ALTERNATOR OR DC-DC CHARGING
I have been asked a few times about the difference between DC-DC charging and simply charging with the vehicles alternator. So I wanted to explain the reason why we have a combination of both to handle All Around Oz’s power requirements in our BT50 and trailer.
This opinion is mine only from quite a few years of playing with 12V systems. We have a 220AH battery bank in the back of the BT50, a 210AH battery bank in the camper trailer and our new van will have a 360AH battery bank.
CHARGING WITH YOUR VEHICLES ALTERNATOR
Charging your auxiliary battery bank with the alternator is a simple, inexpensive and easy way of doing it. The advantage over a DC-DC system is a large charging current to bring low charge batteries back to service fast. The disadvantage is that todays Smart Alternators will wind the voltage and current back as the batteries are charged.
Very few alternators run over 14V, with most having a 13.6 to 13.8 volt maximum. Late model popular Gel and AGM batteries need up to 15 volts to get a 100% charge and to keep these expensive batteries in top condition. Alternators can’t do this.
CHARGING WITH A DC to DC CHARGER
Charging your auxiliary battery bank with a DC-DC Charger is a more expensive set-up. The big advantage of a DC-DC charger is it will be the best way of looking after the batteries that you rely on. It has different programs for different batteries and most have its own solar regulator built in. You can feed the 22+ volts from your panels straight into the charger with no voltage drop concerns.
The only real disadvantage of this charging system is that it charges at a much lower rate. Usually around 20 to 30 amps. A big step back from the 120 amps or so from the alternator. If you have a large battery bank like we have then 20 amps can take a long time to charge them to capacity.
A COMBINATION OF BOTH
We have set up a combination of both in the All Around Oz BT50. The CTEK D250SA coupled with the CTEK Smartpass120. When the batteries are low from a busy day, as soon as the alternator kicks in and the Smartpass120 is happy with the charge rate, it links all the batteries in the vehicle together. This gives full alternator charge rate to the auxiliary batteries. At this stage the D250SA is working as well to bring the charge voltage up to 14.8 volts. A perfect blend for the work we do and the large battery banks we have.
I have kept the technical information on these systems very brief. Just the main differences between the 2 systems so hopefully you can see the pros and cons of both. You will find some more info in our You Tube video below.