Advice from an auto elec needed please

This is for my mate, he has an 05 T/D D4D hilux single battery (no duel set up) he has a 17 foot windsor caravan he bought second hand a few months ago (06 model) it has a battery in the hood compartment with 240V charger monitor set up (all done by previous owner and a good job I must say extremely neat. The van just has your standard 7 pin plug on it so does the hilux. The original owner said he use to be able to charge the caravan battery and also run the fridge in the van (3 way fridge) while driving along on 12 volts, there is a switch in the van that has 12v or 240v when driving along he was told to switch the knob to 12v this will charge the battery and run the fridge from the accesory wire from the 7 pin plug on the back of the hilux, unless using 240 volt main to power light etc when in a park to leave the switch on 12v. Now Im presuming he would need a wire to be run from the battery in the hilux to the accessory terminal on the 7 pin plug so it will send charge through to the battery in the van ?? Im also presuming the fridge is running from the van battery not actually picking up power direct from the 7 pin plug I doubt it would handle that power draw through a 6 mil wire. My asumption is the vehicle charges the battery in the van while driving and the fridge is running off the battery in the front of the van ?? If Im write I would imagine he would need a dual battery controller in the hilux so it charges the main battery in the hilux first then will switch itself over to the wire that will run down to the 7 pin plug and send the power through that to charge the van battery or can he just get away with haing a fused wire direct from his battery to the 7 pin plug ?? or will he have trouble with draing the main battery or the alternator trying to charge 2 batterys at once and end up with 2 batterys neither fully charged. Sorry for the long post but he has been told by many different people including professionals different things evertime, some saying yes others saying no you need to run anderson connections others saying you will burn out wiring etc. He doesnt have the original guys ph number any more to ring him and find out for sure how he had his vehicle set up but he told me the old guy just said you need a permant power at the 7 pin plug and all will work spot on,,,,,,,,,Regards Steve
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Reply By: Wherehegon - Sunday, Feb 28, 2010 at 16:26

Sunday, Feb 28, 2010 at 16:26
Could he do this but instead of running the red 6mil positive wire to an anderson plug he just connect it to the accessory terminal on the 7 pin plug, there is already an earth wire connecting the female and male plug. ?? Also delete the 20amp breaker he wont be needing that ????? Regards Steve
AnswerID: 406527

Reply By: Member - Shane D (QLD) - Sunday, Feb 28, 2010 at 17:17

Sunday, Feb 28, 2010 at 17:17
The wire in the plug is simply too small to run a fridge, let alone re-charge a battery, He will need much thicker wire feeding thru an anderson type plug.
The alternator will charge both batterys at once, just needs twice to time as it would to charge one
AnswerID: 406531

Follow Up By: Maîneÿ . . .- Sunday, Feb 28, 2010 at 17:44

Sunday, Feb 28, 2010 at 17:44
Yes, as Shane has posted:
"the wire in the 7 pin plug is simply too SMALL to run a fridge, let alone re-charge a battery and he will need much THICKER wire feeding through an Anderson plug - the alternator will then charge BOTH batteries at once"

There has to be a battery isolator device adjacent to the Cranking battery, say that here because I'm not going to reread the original post again to see if it was stated (:

Maîneÿ . . .
FollowupID: 676262

Reply By: Battery Value Pty Ltd - Sunday, Feb 28, 2010 at 17:47

Sunday, Feb 28, 2010 at 17:47
As I see it, this is a typical problem (charging of secondary battery) with two almost equally applicable solutions.

As it looks to me, there doesn't seem to be any isolating switch/solenoid or diode in this dual battery setup?
The second battery is just connected in parallel to the first one via 7 pin plug, switch and 6 mil wire?

If so, it would be interesting to find out what fuse there is on the second battery, as some starting current will flow through it.

To make sure things don't go bad and fry the pin 7 wire connection, the 240/12V switch ought to be on 240 while cranking, I'd imagine.

An isolation switch/solenoid basically disconnects the second battery from the first one during cranking or while the engine is off, automatically.
But it could be that the resistance of the existing 6 mil wire/plug/switch/fuse(s) is sufficiently high to limit this current to a manageable level, i.e. not blowing the fuse.
It's a hit and miss affair really.

Thus, an isolation switch/solenoid/diode offers better protection against this reverse current, with the added advantage of the second battery not being able to discharge the first one while stationary.

To your question on the batteries not receiving full charge when wired in parallel: they will receive full charge, even though there is a fridge connected to the second battery.
The thing to keep in mind is the time factors involved. Say your alternator outputs 14V to the first battery: there will be some charging current through this first battery, and also through the second battery. But because there is more resistance in the wiring to the second battery, it'll receive less charging current, hence it'll take significantly longer to have both batteries fully charged. Also, the fridge will compete with the second battery for any 'left over' current from the first battery, meaning there will be even less current available for the second battery while the fridge cycles on - extending the charging times for the second battery even more.
The alternator really doesn't bother about how these currents are divided up between loads and batteries, it'll just output 14V no matter what.

Note that the second battery's charging current is positively influenced by the depth of discharge of this battery, meaning it'll take in more charging current if it's relatively low on charge.
But this also means that the charging rate becomes very low once the battery has received more than 80% of its charge.
So this second battery will have a hard life sitting there partially discharged for much of the time.

Unless, you travel for long periods of time of course (weeks rather than hours/days) which could actually see your second battery overcharged, especially under high ambient temperatures, when the float voltage requirement could be as low as 13.3V

Nevertheless, use the on-bord 240V charger to recharge your second battery every now and then and see how it goes.
You can check the second battery voltage after 6 hours of no driving, to get an idea how much charge is left - I'd want to see at least 12.3V there on average, otherwise there would be potential for undercharging/non reversible sulfation of your second battery. And don't forget to turn your switch to 240V while stationary otherwise the first battery gets discharged as well, if I'm understanding this right.

Best regards, Peter
AnswerID: 406537

Reply By: olcoolone - Monday, Mar 01, 2010 at 10:24

Monday, Mar 01, 2010 at 10:24
What I would be doing and what is the correct way is to run the 3 way fridge on 12V DC only when the vehicle is running.

The 3 way fridge should have no connection to the battery's in the van when the vehicle is disconnected.

The Hilux really needs a DC to DC charger to get the maximum from your van battery's, if not the Hilux will only charge the van battery's to about 70% state of charge...meaning out of 100 amphour battery you may only get 30 to 50 amps max.

There are many DC-DC chargers avaliable, Ranox, RedArc, Ctek.

The Ranox has a function to turn the fridge on only when the vehicle is running, the other two don't but the other two are easier to set up.
AnswerID: 406632

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