DC ELECTRICS - Building a 12 Volt DC Power System for your 4x4 - My experiences

A waltz around the ethereal world of DC electrics!

By my way of thinking, one of the rules of remote outback travel, or any outback travel really is the fact that your vehicle should be maintained to the highest possible standard. I’m a firm believer that time spent on vehicle preparation is never time or money wasted. On top of that, the electrical system you employ on the trips are the 2nd most important thing. Not only the power system that runs your car, but your auxiliary system that powers your fridges, lights, computer, navigation and recharges your cameras, satphone, batteries for the GPS and hand held UHF’s, inverters for 240 volt appliances and anything else that floats your boat. With anything up to two months between resupply and 1000 km or more of terrain to be traversed, power is one of the most important considerations in my vehicle and the expeditions I undertake.


It’s always interesting to note that there is an aura of mystery around DC power that make it a bit hard to get the head around. Its numbers are low like 12 & 24 and yet it has bigger transmission issues than AC or “big number” current. Nothing was drummed home to me more readily than the heat generating qualities of 12 and 24 volt DC current than when bush welding and trying to regulate the power output through the use of cables or wire. It could turn no.8 fencing wire to white hot plasma in no time flat. A lesson for the uninitiated let me tell you.


Before building any vehicle power system, it's crucial that you have an understanding of just what your power usage will be, what it will take to support your system and the affect and interaction between your main vehicle power system and your auxiliary system. Having skirted around the sides of the whole power system set-up for a few years now, I decided to go out and design and build the best possible system for my needs. Thankfully I could use my own prior travel experiences to inform this process but I am no DC expert so a lot of thought and study was required. From the very outset I wanted to incorporate all aspects of DC power generation at my disposal. That means I wanted to support my auxiliary system through vehicle (alternator) power, solar power and also 240 volt from any source I could get meaning mains or generator produced 240 AC.


In addition, I wanted two separate systems with a degree of interoperability. This concept meant I could draw on power reserves for special circumstances or times of high need like winching and/or to totally support vehicle operation if for example, the alternator gave up the ghost. Despite this connectivity or interoperability between both systems, they would still be required to remain very separate circuits. The vehicle battery would also be supported by a 2nd battery under the bonnet. The main battery would drive many of the vehicle accessories such as the Winch, driving lights, internal radios and air compressors. The second battery would be used as a primary back-up should the main (crank) battery go flat or collapse. This is the theory of the basic dual battery system. The main auxiliary system comprising a couple of AGM deep cycle batteries would be responsible for all non-vehicle related power needs includeding the fridge/s, lighting, water pumps, inverter and some of the accessories in the cabin like GPS and computer.




Again in the design phase, I did a lot of research through the Exploroz site, through solar providers and recognised subject matter experts such as Collyn Rivers. Another good avenue was to check out the existing power set-ups on camper trailers and off road vans at things like the Caravan and camping show.
The key resource by far was people I’ve travelled with or met over the years. It is amazing what systems and alternatives a group of keen travellers will come up with over years of experience and investigation. So it was that my first drawings got sent to John, or “Mr Magic” of Mannum for his consideration and input. Having dragged he and Suzettes’s Ultimate “desert Dinghy” camper through some of the toughest terrain, I had been interested in the concept of the DC-DC charger as opposed to a standard dual battery charger. In addition we had been researching the MPPT controllers for optimising solar power generation. Other conversations (as well as the numerous Exploroz forum threads) surrounded AGM batteries, their benefits and special needs for staged charging that were not often met by many dual battery systems on the market today.John quickly sought the input of a mate of his Richard, (another EO member - Olcoolone) in Adelaide who he considered to have a bit of expertise on the subject. Richard provided some great feedback and suggested a few alternatives to my wish list. Fortuitously, it seems that Richard had invited John to a Redarc Trade Dealer night, aimed to highlight and educate their dealers on how the BMS, BCDC1220 and Smart Start Solenoid can be utilised.John came back extremely impressed with several of the Redarc products, their BMS system in particular.


Anyway, My initial concepts revolved around my own limited understanding of DC power and the things I would require to drive the system and for it to power. It also involved a suite of gauges and monitors to let me know the state of play. Here’s my initial list of components;

• Three batteries
• Dual battery system (Piranha DB 180S)& isolator
• 240 volt 3 stage charger such as a CTEK
• Solar Panel
• MPPT solar regulator
• DCDC charger for two auxiliary batteries such as a Rannox.
• Battery monitor (Autron dual monitor or similar)
• Other gauges for battery status and condition(current inflow/draw)

As you could imagine, it added up to a fair bit of loot.

What returned from Richard was basically the same diagram with a lot of simplification, some interesting concepts and a list components that looked like this;

• 3 Batteries
• Redarc BCDC charger
• Redarc Smart solenoid
• Redarc BMS system
• Solar panel

Somewhat simpler...no?



Over the course of a few phone calls and some internet research, a plan came together. While not his general field of endeavour, Richard offered to do the work in Adelaide. The trip would also give me a chance to run the vehicle in. There were a lot of considerations that are not mentioned surrounding batteries, chargers and the likes. I don’t intend to go into them here because it would take far too long but can be gleaned from some great sources. One of them is EO member John & Val’s blog on electricity for camping.

See HERE - John & Val's Electricity for Camping.


So it was that I headed out from Melbourne at 4.45 a.m. one Saturday heading for Adelaide. I arrived at Richards workshop on Sunday morning to meet he and Lyn and do a final run through the body of works. I flew back home that afternoon leaving Richard to begin his masterpiece. Here it is.


Under the bonnet he installed a 100 amp hour 700 CCA hybrid D/C battery (SSI-$290) as the auxiliary battery. To support the auxiliary, Richard installed a Redarc BCDC1220 20 amp three stage DC-DC charger. Rather than use a standard isolator of dual battery system, the BCDC provides proper three stage charging. Under the standard systems you would have only ever achieved 60-70% of the battery maximum state of charge (SOC). The BCDC provides full three stage charging Stage 1 – bulk or boost where it delivers most of the charge. Stage 2 – provides an absorption charge where it starts tapering and finally to a float charge at 100% state of charge. It also helps battery condition because the battery is actually charged as the manufacturer intended. The cabling 2 B&S, between the main and auxiliary batteries and 3 B&S cabling to earth. The smaller cable was used for earthing as he ran multiple earths throughout the system. We used a Redarc SBI212 smart solenoid which is a 200 amp constant rated, smart dual battery isolator. We actually ended up “dumbing” it down a bit and removed the control module to return it to a switchable solenoid state. The reason for using the Redarc solenoid is that they are good quality, readily available throughout Australia. The manual switching from inside the vehicle cab also allows the vehicle to be started from the aux battery should the main be flat and precludes the need to get out and jump with leads. We also incorporated a control feed to the solenoid from the winch so that winching activity will draw power from both batteries.


From the auxiliary battery a 6 B&S cable runs to a high quality 8 blade e-max fuse holder. From these fuses a 3mm feed for a UHF Radio together with 3 x 6mm feeds, one being for the Laptop used for mapping, the second one for a small Inverter to charge camera batteries etc, and the third wire to power a future HF Radio. All the positive wires were accompanied with the same size earth back to a central major earth point. To facilitate the cabin power feeds, a 32mm hole was drilled through the firewall for cable feeds. This was primed and grometted.

Along with the 8 blade e-max fuse holder, 4 standard 4 pin relay blocks were added, 1 for the spot lights, the second one for a Hella Twin Beam reversing light to be mounted on the Rear of the Back Pod and the 2 others are left spare for future expansion. From the starter battery an 80 amp midi-fuse heads down to dual compressors mounted in one of the side under tray boxes. Each compressor is fused with a 30 amp blade fuse. The 80 amp protects the wire heading down to the compressor where it divides into two 6mm wires, each fused with a 30 amp weatherproof fuse holder.

Also from the main starter battery there is a heavy duty 175 amp emax mega-fuse which supplies feed to the permanent rear pod through 3 B&S cable. This is run to a 175 amp Anderson Plug underneath the vehicle allowing the entire rear unit to be unplugged and removed if need be. The main power feed then heads inside the pod to a single side 175 amp Anderson Plug. On that same Anderson Plug terminal there is a 6 B&S cable to power the Redarc BMS Battery Management System. This coordinates and maintains the two 140 Amp Power Sonic AGM batteries. The BMS contains a 3 stage 240AC charger, a DC-DC charger and an MPPT solar controller all wrapped up in one package. The digital readout provides just about any data you could want to know about your batteries condition, state and mode of charge and also includes up to 30 days of usage history.


On the other terminal of the Anderson plug there is a lead straight to the battery. This means when closed with a looped Anderson plug, the BMS is cut out of the loop and power from the two aux batteries will flow back into the main vehicle system. (I know it’s getting difficult. Stick with me here and the photos will help out). There are two plug options for closing this circuit. One looping Anderson plug has a 60 amp fuse to protect the engine and electrics and would be used when feeding power back for engine management purposes, say if the alternator packed it in. The 2nd loop is unfused for maximum current transfer. This is used in times of high power need like heavy winching.

The rear batteries are connected to a custom switch panel that has an expandable 8 blade h/d fuse block and 7 illuminated toggle switches. These switches operate lighting, water pumps, interior lighting (11 watt narva flouro - less than 1 amp per hour draw). LED Strip lighting is fitted under the gull wing doors on the pod and in the interior of the tent. Other DC outlets are situated around the pod for appliances and tools

All wiring has been run through convoluted tubing and formed into looms. All terminals are double crimped and heat shrunk and all sprayed with a Wurth silicone grease. Weatherproof plugs have been used throughout. Dare I mention the custom battery tray, clamps and mounts. Extra 3,4 & 6 mm cabling has been run to the back of the vehicle for future expansion.

Helpful Links

My full ute build blog

John & Vals - Electricity for camping

Redarc - Handy Hints

Redarc - Wiring Guides

Battery University - Learn about Batteries

MPPT Solar contollers (and a heap of other info)

Basic Electrics for Motorhome & Caravan Owners

Later Review of the Redarc products Used

Mick Os Rule Number 3

– You live or die by the quality and reliability of your DC power system (well death might be overstating it but warm beer is not living my friend! A months worth of frozen food thawing out in the middle of the never-never is not fun either! Nor is trying to start your vehicle out back of beyond after suffering a flat battery.)


So it’s all about knowing exactly what it is you wish to achieve (what you want the power system to do), how you build it, what components you use and the quality of it all.

Redarc BMS Smartstart 1215ˆˆ($1642)

Redarc BCDC 1220 ˆˆ($495)

Redarc SBI212 ($356)

(smart solenoid- 200 amp constant rated, smart dual battery isolator.)


The overall charging ability of the BMS system was great. What I liked was the comprehensive functionality of the remote monitor head. This is connected by a 4 metre lead and can be mounted remotely from the BMS unit. With both Amps out (draw on Battery) and volts in (and amps leaving the charger), time to fully charged, battery time remaining (as a percentage of total battery capacity and represented in hours/days remaining at current draw), charging source, and SOC Vs Hour charging logs, Battery status (Temp & charge), load status it makes the need for other battery monitoring systems and gauges obsolete.




Of particular strength to my mind was the MPPT solar function which provided peak charging rate. I found with the raw voltage produced being handled by the unit, I was able to get the batteries back up to from 90% to 99% on near so on most sunny days with 100 Watts of solar panel whilst running an 80 litre combo and other minor accessories and lighting.


In between the two vehicle batteries, I also used a SBI 212 which is a smart solenoid- 200 amp constant rated, dual battery isolator.We actually ended up “dumbing” it down a bit and removed the control module to return it to a switchable solenoid state. The reason for using the Redarc solenoid is that they are good quality and readily available throughout Australia. The manual switching from inside the vehicle cab also allows the vehicle to be started from the aux battery should the main be flat and precludes the need to get out and jump with leads. We also incorporated a control feed to the solenoid from the winch so that winching activity will draw power from both batteries. (I note the latest redarc magazine has a description on how to fit a switched jump and winch assist feature.)



The BCDC 1220 provides full multi-stage charging Stage 1 – bulk or boost where it delivers most of the charge. Stage 2 – provides an absorption charge where it starts tapering and finally to a float charge at 100% state of charge. It also helps battery condition because the battery is actually charged as the manufacturer intended. The unit will act as a dual battery isolator and protect the start battery, should the voltage get too low. The BCDC 1220 has performed faultlessly. The latest generation of this unit the BCDC 1225 incorporates an MPPT solar controller function as well which is of additional value for the outback traveller.

I cannot speak highly enough of these systems. The BMS in particular has blown me away. The MPPT solar controller has made a real difference. With only the peak sunlight hours of winter in the north west, I was able to fully maintain my batteries with a 100W solar panel. This included running the 80 Litre Engel combo (half of which was on full time freezer) lighting and a few other minor sundries. This did involve active monitoring & manipulation of fridge controls but considering we were in low to mid 30 Celsius each day, it was great. The DC-DC charging facility running from the vehicle alternator provided very solid rates of charge that bought the batteries back up from mid to high 70% mark to 100% within a few hours of travel. I am running twin Power Sonic 140A/H AGM’s. To save a lot of confusion and the need for 240 volt certification, I didn’t bother hardwiring 240 into the power system or fridge. The only lead in is for the BMS and this has done a great job when sourcing AC power and comfortably maintains float while running all accessories. The Display unit is exceptional in functionality and provides in one interface, every input/output reading and all the battery condition information that I require and had previously used many separate displays for.


Both units copped a fair flogging over the 3 months of our trip completing over 11,000 kilometres in outback track and off track situations. They were exposed to constant vibration, water (condensation), humidity, heat and dust with Temp extremes ranged from -3C through to 39C ambient and up to 50C internal pod and engine bay temperatures without fault. A lot of money to lay out initially but when you’re protecting over $1600 worth of AGM batteries and the comprehensive suite of power management tools rolled up into the one package, it’s actually a great deal cheaper than what I had intended with separate components and gauges and has a lot more functionality. It’s bloody simple and reliable which means a lot less concern for me.


I would add that to work effectively any PMS depends on the quality of installation and the attendant wiring. Making sure you have quality wiring of adequate capacity is a must. Making sure it is fitted correctly is plain common sense.

Update November 2012

These products have now been installed in the truck for some 2 and a half years and the vehicle has now completed 60,000 kilometres, mostly on tough outback roads and tracks. The Redarc products, batteries and wiring have performed faultlessly. I am about to have the BMS unit sent back tom Redarc to update it with the latest algorithms and user interfaces. I have added three 110W solar panels into the equation earlier this year, all plugged on a full time basis open current into the BMS unit utilising its MPPT solar controller function. This has provided an amazing degree of additional flexibility and peace of mind for those longer remote trips. I now have enough solar input to comfortably run several fridges and even on the cloudy days, the panels and controller pull in enough generation to meet most of my needs.

Update March 2014

A very brief update. Four years and 70K kilometres now across some of the harshest terrain the wide brown land has to offer. Performing faultlessly. This vehicle gets a lot of driveway "downtime" between trips and the solar is perfect for maintaining the batteries in optimum condition and maximum capacity.

A disclaimer of sorts;

I make the clear distinction here and now that while I have some experience as an outback traveller, I am not a technical expert by any stretch of the imagination. It is my personal experience upon which I base both my observation and reviews. This is factual based and not anecdotal (someone telling me about it) experience.

The prices I have quoted are purely a range of current retail prices and were updated in November 2012.


The comments contained in this blog are not designed to influence you towards any particular product. I’m not receiving any financial advantage in doing this, rather I am providing my personal experience & opinion on the quality and suitability of the products I have purchased and used. Any decision about purchasing a product should be made on a thorough analysis of your own needs and budget and supported by your own research (as were mine).