Generator

This article is a Work in progress

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, 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
very good fuel efficiency
low cost
normally supplied as an assembled and painted 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 paintwork 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.

paintwork 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 serpentine path to cut noise. Needless to say lightweight construction isn't what's wanted.

Starting

Pullcords are most popular for portable gens. These are fairly straighforward to use.

Some have a pulley with a notch. The rope knot sits in the notch, and the rope wraps round the pulley. Simple & effective.
Some have an automatic retracting pull mechanism. These are easily converted to the above type if necessary.

Starting handles 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. Correct starting posture is important:

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 if it backfires
Place your hands inline with your forearms, avoid letting your wrists drop
take proper care every time, don't underestimate the potential for injury

Electric starting makes life easier, at a price.

Remote & automatic starts are generally found on large ex-military and ex-corporate machines.

2 stroke engines are relatively cheap, but famous for problems with starting. Consider how failure to start would affect things in your application.

Diesels that are too big/hard to pull start generally have a large flywheel and a compression release. On such units, release compression, spin upto speed then close compression and it should fire. A cloud of thick black smoke is normal when starting a diesel. It contains plenty of toxic carbon monoxide.

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 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 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 heating oil. This is 28 second oil, whereas 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