Oh No Another Battery Question

Submitted: Wednesday, Mar 28, 2012 at 20:33
ThreadID: 92855 Views:3211 Replies:3 FollowUps:9
This Thread has been Archived
Hi Folks,
Sorry to bore you with another battery question but I have a N70 cranking battery under the bonnet, a AC Delco Marine 97 AH auxiliary battery connected via a Redarc battery isolator the auxiliary battery is I presume connected via a anderson plug (there is still power at the anderson plug with the car turned off) to a SSB 130 AH AGM deep-cycle battery in a T-Van and I have just had my alternator overhauled. The AGM battery is helped topped up by a 50w solar panel through a Sunguard Solar Controller.
The question is should I install a redarc 12/40 charger for the AGM battery with the intention of adding 150w of solar latter. I've searched most of the battery threads and was wondering whether I'm one the right track.
Thanks in anticipation.
Back Expand Un-Read 0 Moderator

Reply By: Member - Sonshine - Wednesday, Mar 28, 2012 at 21:25

Wednesday, Mar 28, 2012 at 21:25
Hi Graham,

I have a similar setup and was wondering also about the need for a Redarc 12v charger for the battery in the CT.

A this stage, I have opted just to connect the CT battery directly via 6B&S dual cable all the way through to the Aux battery on the tow vehicle.

I realise this will not provide the optimal voltage to achieve the best charge, but should give it a good kick along while on the move.

The battery life will probably not be as long as if I had the 12V Redarc charger in the CT, but I'll save the cost of the Redarc and wear the cost of a new battery 2 years down the track if I need to.

I have a solar panel on the Van and I have just purchased a 120W portable folding solar panel with its own regulator for charging via the CT Anderson.

Will let you know how it goes.

AnswerID: 481674

Follow Up By: Member - Graham N (SA) - Wednesday, Mar 28, 2012 at 22:46

Wednesday, Mar 28, 2012 at 22:46
Thanks Garry for the reply,
It may be that if we leave out the charger both the auxiliary battery and c/t battery will run, in my case, the 80 ltr Engel in the tow vehicle. I've replaced all the batteries and overhauled the alternator in the last six months so I guess I had some thing wrong with my system.
Thanks again
FollowupID: 757014

Follow Up By: Member - Sonshine - Thursday, Mar 29, 2012 at 09:54

Thursday, Mar 29, 2012 at 09:54
Hi Graham,

Yes, I think that would be possible, having both the Aux and CT batteries effectively in parallel.

I would recommend 6B&S dual cable if you are looking to charge the CT battery from the tow vehicle when on the move. Without the CT 12V charger, you will need every volt you can get at the CT battery.

I expect that I will probably NOT connect tow and CT when camped. The Tow Aux will handle the car fridge, and I will leave the CT battery to handle just the CT needs.

If camped out for some days without travelling, then the portable Solar should charge both Tow Aux and CT batteries just fine.

All good fun, Isn't it?
FollowupID: 757034

Reply By: Member - Captain (WA) - Thursday, Mar 29, 2012 at 02:02

Thursday, Mar 29, 2012 at 02:02
Hi Graham,

I have a simialir setup, N70Z cranker and aux in the crusier, then 2x120A/hr AGM's in the camper. I tried running with large wiring to the camper (63mm2 vehicle, 20mm2 camper) and I could not get sufficient voltage to the camper batteries - was only getting just over 12V when the batteries were needing recharging.

In older vehicles, the alternator puts out a continuous 14.2V or thereabouts, so by the time you have some line losses to the camper, you are still getting a decent charge.

But newer veicles like the 200 series cruiser have temperature compensated alternators. What this means is that the charging voltage is often at 13.2V after the veicle has warmed up. Factor in line losses to the camper and there simply isn't sufficient voltage to charge the batteries.

So I have since installed a Redarc 12/40 in the camper and it certainly keeps the batteries topped up. Not everyones vehicle has the low charge voltage issues so the 12/40 is not always the best solution, but for my circumstances it was.


Its not what you drive, but how you drive it!
LC 200 + AOR Quantum+

My Profile  My Blog  My Position  Send Message

AnswerID: 481698

Follow Up By: Member - Graham N (SA) - Thursday, Mar 29, 2012 at 08:16

Thursday, Mar 29, 2012 at 08:16
Hi Captain,
Thanks for the reply I'll check out the voltage from my vehicle and take it from there.
FollowupID: 757025

Follow Up By: Member - Sonshine - Thursday, Mar 29, 2012 at 09:57

Thursday, Mar 29, 2012 at 09:57

Thanks for sharing your experience with this.

At this stage, I haven't gone the 12v Redarc route, but I WILL measure the voltage at the CT battery when charging.

What do you think would be the minimum acceptable charge voltage at the CT Battery?
FollowupID: 757035

Follow Up By: LeighW - Thursday, Mar 29, 2012 at 10:01

Thursday, Mar 29, 2012 at 10:01
Many are fitting booster diodes to current model vehicles to up
the charge voltage, these devices work very well with no reported
adverse affects and at a fraction of the price of DC DC charges well
worth a look.

Lifetime Member
My Profile  Send Message

FollowupID: 757037

Follow Up By: Battery Value Pty Ltd - Thursday, Mar 29, 2012 at 10:58

Thursday, Mar 29, 2012 at 10:58
Hi Leigh,

interesting point you're bringing up.
Just the other day I had a customer with a late model Prado with this diode boosted alternator.

He was a bit cautious about the unregulated high charging current this increased voltage would cause through a discharged auxiliary battery.
I told him this may or may not be a problem, depending on the size/length of wires involved.

Since the internal resistance of a discharged battery is 4 or 5 times higher, battery heating may become a problem under high charging current conditions.
And since higher battery temperatures decrease the gassing threshold, it'll start gassing at a lower charging voltage.

At 25 degrees, gassing starts at about 14.2V, but this threshold could be as low as 13.6V @ about 50 degrees.
Because the alternator happily pushes 50 amps and more through the battery at this voltage level, and electrolyte disappears at the rate of about 1 gram/Ah while in the gassing region, there's going to be some loss of electrolyte.

Counter measures are thinner and longer wires which restrict the max charging current somewhat.
And you only have to reduce the max current by 30% to achieve 50% less heating (I^2*R), which could be all it takes to keep outside the gassing region.

Aim for at least 20 milliOhm of wire resistance: for #6 wire, that's a length of 14m, for a distance of 7m between aux battery and alternator.

Going heavy and short in wire size in connection with a diode boosted alternator is a good recipe for a dead battery half way down the track.

Another trick to overcome the high charging current problem is, to simply install a second aux battery in parallel.
This helps in two ways: the high alternator current is split between the two batteries, and secondly the depth of discharge will be lower, thus the batteries have lower internal resistance which makes for less heating.

cheers, Peter
FollowupID: 757041

Reply By: Member - Phil G (SA) - Thursday, Mar 29, 2012 at 13:48

Thursday, Mar 29, 2012 at 13:48
Gday Graham,
Not sure what gear you're running in the Patrol or the Tvan. But if you're like most Tvan owners,, your fridge is in the vehicle and your Tvan battery is just used for lights/water pump/radio.

My Tvan's battery is usually an old cranking battery because I don't use much power (only LED lights, water pump, shower and occasionally the stereo). Its kept topped up by a 65W solar panel on the roof and simple anderson plug connection when travelling.

The vehicle has the 2 fridges so it also has the 2 aux batteries and the 120W folding solar panels because it consumes most power. It also means I put a lot of charge back into the vehicle's batteries when I go for a drive.

In your case, I don't think there is any point in getting a DC-DC charger in the Tvan unless your fridge is also in the Tvan, or you have another power hungry appliance in the Tvan.

AnswerID: 481729

Follow Up By: Member - Graham N (SA) - Thursday, Mar 29, 2012 at 20:08

Thursday, Mar 29, 2012 at 20:08
Hi Phil,
you're spot onto what I am running in the T-Van and tow vehicle, during the last six months I've replaced all batteries and overhauled the alternator. Probably the alternator was slowly dying and caused all the other problems, the T-Van battery was about six years old.
Having bought a expensive AGM battery for the van I did not want to kill it unnecessarily but I think you are right the 50 w solar panel and a little help from the anderson plug will keep it topped up.
Thanks for the reply and happy T-Van travelling.
FollowupID: 757087

Follow Up By: Member - Phil G (SA) - Thursday, Mar 29, 2012 at 20:58

Thursday, Mar 29, 2012 at 20:58
Gday Graham,
Out of interest I also bought a 130Ah SSB AGM - arrived last week. I've got a spot in the cool of my canopy for it (its my 3rd battery in the landcruiser). But it will be running the 2 engels, and I've installed a CTek D250S for a couple of reasons - firstly, its an isolator, secondly, it limits the charge current to 20amps so my alternator can't hit it with too many amps and kill the battery, and thirdly it takes the input from my folding solar panels.

The AGMs get killed in a few ways - too much heat; too many amps from an alternator and being chronically undercharged.

So by mounting your SSB AGM in the Tvan, it won't get too much heat, it is highly unikely to get too many amps because of the distance from the alternator, and if you charge it on a 3 way charger every month or two when its sitting at home you'll keep it in good shape. A major issue with the Tvan is that it has a voltmeter connected all the time. this voltmeter consumes a trickle of current but its enough to run the battery flat when its in storage. I've put in one of those kill switches in the main earth lead at the battery so when its in storage, there is no way the battery can be quietly discharged.

FollowupID: 757100

Follow Up By: Member - Graham N (SA) - Friday, Mar 30, 2012 at 07:06

Friday, Mar 30, 2012 at 07:06
Thanks for that Phil, I'll organise a kill switch for the battery but hopefully it doesn't sit around for too long.
FollowupID: 757125

Sponsored Links