Hennie Rautenbach’s Dual Battery & Freezer FAQ


Being a social animal of sorts I often travel in groups. Frequently so with folk I haven't met before. Almost in all cases the number one problem on a trip (call it a safari if you like) is with the dual battery/freezer setup. I saw it in December on the Huntersroad and I saw it again recently on the Nossob Trail. It is only day 2 and one of the participants start idling his vehicle for hours on end in the campsite. Usually at the most god-forsaken time possible. Sunrise or Sunset. When it becomes intolerable I walk over and ask if I may inspect the system. I am often horrified to see the systems installed by so called reputable auto-elec outfits, and at exorbitant cost. It is impossible to cater for every possible setup but a good fundamental understanding of charging systems is imperative to help you to come to grips with the supply and demand problems with regard to alternators/batteries/freezers. Here are a few pointers:


1. YOU NEED A MULTIMETER. This is the most important tool, long before

you buy a battery/CRS (Constant Rated Solenoid).


2. Make sure there are no charging issues to start with. When your

vehicle is idling and the main battery is fully charged your alternator

should push out "more" than 14.2 V.


3. Use sufficiently thick cable between the batteries and the isolator.

Preferably welding type cable with properly crimped AND SOLDERED lugs.


3. DONT use a diode based isolator, UNLESS the guys know what they are

doing. Battery Center in Botha Ave. Lyttleton (Pretoria) fabricates and install a

very good one.


4. Go for a heavy duty Constant Rated Solenoid such as the Cole Hersee

(agents: Elpar) Don't go for a Cole Hersee rip-off.


5. ALWAYS buy a reputable deep-cycle battery of MORE than 100 Ah and

 preferably with screw-on lugs


6. Buy a cheapish digital Voltmeter (Yebo electronics, Philtron, etc.)

and wire it to the dual battery so that you can monitor the charge and

capacity at all times. Get one with a low voltage alarm. The Link 10 system is

best if somewhat cost prohibitive. (Search google.com)


7. If the situation is likely that you will drain the battery of most of

its charge during camp stop-overs you should consider fitting a "charge booster"

to the alternator so that it can deliver its initial heavy charge for

longer to help getting the batteries charged quicker.


8. When the system is engaged and charging from the alternator there

shouldn't be more than a .1 (point one) Volt voltage drop over the

secondary battery, compared to the main battery. Very important.


9. It should be noted that during a trip of 14 days it will be

impossible for the alternator alone to fully recharge the deep-cycle

battery. Always carry a bench charger (preferably an intelligent 3-stage unit that can

deliver 20A at 14.5V) to help you get the best service from your setup.

Always charge (top up) where 220V/250V mains is available.


10. The CRT should ideally be engaged through a relay that is activated

 from the alternator actuator circuit AFTER the vehicle’s engine has started.


11. Always install a circuit breaker of more than 20A between the main

and secondary battery to prevent everything from going up in smoke when

you put a dead short over the deep-cycle battery.


12. DONT use Hella or Bosch plugs on your freezer. They are fine for

Neon Lights, Shower Pumps, 2-Way Radios, GPS etc. Only use Brad Harrison

interlocking plugs for the freezer.


13. Consider a cheap temp sensor for the freezer bin, so you

have peace of mind that the frozen meat stays frozen in there. The most common  

mistake folk make is that they turn the freezer to minus 20 (or more) when

a minus 5 would have been perfect. DONT trust your freezer's thermometer.


14. Always charge your batteries fully PRIOR to embarking on your trip.


15. Never use the vehicle body/chassis as a common earth for the deep-cycle battery, or for the power sockets. Run a seperate (suitably thick) earth (Neg) cable between main and secondary battery with an optional earth to body/chassis.


My 2 cents after having thrown away my fair share of meat on trips.


Hennie.Rautenbach [at] gmail.com