Camper Trailers Tech Tips

Redarc BCDC1225 charger install





redarc bcdc1225 charger


I recently installed a Redarc BCDC1225 which is the latest DC-DC battery charger on the market. This charger is an improvement on the BCDC1220 that charges a vehicles auxiliary battery or more importantly a remotely located battery in a camper trailer which is a long way from the vehicles alternator. Over this distance the alternator is only trying its best to charge the battery. The biggest downfall in a situation like this is the voltage drop over the distance involved, sometimes at around ten metres or more. An alternator is known not to be the best thing to charge a battery to full capacity, commonly only achieving 80%.

The auxiliary batteries in 4wd's or camper trailers are more often than not, deep cycle or have a deep cycle capacity & used to power a large range of power hungry accessories from 12volt fridges, tyre pumps to lighting. A battery which is charged to 100% has more useability, meaning a longer stay in camp without recharging. 

The Redarc BCDC1225 not only charges a battery from an alternator to 100% using the inbuilt 3stage charger feature, but also from a solar panel using MPPT solar charging, extracting the maximum available power from your solar panel at any given time. This is a huge advancement in solar charging & also a big plus for us camper trailer owners. The BCDC1225 is also designed to isolate the auxiliary battery from the main battery to avoid over discharge of the main battery. The unit turns on above 13.2volts & off at 12.7volts.

what is mppt?

MPPT stands for Maximum Power Point Tracking and relates to the solar cell itself. Each solar cell has a point at which the current (I) and voltage (V) output from the cell result in the maximum power output of the cell. The principle is that if the output from the cell can be regulated to the voltage and current levels needed to achieve a power output at this point, then the power generated by the solar cell will be used most efficiently.

MPPT ensures that you get the most power possible from your solar panels during low light level conditions. All this calculation and regulation results in the output from your solar regulator providing the maximum current possible at the required voltage at any given point. During low light level situations it will compensate for the low light level and find the new point at which the solar cell delivers its maximum power output.

what is 3stage charging?

stage one is also know as boost mode & charges the battery at a constant amperage until the battery voltage reaches around three quarters capacity.

stage two is also known as absorption. This mode maintains the elevated voltage from the bulk phase, but adjusts the amperage accordingly. As the battery charge level approaches capacity, the current approaches zero. Absorption voltage output from the BCDC1225 for an AGM/Gel is 14.5volts, standard lead acid 14.9volts & a calcium battery 15.3volts depending on the battery type as set by the orange wire on the BCDC1225 charger at instillation.

stage three is also known as float. After the battery is fully charged the voltage is reduced to a lower level to reduce gassing and prolong battery life. This is sometimes referred to as a maintenance or trickle charge, since its main purpose is to keep an already charged battery from discharging. Float  voltage for an AGM/Gel, standard lead acid & calcium battery are all the same at 13.3volts.

getting started

The best way to start a major project is to draw up a diagram & a wiring job like this is no exception. This way you can plan the length & size of each cable, the terminals or any other hardware needed. I simply drew my diagram in Microsoft Paint. If you do not have the necessary computer skills there is nothing wrong with a sketch on paper. Using different colours for positive, negative & line thickness to represent different wires will also help you plan the job. It is a good idea to have the diagram checked by a auto electrician or someone who knows their 12volt stuff. For the DIYer, Redarc also have technicians on hand to answer your query via a user forum & a phone in centre.

Voltage drop is the number one factor for many accessories not working to their full capacity, especially 12volt fridges. A handy voltage drop calculator can be found on the Redarc handy hints page of their website.

A big thanks to Simon Gedge from Redarc & also Shane Adams at JTS, Jamie's Touring Solutions, formally DSS, for checking the diagram I had drawn up. My own project was complicated by the fact the two 120amp hour AGM batteries are in boxes on each side of the camper which meant long cable runs protected by two 25mm flexible conduits. I had the two batteries already set up & running, so this was more of a rewire adding the BCDC1225 to the system.


The two 120amp hour AGM or absorbed glass mat batteries are wired in parallel, that is positive to positive & negative to negative, making them in essence one big 12volt 240amp hour battery. I used 6B&S twin core cable to join the batteries together as well as the recommended heavier wiring off the charger.

The two 120amp hour batteries are also charged as one. The charger positive goes to the positive on one battery & the charger negative goes to the negative on the other battery. The brown wire from the charger is only a short run to the positive battery terminal in the battery box the charger is located in. The black wire from the charger makes a longer run to the negative battery terminal in the box on the other side of the camper. 

The long nine metre run from the vehicles battery to the charger is with 6B&S twin core cable. All other wiring was run in 6mm such as to the fuse box, the solar panel input & the 240volt charger input. I ran 5mm off the fuse block to the accessories as I had a length of 5mm twin core left over form the Redarc EBRH brake controller install I did a couple of months ago. We had trialled a length of 5mm to Carol's Cpap which worked a treat.

Discharge is the same, with a positive off one battery & the negative off the other going to the fuse block. The Baintech fuse block used has six terminal blade fuses with its own positive & negative bus bar which makes connecting the wires to outlet sockets a breeze. The cover can also store two spare fuses.

All uninsulated terminals were crimped & shrinked wrapped. The connections off the charger where crimped, soldered & shrink wrapped as per instructions. I had bought an uninsulated terminal crimper off Ebay a while back for $30 which did the job perfectly.

Auto accessory outlets do not carry the type of wiring or the uninsulated crimp terminals needed. After a run around to six different businesses in the one day I only ended up with a couple of items. I bought most that was required off Ebay. The ten metres of 6B&S twin core cable was $89 & ten genuine 50amp Anderson connectors for $30. I also needed four red 50amp Anderson plugs at $20.

You need to be careful when buying 50amp Anderson connectors as some ads read Anderson 'type' connectors which imply they are not genuine. The crimp terminals on cheap copies rust, therefore do not make good contact over time. The contacts of genuine Anderson connectors are self cleaning as you push them together, making for excellent contact with each use. There is also an Anderson logo on each genuine plug.

charger input configuration

The wiring diagram that comes with the charger install booklet shows three choices for which the charger will operate depending on how the blue wire is configured -

* the blue wire is connected to the ignition for alternator input
* the blue wire is grounded for solar input
* or if you want an automatic connection for solar & alternator use you can use Redarc's RK1260 relay which is a setup perfect for a van with the panel permanently on the roof. When you turn the tow vehicles engine off the solar panel will automatically cut in.

solar & alternator input

The Redarc BCDC1225 requires unregulated solar input from the panel for the MPPT solar regulator side of the charger to work. Luckily there was enough room in the box on the back of the Kyocera 130watt folding panel we bought from Jamie at Dynamic Solar Solutions, now known as Jamie's Touring Solutions. Other than that I would have had to take the regulator out & put it in a jiffy box to use when needed. Something else to carry & store. I picked up the wires on the back of the panel before they went through the Plasmatronics PL1210 regulator & brought them out to a red 50amp Anderson connector. I used a red Anderson to signify the output from the solar panel is hot ie unregulated.

 A grey 50amp Anderson connector on the solar panel signifies the output is regulated which I can use to charge the vehicles battery or any other 12volt battery for that matter. The two Anderson connectors were secured to the box on the rear of the solar panel with small nuts & bolts. Loctite was used on the threads & a blob of silastic over the bolt heads inside to make sure the bolts didn't come loose, fall in & short something out.

my input solution

 In our situation the 130watt portable panel is carried on the campers bed & setup when camped which meant none of the above scenarios where right in how we would use the charger. With the help of Redarc's Simon Gedge & the Redarc tech guys, they came up with a very simple solution to our situation.

I have run the blue wire from the BCDC1225 through the black unused reverse pin on the trailer plug & joined it to the positive lead from the alternator at the Anderson connector on the back of the vehicle.

When the vehicle is running
the blue wire tells the charger the alternator is feeding & the charger acts as a 3stage charger.

When we are camped the trailers red Anderson at the hitch is disconnect from the vehicle & plugged into the unregulated solar panel at the A-frame.  The campers batteries are then charged with the inbuilt BCDC1225 MPPT solar regulator.

There is also a grey 50amp Anderson on the side of the battery box for the 240volt 3stage charger to connect to the two batteries. A red Anderson will not connect to a grey Anderson so I cannot accidently make a wrong connection. 

vehicle wiring

I ran a 6B&S twin core cable from the vehicle's battery via a 40amp circuit breaker with protective cover to a red 50amp Anderson connector on the towbar next to the trailer plug. This gives plenty of feed to the charger without excessive voltage drop over a nine metre run to the charger. Sometimes 6mm auto cable is mistakenly used instead of 6B&S which is not large enough to carry the voltage required. 

battery type selection

The BCDC1225 will charge a battery depending on its type according to the way you wire the orange wire during installation.
* standard lead acid - grounded
* calcium - connected to input positive
* AGM or Gel - not connected

display panel

There are two displays on the front of the charger that explains what is happening. The first shows the battery type selected during installation.

The other shows the charge status. An LED will flash whether the charger is in boost, absorption or float mode. The longer the flash, the more current the charger is putting out. If the LED in on solid, then the unit is supplying a full 25amps to the battery.

In standby mode the battery type LED will blink at approximately once per second & the charge status LED will be off.

external led indicator

A green wire on the unit is provided that can be connected to an external LED, say in the vehicles dash, that will let you know what the battery is doing. If the LED is on, it means the battery is charging, if the LED is off, the BCDC1225 is off.


I wired in a voltmeter via a switch to the positive on one battery & the negative on the other showing the state of charge at rest which is best achieved by allowing the battery to sit overnight. I find it better to understand the battery capacity by using a simple chart to show a percentage. For best battery life & optimum performance it is recommended that you only discharge your battery to around 50% capacity.     

wiring diagrams




Redarc's wiring for alternator input Redarc's wiring for a panel input


Redarc's wiring using a RK1260 relay my wiring diagram




lefthand battery box wire run lefthand battery box completed non-regulated wire added with fuse



righthand battery box wire run righthand battery box completed red 50amp anderson denotes non-regulated output


Redarc BCDC1225 cable sizes from top - 4mm, 6mm, 6B&S twin core 6B&S crimped & shrink wrapped


6B&S twin core cable & circuit breaker in engine bay red 50amp Anderson with 6B&S twin core on vehicle non insulated crimper


crimper & 50amp Anderson terminal state of charge chart assorted terminals, studs, switches, anderson plugs & fuses

 article by Rob


july 2012