Barryrj Posted August 31, 2015 Share Posted August 31, 2015 Using jump cables/leads can you jump start the engine from the leisure battery if your engine battery if flat without damaging the leisure battery? Link to comment Share on other sites More sharing options...
aandncaravan Posted August 31, 2015 Share Posted August 31, 2015 It is not recommended for several reasons, but can be done if you have a Starter like Dual purpose Leisure Battery. Firstly, Modern Alternators are very powerful, we have seen 180amp listed as an option. If a battery is flat it can place a heavy demand for power on the Alternator which will obliged with a lot of amps. Few Starter battery manufacturers recommend fast charging a battery at more than about 20 - 30 amps for more than a few minutes. Back 20 years ago Alternators were around 50 - 70amp max, so with the draw of other consumers in the MH the Starter battery never usually got more than about 30 amps peak, so usually survived. Most MH Starter batteries charged up from flat off the Alternator now will almost always be goosed afterwards. Secondly, some Motorhome charging systems are not as strong as they might be in the area where Starter and Habitation batteries are linked. What can, and does, happen is that the Starter Motor doesn't get the power it needs so tries to draw it via the Habitation battery which is not as isolated as it might be.A damaged power distribution unit is often the result. Thirdly, not appropriate in this case, but we have seen Motorhomes where the recovery company has used a 'Booster' pack with higher than 14v (the higher the voltage at the starter battery the more easily the starter turns, up to a point) with the result again of a failed Power distribution unit. We suggest you play safe and replace the Starter battery. If it is that flat it is probably past it anyway?. Link to comment Share on other sites More sharing options...
Barryrj Posted August 31, 2015 Author Share Posted August 31, 2015 Many thanks for your reply. It was a hypothetical question as I don't have a problem but wondered if I were ever faced with the situation where the engine battery didn't have the power to start the engine could I simply jump start from the leisure battery, in an emergency situation and replace the starter battery later. So the answer is 'not recommended'. Link to comment Share on other sites More sharing options...
Guest Peter James Posted September 1, 2015 Share Posted September 1, 2015 aandncaravan - 2015-08-31 9:29 PM some Motorhome charging systems are not as strong as they might be in the area where Starter and Habitation batteries are linked. What can, and does, happen is that the Starter Motor doesn't get the power it needs so tries to draw it via the Habitation battery which is not as isolated as it might be. A damaged power distribution unit is often the result. ........ I don't see how that can happen, since none of the starter current should be going through the power distribution unit when he has got them both connected together through jump leads? ....and if the starter battery is so 'past it' you recommend replacing it, does it matter if the alternator is speeding its demise by fast charging it? When you are broken down the priority is to get started, even if it does shorten the life of the old battery a bit more? Link to comment Share on other sites More sharing options...
gocro Posted September 1, 2015 Share Posted September 1, 2015 It should be fine to use to start the van if removed straight away, and let the vans battery take over the charge. You should not do it often as most are not designed for sudden bursts of energy, but we are told repeatedly that the majority of 'leisure batteries' are of automotive heritage anyway. Link to comment Share on other sites More sharing options...
Casimir Posted September 1, 2015 Share Posted September 1, 2015 I asked more or less the same question some months ago. The replies might be of interest to you.http://www.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Yet-another-battery-question/36808/ Link to comment Share on other sites More sharing options...
aandncaravan Posted September 1, 2015 Share Posted September 1, 2015 Peter, you are assuming a perfect connection which jump lead clamps rarely provide when big amps are involved?.Regardless of the physics/theory, I can only tell you what we have seen after a Jump start. Power Distribution/supply issues are common after attempts to start a MH with a flat battery. Maybe the way it was attempted contributed to the issues, I don't know. Getting the full story afterwards is also rare. But I can tell you it causes expensive issues.One of the reasons we advocate a Varta Silver dynamic S5 as both a Habitation and Starter battery, just swap them around. Link to comment Share on other sites More sharing options...
Guest pelmetman Posted September 1, 2015 Share Posted September 1, 2015 How about if you disconnect the habitation battery before using it to jump start the vehicle battery? Surely that would stop you frying your campers electric :-S .............. Link to comment Share on other sites More sharing options...
Guest Peter James Posted September 1, 2015 Share Posted September 1, 2015 aandncaravan - 2015-09-01 10:37 AM Power Distribution/supply issues are common after attempts to start a MH with a flat battery. Could it be the 'Power Distribution/supply issues' that caused the flat battery? Link to comment Share on other sites More sharing options...
Guest Peter James Posted September 1, 2015 Share Posted September 1, 2015 pelmetman - 2015-09-01 10:46 AM How about if you disconnect the habitation battery before using it to jump start the vehicle battery? Surely that would stop you frying your campers electric :-S .............. I do believe a little of my Genius is beginning to rub off on you :-D Link to comment Share on other sites More sharing options...
clifford60 Posted September 1, 2015 Share Posted September 1, 2015 Hi All, I,ve done this recently when my alternator packed in. As far as I can tell, no detrimental effect over last three months. However, my 1996 van doesn't have all the modern computers etc. so best wait until you're in the sh-t before you try it. All the Best, Ian. Link to comment Share on other sites More sharing options...
aandncaravan Posted September 1, 2015 Share Posted September 1, 2015 Peter, Yes it is possible that the Power distribution unit was the cause of the flat battery and yes isolating the Habitation battery would protect the MH electronics. Clifford, Like we said above "Back 20 years ago Alternators were around 50 - 70amp max, so with the draw of other consumers in the MH the Starter battery never usually got more than about 30 amps peak, so usually survived". Your 1996 MH might be in that category? The point I am trying to make is that care is required, or it could work out expensive. The Merc Garage nearby does quite well out of 'fried' ECU's following some Jump starts. I don't know the circumstances or the reasons. But something is going wrong for one reason or another when some Jump starts are being carried out? Link to comment Share on other sites More sharing options...
Barryrj Posted September 1, 2015 Author Share Posted September 1, 2015 Again many thanks for all your replies. I started to read the post in the link provided but I fell asleep. Seriously though it did digressed a little, but useful information for future reference. I now feel confident that if I ever find myself in the situation where the MH won't start on the main battery I think I will disconnect a leisure battery and connect it to the starter battery using jump leads just to start the engine then disconnect. I think this will protect the electronics and will not damage the leisure battery. Cheers. Link to comment Share on other sites More sharing options...
Tracker Posted September 1, 2015 Share Posted September 1, 2015 Barryrj - 2015-08-31 10:31 PM Many thanks for your reply. It was a hypothetical question as I don't have a problem but wondered if I were ever faced with the situation where the engine battery didn't have the power to start the engine could I simply jump start from the leisure battery, in an emergency situation and replace the starter battery later. So the answer is 'not recommended'. YES you can, and very easily, is the answer. BUT be sure to disconnect the leisure battery from the hab side before attaching jump leads and starting. I have done it and it worked for me. Link to comment Share on other sites More sharing options...
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