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Split charge system

Howmanygoes

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england
Hopefully quite simple.

I want to install a 3rd battery in my 100series for accessories to be separated from the starting system. Does it matter which of the 2 batteries I connect the split charge system to? My gut says not but.......
 
Rich, just validate this for me please. Might be hokey.

I'd connect the third battery via a voltage sensing split charge system somehow as you say so that the main batteries always got fed first on start up and so that there was always separation when the engine wasn't running. The alternator is only connected directly to one battery and slaved to the other. There are small losses between the two batteries I have found, so it would be better to connect to the battery that is fed directly by the alternator so as not to add any further complications?

In other words take the strongest source rather than one that's already getting slightly less. I was surprised at the drop between the two batteries on mine. I have uprated cables and proper terminations but I register around 1 volt difference typically. This is what largely killed my second battery which was an Optima.

The DC to DC converter isn't going to suffer and neither will the third battery - it's the aux battery that concerns me
 
Rich, just validate this for me please. Might be hokey.

I'd connect the third battery via a voltage sensing split charge system somehow as you say so that the main batteries always got fed first on start up and so that there was always separation when the engine wasn't running. The alternator is only connected directly to one battery and slaved to the other. There are small losses between the two batteries I have found, so it would be better to connect to the battery that is fed directly by the alternator so as not to add any further complications?

In other words take the strongest source rather than one that's already getting slightly less. I was surprised at the drop between the two batteries on mine. I have uprated cables and proper terminations but I register around 1 volt difference typically. This is what largely killed my second battery which was an Optima.

The DC to DC converter isn't going to suffer and neither will the third battery - it's the aux battery that concerns me
Cheers. Hadn’t considered that. Will feed from first fed.
 
100 series are 12v start. 2 batteries yes but not 24v crank like the 80.
 
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100 series are 12v start. 2 batteries yes but not 24v crank like the 80.
So in theory I could replace the 1st fed battery with a higher ampage (similar to the current combined) and then drop in a 2nd (deep cycle battery) as an aux and fit voltage sensing between the two?
 
Ahh, the old 'will a 100 series starter fit ..' question. The simple answer is no. They are different. The longer answer is yes, if you get the right one!! No that's not much help is it. It's all to do with the number of teeth on the pinion. Someone recently did this and swapped the drive pion over I think. My 12v starter is a 12 volt 80 starter.

On batteries, that's what I did. Pulled out the 24v start to make it like a 100 series, then split the two batteries one for cranking and one aux via a split. Been working since 2013. BUT, I sometimes wish I'd put in a DC2DC module to charge the second battery rather than just tap into the old slave wiring directly.
 
Rich, just validate this for me please. Might be hokey.

I'd connect the third battery via a voltage sensing split charge system somehow as you say so that the main batteries always got fed first on start up and so that there was always separation when the engine wasn't running. The alternator is only connected directly to one battery and slaved to the other. There are small losses between the two batteries I have found, so it would be better to connect to the battery that is fed directly by the alternator so as not to add any further complications?

In other words take the strongest source rather than one that's already getting slightly less. I was surprised at the drop between the two batteries on mine. I have uprated cables and proper terminations but I register around 1 volt difference typically. This is what largely killed my second battery which was an Optima.

The DC to DC converter isn't going to suffer and neither will the third battery - it's the aux battery that concerns me
Whilst I’m not totally familiar with 100 series electrics I believe the alternator feeds one battery and the negative is taken from the other as is the volt sense wire for the alternator, hence it senses the lowest battery. Being 12v all the time, you can connect to either battery. The merits of each might be worthy of test but at least in theory it’s probably best to draw from the battery nearest the alternator. Why? Well, the way I see it is if the nearer battery gets a slightly higher charge than the further one, and that one is what governs the voltage output of the alternator, then the nearer battery will see slightly higher voltage than necessary. If the draw for the leisure battery is from the nearer battery then the charge in that one will be drawn upon and the voltage will consequently be slightly lowered. The other advantage would be mirroring the connection to the further battery, connecting at a central point rather than on the end of the chain, which would lower the voltage at the further battery causing the alternator to boost voltage further, somewhat overdriving the near battery.

That’s my theory anyway. Happy to hear others.

If Optimas are to be used then charging voltage needs to be raised to 14.7 volts rather than 14.4 otherwise the Optima will suffer. A DC DC charger on each would be ideal if the batteries were to be separated as starter only and Body loom batteries as Chris has done.

In short, I think connect to the battery that has the alternator connection and Earth well to the body. Consider what currents may flow (especially if you envisage linking the batteries to account for a failed starter battery) and upgrade the body negative to earth connection to 50mm.
 
I sometimes wish I'd put in a DC2DC module to charge the second battery rather than just tap into the old slave wiring directly.
Interesting as we were posting at the same time.
Incidentally the Intervolt display can take inputs from two DCC pros.

Pinions are easily changed on starters. Robson and Francis can help. There are 11 and 12 tooth versions of both 12v and 24v starters. Both will fit if you should have a 12 tooth and the 11 tooth one will last about 7-8 years where a 12 tooth one should be with a slightly different note on starting. Ask me how I know!!
 
To clear this up I could

a) keep the 2 battery set up I have and try to make room for the 3rd.

b) replace the cranking battery with a higher capacity and increased amp to start the vehicle which would then clear the other battery space for leisure battery. Assuming there is space. Anyone else done this? What did you use?

I like the dc2dc charger idea
 
To clear this up I could

a) keep the 2 battery set up I have and try to make room for the 3rd.

b) replace the cranking battery with a higher capacity and increased amp to start the vehicle which would then clear the other battery space for leisure battery. Assuming there is space. Anyone else done this? What did you use?

I like the dc2dc charger idea
B) would essentially be what Chris has done except that he has split to a dedicated starter battery and the second is a Body battery. I can’t imagine that this option would give any problems at all. @Chris ?
 
No. But I'm a bit unsure about the starter motor question. On the 80 it's not just the pinion that is different; it's the kW too. Can't tell you more than the fact they're different. I personally don't think ther's any need to split them and then up the size of the cranking battery. I'd certainly go with the original one to begin with. I'd dare bet it will still start at the flick of a switch. This whole two battery start thing is frankly somewhat of a red herring in my view. Two must be better than one??? When you look at starting issues on a lot of these vehicles, the majority of the issues stem from having two batteries when almost every other vehicle ever made in the history of mooring only ever has one. Surely the CCA from a std battery will spin the starter just fine. Lots of 100's are single battery aren't they? Or are they twin battery but 12v? Never owned one.
 
Running a 100 with two Optima yellow tops for the past 3 years the biggest i could fit were 75 Ah 975 cca model no 8051 187 and part no 851 187 008882 bit of a tight fit but they are in and working fine hope this helps
 
From memory the 24v 80 series starter is 4.5Kw and the 100series 12v one is 3.5Kw to start essentially the same engine. It’s a simple enough test, disconnect one of your batteries, insulate the clamp, and see what happens. I don’t suppose you’ll notice any difference.
 
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