Power Management

A very hot topic in the Motorhoming community with everyone having their own solutions, many quite different. I started out with the vision of being self sufficient and it wasn’t about saving money it was about being able to go where we pleased and still use the appliances that make our lives pleasant. It was also, to a lesser extent, about trying to “do my bit” against global warming. One thing I have learnt over many years of caravanning and now Motorhoming is that there is no single solution that suits all. Quite the opposite in fact with many people devising solutions that work for them. I suspect however that there are quite a few of us that are having to compromise to make our chosen solution work. Over the years I have learnt a few things and I would like to share my experiences with you. Some are painfully obvious but bear with me.

Understanding Power

This is probably one of the most important lessons there is. We all need to understand what a battery can do and how much energy from that battery can we use.   In general manufacturers will fit one or two leisure batteries in a motor home.  These vary between type and power.  In a nutshell you have a limited amount of power to play with.  For some reason, namely price, weight or space, manufacturers fit around 100AH worth of battery power.  Now you can’t use all that power, only around 50% of it – that’s 50AH to spread between your water pump, heater blower, all your lights etc.  Now if you switch on your lounge lights, in my case that’s 10 x 15W halogens or 1.5AH every hour you have them on.  So if you use nothing else then your battery will last you around 35 hours – not long on a winters night with the fan blowing and a reading light on – and remember, your gas heater requires battery power to blow the warm air or circulate the water.

First Step – switch your bulbs to LED

Most Manufacturers fit lots of lights and most use the 10 or 15W halogen bulbs. Without a doubt the cheapest way to improve your off grid use of existing battery power is to change all your bulbs for LED’s. They are becoming cheaper and there are more and more LED’s to fit the wide variety of fittings. Replacing a 10W halogen for a LED will reduce your consumption to less than 1W. Where you have invested in inverters then using low wattage kettles, toasters and hair dryers etc. will greatly reduce your power consumption. I replaced all our halogen bulbs and that alone increased our wild camping time without having to recharge from 3 days to over 8 days.

Next Step – Batteries

Extra Batteries – a no brainer. One of the cheapest and easiest ways of increasing self sufficiency is to add one or more batteries to your leisure circuit. Unfortunately batteries are heavy and bulky items and some folks will not have the room or payload.  There are one or two manufacturers that produce carbon fibre batteries that can offer higher capacity for the same size yet are 20% lighter.  The down side is that they tend to be more expensive but not excessively so and can sometimes work out more cost effective than buying two led acid types.

Many vehicle alternators will only charge up to 75% of a battery’s capacity, however the biggest problem is that it takes much longer to replenish and even driving a couple of hours may not recharge them fully. Adding sophisticated chargers is one way to improve matters but it still takes more time than you realise to fully charge batteries. We originally fitted 3 x 180AH batteries and a Sterling 80amp Pro Digital 4 stage charger to our system on the assumption that the original 18amp charger wouldn’t cope. The logic was that whacking in 110amps would cut the charging time down, typically to less than an hour. Not so. When we first connect up it pumps in over 100amps but as the batteries recharge the chargers start cutting back so it takes a good hour to get the last 20 to 30 amps into the batteries. This means our goal of only using the generator for an hour or so falls down.  Later we fitted 3 x 220AH batteries, using the Elecsol Carbon Fibre batteries which offer 20% reduction in weight and much better deep cycle performance; you can even draw many more amps from these batteries without doing any damage.

Solar Panels

Solar Panels – absolutely great in summer – provided you don’t park under trees or its raining heavily and cloudy. (cloudy days will still produce power – just no were near as much) I did a fair amount of research before fitting Solar Panels, both on size and fixed or rotating. At that time I came to the conclusion that in summer, large fixed panels were more beneficial that small rotating and I still stand by that. However in winter, fixed solar panels are really very poor if you need them to supply even minimal power. The problem is that in winter the daylight hours are minimised yet the power demand is highest with lighting, heating etc. making higher demands on the batteries. In winter rotating panels are far better than fixed panels OF THE SAME SIZE. You would need at least 2 or even 3 rotating panels to maintain batteries in winter. Most of us don’t have the roof space to fit these, even if we did have the money. A word of caution all the current range of rotating panels by Alden or Ten Haaft will not co-exist easily with existing fixed panels as their regulators are built in.  Further information from Kyocera is that you should never mix different sized solar panels as this will lower the overal efficiency. There are a number of solar panel installers that will tell you that you can mix panels however the Manufacturers say don’t.  New technology has increased the efficiency of solar panels from approximately 12 – 13% a few years ago to better than 15 to 17% currently.  New developments show an increase of over 20% with test systems producing in excess of 55% – the future for solar looks good.

Solar Regulators    Over the past couple of years there have been many changes in solar panels and the type of equipment used to control the power from solar panels.  The early generation of solar regulators as fitted to the vast majority of Motorhomes have used the PWM (Pulse Width Modulator) type of regulator.   The latest regulators are MPPT (Maximum Power Point Tracking) regulators and while much more expensive to buy will provide up to 25% more power than the equivalent PWM regulator.    Solar panels are less efficient in winter as the sun is not directly overhead as mentioned earlier however they produce higher voltages in colder weather – MPPT controller algorithms maximise that additional voltage to produce higher amps in winter – at a time when you need more power.  Several MPPT controller manufacturers claim gains of over 35% in winter.  The current problem with MPPT verses PWM is the cost.   I’m sure that in a few years MPPT controllers will become much more cost effective.  Currently it is a real cost justification issue for existing PWM users to switch to MPPT at a cost of several hundred pounds even for a 35% increase. Bottom line – if you can afford a MPPT controller then fit it from the start as an average gain of around 15% can be the equivalent of an additional panel in winter.  See article reproduced on this site from a leading U.S. Institution on MPPT Controllers.  The problem I have is getting feedback on these Chinese or Taiwan made MPPT controllers at the sub £100 mark.  It would be great to know if they deliver similar gains in amps for £85 as a Morningstar Tri-star costing £500.


Petrol.     (See my article on generators.)  Built in or portable, you either love em or hate em, however they do fulfil a need. It’s all about convenience and cost really. On the downside you have to carry fuel and they are noisy (even the so called quiet ones ) They are certainly frowned upon by neighbours and many campsites now ban their use. The unwritten code says that using generators before 10am or after 9pm is anti social. Built in and portable generators provide 240 volt power and that is used to power your on board chargers. As a by product you also have spare capacity to use any 240 volt appliances, however having 240 volt appliances that can only be used when the generator is running is false economy so an inverter would be better if you intend to use 240 volt appliances on a regular basis.

Gas     Pretty much the same as petrol and some of the data sheets state that using gas is more noisy than petrol. Some of the newer generation such as the Self Energy EG20 only produce 12 volt power for charging batteries so cannot be used for 240 volt appliances. The same criteria applies though and it can take hours to recharge batteries.

Fuel Cells     Efoy or SFC produce several models that will put between 50amps and 130 amps over a 24 hour period into your batteries by burning methanol. This form of battery recharging is becoming more and more acceptable to manufacturers of Motorhomes with many now offering Efoy on their option lists. Its virtually silent and trickle charges your batteries however you have to carry stocks of methanol and methanol as yet isn’t cheap. A word of caution though – Efoy say that you should NEVER fit an Efoy system where the total battery capacity exceeds 250AH.  Efoy have recently announced a new range of fuel cells – the Comfort range.  They have been revised and the range reduced in number and provide a number of updates and features as well as improved efficiency.

Last but not least – Expansion

Plan for expansion.   Many of us use various forms of calculations to assess our power requirements and adopt our systems to match. Not many months later we find that things have changed, a new hair curler, a laptop or DVD player all make additional demands on our limited reserves. I have learnt the hard way and now include a 50% margin on power requirements.  At the end of the day you must also take into account payload and this may dictate the options available.



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