Hello Jules, Lady and Gentlemen
I am going to give you guys a shortened version of the experience I have with dual battery systems. Unfortunately this is still quite a story, so build yourself some coffee, because if you take a beer you will not be able to understand by the end
. Jules I have added some more info as I have had a chance to think about this some more (I am slow, but i get somewhere in the end)
The overlanding/camping/4x4 bug bit my father and I only a couple of years ago, when my dad was in the process of planning his life after retirement. After a lot of research my dad decided on a Hilux bakkie with a removable camper on the back. This came with a National Luna battery box built into the camper. Before we started modifying this drove 2 external and two internal lights, of the long-life variety, and the water pump. We then added the National Luna Weekender 55l fridge-freezer combo, an LED strip light, a 2000W inverter and a 220V charger with an external plug for charging at campsites with power. I then took it on a 10-day holiday to Moz. Although it was December, it rained virtually the whole time and therefore it was not all that hot and we had mains power for about 6 hours every day, but despite me being very carefull with the fridge it was a constant battle to keep the fridge running. While driving back we carried out a number of tests to try and dteremine what the problem was (one of the guys in the party was an electrician) and we discovered that the alternator's output was reducing when it got hot.
We fixed that problem but the system still battles to cope. We have since also installed a cabin monitor so that the operator at least knows what is going on.
Some time thereafter I managed to scrape together enough cash to buy my Patrol. When I got it this came fitted with a home-made dual battery system consisting of a bracket in the engine bay containing a 105A/h battery and the same solenoid used by National Luna, but without the 5-minute delay.
I used this system as-is for a while, but it was not satisfactory. Firstly it battled to keep the battery charged, and then it also destroyed the battery by overheating it. This happens because there is no control over the maximum charging rate and therefore when the battery is very flat it will draw a lot of amps, which a deep-cycle battery doesn't like.
I then replaced the battery and at the same time replaced the charging system with a PBE system, but without the box. This system does not have a solenoid and also has an overcharge protection mechanism. The power is used for the following appliances: a 60l Snomaster fridge-freezer combo, a 400W inverter, a multi-lighter plug driving the GPS etc. and three strip lights in my tents.
In July this year we all went on a two-week trip to Botswana. We had four vehicles, but only two fridges. We used my dad's as a fridge, set at +5degrees, and mine as the freezer, set at -5degrees. Overnight temperatures fell low enough that my dad's fridge did not need to run most nights. We never used my dad's inverter, while mine was used often for charging cammera batteries and operating the laptop (used as storage for the more than 1400 photos we took and for route planning). Despite this my battery's voltage never dropped below 12.5 Volts, while my father's seldom reached that figure.
Fortunately I had my multimeter, so we could conduct some tests. I believe the main reason for the difference in performance is the following: When charging, the voltage in both my batteries is between 13.5 and 13.8 Volts (this is measured at the battery) while my father's system has approximately the same voltage at the car's baatery but only between 12.7 and 12.9 Volt at the second battery. This means that my battery gets about 30 Amps, while my dad's only gets about 10-13 Amps. In other words, because of the voltage drops present in my Dad's system, his battery charges at less than half the rate that mine does. Note that these figures were measured in the early morning, and the situation gets even worse as the batteries get fuller. This is because a battery is only full at 12.5Volt or more, and the charging rate is determined by the difference in the voltage between the battery and the charging system.
The technical reasons for my dad's voltage drop are as follows:
1) The Cole-Hershee solenoid deteriorates over time and creates a drop. (some sources say as much as 1 Volt)
2) The wiring in my dad's system is much longer than mine, however on the flip side it is much heavier, 40mm^2 as opposed to 10mm^2
3) My dad's system has two plug connections (Brad Harrisons), while mine only has one (the fuse).
Before our trip we installed a PBE charging system in one of the other cars, but without any drains. This was done because we expected to have power issues and we wanted a backup. At one point we swopped the battery from this system with the one in my dad's system. When we stopped after 3 hour's driving, the battery was fully charged.
As a footnote I have to say the following:
1) I have received excellent service from PBE. On one occasion I thought my system was faulty, and Pieter Snr spent an hour checking my system on a wednesday night, without charging me a cent.
2) My dad has similarly received excellent service from National Luna
3) I have no knowledge on any other systems than those described here, but I will never install a system using a solenoid again.
Cheers
Peter
