Power on a rally

Many of our rallies are held on sites with an Electric Hook-up (EHU).  Some are not, often called ’Off Grid’.  On some rallies you have a choice.

One of the questions we are asked most is how do you get on without a ‘hook up’. The answer is just fine, as long as you have prepared and are careful.

Your Bailey caravan or motor home is designed to function perfectly without mains power.  The heating, fridge and lighting will work just fine working on gas and the leisure battery. Indeed the heating and fridge are sometimes more efficient on Gas.

Items that only work from the 240v Mains are the microwave, the 3 pin sockets and your battery charger. Everything else, heating pump/fan, lights, water pump etc., work off 12v. i.e. your leisure battery. As your battery is not being charged when you are not on EHU how do I go on? Your battery is a reservoir of power.  It is continually charged when on EHU. For those vehicles fitted with a solar panel/s these charge the battery by an amount dependent on the amount and duration of the sunlight falling on them.

Going off grid is dependent on the reserve in your battery.  How long that lasts is dependent on three things.  How good a battery, how much power you use and how much power you are harvesting from your solar.  Some people advocate using a generator and this will be successful.  However their use is subject to time and nuisance restrictions and a good one will set you back £600 to £1000.  A not insignificant investment and the running costs can be higher than you might think.

So you are going to need a reservoir full of power i.e. a battery.

Lead Acid batteries have been around for over 100 years.  As a consequence they are known technology and cheap. You can buy a good quality 100 - 120amp battery for less than £150.

Dependent on type, you can pay more for AGM or GELL lead acid batteries. The AGM battery (Absorbent Glass Mat) is becoming quite popular as it stands more charging/discharging than a simple one. It also is truly sealed i.e. does not need topping up.

There are also the latest technology Lithium Batteries see separate section below.

Some members double up and carry two batteries giving them over 200 amps of potential power.

All this power is not black and white.  Lead acid batteries will only deliver about 50 - 60% of their power in a usable format of power suitable for a Caravan or Motorhome and need charging if they are not to suffer a shortened life span. 

So to return to the question how long will it last?  In our experience a good, charged lead acid battery will last 3-5 days provided you do not use higher powered devices such as TV's or Inverters. 

To go for longer additional power input (Solar for example) is necessary.  Solar is dependent on the power of light falling on the panel and for how long.  This can vary dramatically on a fine summers day a 100w panel will recharge your battery easily.  On a wet day, you may not harvest anything.  Adding more solar to the roof is a comparatively simple thing to do, as is changing the solar controller to a more effective type.  Both of these things will enable you to harvest more solar power.  

The great thing about a rally is that we have been at this for decades and you will have the support of very experienced members.

A List of typical power consumption is as follows, these figures are very approximate 

19in T.V.                                     2-3 amps per hour.

Led spot lights                            0.3 amps per hour

Blown air heating                        1 - 6 amps per hour

Alde heating                               0.5 amps per hour.

Water pumps vary                      2 - 5 amps per hour

Caravan Mover                           30 - 40 amps

Quad mover                                50 - 80 amps.

Lithium Batteries

Some of our members are changing to the new lithium LiPo4 batteries.  These are half the weight of Lead Acid Batteries and provide almost twice the quantity of power.  i.e a 100amp LiPo4 battery will give you nearly as much power as 2 * 100amp lead acid batteries and weigh in about ¼ of their combined weight.  They can be recharged many 1000's of times.  So yes they are more expensive but long term costs are cheaper.  A good lithium battery can now be had for approx £400 - £600, with some priced as low as £350, an the prices are dropping year by year. Not only do they last many years, they also respond by charging faster, be it by mains or solar.  They are far better for the environment, do not contain acid and are very, very safe.

Your charger in your van will handle a lithium battery just fine, so will a fitted solar panel and controller. Going lithium used to be far more expensive and complicated.  Perhaps the most important thing is you must not charge them if they are below 0 deg centigrade, you can use them to power your van way below this but can damage them if they are too cold when charging.   Remember if you are on EHU it is easy to cut off the charging in very cold weather.  But if your van is in storage for example and fitted with solar panels then the protection is a must.

Part of a Lithium battery is a mini computer hidden in the case to control charging etc., called a B.M.S. This makes them a straight drop in replacement for a conventional lead acid battery. Many now have a BMS that will automatically cut out charging below 0 deg C to protect the battery, so make sure your purchase has this protection. Some lithium batteries have built in heaters as well so they can be charged in arctic conditions but at a cost.

Those of you with Motor homes can buy a box of electronics called a ‘Battery to Battery’ charger.  This will enable the alternator on the engine to charge a lithium battery very quickly when the engine is running.  Nice to have but not essential.

Solar Power Controllers

Some Bailey units are supplied with a solar panel on the roof and a solar charge controller between it and the battery. These are the Alicanto, Unicorn  and  Pegasus Grande Ranges in the caravans and the Autograph and Adamo Ranges in the Motorhomes.  The size of the factory fitted Truma solar panel will be 80 or 100 Watts.

Until the very latest models the Truma PWM (Pulse Width Modulation) charge controller was fitted as standard.


This controller had two outputs capable of charging two batteries.

It is generally thought that a MPPT (Maximum Power Point Tracking) controller is better in keeping the leisure battery topped up. Obviously important on a non-EHU Rally. The science behind this can be found lower down the page.

Quite a few members have decided to change the Truma PWM controller for a MPPT one. This is a very easy change which gives a big improvement. They can be bought for under a £100.  There are various makes available but one of the popular ones is the Victron Unit


This is the one that many of us have fitted to our outfits. and it is a very easy swap for the Truma Unit. Just 4 wires to swap over.  It is an MPPT controller, the 75/15 is the handling capacity, it will take up  to 75 volts from the solar panel and is capable of transmitting up to 15A. More than enough for a 100W panel as fitted by Bailey. One important thing to notice is that it has Bluetooth connectivity.

This means that you can remotely control and monitor your SmartSolar MPPT charger with built-in Bluetooth by pairing it with your smartphone or other device via VictronConnect.

For motor homes and charging the engine battery as well as leisure battery then you may need a controller with two outputs.  Not all have them so check.

By constantly monitoring the voltage and current output of your solar (PV) panels, MPPT technology ensures that every drop of available power is rinsed out of your panels, and harvested for storage. The advantage of this is most noticeable when the sky is partially clouded, and light intensity is constantly changing.

It is generally accepted that MPPT is up to 30% more efficient than a PWM one.

For some of  the very latest outfits, Bailey have started to fit the

Truma MPPT Controller, which will be a big improvement over the PWM device previously fitted.