Battery Question
Submitted: Friday, May 04, 2007 at 09:57
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deserter
I have recently had dual batteries fitted to the car. The wiring is set up so the caravan battery links to the second battery in the car. The thinking is that this provides extra for the caravan fridge when
bush camping - ie when the van battery gets low the second car battery gives more run time.
I am just wondering if this idea is flawed. When will the second battery take over ? Does it wait till the caravan battery runs down. If so - doesn't that mean I am likely to stuff the deep cycle caravan battery by allowing it to lose too much charge?? Techo answers appreciated.
Reply By: traveller2 - Friday, May 04, 2007 at 10:45
Friday, May 04, 2007 at 10:45
If you keep the car and van connected when camped then they will slowly discharge as one big battery, the van battery may discharge a little bit more if the wiring/connection from the car isn't up to the task though.
The downside is that it will take days of driving to adequately charge both batteries
well enough for another extended stay.
The wiring from the aux battery to the connection to the van and from that connection to the battery in the van should be of sufficient size to prevent voltage drop.
I'd suggest using anderson plugs to connect the van to the vehicle.
AnswerID:
237848
Reply By: Robin - Friday, May 04, 2007 at 10:54
Friday, May 04, 2007 at 10:54
No problems with your thinking deserter
Both batteries will contribute to the current flow , but in proportion to
the resistance of the leads from each to the Fridge.
You can wire it 3 ways for different effects.
Assuming equal size cables (and cables are a reasonable size > 6 mm of copper)
Will assume distance from car battery to Caravan 8 meters
Will assume Car & Caravan battery equal size and type
1/ Wire from car battery to caravan battery - then to fridge
(Caravan battery will be used most maybe 4/1)
2/ Wire from car battery to fridge and
wire from caravan battery to fridge.
( Caravan battery gets uses most but not by much maybe 2/1)
3/ Wire from car battery to fridge and wire from
caravan battery to fridge but this time both wires of same 8m length.
( Caravan and Car battery get used by same amount )
Not - charging and best wiring way are a different issue
Robin Miller
AnswerID:
237851
Follow Up By: deserter - Friday, May 04, 2007 at 11:59
Friday, May 04, 2007 at 11:59
Thanks Traveler and Robin. Thats a bit clearer. Traveller - the second car battery feed is to the van via the anderson plug. Wiring is 6mm.
But you comments seem to conflict. Its wired as per Robin's option 1. Does it act as 1 big battery or is the use split as Robin suggests. And I am not sure what 4/1 is ?
FollowupID:
498964
Follow Up By: Robin - Friday, May 04, 2007 at 12:44
Friday, May 04, 2007 at 12:44
Hi Deserter
By 4/1 I meant that most current comes from closest battery by 4/1 as a rough indication based on using same size cables and its further to car battery.
It does act as one big battery but the closest one runs down its voltage first.
Most people would try to have as big a cable as practical to the car battery to minimize the voltage drop and more or less keep both batteries at same voltage and hence charge.
Your 6mm would do for small loads - standard is more like 8mm and above.
Robin Miller
FollowupID:
498969
Reply By: Mainey (WA) - Friday, May 04, 2007 at 14:18
Friday, May 04, 2007 at 14:18
deserter, I can't agree with the wire sizes mentioned, go much larger cable (size of actual copper wire) between the two batteries, to the very largest size that will fit into the Anderson plug.
Both batteries will recharge (assuming the batteries are identical) as just 1 x large battery, and run the fridge as just one battery.
Check the rested voltage of both batteries, if they are identical batteries the voltage will be the same and they will discharge as such, if the batteries are different then you will have the problems nominated above, and yes they will prove to be problems in time.
AnswerID:
237870
Reply By: deserter - Friday, May 04, 2007 at 15:59
Friday, May 04, 2007 at 15:59
Ah - the plot thickens. I just ran a
test light on the anderson plug. Its only active when the ignition is on. So if I am camped in the bush the car isn't feeding the van anyway. Back to ARB methinks.
AnswerID:
237889
Follow Up By: techo2oz - Friday, May 04, 2007 at 20:13
Friday, May 04, 2007 at 20:13
Deserter,
this would indicate that your wiring to the anderson might
well be fed from the main battery, not the auxilliary.
The only proviso to this would be if whoever wired in your second battery, included relays which isolated the load when the ignition is off, which sort defeats the purpose of the second battery.
Cheers
Peter
FollowupID:
499047
Reply By: tdf - Saturday, May 05, 2007 at 07:42
Saturday, May 05, 2007 at 07:42
what type of fridge not the std van 3way i hope...
AnswerID:
238027