connect or disconnect ?

Hello everyone,Recently I was talking to a neighbour who has one of those isolating switches installed so that his car battery doesn,t drain flat whilst parking his van overnight. I have a 7 point flat plug and an Anderson plug connecting a DC battery in than van via a 6mm cable to the car. Why is a isolator switch needed when all u have to do is disconnect the 2 plugs if you stop for any length of time, Is it necessary to disconnect all leads from the car and van when stopping overnight? Thanks johno
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Reply By: Gronk - Saturday, May 19, 2012 at 08:21

Saturday, May 19, 2012 at 08:21
An isolator is NOT long as you don't forget to unplug the anderson plug..

But normally, you shouldn't need to unplug if its only overnight........the combined capacity of both batteries should be plenty for overnight ( depending on what you are running in the van )

A multimeter is what you need...that way you get an idea of what your system is doing, and roughly how long you can leave things hooked up..
AnswerID: 486197

Follow Up By: johno59 - Saturday, May 19, 2012 at 08:48

Saturday, May 19, 2012 at 08:48
Thanks Gronk, Why just the AP and not the 7 point plug? thanks johno
FollowupID: 761439

Reply By: olcoolone - Saturday, May 19, 2012 at 08:50

Saturday, May 19, 2012 at 08:50
Well the same thing could be said about having a key with a remote to unlock/lock your car..... can't you just use the key.... in simple terms it comes down to convenience.

Depending how you car and van are wired for 12v you may need or not need to disconnect.... if it has been wired in a way that the 3 way fridge will run on 12v when the car is not running then yes you have to disconnect.

Your average caravanner that we see through our workshop doesn't have a dual battery set up or an isolator fitted meaning when they stop at a country town for a look chances are their 3 way fridge is going to keep running flattening the starter battery in about 2 to 3 hours.

Some installs use an ignition trigger to a relay so when the car is turned of it stops power going to the 3 way fridge.

Some people still prefer this method but it's much cheaper and better to install a electronically controlled isolator.

One other thing; 6mm cable is way under sized for what you are trying to achieve.

AnswerID: 486199

Follow Up By: johno59 - Saturday, May 19, 2012 at 10:37

Saturday, May 19, 2012 at 10:37
Its 8mm cable installed by our local AE johno
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Reply By: PJR (NSW) - Saturday, May 19, 2012 at 09:09

Saturday, May 19, 2012 at 09:09
Please do not let this little question hijack Johnno's thread but I have a related question.

We are getting a third battery and an isolator installed in the car in few weeks.

My question is: Is there any reason why we cannot control the isolator with a connection to the starter solenoid? So that all batteries crank the motor without the drivers intervention.

Please do not criticise the choice of three batteries as we have our reasons.


PS If the moderators consider this OT then please mods let me know and I will start a new thread. I cannot find it.
AnswerID: 486202

Follow Up By: Racey - Saturday, May 19, 2012 at 09:51

Saturday, May 19, 2012 at 09:51
I have a 75AH Thumper battery as a third battery in our cruiser, which is used to run a 40ltr Engel frig. The Thumper is charged via an Anderson plug mounted behind the rear seats. This Anderson plug is connected in parallel to the Anderson plug at the back of the cruiser to charge the van batteries. Both plugs are connected to a Redarc relay as an isolator from the main batteries, which is a standard setup.

Initially each night I was disconnecting the plug to the van and found the 75AH thumper was not large enough to run the Engel as a FREEZER over night. In one instance the thumper voltage was down to 8.5 volt, which is not good for any battery. So now I leave the van connected to the cruiser which gives a total of just under 300AH of battery capacity for the van and Engel.


FollowupID: 761444

Follow Up By: Dust-Devil - Saturday, May 19, 2012 at 11:32

Saturday, May 19, 2012 at 11:32

There is not one reason in the whole wide world why you cannot do as you have hypothesised.

It's just what you use and how you go about it that matters.

FollowupID: 761451

Follow Up By: PJR (NSW) - Saturday, May 19, 2012 at 11:37

Saturday, May 19, 2012 at 11:37
We have two fridges in the back and use these Jaycar battery protectors to turn off the power to the fridges if the battery got low. One for each fridge.

They work well. And on an overnight stop the fridges were not off for too long to spoil anything. All inside was still frozen in the smaller 20L and nice and chilled in the larger 40L.

But now to eliminate all that worry we are splitting the system imto a single crank and a double accessory setup with redarc smart start controller.

For accessories (the fridges) we have an extra fused 12V outlet (cig lighter o/p) in the back of the car running straight off the battery. On another circuit from the batteries, there is an also additional three outlet one behind the console on the floor.

You may want to consider the same for the fridge in the back.
FollowupID: 761452

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