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Discussion Starter · #1 ·
Just returned from the Cape and have experienced some issues with the second battery for running the fridge. Seeing that I have a 4.8 the second battery is in the back of the truck. The dual system was fitted by ARB.

The issues I had was that the second battery "died" ( showing 11 volt) even after a full day's driving. I measured voltage on the front starter battery( brand new starter battery) while running the engine and found that the same voltage could be found on the Anderson plug at the back of the vehicle ( around 13.98V or something ) I also tested the connectors to the second battery and they showed the same voltage but then connecting it all up and measuring voltage accross the second battery it only showed up 11V.

Being miles from nowhere I presumed the battery was dead. Drove to Weipa, bought a new battery and we were good from then on for around three weeks.

Two days before the end of our trip and driving around four to five hours a day I found that the new seccond battery was showing the same (11V) after a long drive. I have frequently checked all the connections and wiring but could not find anything loose.

Once home I have charged the second battery using a 240V charger and it seemed to have come good again ( ie little green light shows up in the indicator )

Can anyone offer advice on what the possible cause of this charge failure can be and how to cure it ?
 

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Take it back to ARB ?

If that isn't an option... try this... keeping in mind I don't know if you have run a Neg cable to your Aux or used a Chassis earth.

Your symptoms are of a Voltage loss in the charge cct across the Aux

First thing, with the engine running and Aux batt connected. Measure the voltage between the Pos and Neg Terminals of the Aux Battery and also the Pos of the Aux and Neg of the Cranker. If the Aux Terminal voltage is lower than the Aux to Cranker voltage say 12 Volts (Pos Aux to Neg Aux) and 13.5 (Pos Aux to Neg Cranker)respectively you have an Earth Problem and the full Alternator Voltage isn't appearing across the Aux Battery when the Engine is running


If you have run a seperate Neg Supply Cable back to the Cranker
Disconnect the Aux battery.
Connect a load like a compressor, work light or something that draws up to a few amps across the connection terminals for the Aux Battery.
With the engine running, Turn the load on and measure the voltages at
1. The Cranker (Pos to Earth) and this is your reference voltage
2. The Relay on Both Sides (Pos to Earth) and should be very close to the same as the ref Volts
3. The Aux Connection Terminals you have clipped to the load
The readings should all be within .2 to at absolute worst .5 of a Volt depending on load.

If you get a difference of 1 or more volts that is where the Voltage drop is occuring and the grunt isn't getting to the Aux Battery.

Bit hard to explain but hope that helps...
 

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nissan patrol
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Take it back to ARB ?

If that isn't an option... try this... keeping in mind I don't know if you have run a Neg cable to your Aux or used a Chassis earth.

Your symptoms are of a Voltage loss in the charge cct across the Aux

First thing, with the engine running and Aux batt connected. Measure the voltage between the Pos and Neg Terminals of the Aux Battery and also the Pos of the Aux and Neg of the Cranker. If the Aux Terminal voltage is lower than the Aux to Cranker voltage say 12 Volts (Pos Aux to Neg Aux) and 13.5 (Pos Aux to Neg Cranker)respectively you have an Earth Problem and the full Alternator Voltage isn't appearing across the Aux Battery when the Engine is running


If you have run a seperate Neg Supply Cable back to the Cranker
Disconnect the Aux battery.
Connect a load like a compressor, work light or something that draws up to a few amps across the connection terminals for the Aux Battery.
With the engine running, Turn the load on and measure the voltages at
1. The Cranker (Pos to Earth) and this is your reference voltage
2. The Relay on Both Sides (Pos to Earth) and should be very close to the same as the ref Volts
3. The Aux Connection Terminals you have clipped to the load
The readings should all be within .2 to at absolute worst .5 of a Volt depending on load.

If you get a difference of 1 or more volts that is where the Voltage drop is occuring and the grunt isn't getting to the Aux Battery.

Bit hard to explain but hope that helps...
Great response mate......

To the original poster.....what is the dual battery monitoring/controlling system?

Also, because the 2nd battery is in the back, I would be interested to know if the installer fitted-up a circuit breaker close to the 2nd battery? Reason I ask is that if there is any issue with the heavy cable between front and back (say it rubs through the insulation where it goes through the floor/firewall as an example), then there would need to be a circuit breaker in the back so that the voltage isn't earthed-out from the 2nd battery to the body/chassis etc.

Is the gauge of the cable sufficient to handle the amps required by the back battery?

If they've earthed the 2nd battery to the body, i would strongly suggest it be earthed back to the main battery.
 

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Top responses guys. My gut feeling as I was reading the initial post was also that your wiring to the aux battery is inadequate (too thin) or shorted. If ARB fitted it, I'd be putting the pressure on them to fix it free of charge. I'd probably follow the evil twin's fault finding tips first though, so you've got a good idea what they stuffed up before taking it back! I'd also be putting the squeeze on them for the cost of the replacement battery. :angryfir:
 

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Discussion Starter · #5 ·
Hi guys

Thank you very much for the great response ! I will follow Evil Twin's advice and check everything so I have a little ammo up my sleeve before going back to ARB.

To answer a few of your questions:
1) The cable used is the same size diameter as the cable on the main battery. If I had to guess 8 to 10 mm diameter.
2) The earth for the second battery is to the body ( where the fold up seats in the rear used to be ) I have however put in extra earths from the main battery to the front of chassis and also from the body to the middle of the chassis. The original earth to the engine block is there too.
3) There is no circut breaker near the battery that I can see .......
4) The dual system is the ARB type isolator

Whole thing has been in the car for under a year and there is no corrosion on any of the connctions ......

Thanks again for the response. I will report back on the remedy once found.

Cheers
 
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