charging camper battery

Submitted: Tuesday, Apr 22, 2003 at 18:45
ThreadID: 4512 Views:2168 Replies:8 FollowUps:3
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Hello,i am concerned that the battery in my camper may not be being charged gu patrol has two batteries controlled by an electronic controller i had an electrician fit a 6mm hot wire from the second battery to the connection on the 7 pin connection on the van then to the battery on the van. i ran two 1 amp flourous for a total of 7 hours over weekend.After driving for 5 hours the van battery was 12.3v and specific gravity reading was in the red section,the trucks batteries were 12.93v and specific gravity was slightly better .Any advice appreciated thankyou.
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Reply By: raybates - Tuesday, Apr 22, 2003 at 20:25

Tuesday, Apr 22, 2003 at 20:25
Hi Brian,
I have a DS Battery mounted on the drawbar of my caravan. I would suggest that you upgrade the cable to 8mm and fit an Anderson plug and not run these cables through the 7 pin plug which you couldn't anyway as 8mm will not fit into even the large type of 7 pin plug.
The 7 pin plugs on the market are not a very posotive connection and not suitable for carrying high amperages that may occure duing battery charging.
As far as the wiring is concerned I have run both the positive and the negative cables to their power sauce ie the primary battery.
AnswerID: 18121

Follow Up By: Homaten - Wednesday, Apr 23, 2003 at 07:32

Wednesday, Apr 23, 2003 at 07:32
10mm2 is the minimum cable size required and preferably 12mm2 using 2 x 6mm2 twin sheathed cable.
8mm cable is not of adequate size. Use Ohms law to find that out.
FollowupID: 11392

Reply By: Member - John- Tuesday, Apr 22, 2003 at 22:19

Tuesday, Apr 22, 2003 at 22:19
Ray is correct about the trailer connectors (limited to a few amps and notorious for corrosion). A 50A Anderson connector connecting both + and -ve cables directly to your camper battery. You can pick up the -ve (earth) at the rear of your vehicle but it must be a very good quality connection.

Another consideration is your alternator output versus total load in your normal driving mode, ie. 3 batteries to charge, aircon fans, numerous electronic gizzmos, engine and gearbox electronics, etc and you have a big load. Switch on your lights if night driving and the poor old alternator just will not keep up demand, causing discharge of batteries. If the alternator drive belt is a little slack you just won't get enough steam at anytime as well.

Try disconnecting you car mounted Aux battery and see if the camper battery gets fed better (after replacing cabling already referred to). An auto elctrician can also measure all the main currents in your system and quickly assess if your alternator is up to the job.

If this is all OK, you could look at installing a Piranha 150S isolator between your main battery and the camper battery. The camper battery will then only receive charge when the other two batteries are fairly well charged.

Charging 3 batteries is always going to be a challenge without solar panels on top of your camper van to give more charging capacity. Can you live on two bateries?

AnswerID: 18140

Follow Up By: Homaten - Wednesday, Apr 23, 2003 at 07:30

Wednesday, Apr 23, 2003 at 07:30
A Piranha battery isolator is just a GSL dressed up in flash colours and labels at more than double the price. You can get a GSL unit for $120 incl GST. A Piranha one will cost you around $250. I prefer the technically superior Redarc battery isolator to the GSL unit.

I agree, charging 3 batteries correctly to full voltage/capacity is a challange. You would need a manual switching unit to change between two batteries.

Do not pick up an earth on the vehicle, use the same size cable connected directly to the battery negative as you would the positive cable.
FollowupID: 11391

Reply By: Eric - Tuesday, Apr 22, 2003 at 23:34

Tuesday, Apr 22, 2003 at 23:34
The maximum rate of charge for a battery is 8-10amps depending on the temperature,your alternator will be able to do that easily. The problem is to get the voltages right, the voltage regulator uses the voltage at the ignition switch as it referance and the resistance of the wiring loom limits the current to the starting battery, if you connect you extra batteries to the starting battery you won't have the right charging voltage. If you connect directly to the alternator you will get the 14.8 volts you need. The 6mm wire and the 7 pin will be fine if the voltage is right. you can afford to lose .5 volt in the wiring if you start with the full 14.8volts. The resistance in the wire actualy protects you vehicle loom from excesive current.Measure the voltage at the alternator when the lights are on and the engine running and get you voltage reg adjusted if it is less than 14.6. Eric.
AnswerID: 18146

Follow Up By: Homaten - Wednesday, Apr 23, 2003 at 07:24

Wednesday, Apr 23, 2003 at 07:24
6mm2 wire is insufficient in size and a 7 pin trailer plug is not suitable for carrying the current to charge a second battery.
A 50 amp Anderson plug is required with a minimum of 10mm2 and preferably 12mm2 using 2 x 6mm2 twin sheathed cable.
FollowupID: 11390

Reply By: Flash - Wednesday, Apr 23, 2003 at 10:35

Wednesday, Apr 23, 2003 at 10:35
Were you by any chance running a 3 way frig at the same time?
If so you'll NEVER charge the battery properly, unless frig and battery are on totally separate leads from the alternator (theres too much voltage drop otherwise unless you ran humongous cable which is impracticle.)
AnswerID: 18169

Reply By: duncs - Wednesday, Apr 23, 2003 at 17:40

Wednesday, Apr 23, 2003 at 17:40
What condition is the bettery in to start with? How long do you leave it sitting at home without charge and do you try to charge it before you leave home.

It could be that you are asking or expecting too much.

AnswerID: 18194

Reply By: ThePublican - Wednesday, Apr 23, 2003 at 20:56

Wednesday, Apr 23, 2003 at 20:56
Brian,, ok im the odd man out,, I run a 3 battery system also ,thru a Rotronics system self fitted,,all 3 batts same make,size and age,,just over3 years old,,
Alt to batt 1 as per norm,, Rotronics to batt 2 as per norm,, then 8mm Rotronics shielded cable both pos and neg from 2nd batt to no2 and no5 on LARGE 7pin plug,,goes thru same sort of cable on camper trailer to 3rd batt,,,,
Advantage is that only one plug to worry about,one that if need be can be replaced almost any where,{ try buying a replacement anderson plug somewhere like Birdsville}
My volt/charge readings/drop at idle 500rpm .
batt 1 =14.8
batt 2 =14.75
batt 3 =14.7
AnswerID: 18221

Reply By: brian - Thursday, Apr 24, 2003 at 08:17

Thursday, Apr 24, 2003 at 08:17
Thankyou for all the replies some useful ideas,looks like i will be rewiring the rig on weekend.
Flash i left the fridge switched to 240v position while towing,thinking this meant not connected to 12v,i better check this is correct , thankyou.
Duncs cant tell how old battery is it was on the van when i bought it a couple of months ago,but your comments could well be right.
AnswerID: 18259

Reply By: Damian M - Monday, Apr 28, 2003 at 19:13

Monday, Apr 28, 2003 at 19:13
Hi All.

I'm gonna give you all my Two Cents worth of Advice..

I am an AutoElectrican and a Competent one.

If you are trying to Charge your Battery in your Camper you need to make a few checks.
In your post above, You mention that your batteries in your vehicle are charging at 12.93 volts. Well My Friend, Thats not enough. You need to be charging your batteries at 13.8 to 14.5 volts. Make sure you make your Voltage Checks with the Engine running at 2000rpm or more.
Calcium Batteries will take a higher Voltage charge. I think to 15.5 volts.

Amperage is not as critical as most Car Batteries can take almost as much current as you can throw at em but only to the suggested voltages.
If your Battery was dead falt and you Jump Started your Vehicle and The Alternator on your vehicle was rated at 80 amps, That's what the Battery would be charged at. Thing is with batteries is that the resistance is not fixed. As the battery charges to 13.8-14.5 volts, The resistance becomes higher. This reduces the load on the Alternator. At 13.8 volts, The battery may only be drawing 1amp to keep it that level.

The trailer plug cannot handle the current that may be required of it. I would seriously suggest that you fit a seperate socket that would be rated to at least 50amps. You must also understand that you do get a voltage drop through the length of wire that you are using. The more current that you would pull through the wiring, the more voltage drop. Depending on the size of the wire.

Have you ever noticed that the wiring on Vehicles is getting thinner? That's because of the current being drawn. Let's take a Tail Light Bulb. Ok, You do not need a 4mm wire to power up the Tail Lights. This is because the total amount of current that would be drawn by the tail lights is easily handled by a thinner wire and the Voltage drop that would occur is negligable for the Tail Lights to work. Now, What if we were to run the Headlights with that wire? Well, We would then get a severe drop in voltage because now we are drawing more current through the wire than what it's capable of delivering. The wire is now becoming resistive to the load. The wire may even start to get warm or even hot.

It's a pretty complex subject once you really start to get into it.

E.g: Think of your wire as a hose. How much water will come through a small hose as to a large hose. The Larger the hose the more water you can put through it.

For the people who are thinking about Buying Battery Isolators for $125.00 or more, Did you know that a $30.00 solenoid can almost do exactly the same thing? It may even be more reliable.

Regards to you all, I hope this helps. If anyone would like any information on anything to do with Automotive Electrics or Electronics, Please Email me at,
I'll be only to happy to help if I can.

Damian Mueller

AnswerID: 18617

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