Dual battery matters

Submitted: Sunday, Jan 22, 2017 at 13:38
ThreadID: 134164 Views:3934 Replies:8 FollowUps:19
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Hi Folks
After seven years and two under bonnet dual batteries (one deep cycle and one cranking) I have decided to move my next dual battery to the rear of my 2012 Patrol.
The seven years included an eight month lap and plenty of off road KM including some time on the Gibb RR.
I'm sure that the principal reason for the demise of the two batteries in that time is the under hood heat load in the Patrol, no doubt assisted by the nearness of the turbo.
My question is what is the smallest gauge wire that I should consider running from the terminated ends of the existing dual battery system to the new dual battery position next to the fridge in the rear.
By the way, the second battery is only used for my fridge and some very occasional lighting so there's not a major current draw involved.
All comments appreciated.
Regards
TJ
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Reply By: Allan B (Member, SunCoast) - Sunday, Jan 22, 2017 at 13:59

Sunday, Jan 22, 2017 at 13:59
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The current draw of your fridge and lighting has little bearing on the required cable size from the alternator. It is more to do with minimising the voltage-drop to insure proper charging of your auxiliary battery in the rear of the vehicle.
I would recommend a minimum of 20mm2 (4 B&S) cable.
You may find My Blog on Auxiliary Battery Systems useful.
Cheers
Allan

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Follow Up By: steamfire01 - Sunday, Jan 22, 2017 at 14:09

Sunday, Jan 22, 2017 at 14:09
Thanks Allan, I'll check it out.
Clearly I should have said "Cable" rather than "wire"
Regards
TJ
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Follow Up By: Member - Boobook - Sunday, Jan 22, 2017 at 14:17

Sunday, Jan 22, 2017 at 14:17
Yeah, I'm with Allan. You will certainly need good cable to minimise the voltage drop. Or dare I say it, use a DC to DC charger with say 6B&S cable.

You may want to reconsider moving the battery to the rear and addressing the heat issue. IF that is the problem.

Do you monitor the discharge of the battery? That is more likely to be you problem.You shouldn't let the battery discharge below 50%. Draining it flat or near flat will kill it.

Also you can get heat shields. Lots of prople have dual batteries in their vehicle without heat issues.
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Jan 22, 2017 at 16:50

Sunday, Jan 22, 2017 at 16:50
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Yes, Boobook makes a good point re DC to DC charger with lesser sized cables. Actually, that is what I have in the Troopy. The guides in my blog that I referenced above show this alternative. I have two auxiliary batteries, one in the engine bay and one in the cabin with 20A dc-dc chargers on each of them. This not only reduces volt-drop issues but provides the batteries with a better charging regime than direct from the alternator.

I ascribed the all-too-frequent failure of both my cranking and auxiliary batteries in the engine bay to temperature and fitted a heat shield (as photo below) to protect them. It seems to have been of benefit as the current batteries have already lasted much longer. My heat shield reduces heat transfer from the motor but allows cool ventilating air to pass through the battery zone. Insulation alone merely reduces the rate of heat transfer and if the heat that slowly passes through the insulation is not progressively removed by ventilation then the battery zone will eventually rise to the same temperature as if there were no insulation. Accordingly, I would caution about using the commercially available insulating jackets marketed for batteries. These close-fitting jackets have no means of eliminating the heat that continually progresses through the insulation so the heat at the battery will rise, albeit more slowly, to have the same result as no insulation. Indeed, the heat contributed by normal battery charging will not be able to escape thus making the battery hotter than if there were no insulation at all.
Cheers
Allan

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Follow Up By: Deejay - Sunday, Jan 22, 2017 at 20:17

Sunday, Jan 22, 2017 at 20:17
G'day Allan. Deejay here. Saw your reply and thought I'd give you an update on how you helped me with my auxiliary battery relocation and all the cabling. It's now been a year since all the work was done and everything is working great. Have had several long trips away (one of them on very rough roads) and had no troubles. Thanks again.
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Jan 22, 2017 at 21:02

Sunday, Jan 22, 2017 at 21:02
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That's really nice of you Deejay. I'm very pleased that your system is working so well. Happy to have helped.
Cheers
Allan

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Follow Up By: ian - Sunday, Jan 22, 2017 at 23:26

Sunday, Jan 22, 2017 at 23:26
Hi Allan,
regarding your comments about battery heat build-up, is there an advantage in hot conditions in having the bonnet slightly open to get more air through, or does this create more problems?
thanks
Ian
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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 23, 2017 at 09:16

Monday, Jan 23, 2017 at 09:16
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Hi Ian,

No batteries appreciate operating in elevated temperatures so they will perform better if high temp is avoided. In the case of my Troopy, I measured engine bay temperature whilst driving in suburban conditions on a mild (27C) day and the temperature at the battery was 74C. With the heat shield fitted it now runs at the outside ambient.

I have seen comments that lifting the rear end of the bonnet by a few mm allows more air flow through the engine bay. In the case of the Troopy there is ample space for air flow out of the rear of the bay down past the firewall and I would think that would be so for most vehicles.

What my heat shield does is twofold: it is a barrier against radiation from the engine and also prevents hot air from the radiator reaching the battery. There is ample air entering the battery zone through apertures in the bodywork below the headlights and air can exit at the back down past the firewall.

To answer your specific question, I would not think there would be any significant advantage in any vehicle of raising the rear of the bonnet, or of raising the front either if that is what you are asking. In fact having air passing over the engine then out over the windscreen may deposit oil on the windscreen and if the bonnet were slightly open at the leading edge poses a risk of it being lifted open by the wind of the vehicle.
Cheers
Allan

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Follow Up By: Member -Dodger - Monday, Jan 23, 2017 at 15:52

Monday, Jan 23, 2017 at 15:52
A little trick I have learnt is when one is stopped for some time as when camping for the day or a lunch stop just lift the bonnet this then lets the heat disperse quickly. Rather than let the under hood area heat up from radiated engine heat. However be prepared for visitors as there is bound to be someone thinking you have problems.
I do this myself and any visitor is welcome plus we can then have chat.
All good .??????
I used to have a handle on life, but it broke.

Cheers Dodg.

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Follow Up By: Frank P (NSW) - Monday, Jan 23, 2017 at 16:09

Monday, Jan 23, 2017 at 16:09
Quoting Allan:
"I measured engine bay temperature whilst driving in suburban conditions on a mild (27C) day and the temperature at the battery was 74C. "

I did the same with my Prado, but in hotter ambient conditions, and recorded temps around the 2nd battery of around 80 degC.

This was one reason I used a dc-dc charger with a temp sensor for the aux battery. The charging voltage was reduced progressively as the battery warmed up and stopped completely at 50 degC, which is where most documentation says charging a lead-acid battery should cease.

Doing what Allan has done or getting the aux battery out of the engine bay if possible is a better solution.

I am also of the opinion that an auxiliary battery is better serviced by a dc-dc charger, whether or not it is remote from the engine bay.

Cheers
FrankP

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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 23, 2017 at 16:42

Monday, Jan 23, 2017 at 16:42
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Yes Frank, I'm sure my batteries have been hotter than 74C when ploughing through sand in the Simpson on a 40 degree day before I fitted the heat shield.

I also use dc-dc chargers for both auxiliary batteries for good charging regimes.
The charger for the engine bay battery is in the cab behind the glovebox to avoid it being exposed to high temperatures but still close to the battery.

The existing batteries have been in place for 5 years now, as has the heat shield.
I had not realised it was that long until I saw the date of the shield photo.
It's nice not to have to buy new batteries every time I fill up with fuel. lol

Now that I have got rid of the HF radio there is room to move the engine bay battery to the cab, but that can wait until I am utterly bored!
Cheers
Allan

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Reply By: Shaker - Sunday, Jan 22, 2017 at 14:46

Sunday, Jan 22, 2017 at 14:46
Did you say the batteries lasted 7 years, or that you have had multiple batteries under your bonnet for 7 years?
If they lasted 7 years I would be more than happy & leave well alone.

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Follow Up By: steamfire01 - Sunday, Jan 22, 2017 at 17:15

Sunday, Jan 22, 2017 at 17:15
Hi Shaker
During a seven year period I went though two batteries used as dual batteries, one was a deep cycle from Korr (bought via an ad in Exploroz) and the other was a Century cranking battery.
Regards
TJ
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Reply By: Member - abqaiq - Sunday, Jan 22, 2017 at 15:56

Sunday, Jan 22, 2017 at 15:56
Remember when using a wiring size table that the "distance" is the total distance of the circuit (out and back) NOT the one way distance. Fuse both ends of the interconnecting circuit (at engine bay and at the receiving battery), you have a large power source at each end, wanting to find an undesirable 'way out'.
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Reply By: KiwiAngler - Sunday, Jan 22, 2017 at 21:31

Sunday, Jan 22, 2017 at 21:31
I noticed similar trend with aux battery in my 2004 Patrol, especially when travelling through NT and FNQ

My "fix" has been to cut an additional scoop hole in the bonnet above the aux battery - seems to be doing the job as current battery has lasted longer than any previous battery installed prior to modification.

Air temp where i am currently during day is 35-40c hate to think what it is under bonnett whilst driving and towing my camper - I also pop the bonnet as soon as i make camp each night to help get the heat out whilst sitting still
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Reply By: Sigmund - Monday, Jan 23, 2017 at 07:39

Monday, Jan 23, 2017 at 07:39
My theory now about how these basic systems perform is, if measured, it's all between 50% (or less) and 70% charged. The alternator doesn't have the volts or the time or both to get to 100%.

Batteries take around 14.7 V for a bulk charge but how many alternators can produce it? The best my standard unit can do 14.1 V at the input side to the isolator (and 13.7 at the batteries).

Even if it could hit the right voltage, it would take over 30 hours to charge a depleted battery according to the 240 V charger manual (at 15 amps).

Anyway, next week I'll have a different theory!
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Reply By: Sand Man (SA) - Monday, Jan 23, 2017 at 07:49

Monday, Jan 23, 2017 at 07:49
If you are moving your auxiliary battery to the rear of your patrol, besides wire size, you need to consider how you will secure your battery.
Have you considered a "total solution" where you don't have to worry about all the technical stuff. Just purchase a complete dual battery system.
ABR sidewinder have a good product with their "Flyer" battery box which comes complete with cable and available with or without an isolator. You will need an isolator of some kind, be it a voltage sensitive relay as available in the higher priced Flyer, or a dc-dc charger of some kind which will improve battery health by providing a multi-stage charging process.
No financial interest with Derek or ABR Sidewinder, just a satisfied user.
A practical accessory available for the Flyer is a mounting cradle which enables secure fixing while enabling easy removal when necessary.
Sidewinder Flyer
Bill


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Follow Up By: Sigmund - Monday, Jan 23, 2017 at 09:31

Monday, Jan 23, 2017 at 09:31
Yeah, in that vein I'd also look at the Engel Smart Battery Box 2 - close to an all-in-one solution. Comes with a 12v charger, copes with Lithium, and has Engel, 240v, 12v and USB charging outlets. The specs sound like it has a VSR built-in but Engel say it's not for charging but for running appliances.
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Follow Up By: steamfire01 - Monday, Jan 23, 2017 at 12:43

Monday, Jan 23, 2017 at 12:43
Thanks Sand Man;
I have a full dual battery setup, using Redarc isolator and appropriate wiring serving the under bonnet setup. It's the heat that's killing the batteries.
I'll certainly consider the Sidewinder for my next vehicle.
Regards
TJ
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Reply By: Member - Phil G (SA) - Monday, Jan 23, 2017 at 07:51

Monday, Jan 23, 2017 at 07:51
I'd be using 6B&S and a 20A DC-DC charger. I assume you'll use an AGM battery and it will be fused (eg two 60A Maxifuses - at the pos terminal of the AGM as well as the cranking battery).
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Reply By: Dean K3 - Monday, Jan 23, 2017 at 22:15

Monday, Jan 23, 2017 at 22:15
First question what alternator does patrol use most "new vehicles" so to be safe for arguments point from 2000 onwards have either temperature controlled or ecu controlled alternators so start off high voltage and drop back down possibly low as 12 volts its purely designed to charge primary start battery nothing else

This is reason why I have issues with a smart solenoid system in my Prado (120 series) at time of setup bcdc wasn't around (maybe just becoming availible) and I've always had issues with discharged auxillary battery even after a whole days driving it drops off very quickly and often low volt alarm goes off in morning after just one nights stay.

idea of spending another $900 to replace existing system to bcdc isn't a easy one to stomach but know for any decent away bush trips essential
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Follow Up By: Allan B (Member, SunCoast) - Monday, Jan 23, 2017 at 22:27

Monday, Jan 23, 2017 at 22:27
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Not quite $900 Dean. On Ebay Redarc BCDC1225LV $385 and BCDC1240LV $427.
Nothing extra to pay, they drop straight in to your existing wiring at the battery.

Continue with your existing system and you will be up for $300 for a new battery anyway.
Cheers
Allan

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Follow Up By: HKB Electronics - Monday, Jan 23, 2017 at 23:59

Monday, Jan 23, 2017 at 23:59
The OP has already stated he has been using his present setup for several years.

If it has worked well to date then simply moving the battery to the rear of the vehicle and using suitable connecting cable would be the most cost effective solution.

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Follow Up By: steamfire01 - Tuesday, Jan 24, 2017 at 08:35

Tuesday, Jan 24, 2017 at 08:35
HBK;
As an expert, what do you classify as "suitable connecting cable"?
The reason I originally mentioned typical current draw from the dual battery was to demonstrate that I would not be using a large load (winch etc).
Thanks for your interest.
Regards
TJ
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Follow Up By: HKB Electronics - Tuesday, Jan 24, 2017 at 09:20

Tuesday, Jan 24, 2017 at 09:20
Expert, you'll never get two people involved in auto electrics to agree all the time so you going to find it hard to find an expert.

If your not supplying heavy loads while trying to charge the battery then 6B&S should do. If you can source some cheap heavier cable then that would be good.
Also if you can track down some teflon insulated cable, teflon insulation is tough and thin, much small physically than double insulated 6B&S.

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Follow Up By: Dean K3 - Tuesday, Jan 24, 2017 at 19:02

Tuesday, Jan 24, 2017 at 19:02
When i first sussed it out i was thinking of using a intervolt as in theory it would just bolt straight into existing infrastructure, unfortunately the auto sparkie i use

A:won't install a intervolt as they too new to market

B: will design install mounting plate for BCDC so it is cooled by airflow (redarc don't like heat) replaces the existing wiring to that compatible with redarc specs

Intervolt has ability bolt straight up whilst redarc has fly wires which need to be butt joined so 16mm2 into maybe 6mm auto is bit untowards

i know larger cable less resistance and voltage drop, didn't go to TAFE for nothing, know battery will be stuffed inside few years but way it goes and been told not spending more money either

win lotto however what she doesn't know can't be complained about
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Follow Up By: 2517. - Wednesday, Jan 25, 2017 at 16:19

Wednesday, Jan 25, 2017 at 16:19
I have noticed in caravans parks over the years the number of people who return from a day out and plug them frig into 240 volts so the aux battery is all ways flat instead of using a battery charger.My neighbor in a park up north was having a lot of trouble with his frig I suggested a flat battery and he said with his system that could not be ,well he hooked up a charger and could not believe how flat the battery was.Sloved his problem,I think this also is a major problem with short lived aux battery's.
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