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Discussion Starter · #1 ·
Morning,
Had a search on this, but couldn't find anything obvious in the forum to cover this - please feel free to refer me to another thread if you know of one.

I have an ARB duel battery system that came with my car from purchase. I have noticed that the second battery doesn't seem to charge via the alternator. The reason I believe this is that the battery takes a long time to charge via the battery charger when plugged into the wall and I'd expect it not to be the case.

My father in law fed back to me that (and not sure how much truth there is in this) the second battery would never charge until the primary one is fully charged - this is what ARB suggested. I cannot confirm this 100% either way through testing as I only drive my forbee on weekends if that - I get the bus to work.

Can someone please confirm for me that the second battery should charge all the time or would not charge until the first one is full? This dual battery system is not real fancy - has no gauges on it to tell you any voltages, etc... I probably need a new one.....

Any info would be useful as I really don't understand the methodology in charging batteries in a duel battery system.

Regards
KR
 

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I have the ARB smart solenoid (almost the same as Redarc) and what it does is simply switch on (after about a 5 min delay from starting) when the voltage gets up to 14.1 or some pre-set voltage about there to allow the main battery to get all the charge topping up after starting. Then it stays connected till the voltage drops to 12.8 or something where it senses that the main battery needs all the charge again, or when you switch off the ignition.

The little earth wire on the ARB solenoid can cause it to stop working. I had a problem and after fiddling with the earth I heard the solenoid click on. Touched the earth again and click off. So I replaced the earth wire and it is all good again.

1. So first check that the solenoid is functioning and connect a V meter or multi meter to see when the solenoid switches on.

2. Have a look at the thickness of wiring as that can cause voltage drop to the second battery making it charge slowly.

3. The next part of it is due to the type of battery:
• Deep cycles can take a long time to recharge and;
• How much power you are using, are you using more than you can recharge with air-con, spot lights, fridge, radio, DVD, etc running while driving, you could be using enough power that the dual battery is not getting enough charge.
 

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GQ Dual Cab. TD42Ti with fruit.
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My understanding of basic dual battery systems is that this is a common problem. You have a main battery that is almost fully charged and a auxilary that is pretty low after being parked for a couple of days. So the regulator senses what? One good battery and one flat one. So it never quite charges the flat one as good as a direct charge from a charger will. Auto eleccy told me this.

Perhaps some of the big dollar systems may address this problem. Not sure.
 

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My understanding of basic dual battery systems is that this is a common problem. You have a main battery that is almost fully charged and a auxilary that is pretty low after being parked for a couple of days. So the regulator senses what? One good battery and one flat one. So it never quite charges the flat one as good as a direct charge from a charger will. Auto eleccy told me this.
First off and this is not aimed at you GQshayne but for someone “posing” as an auto electrician to make such a grossly inaccurate statement show he needs to get back to school.

Hi geordie, neither your alternator or your isolator has any idea what so ever as to the state of charge of ANY of the batteries in your vehicle.

Most isolators simply monitor the voltage level on their input terminal. When that voltage reaches a per set level, the isolator either turns on, or some go through a short delay then turn on.

These isolators DO NOT know if your cranking battery is fully charged or if it just had enough capacity to start your vehicle and is now nearly dead flat.

When you read advertising statements like “the isolator waits till the cranking battery is fully charged before charging the auxiliary battery” are nothing short of delusional adverting hype.

There are a couple of very expensive dual battery systems that actually monitor the cranking battery and charge it separately but any vehicle with an alternator with an output capacity of 70 amps or greater, can easily charge two or more batteries at the same time, so there is actually no need to separate batteries to charge them off your alternator and by charging them at the same time, you need less driving time to charge all your batteries.

Next, as above, alternators have no idea whether one battery is fully charged and another is not.

Alternator output current is based on the loads being applied to it. If a battery is fully charged it will only apply a very small load on the alternator but if another battery in the system is low it will place a large load on the alternator.

But if you turn on your driving lights or turn up your sound system, you will place similar loads on the alternator and again, the alternator has no clue as to what is placing a load on it, it just works to produce the current needed to meet the different loads.

So as you can see, there is no reason why your auxiliary battery would not charge just because your cranking battery is fully charged.

The most common cause for batteries not being fully charged is because a vehicle is not driven long enough to allow the alternator time to fully charge all the batteries in a system.
 

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What Drivesafe said x 2..

As has been posted many times, these units (no matter who wacks a brand on them) ARE NOT charge regulators, they are voltage sensitive relays.

A VSR will close when the Alternator supply voltage reaches a certain level totally irregardless of battery state of charge or the currents flowing in circuit.

In a paralleled dual battery application VSR's stop the Cranker discharging thru a load connected to the Aux and that is all. Anyone who "authoratively" tells you they will charge the Cranker to 100% or thereabouts before switching the Aux Battery into circuit OR conversely when the Cranker is 100% either won't switch in or if they do they restrict the current flows is full of Kaka .

When the Aux is in circuit it is seen as just another load like say Driving Lights, Cranker Battery, Heater Fan or whatever. The Alternator will supply whatever current (within specs) that the Alternator regulator (which is a voltage "regulating" and current "limiting" regulator) and loads will accept and that includes the equipment hanging off the Aux like a Frig or whatever if the VSR has made the circuit.

Out in the boonies I charge 3 sometimes 4 batteries in a parallel config off my Redarc and have absolutely no hassles unless a battery is shot.
 

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Discussion Starter · #6 ·
Thanks for your responses here guys. I've done a little more homework. Started the car and took some voltage measurements on the primary battery and also the seond one. I actually too one across the dual battery solenoid - sorry if my wording is wrong here - I'm not tech savvy with this stuff.

Anyway, the measurement I got was around 14 volts with the car running.
So it suggests that it is working. I just would have thought that second battery would not charge for as long as it does on the charger thats all..... wanted to prevent an issue before it happened - if there was one to begin with.

Funny thing is that when I charge the batteries in my car, I charge the second battery first and it can take anything up to 3 or 4 hours. I then charge the first battery and it charges in no more than 30 minutes.

Usually, when I use the second battery I have driven 2 hours to where I want to go and then I drive 2 hours home. Would this be enough if all I was running was a engel fridge, a light (fluro 5 watt) and a CB. The run time was not very long - just a few hours for the light, an hour for the cb and all night for the fridge before a 2 hour drive home.

Anyway, I intend to drive the car a lot over the Christmas period so I'll keep a close eye on it. Once again, thanks for your feedback so far!!
 

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GQ Dual Cab. TD42Ti with fruit.
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No offence taken, I am simply passing on what I was told. Made enough sense to me at the time, and to an extent still does.

In regards to the charge time, if it has been run down a lot overnight then two hours may not be enough to charge it again on the trip home. Mine would not be after a weekend trip.
 

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BLACK BETTY
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Just think of the 2 battery as water tanks. If you have one tank empty and one full then open the tape between the two the water will level out between the 2 tanks. You then have 2 half full tanks. If you then put water in one tank both tanks will then fill at the same rate. Just twice as slow.

Well the theory works for me.
 

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Thanks Drivesafe and Evil twin,
good explaination, I get what you are saying about the Smart solenoid not really voltage sensing on the main battery charge state (not being quite so smart or is that a Smart marketing ploy).

I have had two problems with my ARB system, one was it not connecting at all, which turned out to be earthing resistance from corrosion in the piddly and loose crimp on connector they used.

The second problem was that I got the biggest 115amp hour wet cell Trojan battery as I could fit and thought that would be the ducks nutts for running my fridge forever. The problem was that once it had been run down for a couple of days at camp, it would take forever (6 to 8 hours) to fully charge while driving. This often caused problems as it would not be fully charged when I stopped for the next night. Worse when driving the last few hours at night with the extra power consumption of lighting, aircon, fridge etc.

I now have given up on the monster deep cycle battery idea and instead have two identical batteries that are dual purpose cranking and although bit lower deep cycle capacity, they both charge at the same rate. Can both be linked for extra starting and winching.

Solar pannels on the roof keep the third battery running the fridge constantly but can be switched over to run the fridge from car batterys or solar pannels can charge a flat battery if I get stuck.
 

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Hiya Geordie,

Taking a while to top off the 115 AH jobbie wouldn't suprise. I run two Supercharge N70 all rounders rather than a humungous deep cycle under the bonnet for the same reason. My third and fourth batteries are in the CT and are also N70 all rounders

I believe the ZD30 Alternator reg is a 3 stage reg but happy to be corrected if it isn't and the last stage of the regulation is voltage limited current regulated which essentially means trickle charging. Normally a Cranker battery starts at 100% and drops only a very small amount when starting the donk so charging is designed for only a small demand to restore 100% SOC and also to get the best possible battery life out of a Cranker.

Perhaps Drivesafe or someone totally familiar with the Regulator program will know more or correct any fallacies (read BS) in the above
 
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