A generator for your campervan.
If you are very frugal with your use of electricity (only one or two lights and a rarely opened compressor fridge) you will use about 30AH (at 12 volts) per day. If you use your notebook computer, listen to music, charge your cell phone and run your diesel heating system all night you will use more than 70AH per day. Assuming an 80% charged 200AH battery that you do not want to discharge below 50% (and you don't want to do that more than you must) then you only have one or two days of battery capacity.
Of course if you are plugged into the mains 24 hours a day, then providing your battery charger can supply say 5 amps you don't have a problem. The same is true if you drive for say two hours a day. However if there is no mains supply and you are not moving then you have to rely on solar power, a generator or you will have to run your vehicle engine for a couple of hours each day.
There is a lot to be said for solar power but it is nothing like as effective as the salesman would have you believe. For example I have 400 watts (four hundred watts) of solar panel on my campervan and an efficient MPPT solar controller. In November in England (at 52° North) I get, on average, 15AH of charge per day! (Not enough to replace the 30AH I might be using each day, but still enough to double the length of time my batteries will last.) The highest I have ever seen at this latitude was 151AH on 2008-07-21.
The other way to extend the time you can wild-camp is to use a generator (I am currently ignoring wind generators and fuel cells as being unsuited to overland travel). The ideal generator for an overland campervan would be one able to charge your 12/24 volt batteries at say 50/25 amps and run on diesel. It would recharge your leisure batteries in a couple of hours a day.
Unfortunately I have never found such a generator at a reasonable price. The smallest diesel generator I have found is around 4kW weighs over 70kg and costs over 4000 Euros.
If you want a small, low cost generator it will run on petrol. Until recently the only small generators you could easily buy produced mains (230/110 volts AC 50/60Hz), however "petrol battery chargers" are just beginning to appear on the European market. The rest of this page discusses the pros and cons of these two types of generator.
The sort of mains generators that might be of interest to overlanders vary from the small "no-name" ones at 600 watts for about 90 up to the well respected Honda EU20i (1600 watts) at around 1000.
Unfortunately the combination of a small mains generator and a modern electronic battery charger does not always work well. The waveform produced by many small generators does not seem to agree with some chargers. Either the charger does not work at all or it is quickly damaged. For example my 24 volt 10 amp (say 280 watts) Mobitronic mains charger worked happily with my 900 watt Honda EU10i generator, but my 24 volt 25 amp (say 700 watt) charger died after a few hours use. A friend's 24 volt 20 amp (560 watt) charger refused to work at all with my 900 watt generator (it worked with his 2kW generator).
One problem with small petrol generators is the purity of the waveform they produce. Real "mains" electricity has a nearly perfect sinusoidal waveform. The waveform produced by cheap generators may be very distorted, particularly when under load. More modern expensive generators use an inverter to produce a more stable output voltage, frequency and waveform. One measure of how far a waveform deviates from the ideal is the THD (total harmonic distortion). This is near zero for "mains", around 5% for a top of the range inverter generator and over 30% for a cheap no-name generator.
As a rule of thumb your generator should be able to provide three times the implied wattage of your battery charger. So for example if you have a 12 volt 25 amp charger you will need a 900 watt generator. You may also find that the addition of a 100 watt incandescent bulb as an additional load for your generator may help.
One of the advantages of a mains generator is that you can run things like a microwave or small fan heater directly from it. These generators also tend to be "consumer" products, and at least the Honda ones are well made, relatively quiet and very reliable.
A significant disadvantage however is that if for any reason your mains battery charger fails then not only can you not charge from the mains you can also no longer charge from your generator. If a small mains generator is to be used it might be worth considering buying a cheap 10 to 15 amp old fashioned (non-electronic) charger to use with it. That way you are less likely to damage your main (electronic) charger and you have some additional redundancy.
12 Volt Generators.
Petrol battery chargers (i.e.12 volt generators) are essentially a standard vehicle alternator attached to a small petrol motor. Many were initially home made and even the current wave of commercial ones are far from "consumer" products.
Most (all?) of the current ones seem to come from Australia although they may be assembled in the UK. Unlike mains generators you have to adjust the engine speed manually and if you suddenly apply an extra load the engine may stall.
Unless you are happy to use crocodile clips to connect to your battery each time you use the generator then you will need to do some serious heavy duty wiring and fit an external 12 volt high current socket. Note that disconnecting your generator whilst it is running may damage it.
The one illustrated above (made by Christie Engineering in Australia) uses a Honda four stroke motor and a Bosch 55 amp alternator. It weighs 12kg and is only 410mm long.
Whilst significantly noisier (74dba @ 7 metres) than a top end mains generator (say 59dba @ 7 metres) it is considerably quieter than some no-name generators listed at an ear shattering 91dba! It will certainly charge your battery far faster than most battery chargers running from a mains generator and thus annoy your neighbours for less time! 12 volt 55 amp generators are available for around 775 at the end of 2008.
Because the current range of 12 volt generators do not incorporate a proper three stage battery charger they should only be used for bulk re-charging of a well discharged battery.
Unfortunately my testing of the generally well made 55 amp Christie generator (above) was cut short by an intermittent fault with the ammeter after a little over an hour of use. Whilst the generator itself was an interesting alternative to a mains generator my experience with the (only?) UK supplier (BOAB) was unsatisfactory (Trading Standards and my Credit Card company are currently involved and we may yet end up in the courts).
On balance I don't think the current range of 12 volt generators (petrol battery chargers) are yet ready for the overland campervan market. The need to manually adjust the engine speed, the absence of any current limiting electronics (so the engine does not stall when you switch on the inverter) as well as the need to add heavy duty 12 volt wiring together tip the balance in favour of a high quality (inverter) mains generator.
Note that many mains generators also provide 12 volts for battery charging at "up to 8 amps". My Honda EU10i will charge my campervan battery at around 6 amps but only if the "eco throttle switch" is set to off. This significantly increases the engine speed and noise level. With the "eco throttle switch" set to on, it charges at under 3 amps.
If you have any questions or observations about generators for overland campervans please click here.
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