tp002c784tp002c784tp Posted November 21, 2006 Share Posted November 21, 2006 Hi All This is a question that Dave Newell may be able to answer I have recently bought a Lunar Telstar on a Renault Master and the lesuire battery is only 85 amp I have bought another 85 amp battery and box and I am going to fit it in a compartment next to the existing battery I have read numerous threads in the past about wireing the batterys and they recomend positive to positive with an inline fuse and negitive to the chassis but is it neccesary to go to the chassis could I not just wire it to the existing batterys negative and keep the wiring as short as I can to eliminate voltage drop Terry Link to comment Share on other sites More sharing options...
Clive Posted November 21, 2006 Share Posted November 21, 2006 Have a look at http://www.motts.dsl.pipex.com/second%20leisiure%20battery.htm Good luck C. Link to comment Share on other sites More sharing options...
Brambles Posted November 21, 2006 Share Posted November 21, 2006 Hi, Yes you can. It is only a recommendation to take it to the chassis. Ideally if connecting the way you are suggesting, negative to negative, you should take the positive from one battery to feed the leisure circuits and the negative from the other battery. If your leads do not reach easily and as they are so close together it will not present a problem leaving the exsting wires to present battery and just wire new battery in parallel with short leads and a fuse. Use leads at least the same gauge as present and fuse the same as present fuse from battery. Make sure leads are well protected especially the +ve, so it will never short to the chassis by scuffing etc. Technically if you use heavy cable you not really need a second fuse, but it protects you if you ever accidently reconnect one battery the wrong way, or one is fully charged and the other flat. Remember to vent the 2nd battery with a vent tube to the outside world. You should already have a vent tube on other battery, unless they are in an exteral battery box, and no reason why you should not use a T or Y tube connector to join the two together. Hope this helps. Jon. Link to comment Share on other sites More sharing options...
Brambles Posted November 21, 2006 Share Posted November 21, 2006 Hi CLive, In your link there is some missing information. If using two fuses in a Y configuration, then the fuse rating should be halved as they are in effect parallel. Also the 2nd battery is going to the chassis, but no indication where the 1st battery is going, it could be some distance away if at all to the chassis, and I would prefer a heavy copper lead connected to the 1st battery negative as it would result in less volt drops compared with going through the chassis. It all depends on where the batteries are connect to the chassis which ideally should be i a similar location. E.g under drivers seat for one, and under passenger for other. Not trying to be critical or clever, but maybe am giving information overload which I am guilty off at times. KISS approach needed for tpoo2 - as they are next to each other just wire in parallel with two additional leads. If you can swap one of the supplies to opposite battery, but only if convenient, then fine. Jon. Link to comment Share on other sites More sharing options...
Dave Newell Posted November 21, 2006 Share Posted November 21, 2006 Hi Terry, if the batteries are going to be adjacent to each other and the wiring doesn't pass through any metal bulkheads then you do not need to fuse between them, only the power take off will need to be fused. It is perfectly ok to take the negative of the second battery to the negative of the existing battery. D. Link to comment Share on other sites More sharing options...
spartan3956 Posted November 21, 2006 Share Posted November 21, 2006 Is there any advantage by taking the negative from one and positive from the other when they are linked together. pete Link to comment Share on other sites More sharing options...
Brambles Posted November 22, 2006 Share Posted November 22, 2006 If the batteries are close together the advantage is minimal and probably decision should be made on how practical it is to route the cables. The idea is to balance the volt drops to the two batteries. Even if the batteries are quite far apart there is not a real problem, it just means one battery will work slightly harder than the other, but not a lot in it. Being sensible about this, where it is important is for very heavy power drains, like starter motors, forklift trucks and high power emergency supply sytems, electric powered vehicles etc. For our low power demand motorhomes in reality it is not a problem. Best to just do the wiring so it is neat and immune to physical damage/shorts. REMEMBER the vent pipes!!! That is important. Link to comment Share on other sites More sharing options...
Dave Newell Posted November 22, 2006 Share Posted November 22, 2006 From a purely technical point of view it would be the preferable way to do it but if the batteries are adjacent to one another then there is no practical advantage as the cables will be so short as to reduce voltage drop to a negligible level. Just make sure you use good quality, heavy duty cable and make good terminations, finish off with a smear of vaseline over the terminals to prevent corrosion. D. Link to comment Share on other sites More sharing options...
enodreven Posted November 22, 2006 Share Posted November 22, 2006 Hi, On the same topic, can you use 2 different sized batteries eg. a 110 amh and an 85 amh and what if any are the possible problems, Link to comment Share on other sites More sharing options...
Globetrotter Posted November 22, 2006 Share Posted November 22, 2006 I know the answer to that one! :-D If you attach a 110 to an 85, the 110 will only ever charge to the same level as the 85, so you will end up with two 85s effectively. The two batteries need to be matched in size for this to work properly. I think I got this right! (Anyone confirm??) Link to comment Share on other sites More sharing options...
Brambles Posted November 22, 2006 Share Posted November 22, 2006 Sorry Globe, you are misinformed. They will both charge to the same end point voltage so both will have the same %age charge of the rated capacity for the respective battery. You can indeed join a 85 and a 110 Ah battery with no adverse affects. The charaterists of charge discharge are quite complex in this case and is to do with the characteristics of the batteries and is more applicable to heavy loads again. For normal curent drains in Motorhomes there is no real reason not to use diffrent capacities as long as other characteristics and type are similar. Do not mix old with new, as the differences in characteristics would become important. This applies equally to batteries of the same capacity. When you come to replace one after a few years, relplace both. Edit - I should also have mentioned it is preferrable in a perfect world to have the larger capacity with the shorter lead lengths to the supply cables. In effect the lower capacity battery should have the higher resistance/ voltdrop through the cables. Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 22, 2006 Share Posted November 22, 2006 They should be of the same type, the same size, the same construction and the same age. If not, just like the chain, the weakest link will be the limiting factor and the "better" battery will never realise its full potential. Link to comment Share on other sites More sharing options...
Brambles Posted November 22, 2006 Share Posted November 22, 2006 Brain, I agree with same age and type and construction, but capacity is not so important. They will both discharge to the same endpoint voltage and each battery will have lost the same percentage charge of its total capacity so , sulphation and aging effects will be identical. Agree the system will be as good as the weakest link and wil come down to the quality of the 85 v 110 Ah and which ever one has the poorer life. Could be either and then both will have to be replaced. Jon Link to comment Share on other sites More sharing options...
enodreven Posted November 22, 2006 Share Posted November 22, 2006 Hi, The 110 amp is 8 months old, and if we go for the 85 amp it will be new? on that basis would you replace the 110 or perhaps stick with it for a year or so then replace both of them [QUOTE]Brambles - 2006-11-22 11:32 AM Brain, I agree with same age and type and construction, but capacity is not so important. They will both discharge to the same endpoint voltage and each battery will have lost the same percentage charge of its total capacity so , sulphation and aging effects will be identical. Agree the system will be as good as the weakest link and wil come down to the quality of the 85 v 110 Ah and which ever one has the poorer life. Could be either and then both will have to be replaced. Jon[/QUOTE] Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 22, 2006 Share Posted November 22, 2006 EnodrevenIf you are prepared to contemplate persisting with your 110AH battery for another year year or so, why do you want add another 85AH? If you need 200AH, surely that is what you need, and not 110AH? If you don't need the additional capacity, what is the point of adding it, with its attendant weight penalty? On the other hand, if the 85AH battery is to be bought new, why choose to add that, and not another 110AH battery?Or is your question mark to indicate you've been offered a "new" 85AH battery, but are a bit unsure as to its true age? If so, I think your answer is as above, both batterys need to be as close to the same age as is reasonably possible, ideally both starting life together. Link to comment Share on other sites More sharing options...
Brambles Posted November 22, 2006 Share Posted November 22, 2006 Hi Enodreven, I would stick the 85 Ah in with it if you have not abused the 110 Ah. The problem is when a battery gets older it needs a higher voltage to charge it. You will find the 110, may fail before the 85 Ah and it will have an adverse effect on it. It's a cost/life analysis that needs to be done, but put simply, if you wait a year and buy two batteries it will probably cost you more than adding 85 ah now and getting a few years from both. Adding the 85Ah will/should extend the life of the existing battery as you will no longer be draining so much from it between charges. Just remember the most important thing for batteries is to discharge least as possible and then recharge to the max you can as soon as possible afterwards. Link to comment Share on other sites More sharing options...
Globetrotter Posted November 22, 2006 Share Posted November 22, 2006 Aah-sorry, Got it wrong, but I would add that my misinformation came from this group........ >:-( Link to comment Share on other sites More sharing options...
enodreven Posted November 22, 2006 Share Posted November 22, 2006 Hi, Brambles Thanks for the information and advice, its really appreciated Brian Link to comment Share on other sites More sharing options...
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