Camper Trailers Tech Tips

Removable Lithium Battery Box & Compressor Setup





removable lithium battery box
& compressor setup

I have just rebuilt my battery box and compressor box for the Jeep making them easily removable as I only load them when needed.

The battery box is a Hard Korr heavy duty battery box, a strong and neat design. There are two cigarette sockets and a twin USB socket.  It also has 4x 50 Amp Anderson plugs, 3x grey and 1x black. I converted one of the greys to red. It also has 1x 175 Amp Anderson plug and a master switch. There is a readout LED panel for voltage and state of charge which you turn on and off manually, so it is not on all the time. The state of charge part is useless with Lithium batteries.

It easily holds my Sentry 125 amp hour Lithium battery and I have packed it into place inside the box. I have also fitted a Ctek D250S Dual DC to DC charger inside the box, bolted to the lid inside. I disconnected the built in Voltage Sensitive Relay and used the positive from the black Anderson plug to connect to the alternator input on the Ctek. I have a 6B&S lead with fuse running from the starter battery, under the floor mats and the end - with a black Anderson plug, which will also connect to a grey Anderson plug - is stored behind the cargo flap across the back of the back seat. I simply pull it out to connect to the battery box.

The red Anderson plug is connected to the solar Input on the Ctek - I use red Anderson plugs for all my unregulated solar connections and all my panels are unregulated (do not have a regulator attached). I can easily plug either of my 135 Watt or my 100 Watt solar panels to the red Anderson plug to charge the battery through the solar controller on the Ctek. I can even plug both 135 Watt panels to it using a Y cable at the panel end. 

That leaves two grey Anderson plugs which are connected directly to the battery via a circuit breaker and can be used for things like my fridge. The fridge, by the way, is a Waeco 45 litre CFX and fits perfectly between the door and the battery box.

There is a 175 amp Anderson plug on the battery box.  I use this to connect the compressor as it has a peak current draw of 110 amps.  The compressor current drops to around 80 amps after the start up.  I can also use it to connect this battery to the car starter for a jump start as I have made up a pair of crocodile clips on a length of 6B&S cable with a 175 amp Anderson plug on the other end.

The battery box with 125 amp lithium battery inside weighs in at 19 kilograms.

battery box

the battery box Anderson plugs on end of battery box


battery sitting inside the box underside of the battery box lid


battery box specifications old battery box setup

air compressor

The compressor is a twin cylinder Thumper Max from the 4WD Supercentre with a 300 litre per minute rating. The previous air compressor was a Bushranger Max Air. They are chalk and cheese. The Bushranger would take a few minutes to pressurise the air tank and 8 metre hose. The Thumper does it in around 30 seconds.

I used a 150 amp automotive relay to turn the compressor off and on from the driver's seat – the compressor has a pressure limiting switch built in, so it automatically turns itself off and on with pressure changes, the limits being off at 125 psi and on at 90 psi. I simply have a run of speaker wire from the relay to a switch by my right knee to activate it. To connect/disconnect the switch cable to the relay I used a pair of Deans plugs, very popular with remote control aircraft people. It is rated to 60 amps so should handle the switching current, that way I can turn it on and off from the driver’s seat and not have to access the compressor’s own switch. I store the hose coiled up in a canvas bag which I can either leave on top of the load in the back or attach to the rear headrest and hang on the backseat backrest. The 8 metres of hose easily reaches all the car and Crossover tyres and I have an extra 4 metres that came with the compressor and even has Nitto fittings to match my hose and fittings so I can extend the hose to 12 metres and pump up other people's tyres.

I have an 11 litre air tank to maintain pressure in the system.  It has an over pressure release (150 psi), drain plug and pressure gauge attached. A simple plywood casing I made up holds the compressor and the air tank is bolted on top. The unit weighs in at 16 kilograms.

The wiring connected – black 50 amp Anderson plug to the starter battery, grey 175 amp Anderson plug to the compressor via the 150 Amp automotive relay. The red Anderson plug is for unregulated solar and the two spare grey Anderson plugs are for the fridge and anything else I want to plug in.

The pair in situ lightbar, compressor & trailer brake switches


battery box carry handles air hose & wiring from compressor box

The whole setup took around a day to make up.  It takes a few minutes to put it in place and strap it all to the child seat restraints on the back of the backseat.  I only install it when needed so I am not taking up space and carting 25 kilograms around when I don't need it.  The Lithium battery weighs less than half what the old 120 amp hour AGM weighed, has 60% more useable energy, charges faster and maintains the Voltage down to 20% state of charge – win, win, win and win.


 thanks to Dave Jones for this article



august 2019