This article is designed to give you an insight into generators that can be used with your caravan or motorhome. This guide has been written in response to some of the questions that are asked on the caravantalk.co.uk forum.
Using any electrical equipment outdoors always carries a higher risk because of the increased chance of moisture, accidental damage etc.
Please take extra care when using ANY electrical equipment outdoors.
I have often seen postings on caravan and motorhome forums asking the question “What generators are OK to power my caravan?” There has always been a range of answers from “you can use any generator” to “you can only use your leisure battery”
Modern electronic equipment is sensitive to the quality of the electrical supply it is connected to. With the development of switch-mode power supplies and the components in them, many electrical devices now don’t use a step-down transformer and a bridge rectifier to produce the low voltage from the mains voltage that they need to operate.
It is now possible to get a low voltage from the mains using just a hand full of components. Hence the rise in “power cubes”…. the little black cube that plugs into the mains socket and has a lead that plugs into your device to charge or power it.
If you look at the data plate for the device, you will often see that the operating voltage for the supply is 110 volts to 250 volts, 50 or 60 Hertz (Hz). That means you can plug it in anywhere in the world.
Manufacturers make the equipment with a wide operating voltage so the only have to produce one power supply for the whole world market. In the past, the manufacturer of the equipment would have produced different equipment models for different countries. Typically it was broken up into The Americas, UK- Australia-NZ-Japan, Europe and Asia.
Now, to get this same electricity on a campsite for your caravan or motorhome, there are three ways of achieving it. The first is the simplest… just plug your caravan or motorhome into the EHU bollard. This will give you supply exactly the same as it is at home and will only be limited in capacity by the circuit breaker supplying the bollard, usually (in the UK) 16 Amps or 10 Amps. On the continent, this may well be limited down to 6 Amps or even 3 Amps.
The second is via an inverter run off your leisure battery.
Inverters take one form of electricity and convert it into another. The most usual type of inverters take 12 volts direct current – as supplied by a car battery or leisure battery and convert it to 220/240 volts alternating current (AC).
The output of inverters is not always the same as the electricity supplied by the utility companies. Cheap inverters will achieve the alternating current by simply switching the voltage/current from one direction into the opposite direction in steps by literally switching it electronically 50 times a second or “inverting” it.
Most domestic electrical equipment (kettles, toasters etc) are quite happy running on this modified sine wave, unfortunately, a lot of electronic equipment, including microwaves and TV’s are not. Plugin your laptop power supply, LCD TV, Satellite box to a cheap modified sine wave inverter and it will probably be the end of it.
Petrol (gas) Generators
Generators work by having a small engine that can either run on petrol or gas (propane or butane) driving an alternator, which in turn generates electricity.
You have an alternator in your car usually driven by the fan belt. It generates electricity when your engine is running to power your accessories and charge your car battery.
Vehicle alternators are usually three-phase (some high-performance units for 4 x 4‘s are 6 phase) and have a set of diodes (electrical one-way valves) to convert the three-phase alternating current into the direct current to run your cars electrical system.
The standard petrol or gas generator still has an alternator, only this time, we use the AC output directly from the back of the alternator.
On cheap generators, the alternator is single phase and generates the 230 volts without any additional electrical components. The output from these is usually only suitable for running electrical drills, tungsten lights etc. and can be very “electrically” noisy.
On the more expensive petrol or gas generators, the alternator is three-phase, still generating at 230 volts, but will have a simple electronic circuit to combine the three phases to produce a single-phase output. These tend to be more efficient, and often will have a slightly higher output for a given engine size than the cheap single phase alternator equipped generators.
On a big generator that the utility companies run, the RPM of the alternator is closely monitored to give an exact frequency. On your small generator, this is not always the case. As you put more electrical load.. i.e. connect things to it, it takes more energy to move the wire coils of the alternator past the magnetic poles within the alternator.
The small petrol engine is asked to do more work in keeping the alternator turning and it starts to slow down, therefore the frequency will reduce and the voltage will drop as the coils are now not passing the magnetic poles at the same speed. The generator will sense this ( usually a small coil with a plunger inside connected to the carburettor) and via a mechanical linkage, open up the throttle on the engine, letting a bit more petrol through and increasing the speed of the engine…. got it yet?
The frequency and voltage will fluctuate as the load changes on the generator. This is also compounded by the fact that small single-cylinder petrol engines don’t maintain a stable speed even with a stable load on them, they tend to “hunt” within a given RPM range.
So to sum up, a generator going on to full load will reduce the frequency and reduce voltage. As it comes to offload the frequency will increase along with the voltage. This is a problem, so how do the generator makers get around this?
Well, the frequency is not too much of a problem for 99% of equipment. The issue for the generator manufacturers is to stop the generator’s voltage rising too much or dropping too much, so they get round it in a rather simple way. Instead of generating the correct voltage – 230 volts, they use alternators that generate about 300 volts and use an electronic circuit to “clip” the voltage.
This clipping stops the voltage rising above a preset limit – usually 230 volts and because the alternator is generating a higher voltage, if it does slow down due to additional load on it, then the voltage should still be above the clipped limit, therefore maintaining a relatively constant output.
Inverter Petrol Generators
Some generator manufacturers realised that there was a market for small units that didn’t have any of the associated problems, so they came up with the idea of a generator equipped with an alternator that could produce a three phase, high frequency high voltage output and feed this to a box of electronics similar to an inverter, where it is electronics that produce the nice smooth sine wave output at a stable regulated voltage. Electronics can react a whole lot faster than a petrol engine.
One of the first companies to recognise that generators need to be improved was Honda. They saw a huge market in the USA where generators are used by householders that have lost their supply from the electricity company due to downed power lines. They produced some of the first generators that could be permanently installed and would run all types of equipment in the home from fridges to TV’s.
Soon people were asking about smaller units to be able to take in their mobile homes and Honda produced a portable range of inverter units which in Europe is the EU10i, EU20i and EU30i range.
One unique feature of the Honda range is the ability to link two identical model generators together to double the output. (This is a feature that was introduced in the early emergency generators for the US market and has been maintained through out the range) As the inverter technology will sense the phase of the sine wave of it’s partner unit, it will compensate it’s phase and timing to match, so effectively “adding” its output to the other unit.
WARNING: DO NOT TRY TO CONNECT ANY OTHER GENERATORS TOGETHER OR AN Y OTHER GENERATOR TO ONE OF THE HONDA UNITS!!!
They WILL go “BANG”
Honda produce a special lead for this, and only this lead must be used.
Earthing your generator
Something else you might want to think about is “earthing” or “grounding”.
Most small generators are configured differently to the electrical mains supply in your house. Small generators have what is called a “floating” supply, that is to say that the earth is not connected to neutral. Now for using a single piece of equipment plugged into the generator, this is not a issue, but as we will be connecting a caravan, it is deemed that there will be more than one piece of “class 1” equipment connected, and therefore has to be treated differently.
It is important that the neutral is connected to the earth at the point of generation, therefore the neutral should have a link bonding it to the earth terminal on the generator.