Triple battery set up
Submitted: Tuesday, May 18, 2004 at 14:31
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Lachlan
I have a standard toyota set up with dual batteries in parrallel.
I have a third battery (AC Delco) which I want to connect up in the rear of my car for running a fridge, similar to a camper trailer set up.
I want a simple system and was wondering if I can connect the third battery directly to the outlet on the alternator. Will such a set up still drain my other batteries when the car is not running? If so, can a simple switch disconnecting the third battery when being used prevent draining the other batteries.
I do not want to spend big dollars on isolaters etc.. and am happy to use manual switches.
I have read a lot of previous posts but none seem to address this option.
Any advice or direction greatly appreciated.
Thanks in advance
Lachlan
Reply By: Rosscoe - Tuesday, May 18, 2004 at 15:06
Tuesday, May 18, 2004 at 15:06
I know lots of people carry additional batteries in the cabins of their vehicles but is this a good idea? Is the AC Delco a sealed lead acid or gel filled unit?
Is it "legal"? - Even if it's sealed.
I'd hate to have a battery with all that acid flying around if I was in an accident.
If you do it, I'd make sure the battery is installed in a properly constructed and vented battery box and anchoured down
well. A number of people on the
forum have reported doing this and seem very happy with the results.
In most modern caravans, motorhomes and camper-trailers the batteries are mounted in enclosures separated from the living areas and vented to atmosphere or mounted externally on the draw bar or similar.
I would go for simple manual battery isolator/switch if you have the dicipline to throw the switch whenever you stop for any lenth of time.
Check the 12 volt
shop in Auburn
Sydney or similar organisations in other states.
They use these isolator switches both internally and externally in ralley cars.
AnswerID:
59080
Follow Up By: Lachlan - Tuesday, May 18, 2004 at 15:54
Tuesday, May 18, 2004 at 15:54
Rosscoe,
Thanks for the reply. I have a battery box and was intending to vent outside. The main issue I am not sure of is the whole charging 3 batteries set up and whether the third battery will drain the others if not isloated and any other potential problems. In other words, will the third battery when in use drain from the other batteries via the output on the alternator.
Lachlan
FollowupID:
320724
Follow Up By: Rosscoe - Tuesday, May 18, 2004 at 16:10
Tuesday, May 18, 2004 at 16:10
Lachlan,
My logic (which sometimes aint great) say yes, you need to isolate the battery. Effectively you're connecting it to the main battery in parallell and any load will draw on the main battery as
well as the rear mounted battery. Lots of people use a simple manual switch BUT if you forget to change it over when you stop you could end up with a dead cranking battery.
The automatic smart separators (Piranha, Sure, Rotronics etc) do this when the ignition is off and or when the main battery drops below a preset limit.
The other way is to connected the rear mounted battery to the vehicles auxiliary battery assuming it's separated from the cranking battery by a smat solenoid/separater.
FollowupID:
320732
Reply By: -OzyGuy- - Tuesday, May 18, 2004 at 17:32
Tuesday, May 18, 2004 at 17:32
lachlan,
connect your AC DELCO battery Positive lead direct to the positive connection on the FIRST battery lead from your altinator.
Have a decent "smart" solenoid eg Pirahna etc, in-line to the AC Delco battery.
Earth your AC Delco battery to an effective common earth that is used by the other batteries, eg maybe chasis rail.
This way the altinator power is going to BOTH systems inderpendantly and the AC Delco battery is isolated when the ignition is off. that way you don't drain the original batteries.
AnswerID:
59113
Follow Up By: Eric Experience. - Thursday, May 20, 2004 at 21:37
Thursday, May 20, 2004 at 21:37
OzyGuy.
The modern charging systems use a diferent set up to the older units. in the older machines the alternator was connected directly to the battery, but in the vehicles with fusable links the alternator output and the referance for the regulator go to a distibution piont usualy where the fusable links are and then a feed is taken from there to the battery. The result of this is that when the alternator is working hard the output can be more than 1 volt higher than the mian battery this is why it is best to connect to the alternator, the deap cyle battery needs the extra voltage. Eric.
FollowupID:
321130
Reply By: Lachlan - Wednesday, May 19, 2004 at 09:23
Wednesday, May 19, 2004 at 09:23
Thanks to everyone for the helpful advice.
I have one last question. If I were to connect third battery direct to alternator with a manual isolation switch (and fuses) do I need to hook up some device to discharge the battery when the fridge is not connected (and third batterey not isolated) to prevent overcharging. Most of the time the 4wd will be driven around the city and the third battery will not be isolated (ie being charged). Am I correct in assuming that if it is connected to the alternator there will be devices (such as the alarm) drawing on it (and the other two batteries) or should I just connect the alarm straight up to the third battery so there will be some draw on the third battery when vehicle is not being driven.
My limited 12v knowledge (and previous posts) would say that if the third battery is connected to the alternator and no battery is isolated they are all effectively in parrallel and it would not matter which battery I connect the alarm to, it will draw on all three batteries.
I hope this makes sense.
AnswerID:
59219