The two 12volt AGM deep cycle batteries in our camper trailer were slowly dying, so this was the perfect opportunity for a LiFePO4 Lithium battery upgrade. I had installed two Ritar 120amp-hour AGM deep cycle batteries in 2012 along with a Redarc BCDC1225 DC to DC charger, then adding at a later time an Enerdrive Elite monitor for more precise battery monitoring over a voltmeter.

Recently I installed a Redarc Smart Battery Monitor that uses bluetooth technology to view the battery charging, discharging & capacity via an app on our iPad & iPhone. A bonus of this monitor is Carol can check the batteries state of charge while we drive which also gives an estimate for the length of time until the batteries are fully charged. 

The Redarc BCDC1225 had proven itself in charging our camper trailer batteries & with no problems encountered during all this time. The DC to DC charging side puts out 25amps in boost & has fully charged the camper trailer batteries to 100% from the vehicles alternator as we drive between camps & then via solar panels through the inbuilt MPPT solar regulator when camped. Undercharging AGM batteries causes sulphating which is a battery killer.

We had nine years service from the two Ritar 120amp-hour AGM batteries, no doubt thanks to the Redarc BCDC1225 3-stage charging, however in the end they were only achieving 12.6volts at rest. They were replaced by two PowerSonic 120amp-hour AGM batteries which after only four years are reaching the same 12.6volts at rest. Time to upgrade to LiFePO4 Lithium batteries.

voltage drop

Voltage drop is the biggest downfall when charging deep cycle batteries in a camper trailer which are often at a distance of ten metres or more from the vehicles alternator. To make matters worse modern smart alternators are only designed to recharge the starter battery & do not produce the correct voltage to fully charge a deep cycle battery. A DC to DC charger overcomes both these problems when using the recommended wire gauge for the distance involved. 

what is multistage charging?

The Redarc BCDC1225D is a 3-stage DC to DC charger operating from the vehicles alternator & solar panels to provide the best possible charging to fully charge a deep cycle battery. 

boost mode maintains constant amps for a LiFePO4 Lithium battery until it reaches absorption voltage. The amps may vary in order to maintain a safe operating battery temperature or to limit the difference between input and output voltages.

absorption mode maintains a constant voltage level for a predetermined period of time or until the amps being drawn by the output battery drops to less than 4amps for 30 seconds, after which the charger will enter float stage.

Float mode In LiFePO4 Lithium battery charge profile the charger will turn off, but will move back into boost mode when the voltage drops to a predetermined level. In AGM battery charge profile the voltage is held at a preset level to keep the battery fully charge without damage, preventing sulphation which shortens the life of an AGM battery.

what is mppt?

An MPPT solar regulator (Maximum Power Point Tracking), regulates the voltage & amps output of a solar panel to achieve the maximum power output needed to fully charge a 12volt battery at any given point in time. During low light level situations it will compensate for the low light & find the new point at which the solar cell delivers its maximum power output.

why a lithium LiFePO4 battery charger

It is important a battery charger that is designed for LiFePO4 Lithium battery charging is used. The current must be terminated when full charge is achieved as this battery type cannot absorb overcharge. The correct charger will also ensure the battery is charged safely & efficiently, therefore maximizing its lifespan & performance. A LiFePO4 Lithium battery that has received a fully saturated charge will keep the voltage elevated for longer than one that has not received a saturation charge.

lithium LiFePO4 battery upgrade

LiFePO4 stands for lithium iron phosphate, a type of rechargeable lithium-ion battery:
Lithium (Li): The lithium component in the battery
Iron (Fe): The iron component in the battery
Phosphate (PO4): The phosphate component in the battery

The price of quality LiFePO4 Lithium 12volt batteries are now becoming more affordable so this was a good opportunity to look at an upgrade for our camper trailer. LiFePO4 Lithium batteries have some major advantages over an AGM deep cycle battery. They weigh only half that of an AGM which is a huge plus in a soft floor camper trailer with minimum payload, they have a faster charge rate, along with many more battery cycles when shallow discharging. A cycle is a discharge of the battery to whatever the depth & then fully recharged. The deeper the discharge the less number of cycles. Be aware not all LiFePO4 Lithium batteries are created equal, so it is worth doing your research & not necessarily on the battery manufacturers website when looking for the best cost & service life to suit your own needs & budget. 

Dimensions vary, however the 100 to 135amp-hour range LiFePO4 Lithium are around the same size as the 120 amp-hour AGM battery so are a direct swap into the same space. Our Redarc BCDC1225 is twelve years old & unfortunately does not have the preferred Lithium charging profile. After a faultless service a Redarc BCDC1225D upgrade was a no brainer.  

redarc bcdc1225d

The Redarc code BCDC1225D stands for Battery Charger Direct Current 12volt 25amp & D for solar 'green power priority' technology. The 25amp output is suitable for a 75amp-hour to 200amp-hour size battery bank. A LiFePO4 Lithium battery will except a higher charge rate than an AGM, therefore we could have use a BCDC1240D.

However a 40amp charger would have meant an extra huge expense & time removing all the 6B&S cable right from the vehicles starter battery to the camper trailer batteries, plus larger Andersons & rewiring with the Redarc recommended 4B&S twin core sheathed cable at around $30 a metre. The 25amp charger had already proven itself suitable charging the AGM batteries on drives between camps.

As a general rule of thumb a LiFePO4 Lithium battery will accept a charge rate of 1C, that is a 100amp-hour battery will accept a 100amp charge, whereas an AGM deep cycle battery will except a charge rate up to 0.3C, that is a 100amp AGM battery will except a charge rate of 30amps.

Like the Redarc BCDC1225, the BCDC1225D is a 25amp DC to DC charger with input from the vehicles alternator as well as an inbuilt MPPT solar regular to fully charge a deep cycle battery. The D model now includes a Lithium charge profile along with its own solar input connection cable. The BCDC1225 model had a shared alternator & solar input cable needing a relay to switch to the roof mounted solar when the engine was turned off. The D will automatically switch to solar when the engine is not running, perfect if you have solar panels on the roof. The solar input is priority when driving unless the charger needs more input to fully charge the batteries & will then bring in the vehicles alternator.

The BCDC1225D will also automatically limit the power input from solar if the solar exceeds 375watt. Having additional solar panel wattage is beneficial for battery charging in low light levels such as a cloud day, early morning or late afternoon.

planning

The best way to start any project on your camper trailer is to draw a diagram to give you an idea of the materials, components or parts along with the skills & tools needed. Even though this was a replacement job, extra cable, fuses, terminals, Anderson connectors, ply, screws & bolts were needed.

If you are doing a DIY wiring job, it is always a good idea
to have an auto electrician check your proposed wiring diagram.

As I am replacing the existing Redarc DC to DC charger with the latest model there was minimum wiring required. The 100amp-hour LiFePO4 Lithium batteries are of similar dimensions, however I did take this opportunity to change a few things.

* There is a battery box each side of the trailer forward of the axle. I had originally placed the AGM's in the boxes towards the axle end in a hope their 80kg combined weight would have less impact on the ball weight. The two LiFePO4 Lithiums have a total weight of 32kg, so I mounted them towards the coupling end of the battery boxes which also gave me a better opportunity for a neater wiring layout.

* While I had no trouble from the automatic reset 40amp fuse, however I decided to put Midi fuse in their place as recommended by Redarc.

* There was no room for the Redarc smart battery monitor shunt to be positioned on the panel next to the battery when I installed it. There is a button on the shunt that needs to be pressed as part of the pairing of the setup app & operating app. Again there was no alternative but to mount the shunt behind the panel.

* I installed busbars near the positive & negative battery terminals replacing the insulated studs making for a neater job in the limited space.
 
wiring

The two 100amp-hour LiFePO4 Lithium batteries are wired in parallel, meaning the batteries are wired positive to positive & negative to negative, making them in essence one big 12volt 200amp-hour battery. With both batteries being charged as one they should be of the same battery type, capacity & age. The charger positive goes to the positive terminal on one battery & the charger negative goes to the negative terminal on the other battery. The Blue Sea fuse box is also wired to the same terminals & has its own inbuilt negative busbar making for easy wiring runs to each of the 12volt accessory outlets.  
 
All wiring was 6B&S twin core sheathed cable including that from the vehicles alternator keeping within Redarc's instillation guidelines, the connecting of batteries, from batteries to the fuse box & from Anderson connectors to the Redarc charger. 6mm auto twin sheathed wire was used for all other wiring from the fusebox to the accessory outlets & solar input leads from the solar panel unregulated output to the Anderson connector.

Any 12volt connectors exposed to the elements are Anderson connectors as the terminals are self cleaning when connecting. All cigarette sockets & USB ports are inside the lockers of the camper trailer.  

Space was at a premium for wiring next to the batteries all the while trying to keep the whole job as neat as I could. Four post busbars were used on both the positive & negative connections keeping the battery posts uncluttered. There is only one cable from the Redarc smart battery monitor to the negative battery terminal so all amps in & out are counted through the shunt.

component sourcing

You will find a large varying price range in sourcing quality 12volt components, parts & wiring so it is worth shopping around. Google is the best place to look.  

charger input wiring 

The wiring is fairly simple & straight forward.

Red cable is the charger input from the vehicles alternator with a 40amp fuse next to the starter battery. There is an Anderson connector at the rear of the vehicle.

Yellow cable is the charger input from the unregulated solar panel.

Brown cable is connected to the positive battery terminal with a 40amp fuse next to the terminal.

Black cable is connected to the negative busbar.

Blue wire is left unconnected for a standard alternator input for our alternator type.

Green & Orange wires are connected together to set the charge output for Lithium battery charging profile.

All uninsulated terminals were crimped & shrink wrapped. The connections to & from the BCDC1225D charger cables where crimped, soldered & shrink wrapped as per the Redarc instillation instructions.

battery & alternator profile blue wire

Battery profile The BCDC1225D can be used for charging a range of 12volt batteries including automotive lead acid, calcium, Gel, AGM, SLI, deep cycle or Lithium. The charging profile is selected depending on how the battery profile wires are configured. I am using LiFePO4 Lithium batteries therefore the orange & green wires are connected together.

Starter battery type triggers the chargers on & off voltage. Our vehicle has a standard alternator so the blue wire is left unconnected or it can be earthed. For a standard alternator the charger will turn on at 12.9volts when the vehicle is started.

If a vehicle has a smart alternator the blue wire is connected to the vehicles ignition via a fuse. For a smart alternator the charger will turn on at 12.0volts when the vehicle is started.

The BCDC1225D is also designed to isolate the vehicles starter battery from the auxiliary battery when the vehicle is turned off.

display panel

The front panel features seven LEDs that display the battery set charge profile and also the charge status.

Charge profile LED will be solid on the battery type selected when the unit is operating and charging. A flashing profile LED indicates that the unit is in standby mode and not charging. In my case the Li LED is lit.

Charge status LED indicates the input is from solar or the vehicle alternator. When the solar & vehicle LEDs are on at the same time it indicates both input sources are available & in use. The dual input uses 'green power priority' technology to supply as much power as possible from the solar before adding input from the vehicles alternator to gain maximum output to fully charge the battery.

Stage LED indicates the charge mode by the sequence below.

I have printed this off to remind me of the flash code

photos