Simple cheap dual battery setup
Submitted: Tuesday, Feb 24, 2004 at 23:21
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MartyB
Ok everyone this is not a 4wd question but I will ask it anyway.
Firstly my 4wd has a dual battery setup with a decent size fridge. Problem is my missus does not like driving the 4wd but drives her Camry instead. My fridge is too large for her to load into the Camry plus all we need in the Camry is to be able to keep the groceries cold for an hour or two, so no replies on how to install a setup that will last across
the desert.
Last night I bought a 12v cooler for $60 (new). You know the type, pieltzer (spelling) device, drops the temp by 20 deg and draws a constant 5 amps. this cooler is 24 litres, plastic and therefore suitable for the missus to carry in & out of the car. All it has to do is keep the food cool for up to 2 hours between shops.
I have a couple of 40 ah sealed lead acid batteries. My idea is to mount one in the boot & connect it as follows. + from accessories connected to one side of a relay coil, plus the make (normally open) contact, plus dioded to the aux battery +. current flow from the main to the aux battery. Aux battery connected to the break (normally open) relay contact. + of a cig lighter socket to the relay common contact.
Neg to the other relay coil contact plus cig lighter socket -. Draw this out to see what I am talking about.
The theory is when ignition is off the aux battery will power the cig socket, ie the cooler when plugged in. When ignition is on or acc the main battery will run the cig socket plus the main battery will charge the aux battery.
As the cooler draws 5 amps plus the battery is only 40 ah I am only talking about using a 30a relay & diode, 25 amp fuse in line to protect.
So shoot me down in flames & tell me what is wrong with this theory, I realise the aux battery will only float charge due to the 0.6 v drop with the diode. I don't think this will be a problem as car is driven every day & cooler will only be used once a week.
from Marty.
Reply By: V8troopie - Wednesday, Feb 25, 2004 at 02:04
Wednesday, Feb 25, 2004 at 02:04
The cooler is not going to do much better than a simple esky for the hour or two you intend to use it,
UNLESS you fill it up with frozen freezer bricks BEFORE you go shopping.
These Peltier coolers manage to keep things cold, IF the things you put into them are cold AND the cooler's inside is also cold ( has been running for some time or filled with freezer bricks).
Just my 2 cents worth. I have a small Engel permanently in the back for those shopping days, it barely manages to keep cold things at the same temperature for the hour or so its used if I only turn it on as I fill it with shopping.
Ah, yes, your "circuit diagram". I'm afraid its a 3 Becks affair, a bit muddled and overly complicated. Why do you need a relay? If I were to do that I would wire the aux battery to a cig lighter plug and a socket. Plug the cooler in this socket. Plug the Aux battery into the car's cig lighter socket.
The car's cig lighter is off when the ignition is off - Aux battery runs cooler.
Ignition on powers cooler and recharges aux battery from the car's lighter socket.
If the 40Ah aux battery only powered the cooler for one hour or so it should not draw too much charging current as you turn on the ignition.
P.S. I know what a packet of Becks is, have seen people addicted to it, a sorry sight indeed.
Klaus
AnswerID:
47976
Follow Up By: Member - Bob - Wednesday, Feb 25, 2004 at 09:25
Wednesday, Feb 25, 2004 at 09:25
And I thought you got Becks in slabs. A Bex and a good lie down was standard self stress management from the era when you could scoff a Vincents powder, and the phenacetin stuffed peoples' kidneys.Bob
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Follow Up By: joc45 - Wednesday, Feb 25, 2004 at 13:46
Wednesday, Feb 25, 2004 at 13:46
In serious cases, it was a cup of tea, 2 Bex and a lie down.
Gerry
FollowupID:
309947
Reply By: Sandie - Wednesday, Feb 25, 2004 at 19:22
Wednesday, Feb 25, 2004 at 19:22
No need for all that.
Just a rely opened when engine is off driven by cig lighter socket grounded all to one point!!
This isolates the 40amphr battery from the main battery, like a switch!! Don't forget that fuse!!
Your using the diode as a control for when the car is running which you don't really need since everthing is running parrallel to the main battery at 14.2Volts. When the engine is off your cutting out the main battery and alternator.
I take it you don't have an aux battery already installed in the Camry.
I use this method to charge my 7.2ah battery while on the go!! Works a treat.
Another way to charge the battery and run the cooler is to use an inverter with a 12V charger connected to the battery. Make sure the inverter has isolation protection. However you will need at least a 5amp charger to cope!
Hope this helps
Marty, yes i'm Marty too, Sandie is my other half!!
AnswerID:
48071