3RD battery questions

3RD battery questions

Postby ktruck on Wed, 11 Jul 2012 8:13 +0000

Currently I have a 08 Hilux with a ARB dual battery installed and am looking to put another battery in my new "jack off" canopy.

I am slightly worried that in doing this I might be putting some undue stress on some of the standard components in my car like the alternator by doing this though.

My current understanding (and feel free to correct me if I'm wrong) is that if I run it in series with the current second battery it will just take longer for both the charge fully.

If another dual battery system is needed I was thinking of using something like this in the canopy.
http://www.ebay.com.au/itm/DUAL-BATTERY ... 247wt_1270

Any thoughts on the matter would be greatly appreciated.
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Re: 3RD battery questions

Postby Wing on Wed, 11 Jul 2012 8:26 +0000

I suppose "in series" means "in parallel" in your case. In your case, the battery will not be 100% charged up. Say, you have a 100ah as second. maximum 80% charge and "never drop below 50%" means that you have 30 usable Ah. If you get a ctek type dc dc charger, you have 50 usable ah. Not far from a 3rd battery in the tub. Not to mention the cable work, circuit breaker....
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Re: 3RD battery questions

Postby ktruck on Wed, 11 Jul 2012 8:43 +0000

So the 3rd battery in the tub would DC to DC charge (with this DC charger) off the Current Aux Battery?

And Just connect it with some heavy duty cable and 50A anderson plugs to the battery in the Canopy?

I must investigate about these DC to DC chargers (was browsing the other thread about alternators just after I wrote this and was the first time I'd heard of them).
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Re: 3RD battery questions

Postby cooganstein on Sun, 09 Sep 2012 9:13 +0000

try a search on ebay for an alternator booster diode. it raises the alternator voltage by roughly 0.5 volts. it says they can be useful in 2nd and 3rd battery apps. let us know what u sort out.
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Re: 3RD battery questions

Postby VMN on Sun, 09 Sep 2012 11:41 +0000

I've had a second AUX battery in the tub with an ARB setup under the tub, and a third AUX battery in my van when it is hitched. These are all tied together and charged from the single battery isolator under the hood. About 12 months ago, I added a charging diode and it all works really well.

In your situation, I would fit a 100 amp mega fuse on the ARB battery tray (holes are there to mount one without drilling) and run a single thick cable (B&S3) from the from to the rear and terminate it on another mega fuse at the rear. I ran this cable though the chassis rail. The two fuses are required because when hooked up, both systems are live so you need to protect from a catastrophic short on this main wire. Plus, it will provide a convenient terminal for the next part. Get some 6 b&S cable (the thickest you can put in a 50 amp Anderson plug) and run a red one from an Anderson plug mounted on the vehicle to the back mega fuse and a black one to an earth polished to bare metal with an angle grinder on the chassis.

So now all you need is another Anderson plug and 6b&s cable running to the battery in the jack off. You may want to add a third fuse on the positive close to the jack off battery.

I would not bother with the fancy battery box, just get a basic one with no wiring on it and grab a couple of battery terminals to finish it off.

The advantage of this setup is that when the truck is connected, you will be pulling power from both batteries and if you jack off, consider getting a 6 B&S Anderson Plug extension lead so you can plug the vehicle in when camped. This is what i do.
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Re: 3RD battery questions

Postby skirex on Sun, 09 Sep 2012 12:17 +0000

Just Put a DC DC charger before the third battery so it is regulated and there will be less strain on the alternator.
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Re: 3RD battery questions

Postby VMN on Sun, 09 Sep 2012 1:38 +0000

skirex wrote:Just Put a DC DC charger before the third battery so it is regulated and there will be less strain on the alternator.


I don't agree with this. You have a perfectly good charging system so why spend any more than you have to?

By adding a DC-DC charger in the jack off you won't have the ability to use the vehicle mounted AUX battery in the jack off as the DC-DC charger will isolate the two batteries. You want to be able to charge both the vehicle AUX and the jack Off AUX at the same time. If you ever add solar panels to the jackoff this will also let the trucks AUX battery to be charged from solar which is desirable.

If you must use a DC-DC charger, you would be better off replacing the current isolator in the truck with one to achieve what I stated above, but as I said, why spend more than you have to? $40 for a charging diode is a lot easier to digest if you find it is necessary to add more charging capacity.

What is rarely mentioned is that a DC-DC charger places a constant load on the alternator whereas a conventional isolator does not.
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Re: 3RD battery questions

Postby skirex on Mon, 10 Sep 2012 11:06 +0000

Sorry mate didnt think of the third being isolated. I got a redarc smart start isolator for my 2nd battery. My uncle is a auto elecy and trying to push a redarc dc dc charger onto me so the battery is always 100%
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Re: 3RD battery questions

Postby VMN on Mon, 10 Sep 2012 11:40 +0000

Just get one of these from LeighW on Pradopoint

http://www.ebay.com.au/itm/Prado-Hilux- ... 2066wt_922

A hell of a lot cheaper and have been happy with mine over the last 12 months. Battery is always full!
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Re: 3RD battery questions

Postby Alby on Mon, 10 Sep 2012 2:29 +0000

I assume that the third battery in the Jack off will be the one with the load from fridge etc, is there any power being drawn from the second battery as well or is it then a reserve power supply?

To keep it simple and cheap why not just put a 3 way battery switch in like they use on a boat 'A' or "B' or 'A plus B" together. That way you can choose to charge the battery that needs it and also draw power from whatever one you want.

A DC-DC charger or the Diode that Rod has suggested would be a great inclusion into the system as well
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Re: 3RD battery questions

Postby ktruck on Wed, 31 Oct 2012 3:31 +0000

Well I never ended up putting a battery in the tray. I figured if it wasn't on the car then I wouldn't need power or the fridge would be in the cab.

I ended up running two power sources to the back. One that turns on with ignition for my 2nd reversing camera. And another that's on all the time for the fridge and interior lighting.
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Re: 3RD battery questions

Postby GeeTee on Wed, 31 Oct 2012 6:40 +0000

yeah two batteries is plenty of capacity - and relatively simple - for most people. Need more? Get solar or simply idle your truck for 30 mins each day ;)

Alby, good idea on the marine-style A+B rotary switches but the DC-DC chargers offer no real advantage in real-world situations; much better to simply use quality wiring when installing your second battery. The alternator hot-up is an asset, too
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Re: 3RD battery questions

Postby Alby on Wed, 31 Oct 2012 2:31 +0000

GeeTee wrote:Alby, good idea on the marine-style A+B rotary switches but the DC-DC chargers offer no real advantage in real-world situations; much better to simply use quality wiring when installing your second battery. The alternator hot-up is an asset, too


GeeTee cable thickness is only part of the solution. I have wired my second battery up with 2 B&S tinned battery cable so voltage drop is not an issue but our alternators do not provide sufficient charge to recharge a depleted second battery properly, you only get about 80% of its capacity so you need the DC-DC charger to create a load on your starter battery to stop the alternator going into sleep mode and keep cranking the amps. Also the charge rate is lower than is ideal for an AGM type battery.
I fitted a DC-DC charger when I got a second fridge which I run as a freezer to give me a better capacity and I definately are getting more out of the same battery setup
If you have a look there is a thread on the subject that goes into more detail, I am only a novice on the electrical side of things but did a fair bit of research on the subject to better understand it. I believe there is a similar thread that run on Prado point
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Re: 3RD battery questions

Postby GeeTee on Wed, 31 Oct 2012 5:18 +0000

That 80 percent figure has no real basis in fact ... provide a battery with adequate current with sufficent voltage (as your alternator does) for long enough and it will reach '100 percent' every time. It's a bit like a dripping tap always filling the bucket under it. A big-current Hilux alternator is more than capable of charging a second - or third, even a fourth - battery in a vehicle to a full charge (let's call that 100 percent) but it takes time.

A DC-DC charger raises charging voltage a little (as does the alternator hot-up diode thing) but then restricts charging current to 10A (or 20A depending on your unit) so increases charging time of an almost -flat battery compared to the amount of juicy goodness your standard 100A (?) alternator can provide.
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Re: 3RD battery questions

Postby Alby on Wed, 31 Oct 2012 6:39 +0000

What you are saying may be true but there are not enough driving hrs in a day to get the 100% SOC in practical terms .

There is a thread here from a few years back from an old forum member ' Olcoolone" Going into the technical details and testing of our alternators showing the charge rate dropping off dramatically when it senses the cranking batteries close to charged and then only delivering a trickle charge , the second battery is not detected so is left with a trick charge of low voltage to recharge with
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Re: 3RD battery questions

Postby 07luxyTD on Wed, 31 Oct 2012 6:48 +0000

Mate travelling up cape york atm is running 3 batteries, 2 under bonnet 1 in jackoff. Had a smart isolator and his voltage never went over 14v. installed a dc-dc and raised to 14.7 he notcied the difference in the running time of his fridges when parked up for 4-5 days, when charged at 14.7 but to charge them up took to long with the dc-dc so he went back to the smart isolator as he just let it run for 30mins every second day or so.

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Re: 3RD battery questions

Postby Ciboats on Wed, 31 Oct 2012 7:16 +0000

Hi guys

Im not up on % of charge and all the other stuff. Here is what i did and ive had no issues.

Dual battery set up with a switch in dash if required giving me crank power. 4 mm wire connects directly to dual battery with a diode to prevent current back flow. This dual runs my whole world. Fridge, winch, tray power with camp lights, cig, andersons, etc,

Then i have a main battery connection with 5mm 2core going directly to tray that charges my 3rd portable deep cycle gel that i use on a daily basis to get me out to my boat with a 55 lb electric boat motor. I have never used a battery charger on any of them. And i can often flatten my deep cylce battery getting to & from my boat multiple times a day.

All i do to monitor this is a cheap led cig plug in meter which tells me im charging 13.5 to 14 v. Every time i start the car

So far works a treat.
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Re: 3RD battery questions

Postby Qwerty on Wed, 31 Oct 2012 7:31 +0000

Using dc-dc charger to charge auxiliary battery on an isolated aux circuit, will absolutely give you more run time , less battery damage, and maximum potential from your charge/discharge scenario ... The 70/80% SOC factor vs 100% is definitely relevant.

Go a 40 amp dc-dc if you're concerned about timeliness. But be aware of your overall load and alty capability at idle.

Leave starter for engine duties only, charged by alternator.


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Re: 3RD battery questions

Postby GeeTee on Wed, 31 Oct 2012 9:25 +0000

Alby wrote:What you are saying may be true but there are not enough driving hrs in a day to get the 100% SOC in practical terms .

There is a thread here from a few years back from an old forum member ' Olcoolone" Going into the technical details and testing of our alternators showing the charge rate dropping off dramatically when it senses the cranking batteries close to charged and then only delivering a trickle charge , the second battery is not detected so is left with a trick charge of low voltage to recharge with


Yes that is the biggest drawback with DCDC chargers - they need a dozen or more hours to do thier thang but it doesn't say that on the box ;) Much quicker to get oodles of juice straight from the alternator using a piece of fat wire.

Regarding charge 'rate': if this "rate" (voltage) didn't 'drop off' it would fry the batteries... cars have been adequately dealing with that for a century.

This 'detection' you speak of? Two batteries connected with each other, and to an alternator, get charged by the alternator. Easy.
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Re: 3RD battery questions

Postby Qwerty on Wed, 31 Oct 2012 9:42 +0000

I've done umpteen 1 week to 1 month trips touring and use a dc-dc charger. No dramas at all and it gets the battery up to 100% SOC and giving me longer run times.

Previously when I used just my alternator , id be seeing 11.9v a lot sooner , without fail. (I never ever take a battery below 11.9v). Auto SParky mates of mine (who are part of my 4wd'ing crew) say it's closer to 70% SOC than 80% with alty

Sure , an alternator will charge a flat battery to 70-80% SOC a little faster than dc charger will , but then doesn't take it to sweet spot of chemically healthy 80-100% (which you get to retain in following days if you don't indeed use it). At the end of the day I'd rather have ability to extend run time and maintain battery up around 80-100%. This means in the days following a full charge I have more runtime available before going flat , and therefore will be further along the charge percentage compared to if i had only been at 70-80% to start with.

My starter always settles to around 12.7 overnight , Aux will be sitting around 13.1v overnight (assuming no load).

I just prefer to be always hovering 70--100% SOC (which is realistic) , than 50-70/80%.

In essence, think of the battery as a glass of water ... the bottom 50% you shouldn't tap into (damages the battery) ... I'd prefer to be able to fill my glass of water to the top, even if it takes a bit longer (never ever been issue for me mine seems to do fine) than to fill it really quickly but only to 70% (80% is a very optimistic figure). At end of the day the runtime outweighs the perceived slightly slower charge rate. Assuming I drink half a glass of water per night , I'm still ahead on the next driving day because I had full glass to start with. Taking a battery below 50% greatly reduces its life.

If you can hold more than a non dc-dc setup "in the tank" then you're stilll going to be ahead "on the next drive"

I also believe in the starter battery only ever being the starter, not part of a smart solenoid scenario. Aux / house battery can be raped no worries but that starter is for engine only. It rarely ever deviates from its SOC and is never used for house duties. (Even stereo system draws power from aux circuit and no need for key ignition).

In terms of speediness of charge (to the 70-80% mark, only the 80-100% mark is relevant for DCDC) ... My alternator is 80amp , a redarc 40amp dc charger is chewing half the alty output ... Frankly don't think with all that other loads sucking on the alty that you're going to get much more than 40amps dumping into a battery even with alty directly connected.

Dc chargers are also 3 or 5 stage and set to the battery type (important for non standard batteries) , giving a healthier and longer life for the batteries that are constantly in discharge / recharge use scenarios. They're temperate aware and kinder to battery chemistry in charge / discharge cycling.

In bulk charge mode it hovers between 13-14v lots of amps, then up to 15v when hits absorption phase (90-100%, less amps). , then floats at 13.3. Almost always mines on 14.9 to 15v (90-100% SOC). Unless I've had a heavy time with amps / subs / fridge working hard / mrs watching DVD with inverter on, then she will bulk charge for couple hrs on next drive.

Image

My vote goes to using dc-dc chargers. (And Ac-dc chargers when appropriate such as access to genny power).

At end of day if you're going to be sucking power galore for days on end with no driving you're going to need some other source of power. (Solar / genny /240v : Ac-dc 7 stage charger)

At a min , get yourself an Ac-dc charger so u can top them up to 100% before venturing off. (I take mine with me and plug in when stopover at family farm for a few days of no driving , with fridge and freezer full and still running when enroute on way up north as part of a longer trip)


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