Wiki: Generators

[Tabby]

....

==Power== Firstly a gen's advertised rating is often an intermittent rating, not continuous. Continuous output is less.

A generator cares less about power consumption than VA consumption.

• VA = power consumption divided by power factor

• The VA figure is the same as power consumption for resistive loads

• VA is noticeably higher than power for inductive loads such as motors.

• Where VA rating isn't known, a good estimate for a motor is about

20-25% above its power rating.

Decide what you want to run on it and add it all up. Often that power requirement works out too expensive, and you can then decide where to cut back.

==Alternatives== There are other options than a generator, depending on what you want to run. Eg a UPS, a [[lead acid battery]] & charger, [[Backup power| gas lighting]] etc. Probably all of those are more reliable than gens, a lot less noisy and easier to use. See [[Backup power]] for more info.

==Life expectancy== Life expectancy varies widely. Some machines are designed with short lives of under 100 hours run time. High reliability machines like Listeroids can run daily for decades. Ensure your choice can do what you need.

==Outputs== Generators with 240v, 110v and 12v charging outputs are all available. Consider future use as well as immediate use.

• 12v output can charge car batteries and run some 12v appliances

• Running a 240v tool on a 110v output can enable use of a tool with greater power consumption than the generator can provide, though the performance penalty is heavy

==Listeroids== Listeriods are a very different breed of machine to the others on the market. These are copies of a 1929s Lister design, still made as the original.

• extremely long service lives

• large, heavy, and definitely not portable

• low rpm engines

• [[Save Energy & Money|very good fuel efficiency]]

• low cost

• normally supplied as an assembled and [[paint]]ed engine, but with no further work done

** no generator fitted ** no final testing ** sometimes incomplete cleanout of moulding sand from the engine ** no cooling radiator ** no [[oil]] etc

• standard of [[paint]]work can be inadequate

• Listeroid introduction]

• Typically shipped in from 3rd world countries, where they're popular

To make one usable,

• any grit in the engine is cleared out

• a generator is added, usually belt drive

• a cooling system is added. An oil drum is a popular simple radiator choice.

• [[paint]]work is patched or repainted

• engine [[oil]] is added

==Noise levels==

Noise is a big issue for many users.

• Most open frame generators are 96dBA or more

• "Silent" rated generators can produce 70dBA

Some gens are available with built in soundproof shrouding at extra cost. Its also possible to put generators in a vented enclosure to reduce noise, and this may be a good idea if you're going to use one a lot. Air inlet and outlet ports can use a [[Baffle box|serpentine path]] to cut noise. Needless to say lightweight construction isn't what's wanted.

==Starting== Most portable gens are pullcord start. These are fairly straighforward to use.

Starting handle gens also exist. These are used where more physical force is required than suits a rope pull, eg on 7kVA units. The main issue with a starting handle is that a single backfire can break thumbs or ribs and injure wrists. Always check your thumbs are on the same side of the handle as your fingers, never let a thumb wrap round the handle. Its possible to break a rib if a backfire forces your arms into your chest with great force, or damage a wrist.

• Stand with enough clearance to avoid chest injury

• Place your hands inline with your forearms, avoid letting your wrists drop

Electric starting makes life easier, at a price.

Remote start ?

2 stroke engines are famous for problems with starting. If looking at a 2 stroke unit, consider how failure to start would affect things in your application.

==Oil== Portable generators usually have no [[oil]] warning system. You need to check the oil from time to time, a neglected oil system can kill the machine.

==Earthing== Portable generators use [[Earthing Types|IT earthing]], meaning no effective earth system.

==Connection to a house== Connecting an extension lead to a portable gen is simple and reasonably safe. Connecting a generator to a house installation introduces complications requiring solving, at least one of which can result in death if overlooked (backfeeding power).

==Starting spray== Starting sprays (eg Easystart) are often used with generators. These are aerosol cans of a volatile fuel designed to start under a much wider range of conditions than regular petrol or diesel. Useful to get them going when stubborn, as often happens, but I'm told regular use can end up damaging the engine. more info?

==Power quality issues== Generators are prone to power quality issues.

There are some conditions under which generators can produce heavy voltage sag, resulting in appliances running slow or not working. This carries a risk of frying [[Fridge|refrigeration compressors]].

Generators are inductive sources, and can in some situations produce damaging voltage transients if a load switches off. This isn't usually a problem. Google 'load dump.'

Some generators produce a less than steady output, with visible flicker on [[lighting]]. This seems to be due to a design issue with the voltage regulation system.

Invertor generators use electronics to produce the mains output. The result is a much cleaner more stable output, but also a less electrically robust machine.

==Fuel== Petrol goes off when left in storage. The volatiles evaporate and gum forms. Don't expect last year's petrol to start a generator ok, but it can be mixed with new to gradually use it up.

Diesel generators can be run on red diesel, much cheaper than road diesel.

Occasionally people run generators off domestic [[Oil|heating oil]]. This is 28 second oil, whereas [[Oil|diesel]] is 35 second oil. Heating oil lacks the lubrication of diesel, some engines don't seem to mind it, some don't last long. Its not a recommended practice.

Diesel isn't volatile and can be stored from one year to the next.

==Servicing== Proper servicing can make a big difference to engine life.

==Stretching the power rating== Its possible within limits to run appliances on a gen of lesser VA rating.

• Power tools etc can be used in series with a [[dropper]], or 230v tools used on a 110v output. Performance suffers badly of course.

==Maximising return== Diesel generators can be run on [[Oil|red diesel]], much cheaper than [[Oil|road diesel]].

When a generator is used long term, it can be set up to produce [[DHW| hot water]] from the heat of either

• the cooling system, for machines that use water cooling

• or the exhaust.

Cooling system heating: A heat exchanger is used. A coil of [[Plumbing|microbore]] dunked in the water tank is a simple option.

Exhaust heating:

• Heat output is far greater

• Exhaut can be directed through a metal pipe a few inches wide as a simple heat exchanger, or exhaust output can just be directed onto the bottom of the HW cylinder

• A more efficient way is to direct the exhaust fumes around the cylinder, preferably going from top to bottom.

• Exhaust fumes in contact with a [[DHW]] cylinder implies a cylinder either outdoors or in a well vented [[shed]], for [[safety]] & noise reasons.

[[Category:Basics]] [[Category:Electrical]] [[Category:Tools]]

[The Medway Handyman]

Personally I wouldn't touch anything that didn't have a Honda engine. Neither will 99% of the tool hire trade IME.

Usually start first time every time, very little hassle.

[Andy Burns]

Not saying it's unimportant, but perhaps not the best opening paragraph; if someone is unfamiliar with the difference between Watts and VA, then giving a definition in terms of power factor is unlikely to be an immediate help.

Thought you were just making up words for a minute, I hadn't heard of them, some look interesting to start ...

Invertor generators use electronics to produce the mains output. The

Useful if the generator is supplying IT equipment for e.g. a home office, though I suppose a UPS with boost/buck functionality would do the same job, I've known the occasional UPS that gets upset by unstable generator supply.

[Dave Osborne]

You need to expand on this and explain such terms as prime power and standby power.

VA isn't consumption. Power is consumption. VA is partly consumption and partly "revolving credit".

It is usual to start an explanation by saying that power = VA x power factor, then to offer the observation that if you know the rated power, you can calculate VA = power/power factor.

You might want to put in a section that explains that generators come in a very large range of sizes and fall into classes, viz:

Small generators 300W to 5kW (portable)

5kW to 80kW (skid-mounted or towable) 100kW to 315kW (skid-mounted) 500kW to 2MW (back of an artic.) 2MW+ (installled).

You should explain that this article only really covers gensets between (say) 300W and 20kW (i.e. from the smallest available to the largest generally found in domestic situations).

Please put (see below) after Listeroids. I'd never heard of them either.

You need to make it clear that the above paragraph only really applies to small gensets. Anything over 5kW is likely to be good for thousands of hours.

As are 415V 3-phase sets, which can be useful if you have a home workshop which needs to run three-phase motors.

I wouldn't even mention this as an option. I don't think there's any mileage in putting this idea into people's heads.

"Super silent" sets go down to under 50dBA

e.g.

should mention that noise levels of modern gensets are often reported in LWA (which is the sound pressure level in dB(A) @ 7m or 21 feet distant from the genset).

You should also mention that noise levels increase as load increases, so (all other things being equal) a larger generator under-run is always going to be quieter than a smaller generator maxed-out.

Should that read "Air inlet and exhaust ports"?

Again, only small ones.

These are fairly straighforward

Auto start (i.e. AMF - auto mains failover).

Again, only small ones.

You need to expand this to say that it is usual to make your genset a TT supply by having a local earthing rod. You need to explain that if the DNO mains has failed then the integrity of the DNO Earth can not be relied upon, so connecting an IT generator to your home means potentially no effective earth at all.

What complications? You should mention the implementation of a change over switch, introduce the idea of load-shedding and talk about automatic failover.

I've heard this as well, but never seen any justification for it.

what conditions, other than overloading?

under which generators can produce heavy

I would not use the word frying. Consider "overloading" and "permanently damaging".

What situations? Don't tease!

ITYM poor or non-existent voltage regulation.

ITYM inverter. Some electronics still don't like inverter mains. We had this discussion a while back in re keeping your central heating going, because one or two people mentioned that their central heating timer didn't like the mains from the inverter.

I don't quite see the point in introducing the 28 sec. oil vs 35 sec. oil thing. Nobody knows what it actually means in any context, never mind generators. I would just refer to domestic heating oil (a.k.a kerosine/paraffin) vs diesel.

Diesel *is* volatile, just less so than petrol. If it wasn't volatile, you wouldn't be able to smell it!

As I said before, I wouldn't even mention this as an option. I don't think there's any mileage in putting this idea into people's heads.

[Dave Liquorice]

And may require 2 to 3 times its rated power to start.

Like what? I guessed Lister engine based sets but using clone engines but then I knew about Lister engines.

Maybe add a bit about starting a diesel with a pullcord. It's almost impossible to pull a diesel through compression, you have to release the compression with the "decomprssion lever" pull the engine several times to get it spinning and energy into the fly wheel then let go the decompression lever and hope it will go through compression, fire and pickup. Small electric start diesels may also need the decompression lever as the starter motors are a bit weedy.

Make the bit about having ones thumb the same side of the handle as your fingers a bullet point. It is very important, lose or damage a thumb and you lose the ability to grip things properly.

As I understand it, the spray (mostly ether) goes off with a some what more rapid and powerful bang than petrol/diesel. This stresses the combustion chamber, valve seats and rings. If there is an weakness it is found out...

Add the words "diesel engined" between "run" and "generators". A petrol engined set wouldn't run on diesel or kero. B-)

Petrol based sets can also be run on LPG (normally propane, orange cylinders) with a suitable conversion kit.

You've only just said that, remove it from the Fuel section.

[Dave Liquorice]

Does LWA specify the distance? It is vital to know the distance for the numbers to be any use but I don't think LWA specifies it.

"Always"? Rather definate.

"... a larger generator under-run is likely to be quieter than a smaller generator maxed-out."

kill

All the small 4 stroke/diesel set's I've looked at have an oil shutdown system. They will either stop running or not start in the first place if there is not enough oil. Admitedly there is often no warning lamp or other indication that this is why it has stopped or won't start...

[John Rumm]

I don't know how much power factor info I would include in this article, since we can refer to the one on Power Factor one for some of the detail if folks are interested. Suffice to say the power is usually quoted in kVA, and you can think of these a slightly undersized kW in most cases.

It is worth mentioning that unlike when sizing normal circuits etc the inrush current requirements are more important with the smaller gensets. Its easy to arrive at the situation where you have a generator that can theoretically support a load with ease, and yet is not able to start the load in the first place. (or a combined load of several appliances, where the order in which they are started matters)

The decision of conventional Vs inverter is also significant here when you consider what equipment requires supporting.

agreed...

Is it worth singling out one particular brand? I am sure there are a number of reputable long life gensets available.

Also worth mentioning for those planning to use a genset for backup during powercuts etc, the some boilers flame detection relies on having proper earthing to work. Hence if you don't make it TT it may not keep the CH running.

You may need to consider a dedicated CU for circuits that must be maintained, and ensure it is setup so it can safely run TT.

The stepped sine wave output can make some motors noisy - same as with online UPSs.

How true is this for fuel kept in a well sealed can, rather than sat in the gen's tank?

[Tabby]

snip all the feedback

Lot of good suggestions here, thank you. When I get some time I'll work on it some more.

NT

[Andy Burns]

But if you massively overspec the generator it will run with lower fuel efficiency (e.g. when run under 50% )

[Dave Liquorice]

Please trim out all the bits of the post that your are following up that aren't relevant to your comments.

The vast majority of domestic oil boilers are pressure jet based. The main exceptions being Rayburns and Agas.

Only very old domestic boilers use 35 sec oil these days.

[Dave Osborne]

Yes. Industry standard for gensets is to quote LWA @ 7m. If you're lucky the supplier will tell you if that's at full power or what.

Google for generator LwA 7m

I concede. I was thinking (all other things being equal) of the larger generator being "the next model up".

[Dave Osborne]

Of course a larger genset costs more to run, but potential noise nuisance is often an important factor. I wasn't advocating massively overspeccing, I was thinking of "the next size up".

[Andy Burns]

I didn't say you were, and a bit of spare is no bad thing, just that if someone got the impression that the way to quieten a generator was to get a more powerful one, they might regret it, if it ends up costing a lot more to run - though realistically I assume were talking about people with a temporary need here.

[AlanD]

In my experience it depends on the type of inverter. Cheap 12v > 240v mains interters usually output a 'modified sine wave' which is pretty nasty to look at on a 'scope. Any true sinewave inverter should produce a pretty good output, which most things should be happy with.

I've used several 'Kipor' branded (Honda clone) inverter generators, which produce an excellent sinewave, including under load. I've used these to power central heating, computers, TVs HiFi etc and all is perfectly happy with it. Even X10 home automation still works when supplied from one of these generators. I'd assume the genuine Honda inverter generators to be just as good.

Alan.

[Tabby]

All useful info.

If they develop a carb fault and run too rich, would they be smoked kipors?

NT

[AlanD]

Yes, but not sure I'd eat them!

Side note while I remember, they have a 'smart throttle' that automatically adjusts engine speed to match the required load (via a stepper motor on the carb butterfly) so they run at the slowest speed they can. Much better for noise / efficiency / engine wear than the usual '3000rpm at all times' of a traditional generator, which needs to maintain speed for the correct voltage / frequency output. As the inverter generators produce the output electronically from a 3-phase alternator internally, the engine speed does not affect the output frequency etc.

[Steve Firth]

I can't agree with that statement. I use both gensets and UPSs, the UPS takes more maintenance and is more failure prone than the generator. I'm now looking to buy yet another set of LA batteries for the UPS, the problem being that until you try to run off the battery you have little knowledge of just how knackered the battery is. Also the runtime is much lower, the quality of AC is extremely poor and will lead to failure of switched-mode PSUs and the only way round that is to buy an expensive line-conditioning UPS which will cost more than an equivalent generator.

You seem to have some fetish about "Listeroids" these are utter bastards and anyone who advocates them can't have used one. There are far better gensets available.

[snip]

Barely scratching the surface here. Electric start is available on generators at remarkably low prices, particularly diesel generators which are difficult for many people to start on a pull cord. So the "at a price" seems to me to imply some huge price premium which does not exist in fact.

You also need to cover both remote start (a difficult to find option in my experience) and ATS (Automatic Transfer Switching). ATS permits a generator to be used as a UPS by automaticall starting the generator when mains power fails. ATS generators usually have capacities >4KVA and are, in my experience, almost all diesel "silent" generators.

Any generator with ATS will need an extra external ATS box to connect into the domestic supply. This isolates the mains on failure of the mains, sends the signal to start the generator and when power stabilises switches the generator on-line.

Generators with ATS are remote start capable but finding a supplier for remote start is difficult in my experience.

Also, oddly enough, silent generators intended for use with ATS are marked to indicate that they must not be operated in the rain. Since it's impossible to predict the conditions when the mains will fail, but it's also a fair bet that it will happen in storms, each generator will need a suitable weatherproof housing.

[snip]

Yeah, well you'd look at bit better if you gave some practical advice at this point instead of shouting "look at me I found a problem". Explain that the connection of a generator to domestic mains needs either an appropriately rated changeover switch or an ATS box (which can only be used with a specific type of generator as mentioned previously).

[snip]

That last bit it largely c*ck. Cheap inverter machines may be less robust there's no problem with the Honda ones for example.

You have also skipped over AVR gensets which are halfway between the cheapsets and the inverter models. These use an AVR control module to stabilise voltage output and are extremely effective. A useful point is that AVR can be retrofitted to many gensets which produce flickering output.

You also make no mention of generators with digital control panels, which to me are superior to all the others. They can be started with a key if required but can also be configured from the panel. Typically a panel offers push-button start/stop and auto run. It also provides monitoring for the generator including engine hours, power output, voltage, time to service etc.

Old wives tale.

Cough diesel is volatile, it's just not as volatile as petrol. But it can be stored *dry* for extended periods. However it it gets wet then it can suffer from the growth of microorganisms which will clog fuel lines and filters.

[snip]

Night follows day.

Try to make the section actually useful rather than pompous waffle. Although all you can really do is to reiterate what's in the service manuals. Change filters (all filters) at the recommended intervals, use the oil grade recommended by the manufacturer, and note that 2-strokes need very little maintenance compared to 4-stroke petrol or diesel gensets.

Just remove this section, it's stupid.

[snip]

Cobblers again. and indeed for the rest of it. The only sensible way is to use a proper heat exchanger and even then it must be designed with caution. It must operate safely in the absence of flow to DHW (i.e. it must not boil and explode), it must be made of materials that will resist corrosion by exhaust gasses, it must not fail by dumping the contents of the DHW cylinder down the generator exhaust, it must not cool the exhaust so completely that the exhaust gasses condense in the exhaust or must be constructed so that the condensate runs safely away with adequate disposal of what will be an unpleasant chemical cocktail.

I don't know where you got all that half-arsed c*ck about ways of heating DHW using exhaust but its stupid, potentially dangerous and if someone is dimwitted enough to believe it they are probably stupid enough to try it with an insulated DHW cylinder (can any other sort be purchased?) and then they will have an amusing fire on their hands.

[Steve Firth]

I've had to do that after a 3KVA genset proved to be just too small for the job. That also taught me that I needed to spec a mains electricity supply greater than 5KVA (the place where the farm is only permits

3,5,7KVA supplies) and suffer paying the premium to get it installed.

I ended up buying a 6KVA diesel genset in a "silent" cabinet. It is wheel mounted but weighs over 200KG so the wheels are only good for positioning. It's turned out to be economical compared to the previous model and provides our needs for about 40 litres of diesel a month. That's cheaper than it would have cost to use the mains supply, if we had it.

[Steve Firth]

FSVO of "hardly" they can be up to 70 dBA even in an acousting housing. That's not "can hardly be heard" that's "f*ck me, my lungs are vibrating". There are gensets that get much quieter than 70dBA. The prices are amusing. A pramac 6000s for example - cracking genset with a Yanmar engine 58 dBA at 7 metres but an ear-splitting 90 dBA standing by the side of it. It'll cost you around £3500 which puts it well outside most people's budget. At the other end of the range there's the Kipor

6700 range. An earsplitting 77 dBA at 7 metres and beyond the threshold of pain to stand next to. But they cost less than a grand and can be had as low as £600-700 depending on the value of the £.

So, the gensets you are thinking of are either hideously expensive or figments of your imagination. Or, possibly, petrol models which are a lot quieter than diesel gennies but cannot be run on cheap red diesel.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Dave Liquorice" saying something like:

Yes; often the top land of the piston.