Caravan battery electrics ??

Submitted: Monday, Mar 26, 2018 at 11:11
ThreadID: 136474 Views:1525 Replies:6 FollowUps:4
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I have a 96 Coromal Apollo 400 which didn't come with a house 12v battery but somewhere along the line of ownership someone has added one.

I am not particularly electronic savy but my question today is, if that battery went flat or say down to 9v would it affect the electric brakes, indicators etc., when hooked up and running with the car. If so, is this type of set up normal when adding a battery to the van or has it been done by a 'backyarder/DIYer'?
Or should the power from the car suffice to run these things. I know the battery is being charged by the car's alternator but does a flat van battery throw a spanner in the works?

I am charging this battery as I write this and hopefully this will correct my problems but just interested in your comments.

many thanks,

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Reply By: baznpud - Monday, Mar 26, 2018 at 11:57

Monday, Mar 26, 2018 at 11:57
There are people on here better qualified to answer this than me, but i think you will find that the house battery has nothing to do with the indicator, brake and tail lights, these should be controlled from the vehicle, same goes for the electric brakes.
Go caravaning, life is so much shorter than death.

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Follow Up By: Allan B (Sunshine Coast) - Monday, Mar 26, 2018 at 12:12

Monday, Mar 26, 2018 at 12:12

Who could be sure how your house battery has been wired. However, I think Baz is probably right that it powers only the van internals and has "nothing to do with the indicator, brake and tail lights". And it certainly should not either.

If you want to be sure, simply disconnect the house battery and then, with the car connected to the van, operate your vehicle lights and brakes..... if they still work then they are being supplied from the vehicle as they should be.

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Follow Up By: Allan B (Sunshine Coast) - Monday, Mar 26, 2018 at 12:20

Monday, Mar 26, 2018 at 12:20
Wayne, further to the above, what problems have you been experiencing?

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Reply By: Member - Bigred13 - Monday, Mar 26, 2018 at 12:12

Monday, Mar 26, 2018 at 12:12
Hi Wayne ,I would think the battery was put in to run lights etc ,it would not in any way affect your lights,indicators,or brakes as they are supplied from the tow vehicle .The only time your van battery powers the brakes is if it has a break away system fitted ,which is a cable that attaches to you vehicle and in the event you and your caravan part company ,while driving ,the cable will disconnect a switch which will activate the brakes on the van ,to stop the van from doing too much damage to itself and anybody else .The battery break away system will hold the van on a ,I think 15% slope for at least 15 mins .
If your battery is down to 9 volts ,it is well below being flat and if it is an AGM battery it is on its death throws ,12.2 volts is considered flat or 50% discharged .
Just for your info ,if you are charging solely from vehicle ,your van battery will ever only be charged to 75% of its capacity ,as alternators are designed to top up start battery ,not charge aux batteries to 100% .In other words if your Aux battery is say 100 AH ,the most you will get into it is 75AH ,and for an AGM battery to last it must not be taken below 50 %, so in actual fact you have only 25 Ah to safely use .A portable fridge will use approx 4 amps per hour ,so you will run it for 6 hrs only ,without charge ,a three way fridge will use 11 Amps per hour ,so two hours will be all you will get safely without damage to your battery .
If you require any more info on how to run your aux battery ,send me a PM and I will gladly help
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Follow Up By: Allan B (Sunshine Coast) - Monday, Mar 26, 2018 at 12:54

Monday, Mar 26, 2018 at 12:54

Your expression about charging from "solely from vehicle" is simply not correct.
A correctly installed and wired system is quite capable of charging an auxiliary battery from the vehicle alternator to its full State of Charge. Problems come about with inadequate wiring and connections.
Long runs of wiring require large cross-sectional cables or dc-dc chargers installed at the auxiliary battery.
Additional charge input from solar etc. may be required if the auxiliary battery is not receiving frequent charges from the vehicle.

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Follow Up By: Member - rooster350 - Monday, Mar 26, 2018 at 14:52

Monday, Mar 26, 2018 at 14:52
Our caravan battery (100ah dc) is charged up by the generator of our car while we are traveling and it certainly does get charged its full capacity , and has been the case for some years now...cheers
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Reply By: Nomadic Navara - Monday, Mar 26, 2018 at 12:20

Monday, Mar 26, 2018 at 12:20
The van would have come with all the navigation lights wired to their individual pins in the trailer plug. These would have been connected to the Australia standard as shown in this page. You will notice one of the pins is allocated for "reverse," which means reversing lights if the trailer was fitted with them. As most caravans were not fitted with those lights the van manufacturers "borrowed" that pin to power the house lights from the tugs battery and also power the fridge on 12 V.

Subsequent owners should have simply added the van battery on that house lighting circuit. They may also have added a battery charger as well. Unless they did something silly there should be no connection between the brakes and navigation lights with the house lighting system.

There is a major problem with the original wiring system to the house system. None of the manufacturers provided heavy enough cabling. It is so light that the fridges did not work properly on 12 V (that is why people will tell you that fridges do not work properly on 12 V - if you rewire with heavier cable they will work properly.) That light cable will also result in your battery not charging properly as well. In fact if you try to run the fridge whilst charging the battery then the battery will not receive any charge due to the voltage drop.

If you wish to charge your battery effectively from the tugs alternator then I suggest you rewire the battery with 8 or 6 gauge cable all the way from the tugs battery via an Anderson connector. I would also suggest you need to do the same with the fridge if you wish to power it from the tug whilst travelling (but use an ignition switched relay to disconnect the power to the fridge whilst the motor is switched off or you will bugger your starting battery. See the following diagram.
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Reply By: HKB Electronics - Monday, Mar 26, 2018 at 18:26

Monday, Mar 26, 2018 at 18:26
Short answer is yes it could affect your electric brakes, it depends on how the battery has been wired in.

If the battery has simply been connected across the vans electrics and the van wasn't wired for the battery then the large inflow of current into the flat battery could case a voltage drop across the negative wire from the car and this could impact on the electric brake performance of the van till the current drawn by the battery decreases.

The van will most likely be grounded by the hitch and safety chains etc so they would may cancel out the above somewhat but it depends on the conductivity of them etc.

If the van has a breakaway system then it may also be affected though as I don't have one on my van I don't know how they are wired.
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Reply By: swampy - Wednesday, Mar 28, 2018 at 19:27

Wednesday, Mar 28, 2018 at 19:27
First your vehicle runs your van lights, elec brakes etc

Do u have breakaway brakes ???

The aux battery runs accessories
compressor fridge 12/240v
camping led light

3 way fridge
12v vehicle supplies power whilist driving only [ignition operated]
12v power can come from van aux battery if fitted with movement switch
240v van park
gas camp site

Van Battery charging
dc to dc charger
direct vehicle altenator charging
Both use very large cables . Good voltage is important

Solar on van /portable min 200watts
240v 25 amp min charger

Battery Protection
Low Volt disconnect mounted to aux van battery [+] post [12.00 volt cut off ]
Battery isolater in [-] aux van battery post
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Reply By: Member - McLaren3030 - Thursday, Mar 29, 2018 at 11:18

Thursday, Mar 29, 2018 at 11:18
Hi Guys, All the advice given in these replies are predicated on one thing, the trailer plug & van are wired to the correct standard. First thing I would be doing is going to a reputable Auto Elec. and have them check all wiring on both the van and the trailer plug on the car, then be guided by what they find.

I have seen a number of vans/trailers & trailer harnesses on cars that have not been wired to the standard.


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