Ever wondered how charged your battery actually is ???

[jamesc76]

Its also changed my understanding of a split charge system - I thought it only sent current to the leisure battery once the starter battery was fully charged...whereas from your explanation it sends current to both batteries, irrespective of the charge state of the starter battery, as long as the alternator is turning.

James

No if the alternator warning light is on then the relay switches out and only the starter battery get the charge (if any!)

[California Dreamin]

Thanks Martin,
lots of things I half knew there, all now clear in my head.
Its also changed my understanding of a split charge system - I thought it only sent current to the leisure battery once the starter battery was fully charged...whereas from your explanation it sends current to both batteries, irrespective of the charge state of the starter battery, as long as the alternator is turning.
makes sense and explains where the 13.? comes from....
cheers,
James

The regulator sees (regulates) as if it is seeing just one 'large capacity' battery. If I'm honest this is the main drawback of a traditional split charge system as this can lead to one of the batteries (usually the larger capacity leisure) being under charged.
Think of it this way...starter 80% charged but leisure only 20% charged...the alternator sees one battery at about 50% charged...it then regulates to fully charge the combined battery to 100% which results in the leisure only reaching 70% charge state...this is all theoretical of course.
Even with it's drawbacks a traditional split charge system remains the most popular option for charging on the move. I have found a good 'work around' is to charge each battery seperately every few months with a standalone charger baring in mind that the bigger leisure will probably need longer to reach full charge.
As long as the alternator is turning well yes but obviously I mean at a reasonable speed ie (just above idle normally is enough to turn the charge light off) The alternater charge voltage hits it's regulated setting (13.9 - 14.2) the instant the charge light goes out so it is not until this point that the 'smart relay' connects both batteries together.

Martin

[AdrianC]

The regulator sees (regulates) as if it is seeing just one 'large capacity' battery. If I'm honest this is the main drawback of a traditional split charge system as this can lead to one of the batteries (usually the larger capacity leisure) being under charged.
Think of it this way...starter 80% charged but leisure only 20% charged...the alternator sees one battery at about 50% charged...it then regulates to fully charge the combined battery to 100% which results in the leisure only reaching 70% charge state...this is all theoretical of course.

<slaps forehead>
Of course! Thanks for that, Martin - I'd been wondering why the leisure battery was said to never get to full charge with the standard Westy system. That makes perfect sense.

Maybe you can answer the other question that'd been gently floating around in my mind about the standard Westy charging. The original charger had a three-pin multiplug for the 12v side - one earth, one leisure +ve, and one that doesn't seem to do much. What's that for? At the mo, our new charger's just connected to the earth and leisure +ve - lights/stereo etc are on the leisure, so that leaves the starter battery more or less totally separate.

[California Dreamin]

Hi Adrian,
I've never gone into the wiring on a Westy BBB but what I do know is that when on mains hookup both Leisure and Starter batteries are charged. This means the BBB has two charging outputs.

As long as you have carried out the well ducumented interior light/radio mod (which swaps supply to those items from starter to leisure battery) then there really is no need to have the starter battery being charged on hookup and so replacing the old BBB for a more modern leisure charger with one 'output' is fine.
Original BBB was 6amps I believe, so any replacement needs to be at least that (8 plus recommended) but must have 'floating charge' feature so it can be left permenantly on.

Martin

[AdrianC]

I've never gone into the wiring on a Westy BBB but what I do know is that when on mains hookup both Leisure and Starter batteries are charged. This means the BBB has two charging outputs.

Which I'd have thought implied that the third pin would be to the starter +ve - which it isn't (at least, not in a straightforward way...) - putting a multimeter to it gives no continuity to earth, and no voltage against earth.

The wiring diagram shows it going to the main VW loom via the split-charge relay, which is about where I lost the plot.

As for charger, we've gone for a Ctek MXS5.0 - "only" 5A, but I don't think it's ever going to need to play "catch-up" with consumption at that rate, so should always be on a positive charge rate, if not a high one. Ctek reckon that it's about the right size for a battery of the Ah rating of those in our vans.

[California Dreamin]

"only" 5A, but I don't think it's ever going to need to play "catch-up" with consumption at that rate, so should always be on a positive charge rate, if not a high one.

Fair dinkum!
As for the BBB wiring...without looking at the diagram ..besides, you've all changed over now so it doesn't really matter.

Martin

[trentjim]

Thinking in terms of keeping both batteries FULLY charged.
After a bit of consideration I'm coming to the conclusion that I probably want my starter battery to ONLY crank the starter motor. Use the alternator to charge the leisure battery, and devise a circuit which monitors the resting voltage of the (otherwise isolated) starter battery and throws a relay to connect it to the leisure battery via a diode if its voltage drops below 12.65V (or whatever the full charge voltage happens to be - I'd calibrate via a potentiometer).
The leisure battery would have a permanent top up from solar panels via a charge controller.
I wanted 19v anyway for laptops, so if i installed a 12v-19v switched mode DC converter which fed the charge controller as well as a couple of laptop jack sockets this would ensure a few amps to finish off the last few percent of the leisure battery that the alternator cant do on its own.. (I'd put this circuit on a "Battery boost" manual switch)
I'm thinking this setup would this would work well as a trickle charger/conditioner, as well as make sure i've got batteries that brimmeth over when I reach my destination.

my last puzzle is deciding how to determine that the starter is fully charged so I can disconnect it from the leisure battery - I'm currently thinking that a 555 could disconnect the relay after 10 mins, recheck the resting voltage and reconnect if it is still too low, but this seems a bit inelegant - I could probably infer a charged battery by monitoring current... thats as far as I have got....

[California Dreamin]

To be honest I stopped reading at the 'only have my starter battery to crank the engine' bit. This reads as if the starter is the only thing that takes power from the starter battery?
What about the ignition system
Lights
Heater blower
Heated rear window
Washers
Wipers
Horn
Etc

I honestly cannot see any issues in running a traditional split charge system and giving the leisure battery an overnight boost with a standalone battery charger before each big camp.
Tis what I've been doing for years without any issues what so ever.
Have you seen the size of that 'Sterling Box' and all it's massive wiring loom that Lloydy uses, come on it's all a bit extreme and totally unecessary for all but the most ardunt of wild campers.

BESIDES...if you carry out the interior light/radio mod then absolutely nothing is taken out of the starter battery whilst camping. All Leisure circuits using the leisure battery and keeping the starter battery solely for starting, so absolutely no worries about breaking down with flat starter battery.

Martin

[trentjim]

What about the ignition system
Lights
Heater blower
Heated rear window
Washers
Wipers
Horn
Etc

they would all be running off the alternator - buffered by the leisure battery.

[trentjim]

I honestly cannot see any issues in running a traditional split charge system and giving the leisure battery an overnight boost with a standalone battery charger before each big camp.

nothing wrong with that at all - though its not flattening the battery while camping that I am thinking about - its keeping the starter conditioned when its not being used and "what charges what" in a master/slave sense... also with solar input I like the idea of it looking after itself...

come on it's all a bit extreme and totally unecessary for all but the most ardunt of wild campers.

absolutely agreed, but i'm used to (mentally) working through optimal solutions.... before eventually dismissing them on grounds of practicality and bodging it!

E D I T - P.S. now I've got to look up what is in lloydy's box of tricks - see what I might have forgotten

[kevtherev]

To me optimal is a one stop charge and not to worry about topping up during the holiday.
so a type of battery with the ability of sustained amp hour delivery over a lengthy period of time, say a month before a full 3 phased recharge sounds like another option.

[California Dreamin]

Lloydy's setup is brilliant but a bit 'extreme' for most...my wife would be throwing a wobbly at the very thought of big black boxes screwed to the back of one of the seats and all that plumbing

Martin

[AdrianC]

What about the ignition system
Lights
Heater blower
Heated rear window
Washers
Wipers
Horn
Etc

they would all be running off the alternator - buffered by the leisure battery.

Umm, isn't that exactly how they normally work, but buffered by the starter battery? Seems to me like a lot of wheel-reinvention for zero gain.

[trentjim]

not zero gain,
if the starter battery is permanently connected to the alternator it will prevent the leisure batteries reaching full charge.
there are other advantages of detaching the cranking system too from a homebrew (e.g unique) security perspective, not to mention having a big red "engine start" button!

now whether the gain/effort ratio is worth it for two fully charged and perpetually conditioned batteries is a different question.