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Generation 4-4 Pajero NX model 2014 -

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  #41  
Old 21-07-18
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Originally Posted by nj swb View Post
What size AGM battery do you expect to charge at 50A? How long do you expect it to charge at 50A? Lead acid batteries "self regulate" their charge current, in that they draw as much current as they want, based on the voltage available. Even under the bonnet, an AGM shouldn't be drawing 50A for long, unless it has been quite deeply discharged - which isn't good for the battery's longevity.

If you want to stick in the back, use AWG 4 or 2. It will work fine.
Manufacturers recommend limiting intial charging current to around 25% of capacity, so unless you have a 200aHr battery, you are shortening its life by charging at 50 amps.
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  #42  
Old 21-07-18
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. . . There is the theoretical possibility of the main battery losing its contact with the earth cable to the chassis which is one of the main reasons to not directly earth accessories to the negative battery terminal but to use the chassis - but if the auxiliary battery is not connected to chassis ground at all, this shouldn't be a problem - as long as I use chassis ground for any devices e.g. fridge that are connected to the auxiliary battery. . . . .
This is only an issue for radios which are also earthed via the antenna coax. If the main earth link fails, the earth current will attempt to return via radio negative lead and the antenna coax outer conductor.
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  #43  
Old 21-07-18
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. . . . . It looks like both the charging and float voltages of AGM and lead-acid batteries are within 0.1V of each other so there may be no significant ill-effects from linking them in parallel as you describe. . . .
This is the specification on my Remco AGM - Float 13.5 -13.8, Cycle 14.4-14.7. The actual voltage varies with temperature of the battery.
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  #44  
Old 21-07-18
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Originally Posted by Pajshomoneroguntero View Post
. . . The big bonus of the system is that I've got both batteries available to share the load whilst winching. Granted there is a bit of a run from the back of the car but if the winch is pulling 400A that's 200A from each battery and it will be less because the alternator is providing current during the winching operation too. . . . .
Even if you ran 0Ga wiring to the rear battery, there's is no way you'll get equal current sharing between the two batteries.

Also assuming the Rear battery is a Deep Cycle and not a starting battery, it would supply much less current to a winch, even it were directly beside the Starter Battery.
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  #45  
Old 21-07-18
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Originally Posted by Mike DiD View Post
Even if you ran 0Ga wiring to the rear battery, there's is no way you'll get equal current sharing between the two batteries.

Also assuming the Rear battery is a Deep Cycle and not a starting battery, it would supply much less current to a winch, even it were directly beside the Starter Battery.

Deep cycle do not like a large amount of amperage being taken from them in a short space of time. They prefer long, low draw periods with recharging often to keep near full charge. .
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  #46  
Old 21-07-18
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Originally Posted by miniyazz View Post
. . . Do you have a setup using this principle, and if so, what gauge wire did you use? It is certainly a strong argument for mounting the second battery in the engine bay - but that has its own problems with added heat likely to shorten its lifespan, especially given I am based in Central Aus.
No, I have an AGM Battery in the rear compartment, manually plugged/unplugged to connect directly to the Starter/Alternator. I have never found the NX battery voltage to drop below 13.9 volts when the RPM is above Idle and have never had a problem with charging the Auxiliary. I have a 4Ga wire running from Starter +ve to the Rear with the Aux -ve connected to the body.

Based on actual testing of voltage drop, the body return has the same resistance as a 6 Ga cable.
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  #47  
Old 21-07-18
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Originally Posted by Mike DiD View Post
Even if you ran 0Ga wiring to the rear battery, there's is no way you'll get equal current sharing between the two batteries.

Also assuming the Rear battery is a Deep Cycle and not a starting battery, it would supply much less current to a winch, even it were directly beside the Starter Battery.
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Originally Posted by Dicko1 View Post
Deep cycle do not like a large amount of amperage being taken from them in a short space of time. They prefer long, low draw periods with recharging often to keep near full charge. .
Correct and understood before I decided to go this way. The secondary battery I have was touted to be dual purpose and I've just put a YellowTop in as the primary. I might not get equal current sharing but with a DCDC down the back I get nothing and I'm left with the potential of pulling 475A out of one battery (less alternator supply). That is a lot of load for anything that fits under the bonnet. Perhaps I look at my secondary battery as more consumable than what others would do. In any case I am happily justified with my decision.
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  #48  
Old 21-07-18
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Quote:
Originally Posted by nj swb View Post
What size AGM battery do you expect to charge at 50A? How long do you expect it to charge at 50A? Lead acid batteries "self regulate" their charge current, in that they draw as much current as they want, based on the voltage available. Even under the bonnet, an AGM shouldn't be drawing 50A for long, unless it has been quite deeply discharged - which isn't good for the battery's longevity.

If you want to stick in the back, use AWG 4 or 2. It will work fine.
Fair point. Adjusting the figures to say 30A then should cover approx 25A battery charging + powering a fridge other relatively low powered electronics, with approx drops of - 0G=0.14V, 2G=0.22V, 4G=0.34V, 6G=0.54V.


I'm now leaning back towards a DC-DC charger given a V3 IDC25 is available for <$250 with the flexibility to add a solar input and less of a headache about wiring..
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  #49  
Old 22-07-18
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Quote:
Originally Posted by Pajshomoneroguntero View Post
Correct and understood before I decided to go this way. The secondary battery I have was touted to be dual purpose and I've just put a YellowTop in as the primary. I might not get equal current sharing but with a DCDC down the back I get nothing and I'm left with the potential of pulling 475A out of one battery (less alternator supply). That is a lot of load for anything that fits under the bonnet. Perhaps I look at my secondary battery as more consumable than what others would do. In any case I am happily justified with my decision.
With so many variables, the only reliable way is to actually measure the current while winching.

a) DC Clampmeters are quite cheap. So handy when you don't want to open a wire to measure its current.

b) Measure the voltage drop across the wire from the Rear Battery - use any thin bit of wire from the +ve of the Starter Battery to the Multimeter -ve. Use the length and size of the Battery cable to work out its resistance and then calculate current.
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  #50  
Old 22-07-18
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Originally Posted by Ian H View Post
Lots of different opinions here but caravans and campers normally charge via an Anderson directly linked to the starter battery. My Tvan has its own Redarc with charge coming from the starter battery to charge the 2 105ah batteries, which is the set up Track Trailer insisted on before I could hooked up and also confirmed by my auto electrician when I got the wires tested. Charging 3 batteries in the trailer I'd expect you need (or already have ?) a charger in there.

My car also has a Redarc charger for the aux battery which runs the fridge/freezer.
There's a wiring diagram on the Redarc site showing how to connect everything as per the picture below.



sAME SET UP AS MY nw BUT i USED ONE THICK WIRE FROM MAIN TO AUX AND BRANCHED OFF WITH ANOTHER TO TRAILER , WHERE A pROJECTA 25AMP DC/DC IS FITTED TO FEED X 120 AMP FULLRIVERS. wORKS WELL AND SIMPLE
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