generac GP2200i that uses a 3-phase generator with a control field winding and then an inverter.  It supposedly has less than 3% THD and it runs a fridge, a freezer, computers, monitors and the internet stuff just fine.  I haven't scoped it, but the only time it trips the UPSs is when it is on ECO mode and the bigger fridge starts up and the power sags for a second. 

[octillion]

Keep in mind the impedance of a portable or standby generator is significantly higher than the utility.  When driving non-linear loads the end result is higher distortion than utility, even if the generator had a zero distortion output before loading.

Here's a detailed writeup on various types of portable generators and distortion, in the context of motion picture lighting: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

[IDEngineer]

Thanks to everyone that responded. Some really good links for RTFM'ing in there. The one from the movie lighting industry had surprising depth.

I understand now how the low-end regulation techniques can yield trashy power.

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

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!

[Vovk_Z]

Seems to me that an alternator rotating through a magnetic field should be the literal definition of a sine wave,

Alternators may give pure sine only in absence of a load. When current starts to flow through a stator winding it distorts a magnetic field quite high. So to have pure sine at a rated current is not an easy task.

[james_s]

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!

I run my whole house from the EU2000i. It requires a bit of manual load management, I can't run the microwave or the dryer and if I need to use something like the toaster oven, bread toaster or electric griddle I need to turn down the thermostat so the furnace doesn't come on but I can live with that for the duration of the typical outage. My heating, hot water and kitchen stove are all gas so very little power required. With eco throttle enabled the UPS's will often kick in each time the fridge starts but they switch back to line almost immediately. If I had more frequent outages I would consider the EU3000i, or parallel a couple of the smaller units.

Yes, with Honda you are paying for the name to some degree, although the name also gives it excellent resale value and they have a proven track record of being extremely reliable. The other downside besides the cost is the high attractiveness to thieves. Having played with a few different competitors I still think Honda is the best, but it may not be the best value and there are certainly other good ones. I live in a fairly dense suburban neighborhood so quiet was the top priority, so that meant inverter. The cheapest loudest inverter generators are still quieter than the quietest conventional portable generators, at least under light load, and the fuel economy makes them a clear winner. A conventional generator may actually have an edge if you are running it close to rated load, but most consumer backup generators are going to spend 90+% of their time lightly loaded. Obviously the generator needs to be sized for the maximum load you require it to handle though regardless of how little time it spends doing that, unless you want to have multiple generators. 

[floobydust]

That looks like a great generator, the Honda is a top brand and priced accordingly but let's face it, this is mission-critical to have power during outages and the food saved it pays for itself.
The cheap copy Predator 2000 at Harbor Freight $550.

Inverter-generator looks worth it if you don't have to rev at synchronous all the time. I wonder what the output waveforms look like?
I think SMPS with active PFC would not do well with some low quality modifed-sine inverters?

This guy looked at a bunch of different UPS output waveforms.

[Renate]

My Onan MicroLite 2.8K has a rotor with an inductance of 1,000,000 Henries so that the PWM doesn't really cause any variation.
What an inverter generator does is whatever it does.
(I don't actually use it because my 600 Watts of solar panels is sufficient.)

[Johnny B Good]

@IDEngineer

 I had a cheap Aldi 2.8KVA/2.5KW 3000rpm AVR gasoline emergengy genset a few years back which I'd hoped would supplement my APC SmartUPS2000 backed protected supply. Unfortunately, the 2KVA UPS reacted very badly despite configuring it to its "Dirty Mains" settings (a smaller APC SmartUPS700 could tolerate the genset's "Dirty Supply" but this wastrel weakling was due to be given the sack - it consumed 20W to maintain just itself even with the 24v battery pack disconnected, a high price to pay for a lousy 450W max continuous inverter output rating).

 I'm afraid to say I had bought into the lie of "poor, noisy, distorted and unstable frequency output" of these AVR gensets so it took quite a while for the penny to drop as to the actual issue. I had examined the output waveform using an ancient 1940s boat anchor scope (its 1v calibration source rather conveniently was just a low voltage output secondary winding on its mains transformer which avoided the need for connecting another low voltage output transformer by which to safely see the mains voltage waveform).

 I had previously compared the 50Hz 240v mains supply against the inverter output of the SmartUPS2000 revealing the now classically distorted utility supply (a little flat topped with a small amount of slope towards the zero crossing point on both positive and negative peaks which I now know to be an artefact of the AC coupling in this boat anchor 'scope - a modern DSO only shows this when AC coupling is deliberately selected otherwise it's a dead flat top form of distortion in DC coupled mode).

 When I disconnected the mains input to the UPS to examine its output waveform, the wave trace turned into a shining example of the classic sine wave (with just a low level of 5KHz or so PWM ripple riding on the trace). When I repeated this comparison between mains and the genset output waveforms, the genset, funnily enough looked almost identical to the UPS output. There was a subharmonic 25Hz component due to the use of a 4 stroke single cylinder gasoline engine directly driving the generator head, complete with a high frequency 'slot ripple' similar in frequency and amplitude to the PWM ripple of the UPS's inverter neither of which effects (including the 53 to 48Hz variation with loading) were the slightest bit troublesome to the UPS.

 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.

 Close examination of the circuit diagram I had managed to track down for the SmartUPS2000, revealed the presence of a pair of 4.7uF caps in the mains input circuit which under mains fail conditions got disconnected from the incoming supply when switched to battery power, neatly explaining the horrible interaction between genset and UPS whereby it would keep cycling between generator and battery power until the genset was disconnected and mains power plugged in to give the battery pack a chance to recover before becoming completely depleted.

 Although I had considered using a 275v autotransformer tapped for 240v output with a 4.7uF on the genset side to force it into saturated output mode to provide a more stable 240v feed, I was concerned that the increased field current would shorten the life of the generator head so I sold it on, ending my plans for a more robust emergency back up supply until I could get hold of an inverter genset at a less eye watering price than those Honda units.

 Now I don't believe this behaviour with modest capacitive loads and AVR gensets is unique to the particular brand that had let me down so badly, so it seems to be a glaring omission in the list of reasons for problems that arise in their use for "Sensitive Electronic Loads", hence my tale of woe to put the record straight.

 I did eventually find myself a real bargain in inverter genset technology two or three years after that unfortunate episode, almost two years ago now. It took the form of a Parkside PGI1200B2 1200W peak (30 seconds timeout) 1000W continuous "Suitcase" generator purchased from Lidl for a mere £99.95 (about 10% of the price of the cheapest Honda inverter suitcase genset). I'd have preferred a higher output rating but, at that price, beggars can't be choosers, besides which, I was curious enough to make the modest 100 quid investment to test my theory that only the inverter genset designs were up to this particular task (free of the overvolting effect of capacitive loading) to unequivocally answer this question.

 Long story short (the first two had show stopping, yet as I later discovered, trivially easy to fix, stock faults), this inverter genset did solve the problems I'd had with my first generator purchase. 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.

 I did try out three examples of the rather shitty Workzone 2KVA inverter gensets being sold in Aldi stores about six months later but they all proved to have an unacceptable response to changes in loading (almost completely stalling with a step increase of loading even when preloaded to 50% before applying a further 40% of loading).

 Those little Parkside generators showed hardly any drop in engine speed when their loading went from 0% to 100% even when switched into 'Eco mode"(after a few minutes of warm-up - I did manage to stall one by not allowing the extra couple of minutes warm-up time before switching to 'eco' mode).

 Those Workzone units had no eco mode switch option - it ran permanently in 'eco' mode meaning you'd have no choice but to wait the several minutes warm-up time before taking the risk of applying a load - unlike the Parkside unit which could be loaded within 15 seconds or so of startup in 'normal mode' before making the switch into eco mode, plus the ignition kill switch was integrated into the fuel shut off tap, preventing the carb float bowl from conveniently being run dry, unlike the Parkside's separate fuel shut off tap and ignition kill switch arrangement which allows such convenience.

 The only irritating omission with the Parkside being the absence of a fuel lift pump priming lever to save the need to crank it with the pull starter with ignition off leisurely enough to save your strength before attempting an actual starting yank in the hope that it starts "first go" without it snatching back.

 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.

 This task would require hall effect sensor input physically synchronised to the rotor position or a shaft encoder that could simulate such sensor inputs with better accuracy and consistency than actual hall sensors embedded into BLDC motors during their manufacture. Such sensors do exist and are even affordable (around 15 dollars US complete with disk magnet to attach on the end of the motor shaft). However, I'd have to determine whether the PM alternator is a 6 or 7 pole pair design (18 or 21 stator poles) and deal with how best to attach the magnet and mount the detector board. This was a lot more time investment than the purely electronic project of a sensorless setup I'd first envisioned and hoped would suffice so I called a halt to the whole project at that point.

 Using a 60v rated BLDC controller with a BLDC that could be run up in very short order to generate some 280 volts rms back EMF would call for additional protection circuitry (isolating relays) to save frying the controller, making the project a whole lot more complicated than I was prepared to invest any further time into.

 All I have to show for my efforts so far is that the concept of making the PM alternator pull double duty as both a generator and a 'starter motor' looks to be a practical reality given enough time and attention to all the nitpicking details involved.

 Should I ever decide to try and take this project into any further development, a microphone by the spark plug hole to generate a timing datum point signal by which to count pulses from one of the stator coil connections on a DSO display by cranking with the pull cord will answer the pole pair count question and, if there's enough flux leakage on the outer surface of the flywheel, I might be able to lash up a set of 3 hall sensors salvaged from my retrieved PC AT and ATX cooling fan collection to mount just clear of said flywheel to generate the required rotor locked source of commutation pulses for the BLDC controller.

 Only if this overcomes the stalling issue with the spark plug fitted can I then look to solving the issue of disconnecting the controller swiftly enough on a successful firing of the engine to eliminate the over-voltage burnout hazard and then deal with how best to supply the 48 to 56 volts required to drive the whole shebang should the project ever reach this penultimate stage.

 As interesting an exercise in DIYing an electric start add-on to a cheap as chips inverter generator as this would be, I might just 'cheat' and throw a wad of cash at the problem by buying a good quality higher output electric start inverter genset and have done with the whole "Blood Sweat and Tears" commitment which could just as easily become a folly as a success.

 When I was searching the internet to see whether anyone else had had a similar stroke of genius in using the PM alternator as a BLDC starter motor in inverter gensets, I came across a 20 year old patent application by Black and Decker on a variation of my own add-on starter circuit. In this case, they cheated a little by using a modified alternator with low voltage taps to facilitate the direct application of the 12 or 14.4 volt starter battery voltage. Their interest seemed to be in the way of expanding the market for their 14.4v cordless tool battery packs.

 I suspect this no-brainer electric start option in even small cheap inverter gensets has been held back by Black and Decker's patent application. Once that patent has expired (less than 5 years to go?) we may well see the market flooded with cheapish inverter gensets in the 1 to 3 KW range all offering an overpriced electric start upgrade option for the cost of a cheap 7 or 12AH 12v SLA and a license code to enable this built into the inverter module function, possibly with a luxury 12.8v 4 cell LFP battery pack option for those who'd like to test run their gensets once a week over the next four or five decades in between battery changes.

 Anyhow, I digress (and then some!)

John

[IDEngineer]

If I had more frequent outages I would consider the EU3000i, or parallel a couple of the smaller units.

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.

[IDEngineer]

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.

YIKES!   

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.

Yep, that's precisely why I switched all but (I think) three bulbs in the house to LED: So the family didn't have to load-manage the lights in the house! Previously we had lots of halogen track lighting which consumed 50W per bulb and we had 6-8 on every track. That eats up the amperage pretty darned fast. The LED replacements are just as bright, have a similar color spectrum, and consume perhaps 10% of the current.

Thanks for the fun and very thorough writeup of your genset adventures!

[Renate]

Which subset of inverter generators are permanent magnet excited?

I'm always amazed at how people size generators.
They buy them without ever knowing what the load is.
They run them without seeing how much power is being used.

LED bulbs rock.

I've had good luck with Aldi "Work Zone" products. YMMV

[IDEngineer]

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.

[bdunham7]

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.

If you are running a 120/240VAC portable non-inverter generator wired into your house, you can add phase imbalance to the list of things making your power quality poor.  Also, most of those inverter generators are 120VAC only and the large plug you may see on many of them is just a 120VAC 30A 'RV' plug.  The Champion one you listed is about the size they start being 120/240 split phase.

[IDEngineer]

Agreed, I noticed that a while back. It's critical to confirm that the "big socket" on the panel lists 240VAC and not 120VAC.

Our portable 2KW inverter only has traditional 120VAC sockets so no confusion. But you cannot run the house from it since it's only a single phase (in addition to being too small). Our existing big generator has both the 240VAC socket as well as an array of 120VAC's, the latter of which are split across the two phases so you can load them somewhat equally - which presumes the user is even thinking about that....

[james_s]

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.

They don't work like that. Parallel is just that, they're connected in parallel, the parallel cable sockets are internally just wired straight to the output receptacle. The way it works is whichever unit starts up first becomes the master and then when you start up the second unit it locks to the output of the master and comes on line, doubling the amount of current you can draw. If one fails or shuts down for some reason you drop back to the capacity of a single unit. The advantage is a significant fuel savings during times when only one is needed. The disadvantage is having two units to store and maintain, and that it's still only 120V, as far as I know none of the small inverter units produce split phase. You could use a transformer but what I do is just feed both sides of my transfer switch  in parallel, there are no 240V loads wired to that anyway and if there were I don't expect having both sides floating 120V to ground with 0V between them would cause any problems. We don't have the shared neutral you sometimes see on kitchen circuits in Canada so that isn't an issue, and a 2kW generator is not going to overload a circuit anyway. It's an emergency backup generator so I can deal with some limitations, beats the pants off the candles and flashlights we used when I was a kid.

[Renate]

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.

[james_s]

Sure you can. Just jumper the phases in the main panel.
Hint: Try to remember to pull the jumpers before restoring normal power.

I jumper the pins in the socket on the end of the cord that plugs into the generator inlet. This is a lot safer since the transfer switch is interlocked so the utility power can't backfeed the generator inlet.

[IDEngineer]

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.

[Renate]

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.

[IDEngineer]

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.

Or you could just buy a two phase generator so that ALL loads would have proper power. It's fun to play "What can I Rube up and make work in a pinch today" but when dealing with line voltages that can be a dangerous game.