miggit Posted September 5, 2018 Share Posted September 5, 2018 4 hours ago, Bowie69 said: That is exactly what I am disputing. Any 12s socket from back of the car is normally relayed to be only when the ignition is on, i.e. the engine is running. All the kits I have ever fitted have always relayed the feed, so if you have had experience of them being permanent live, then I suspect a bodger had been at it. From the number of cars that I've had dealings with the 12s side of things they have been permanent live.... you've got me wondering what is standard now.... I feel a multimeter on the factory fitted 13pin socket on my ML is in order just to see.... I will report on findings... Quote Link to comment Share on other sites More sharing options...
miggit Posted September 5, 2018 Share Posted September 5, 2018 4 hours ago, Peaklander said: About ‘nearly’ at alternator volts, the problem is that it only ever gets ‘nearly’ charged and over time this will lead to early failure. You have misunderstood me.. if the battery is of the same type as the cars, or, you have the right type of second alternator for the slave, when it's nearly charged then the power will only dribble in... however when you've had your fridge, curling tongs, 5 iPads etc. on for a day or more, the poor old slave battery will be lucky to be still reading double figures on both volts and amps, so it will take all the power you can give it. If you've a 45 amp alternator it will get 45 amps, and would take a few hours of running to restore anything like normal levels. But if you've got a 120 amp alternator it will get to the normal-ish level in roughly a third of the time. Now I'm not saying that the second alternator should be a monster, as you'll be in to multiple drive belts.. but 70-80 amp units will run on a single belt without sounding like a stuffed pig.. In fact I had a 105 amp on one of my 'ang' 'overs and it was quite happy with a single belt, but the 130 amp unit on my Tbird was less than happy!! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 5, 2018 Share Posted September 5, 2018 No, I think you misunderstand, a 'normal' lead acid battery will only take around 20-25A, absolute maximum, due to its own internal resistance. So a 45A alternator will be 'ample' for up to two batteries. Quote Link to comment Share on other sites More sharing options...
Peaklander Posted September 5, 2018 Share Posted September 5, 2018 What he says ^^^^. Amps are no good if they can't flow. For that you need to create a potential difference. Once the pd between Alt and Aux battery reduces, as the battery charge moves towards the voltage from the alternator, then the amps reduce to nothing. If the battery is still not at 100% then it will never be. With a split charge setup, putting the (much more highly charged state) Starter battery in parallel will only serve to exacerbate this. Quote Link to comment Share on other sites More sharing options...
ianmayco68 Posted September 5, 2018 Share Posted September 5, 2018 So am I right in thinking that over time as the battery never actually gets fully charged , numbers are just for helping to understand this , that if the battery is only reaching 90% of its full 100% charge that over time the 90% will actually become 90% of the original 90% charge , meaning 81% of the 100% charge . Meaning that the overall capacity of the battery reduces significantly. Or am I talking a load of horse poop . Quote Link to comment Share on other sites More sharing options...
Peaklander Posted September 6, 2018 Share Posted September 6, 2018 I suppose a healthy battery has to follow a discharge path over time, that is determined by the voltage it can sustain at a specified current drain (load). Maybe if it is in poor condition it can never follow that or even start at the right point. Quote Link to comment Share on other sites More sharing options...
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