spospe Posted December 10, 2008 Share Posted December 10, 2008 In the December 2008 issue of MMM, on page 196, Clive Mott-Gotobed has again shown a circuit diagram of how to connect the vehicle and leisure batteries together, via a bridging fuse. This has been done for the purposes of allowing a solar panel to maintain the charge in both, whilst the motorhome is not being used. This is an excellent and simple idea and I have such an arrangement installed in my 'van (Autosleeper Duetto). However, there are a few points that Clive has not mentioned and which do really need to be considered before carrying out this modification, they are: 1) The batteries really should be of the same type, i.e. both liquid lead-acid or both gel types. It is not I think good practice to parallel the different sorts, as they have different charging requirements. My Steca solar regulator has different charging regimes for the different types of battery and expecting the liquid lead-acid program to suit a gel battery is against the manufacturers advice and recommendations. 2) Both batteries should ideally be of similar age and condition. If one battery is failing, then it will end up drawing current from the healthy battery, especially at night when the solar panel is not producing any output. This problem is especially acute during the winter months when the solar panel will only be giving an output for about 8 hours per day. A suggestion of mine to improve on Clive's basic circuit, is to add a 12 volt relay, powered by the solar panel itself and use it to make the connection between the batteries (the rest of the circuit being as per the diagram in MMM). During the day the relay joins the batteries and at night they are separated, so no current can flow between them. This overcomes any transfer of energy between the batteries. I have written to MMM detailing the above. Link to comment Share on other sites More sharing options...
Clive Posted December 13, 2008 Share Posted December 13, 2008 The simplicity of the bridging fuse is its simplicity! All batteries likely to be used in motorhomes are Lead Acid and most solar regulators provide an output which provides a maximum voltage which will not overcharge wet, gel, AGM. It would also, especially during the winter mean that valuable charging current would be used to power a relay. Sorry, but from my viewpoint the suggestion is over complicated and unnecessary. Clive Link to comment Share on other sites More sharing options...
spospe Posted December 13, 2008 Author Share Posted December 13, 2008 Clive My relay only draws 30 mA, I am quite prepared to loose this much charge current during the day ! You are correct in saying that your system is simple and that is indeed a virtue. I am however correct in saying that for best performance it is best for mixed batteries not to be charged together and also that a degree of cross-charging can take place overnight. My idea of using a relay overcomes the cross-charging problem for those people who are prepared to install it. If you think that this is an example of guilding the lilly, then fair enough. I only thought that it should be mentioned for the sake of completness (choice is what it's all about, give the consumer more choice). Michael Link to comment Share on other sites More sharing options...
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