Dual Batteries for dummies

Re: Dual Batteries for dummies

Postby KenLux on Fri, 20 Dec 2019 8:30 +0000

OK new member
Early 2015 diesel extracab tray
I have a slide on camper with a portable AGM battery, redarc bcdc charger and solar panel in/on the camper. Redarc as it fitted in the battery box.
I have just installed a second battery deep cycle flooded in a ARB bracket under bonnet being charged via a Redarc isolater solenoid with a switched 10mm, 35mm2 jump start cable, as a Quick installation before a trip, while I work out a BCDC charger. THis goes to an in cabin fridge, and various electronics charging. Unsure if this needs a voltage boosting diode, Have a cigarette socket voltmeter in car and house sockets to check on this trip. Probably should monitor engine bay temperature at battery position.
I have just read the 49 pages of this thread, then a century battery spec sheet, as that was the battery ARB and battery world recommended and could supply and fitted, then onto a page that lists charging and gassing voltages at various temperatures for lead acid batteries.
https://www.powerstream.com/SLA.htm
As temperatures rise to common under bonnet temperatures the gassing voltage can be below the charging voltage. This would be what the temperature compensating alternator is trying to allow for. Could this be what is happening with BCDC chargers when there is boilover? That the BCDC is charging to a fixed voltage and backs off the current at higher temperatures , rather than cutting the the voltage.
Also if the BCDC charger is located out of the heat such as in front of the radiator on the redarc bracket, then the unit will not sense the battery heat back in the far corner of the engine bay, so output reduction at high temperatures may not happen, and boilover may be worse.
I am no expert but am puzzling over the best way forward.
Will see if Redarc have any further information next year.
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Re: Dual Batteries for dummies

Postby Chopps on Sun, 22 Dec 2019 7:15 +0000

I'm def no expert either but those voltage diodes are usually for the cranking battery
I'd imagine the BCDC would regulate the charge correctly without a diode for your aux

A question for those in the know
Wouldnt a voltage boosting diode increase the risk of battery damage?
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Re: Dual Batteries for dummies

Postby martynvella on Mon, 23 Dec 2019 6:54 +0000

Dont over think it, perfection is almost impossible to achieve.
If it is a "T" type century it should be happy with anything from 13.5 to 14.5 volts, you havent mentioned what your charging voltage actually is, varies from original alt to after market.

Yes, a diode will up the chg rate by roughly half a volt which will make a big difference to chg current, personally I dont recomend them, a flooded aux is very similar chemistry to your LA starting battery so should run fine without a diode.

Temp compensated alternators are more for alternator protection than battery protection. They can only sense alt temp not engine bay or battery temp.

Boil overs are most commonly caused by over full cells and rough tracks or faulty batteries, or over charging alternators. Just enough electrolyte to cover the tops of the plates is all you need.

Leave the DC DC charger where it is, you cant use it to charge 2 different types of battery.
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Re: Dual Batteries for dummies

Postby KenLux on Tue, 07 Jan 2020 8:56 +0000

Touring with slide on camper.
D4D diesel with dual battery in ARB tray early 2015 lux.
Start battery voltage/alt voltage when running 13.2-13.8 V.
Redarc battery isolater charging under bonnet auxillary. Fridge 40 litre Engel, run off under bonnet auxiliary. Minimun battery voltage 11.9 When stayed in 1 place more than 2 days ran fridge off camper battery and solar.
Environment temps 20-30 deg C, Highway speeds bitumen
Second battery temp via a probe sitting on top of battery, I could attach to when stopped.
Stopped when refueling or lunch in towns, or end of day, ie not at the end of a long climb.
Battery temperature 25-30 degrees above ambient as measured by Hilux centre console, wherever and however that is measured, but equated with my multimetre probe when I checked once or twice.
Max of 49 deg C measured, but not available to me while driving.
So with slow travel at high work loads, less cooling and more heat and add a hot day of 40 deg C or more that could be 70 deg for battery.
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Re: Dual Batteries for dummies

Postby torquative on Fri, 21 Feb 2020 9:25 +0000

posted in wrong forum ...
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What 12V Dual battery Setup?

Postby TBJ on Tue, 14 Jul 2020 4:26 +0000

So I want to put together a proper dual battery set up into my Lux, and cant figure out what I need and how far I actually need to go to run what I want to. So I want to be able to run my 80L Engel fridge constantly everyday, to keep lunch cold and beers cold for knock off. I also want to be able to run my Travel Buddy 12V Marine Oven in order to heat up my lunch, as well as cook some pies and other stuff on trips. I'd also like to run some work lights, and be able to charge some stuff up in the back too, mainly phones, my speaker and maybe my laptop when I'm camping. I'm also thinking of putting a solar panel on the top of the dog box, So with all of this what sort of setup would you suggest? I'm thinking of going Red Arc? but how far do I need to go? what parts would you suggest? What size battery? and how much am I going to be spending on this setup if I was to get someone to do it?
thanks
-2013 MY12 SR5 3.0D4D Manual 4x4 Dual Cab
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Re: What 12V Dual battery Setup?

Postby Diezel45 on Wed, 15 Jul 2020 6:11 +0000

It all depends on how long you are wanting to run these items between charges. You could easily get away with running that stuff on one extra battery if you plan on driving a couple times a day to charge the battery.

The travel buddy draws 8.3 amps per hour. If you have a 100a/h battery, you only get 50% of that to be usable, so 50 useable a/h. So one hour of oven usage, depletes your batter by 16% of your battery life. This compared with your fridge. chargers and everything, you are going to want more than one battery unless you plan on charging your battery a couple of times a day through either a generator or solar panel.

The way i work it out, is find out how many amps you want to run with everything (Fridge, Oven, Chargers, Lights ect) and work out how long you want to go between charges and that will give you an idea of how many batteries you need which in turn will let you know what sort of charger you need.

For my setup, I run two 40L Fridges (2.75A), 2 x Lights (0.7A) - Total 3.5A

I want to be able to run for 48 hours without charging.

3.5a x 48h = 168 a/h of usable battery storage meaning i need 336 a/h of batteries total.

So i run 3 x 120 a/h batteries. So i run a 40A Redarc Charger.

I hope at least some of this makes some sort of sense. But like i said, thats just how i work it out. :lol:
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Re: Dual Batteries for dummies

Postby hiluxxury on Wed, 15 Jul 2020 8:06 +0000

Plenty of info in this thread ;)
I might be wrong.

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Re: Dual Batteries for dummies

Postby martynvella on Wed, 15 Jul 2020 9:27 +0000

Quality advice diezel.
The only things I would add is if you run multiple batteries a 40 amp dcdc charger would be best but they put extreem load on a std alternator so an upgraded alternator is advisable, if not just run a 25 amp unit.

Also solar, as much as you can fit with a seperate reg such as a victron 100/30 and configure the panels in series for the highest possible panel voltage and make sure each panel is fitted with a bypass diode.
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Re: Dual Batteries for dummies

Postby Diezel45 on Wed, 15 Jul 2020 12:00 +0000

martynvella wrote:Quality advice diezel.
The only things I would add is if you run multiple batteries a 40 amp dcdc charger would be best but they put extreem load on a std alternator so an upgraded alternator is advisable, if not just run a 25 amp unit.

Also solar, as much as you can fit with a seperate reg such as a victron 100/30 and configure the panels in series for the highest possible panel voltage and make sure each panel is fitted with a bypass diode.


Never thought of the strain on the alternator. When it gives out, ill make sure i upgrade it!

Thanks for that!
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Re: Dual Batteries for dummies

Postby 2012 Hilux duel cab on Sun, 16 Aug 2020 8:42 +0000

Hi guys

I've got a 2012 D4D Hilux, what I get from this is that it doesn't have a smart alternator, but a Temperature sensing relay inside the alternator ?

Thanks!
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Re: Dual Batteries for dummies

Postby TOYZX on Mon, 17 Aug 2020 8:04 +0000

Temperature sensitive is correct.

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Re: Dual Batteries for dummies

Postby specwarop on Thu, 17 Feb 2022 4:19 +0000

Hi All, so whats the latest on under bonnet options?

I had a Century N70T for all of 10,000km. In that time I had to fill it twice as it was leaking everywhere. Got a refund just today.
I dont really want to go for another N70T, and was hoping to find an alternative. My requirements are only 80-100AH and I dont need anything expensive like a Lithium. A sealed N70T would be ideal but havent found anything as yet. Whats out there any help?
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Re: Dual Batteries for dummies

Postby dave g on Fri, 18 Feb 2022 3:38 +0000

What is the charger you are using for your setup.
If you are over charging the battery it will leak acid.
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Re: Dual Batteries for dummies

Postby specwarop on Fri, 18 Feb 2022 6:20 +0000

dave g wrote:What is the charger you are using for your setup.
If you are over charging the battery it will leak acid.
REDARC BCDC1225D is what I am using.
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Re: Dual Batteries for dummies

Postby dave g on Sat, 19 Feb 2022 6:53 +0000

Redarc bcdc1225
Change the wire to the agm setting
And It still over charged acid every where
I now have a Optima blue top as ass.
Never had a problem since.
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Re: Dual Batteries for dummies

Postby specwarop on Sat, 19 Feb 2022 8:01 +0000

And you put that Optima Blue in your engine bay?
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Re: Dual Batteries for dummies

Postby dave g on Sat, 19 Feb 2022 8:39 +0000

Yes in a arb tray it is under the weight the tray can carry
PM me your mb number and I send a photo
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Re: Dual Batteries for dummies

Postby dave g on Sun, 20 Feb 2022 12:27 +0000

Hope the photos help.
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Re: Dual Batteries for dummies

Postby specwarop on Mon, 21 Feb 2022 7:32 +0000

Do you guys install a charger isolation switch, so you can stop the battery being charged when you aren't intending to use the auxiliary battery for long periods?
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