FRIDGE, BATTERY AND INVERTER MODULE

Design and Build

FRIDGE, BATTERY AND INVERTER MODULE

Design and Build

When fitting out the 300, I decided to create a fully self-contained module, which includes a fridge, fridge slide, LiFePO4 battery, DC-DC charger, Inverter and enclosure.

Incorporating all this functionality into a single, easily removable module offers significant advantages for my needs over the permanent fitment of a dual battery system and the removal and installation of a fridge alone, into the load area.

In this article I'll provide the details of the design and components of the module for anyone else who wishes to construct something similar.

Affiliate link notice: This page contains eBay affiliate links, for which I may receive a commission if you click on a link and make a purchase of any item on eBay. The price you pay is unaffected. 

FRIDGE AND POWER MODULE - CONCEPT

NOTE ON ORIENTATION: When discussing the module, I'll consistently use "rear" to describe the end of the module at the rear of the car, and "front" to describe the end of the module towards the front of the car.

My 300 is typically used as a daily drive when I'm not on a trip. For this reason, I don't want to install a permanent storage system (such as drawers) or a large fridge into the load area, because it would reduce the functionality on a day-to-day basis, and prevent the use of the 3rd row seats.

In previous vehicles I'd always installed a permanent under-bonnet dual battery system, to support a removable fridge and other accessories, which mean't carrying around an extra 40kg all of the time, even when that extra battery capacity wasn't required. When I looked at my battery requirements for the 300, it became apparent that the only item to use much power without the engine running would be a fridge, so it seemed a bit pointless to lug another battery around day-to-day when a fridge wouldn't be present much of the time.

Lithium Ion batteries (specifically Lithium Iron Phosphate -LiFePO4) provide a great weight saving, limiting the issue with a permanent installation, but placing them under the bonnet isn't ideal because they lose life and performance at the temperatures commonly found in the engine bay. However, their versatile shapes and high energy density make installation within the vehicle a viable proposition.

Put it all together and the idea of a fully removable, self-contained fridge and power module made a lot of sense for my needs. The more I thought about it, the more the idea grew, and I decided to add additional functionality in the form of an inverter and other charging and power outlets.

DESIGN BRIEF

I wanted the module to fulfil several roles:

  • Contain a fridge with easy access;
  • Be securely mounted, but easily removable;
  • Have its own power supply, sufficient to run the fridge and other equipment;
  • Provide a 240v power supply, to operate assorted equipment;
  • Contain a charger to maintain the battery.

 

FRIDGE AND POWER MODULE COMPONENTS

FRIDGE:

I decided to design the module around my existing fridge, a Trailblazer 50 which I've had for over 20 years. These fridges are relatively large due to thick insulation, with the 50L Trailblazer having a similar footprint to a 60L Engel.

FRIDGE SLIDE:

Looking at the various fridge slides available, my ideal option was to be a fridge drop-slide, such as those made by MSA. However due to the design of the 300's cargo area and the distance to the edge of the rear bar, a drop-slide can't be readily installed. Instead, I decided on a Dunn and Watson 'tilt slide', which allows the fridge to slide out then tilt down, allowing access for shorter people or children. I also installed a couple of slide bolts (padbolts) at the back of the slide, which essentially locks the tilting mechanism if I don't want it to tilt.

The power for the fridge is supplied via a Fridge Cable Caddy.

ENCLOSURE:

I wanted to make a complete enclosure to improve practicality in the back of the Cruiser. Enclosing the fridge means there's no wasted space above the fridge, and stops it being obstructed or jammed by items leaning or falling on to the side of the fridge. It also provides some air space for more efficient operation and a mounting surface for other components. I used aluminium for all of the enclosure, to minimise weight and volume compared to plywood. The enclosure is mounted to a false floor which helped secure the module, and I applied some marine carpet for aesthetics. I bought the aluminium sheet from a local trade supplier, and had it folded up by a mate.

BATTERY:

There are a large number of LiFePO4 batteries on the market now, in numerous different capacities and form factors, at a wide range of price points and quality levels. I examined many different brands and options, and eventually decided on a 100Ah slimline battery made by Custom Lithium and supplied by Richards Auto. It has excellent specifications, a 7-year warranty, and is made in Australia.

A huge part of choosing this battery is its very high maximum power output. Many slim 'Lithium' batteries have outputs limited to 100 amps or even less. This makes them unsuitable for high drain devices such as inverters. The Custom Lithium battery's BMS is rated to a continuous 180-amp output making it ideal for my module, simultaneously being able to run the inverter (Max 135A), plus the fridge and other items such as assorted chargers I use for battery tools, cameras etc.

BATTERY MONITOR:

To monitor battery State Of Charge (SOC), plus consumption and charging rates, I installed a REDARC Smart Battery Monitor, again supplied by Richards Auto. The monitor works via bluetooth to a REDARC app on my phone, to keep track of the battery.

DC-DC CHARGER:

Keeping the Custom Lithium battery charged is another Australian REDARC product, the BCDC1240 CORE charger. Essentially an unsealed (in-cabin) version of their acclaimed 40A DC-DC charger. Once again supplied by Stefan at Richards Auto. The charger is fully compatible with LiFePO4 batteries, which is a vital part of a safe lithium battery installation. It has a maximum charge rate of 40 amps, meaning it can fully recharge the 100Ah battery with a few hours of driving.

The charger is powered by a custom version of the Richards Auto rear power outlet kit. This provides power from the main start battery/alternator via an Anderson plug located in the rear cargo area, whenever the engine is running. I also added a second Anderson plug to the charger for solar input.

INVERTER:

The final major component of the module is a REDARC pure sine wave inverter, once more supplied by Richards Auto. The model I've chosen is rated at 1200w continuous output, making it ideal for my needs, running a microwave oven, assorted battery chargers and a starlink system. It can cope with up to 1380-watts for 10 minutes, and also a startup surge of 2400 watts for a couple of seconds.

Although there are cheaper inverters available, some of which may even be generously described as being "pure sine wave", they rarely provide 'clean' power. For anything that depends on precise voltage (such as electronics), it's very important to ensure the supplied power is voltage-stable, and truly "pure sine wave". Don't skimp on a cheap inverter if you plan to use it for anything with fragile electronics.

ADDITIONAL COMPONENTS AND FUNCTIONALITY:

I also added a switch and relay to power the fridge, and some USB and USB-C power outlets from Air On Board to run equipment and chargers. Keeping the module safe is a 4-way MIDI fuse block for the major components and charger, plus an 6-way regular blade fusebox for the fridge and power outlets. Additionally, the fusebox supplies an additional Anderson plug inlet/outlet, which can be used to run additional items (such as another fridge/freezer) or also as an input so the battery can be charge from mains input via a 240v charger if required. I've got a KickAss 22A lithium-compatible smart battery charger for that purpose.

DESIGN, CONSTRUCTION AND ASSEMBLY

DESIGN AND CONSTRUCTION:

Working around the Trailblazer 50 as a starting point set the size of the enclosure and the choice of fridge slide size. The length and wheel arch shape/position of the 300's cargo area also determined the best positioning of the electronic components.

The side of the enclosure is positioned hard up against the wheel arch trim at the bottom, with the electronic components positioned on the side to minimise the amount of dead space beside the unit. The battery is located above the wheel arch and the inverter located in the void behind the wheelarch and between the side of the enclosure and the trim of the load area.

I didn't want to waste the space on top, so turned it into a shelf area, including a hinged section which folds down to cover the area between the main enclosure and the inside of the cargo area trims. As you can see in the photos below, I use this large flat area to store a variety of items from chargers and electronics, through to cooking and communications hardware.

The folded box of the enclosure is attached to the fridge slide and the false floor using bolts, rivets and Silaflex 227. To prevent flexing, the end of the enclosure is boxed in, and the front face also has a plate to prevent twisting/flexing. However, I originally used 2mm aluminium for this plate, with square-cut internal corners. This cracked on the CSR trip, so have since replaced it with 3mm aluminium and also radiused the corners. I have not had any issues with cracking since these upgrades.

The top shelf, centre side of the enclosure, and the false floor are all covered with marine carpet. This prevents items sliding around and can also be used to secure smaller items with self-adhesive velcro. I added numerous saddles to the enclosure and false floor for securing larger items with tie-down straps.

ASSEMBLY OF COMPONENTS:

The electronic components are attached to the side of the enclosure using button-head bolts with nyloc nuts. Wiring is well protected using split tube, secured with cable ties and cable clips to prevent chafing or damage. All earth/ground wires are secured with bolts and star washers to ensure a good connection.

The charger is located to the status lights can be seen from the rear face of the module, and solar input can be readily attached via the same face, accessed by opening the tailgate.

All connections are fused for safety, and all wiring connections are crimped and soldered to ensure reliability.

IMPORTANT SAFETY INFORMATION

All types of Lithium-Ion batteries (including Lithium Iron Phosphate batteries), store a large amount of energy for their size. Although quality products which have been installed and used correctly are extremely safe, it's vital that you follow directions and use common sense when using and installing these batteries:

  • Ensure you follow the manufacturers' latest directions and recommendations for the installation and wiring of the battery and charger(s). They may differ or have been updated since this article and video were produced;
  • Ensure the charger(s) you use are designed and set for a Lithium Ion battery type;
  • NEVER charge a Li-Ion battery using a charger designed only for lead-acid, AGM or Gel batteries;
  • NEVER charge a Li-Ion battery using a simple connection from another battery, or raw voltage (eg: from an alternator or 240v power adaptor) unless the battery manufacturer specifically recommends such a connection;
  • NEVER put a Li-Ion battery in parallel with a Lead-Acid, AGM or Gel battery;
  • NEVER puncture or cut a Li-Ion battery;
  • NEVER use a Li-Ion battery which has been damaged;
  • Consult or employ a qualified auto electrician to check or complete your installation.

If you undertake your own build/installation, you do so entirely at your own risk.

CONCLUSION AND
1-YEAR REVIEW

I write this conclusion about 12 months after I manufactured the module, and following extensive use including on the Canning Stock Route trip, where I used the module with its own fridge plus a second fridge running as a freezer. The inverter was used almost continuously to power assorted items including a microwave; Makita chargers (running tools and a kettle); Starlink; plus assorted camera, laptop and drone batteries and power supplies.

Despite the extremely rough terrain of the Canning trip, all of the electronic components performed (and continue to perform) flawlessly. Due to the stable voltage as SoC declines, in practical terms I found the 100Ah lithium battery to be the equivalent of a far larger lead-acid or AGM battery, probably around the 150Ah mark. It was more than capable of running the fridge (Trailblazer 50L), plus the freezer (Engel 29L) overnight without a problem. In addition to the fridges, after stopping each afternoon the battery would typically power the following items:

  • Power a laptop to import and process video/photos for approx. 3 hours;
  • Power a Starlink v3 for approx. 4 hours;
  • Power a microwave for approx. 5 minutes to reheat food;
  • Recharge GoPros and drone batteries.

After this usage, the following morning the battery would typically have a SoC of around 20%, and would then be back to 100% by the time we stopped for morning tea. If we stopped early or stayed a couple of days in the same location, then I would deploy some portable solar panels to help top the battery up during daylight hours.

The module did suffer one structural/construction failure during the extensive corrugations experienced on the Canning, with the 2mm aluminium face plate suffering stress fractures (due to flexing) in the top corners. After the trip I replaced the 2mm plate with 3mm and included radiused corners to reduce point stresses. Additionally, I increased the width of the face plate edges from around 40mm to 60mm. Since making these changes, the structure has remained sound.

Fridge & Lithium Battery Power Module
Photo gallery

Below, find a series of photos showing the various aspects of the module design and construction. The specifications of the module will vary based on the fridge, so I thought it better to show photos of the the major aspects rather than share exact specifications or reverse-engineer a CAD file, because it's likely that most people will need to make something slightly different.

Overview

Due to the size of the fridge, the module is quite large, occupying about half of the width of the cargo area. Obviously this could be reduced through the use of a smaller fridge.

You can see the front face here, which serves to provide structural integrity to the fridge enclosure, by preventing it twisting and flexing. Down the left side you can see the REDARC charger status visible through the top cutout; the solar input Anderson socket; the fridge switch and USB charger outlets, plus the REDARC 1200W inverter at the bottom. The 50L Trailblazer fridge slides out (and tilts if required) by releasing the levers on the slide unit.

The top of the enclosure serves as a shelf for additional storage, including a microwave if required.

Fridge and Slide

The slide is a Dunn and Watson 'tilt slide'. They make these in numerous sizes to suit assorted fridges. You can find them on eBay.

I added some small padbolts to the front end to lock the tilting mechanism when it isn't required. If you're average to tall height, you won't need the tilting functionality unless your fridge is very high. But it's useful if you're shorter or have kids that need to access the fridge. As an alternative to using the tilt slide and locking it, you could also use a regular fridge slide with no tilting mechanism.

The power travels from the module to the fridge via a Fridge Cable Caddy. Something like this is required to protect the cables from damage caused by the sliding mechanism.

The power travels from the fusebox, via a relay out to the fridge. The relay is switched via a Carling-type rocker switch from Air On Board, in the same form factor as the USB/USB-C power outlets, with all three mounted into a plastic switch panel.

Although the switch is rated at 20 amps, and the fridge should never draw more than 15, I decided to use a relay to minimise voltage loss.

False floor

The enclosure is permanently attached to a false floor, which covers the entire load area. It's hinged beside the enclosure to make removal and storage easier.

I did this for a couple of reasons: It provides a base for the enclosure, which can be secured using the existing factory tie down points. And it protects the factory carpet from damage.

The false floor (and therefore the module) is secured using the captive nuts of the four factory tie down points. I bought some longer bolts (6mm metric) and large 'mudguard' washers to secure the false floor into the captive nuts after removing the factory hooks.

I also added a series of tie down loops on the floor outside the module (and also on the side and top of the enclosure) to secure cargo using webbing straps.

Enclosure top storage

Fully enclosing the fridge provides a large shelf which can be used for storage. As with the floor, I carpeted this area to help prevent items moving around. The carpet also makes a useful surface for securing small items using velcro.

There is a hinged section over the top of the module electronics to maximise space and bridge the gap between the enclosure and the side of the vehicle.

I use this area as storage for assorted items. For example, on the CSR trip I had a small microwave oven; A Starlink kit; A Makita 2x18v kettle; A Makita 18v rapid charger; plus chargers for the DJI drone, cameras etc.

Module electronics and wiring

All of the major electronic components are mounted to the side of the module, occupying the space between the enclosure and the side trim of the vehicle. The wheel arch position defines the distance of the enclosure to the side trim. Placing the components above and behind the wheel arch trim maximises what would be a dead space between the fridge enclosure and the side trim.

You can download a high resolution wiring diagram here.

The battery is located above the wheel arch on the forward end of the enclosure. The battery negative cable goes through the REDARC battery monitor, then connects to a common ground point on the aluminium of the enclosure, plus a heavy cable straight to the inverter. The battery positive cable goes to the busbar on the 4-way MIDI fuse block. There are then positive output cables running from the fuse block to the Inverter positive; the DC-DC charger; and the main input for the 6-way blade fuse holder.

The DC-DC charger is mounted at the top of the enclosure towards the rear end of the enclosure. It has dual inputs, being fed from the main start battery via a customised Richards Auto cargo area power kit. Instead of the kit's Anderson connector being fed from the rear fusebox as is the case with the standard kit, Richards made me a custom heavy cable running from the second relay of their Trailer Power Cable Kit I installed previously. This means it's rated to a full 70 amps, which is perfect for powering the 40A DC-DC charger.

The charger includes a solar input which is fed from an Anderson plug accessible from the face of the enclosure.

The inverter is mounted to the lower side of the enclosure towards the rear, with the switch, 240v outlet and 240v circuit breaker/RCD. All accessible from the rear face of the enclosure.

The 6-way blade fuse holder is fed from a 30A fuse in the MIDI fuse block. It then has fused outputs for the main fridge via an isolation switch and relay; A secondary Anderson plug which can be used for both an additional load (such as another fridge) or as an input to charge the battery using a 240v charger. The blade fuse box also supplies power for the USB and USB-C power outlets located on the rear face.

All of the cables are neatly bundled, cable tied and clamped to the enclosure to ensure there's no possibility of shorts or chafing.

REDARC Redvision App, showing battery status

Promotional and advertising content declaration

Undeclared promotion is rife in the 4WD "influencer" industry. Project300 is different. In the interests of full transparency, every page on Project300 will contain disclosure of what -if any- benefits were received in the process of choosing and installing the listed product(s).

I plan on owning and driving the Project300 LandCruiser for at least a decade. I'll only ever choose and install products which I believe to be of the highest quality, and which will serve me reliably throughout the life of the vehicle.

Disclosure for this article:

  • The battery, inverter, charger and monitor were supplied by Richards Auto at no cost;
  • All other components were purchased retail with no discounts;
  • No monetary payment was or will be received from anyone to use or recommend their product;
  • I have no obligation to only make positive comments, and am free to say or write whatever I choose about the products, now and in the future;
  • This page contains affiliate links to eBay and/or Amazon. If you click on a link and then purchase any product at eBay/Amazon within a 24hour period, then I may receive a small commission on the total sale amount. The price you pay is unaffected;
  • This page contains advertisements from Google Ads, for which I receive a small payment. I do not control the content of the advertisements and do not necessarily endorse the products being advertised.

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