Dual Battery Systems - Article 09-2013...
It is advisable to read the first article: "Dual Battery Systems - The Beginning" before reading this article, to get a clear understanding of certain information given in this article.
What will be covered in this article?
1. Do I need a DC-DC Charger in my dual battery system?
2. What are the advantages / disadvantages of a DC-DC charging system?
The auxiliary battery is a power source for all the appliances used while camping, without using the vehicle engine/starting battery.
The auxiliary battery needs charging, how do we do it?
Running the fridge, lights and other DC accessories, use the limited energy stored in the battery, and the battery will stop supplying power eventually if it is not re-charged.
1. Do I need a DC-DC Charger in my dual battery system?
The most cost-effective system, relating to power output performance, is the dual battery charging system fitted to the vehicle. The vehicle alternator is the powerful source used to re-charge the battery of the vehicle while driving. The alternator can also be used to re-charge the auxiliary battery, by means of a dual battery charging controller. Read more about the MacroMaxi Dual Battery Charging Control System. This system supplies 45 Amp (and limited to 45 - 48 Amp) from a standard 70 Amp alternator.
The theory around DC-DC charging is that it allows charging of higher voltages (in the Boost voltage ranges) than what the normal standard alternator of vehicles can supply - although some vehicles already have smart alternators that allows for charging up to 14.8 V for a period and then settle lower at 13.3 - 13.6 V.
In reality, if you only use 15 - 20 Amp DC-DC system, it does not really help you, unless you are driving for 8 - 10 hours per day. In fact, the 20 Amp recharge current supplied (if we assume that it will run at its maximum the whole period, which does not really happen) takes minimum 5 hours of charging to get the battery above 95% full.
If you look at a standard alternator voltage of 13.8 V - 14.2 V, and you can apply the voltage to a discharged battery at around 30% state of charge, you can charge at 40 - 50 Amp initial charge rate, for at least the first hour, and then average 26 Amp in the second hour, meaning that you have recharged over 75 % of the battery capacity back into the battery in the first 2 hours of charging, while the DC-DC at 20 Amp would only have done 40% maximum. The only time a DC-DC of 20 Amp is going to benefit you, is if you run the vehicle engine for 8 - 12 hours per day, or driving very long distances, and it will only start to benefit you after the 7th hour of charging.
So tho answer the question if you absolutely need a DC-DC charging system;
1. Normal lead acid deep cycle battery - No
2. AGM Type batteries - No (although that there are some claiming that the alternator can not re-charge these batteries, if you look at the datasheet, the float voltages are 13.6 volt still, and boosting from 13.8 - 14.8 V is recommended, you can still charge 95% of the battery capacity with a standard alternator.Which in the camping application, is good, very good. You can always come back at home and boost the battery a short while and float for a day if you really need the extra 5% back into the battery, with a proper charger working from 230 V AC mains.)
3. GEL technology batteries - This is dependant on what battery you use, but most of these can also be charged by standard alternators.
To be continued soon...
Key benefits of PBE Dual Battery Charging Systems (alternator charging):
Cost-effective - High power output, reliability, extremely low maintenance, long serivce life
Very low risk - The PBE Dual Battery Charging Control system risk of failing is extremely low
High reliability - The PBE Dual Battery Charging Control system is highly reliable
High power output - The PBE Dual Battery Charging Control system ensures high power charging
Safety - The PBE Dual Battery Charging Control system incorporates various safety & protection features
Alternator Protection - The PBE Dual Battery Charging Control system protects against alternator overload
You are here:  PBE Products Home > Products > Dual Battery Systems > Article 1 - The beginning...
Quick links to Products and Services:
Dual Battery Systems - Dual Battery Charging System kits
Power Units for off-road Trailers, Caravans & Campers
Battery Chargers - portable or fixed units
Solar Power Systems - Camping solar systems 
Custom Fridge Sliders with protection cages
The auxiliary battery is re-charged by using the following options independantly, or in conjunction with each other, working together as a system:
1. Dual Battery Charging System fitted to vehicle - PBE System - see The MacroMaxi Dual Battery Charging System
2. Solar Charging System - portable or fixed - PBE System - see PBE Solar Charging Systems
3. Battery Charger - portable or fixed - PBE system - see PBE Battery Chargers & PBE Power Units for trailers, caravans and campers
4. Battery to Battery chargers - PBE system - see PBE Energy Transfer Unit (ETU)
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