4WD MODIFICATIONS - ELECTRIC & LIGHTS
These days very few people travel without a portable fridge and camp lighting, and that dictates some form of auxiliary battery power. What do you need?
This article describes the auxiliary battery choices for a 4WD vehicle that has to power a fridge and some camping equipment. In our Camping and DIY sections we cover the situation with slide-on campers, camper trailers and cross-overs.
The typical 4WD traveller has a fridge in the back, filled with food, white wine and beer. Failure to keep drinks at the right temperature is disappointing, but failure to keep food at the right temperature can be health-threatening.
The traditional way to ensure your vehicle fridge will run overnight, when the engine isn’t operating, is with a deep-cycle battery. If the fridge is connected to the deep-cycle battery all the time, it will keep the power flowing as long as it has sufficient charge.
Incidentally, if you’re not familiar with battery jargon, read our Understanding Batteries story.
Dual battery systems are designed to ensure the deep-cycle battery is charged by the vehicle’s alternator, without the chance of the vehicle’s starting battery being discharged.
There are several ways of achieving that, from a simple, manual rotary switch to mini-computerised electronic devices. Before the arrival of electronic dual-battery isolators the state of the art solution was a solenoid device and these are still popular for fitment to older vehicles.
The function of an isolator is to disconnect the deep-cycle battery from the vehicle’s starting battery when the deep-cycle battery is operating the fridge. It also must maintain that disconnection when the engine starts, until the starting battery is fully charged, after which it allows charging current to flow to the deep-cycle battery until it’s charged.
The latest electronic devices take the process a stage further, by monitoring both batteries and adjusting charge rate to suit battery age and condition.
Some dual battery isolators have a function that allows the deep-cycle battery to act in conjunction with the starting battery, to boost starting power should the starting battery drop voltage.
That system functions well where cranking loads are small, but a dead-flat starting battery may not receive enough power from the deep-cycle battery to start a large-capacity diesel engine. You can then be stuck with a dead engine and a dead fridge.
Some electronic isolators with override have a block on the dual connection that prevents draining the deep-cycle battery if the starting battery has too little power to effect a dual-battery start.
As important as the type of isolator you select is the way the dual-battery system is fitted.
Traditionally, a second battery goes into the engine bay, but most of today’s engine bays are full of other stuff. Also, today’s engine bay temperatures are higher than those of yesterday and batteries hate too much heat – particularly absorbed glass mat (AGM) and lithium types.
The emergence of quality power packs, or power stations, as they’re sometimes called, has changed the auxiliary battery scene considerably. The quality ones come with multiple power outlets as well as solar input and can effectively replace the rather crude second battery in a box, in the back of a wagon or ute.
These power packs are also portable and we’ve tested several of them.
A deep-cycle battery or a power pack and most types of isolator can be fitted into the back of a wagon or ute, but don’t scrimp on the size of cable connecting the starting battery to the auxiliary, or you’ll suffer from voltage drop. You can buy protective cases for deep-cycle batteries that have to be stowed inside vehicles.
A simple isolator won’t be enough for many modern 4WDs that have electronically regulated alternator outputs. What’s required is a purpose-designed auxiliary battery DC-DC charger, sometimes called a BC-DC charger.
Be particularly careful with packaged battery power packs that come with cigarette-socket chargers. These vehicle outlets can’t provide sufficient amps to charge these units, but the better quality power packs have optional compatible alternator-connected chargers.
All connections, including earth terminals, must be of top quality material and securely fastened with Nyloc nuts and correctly crimped connectors. A loose connection will cause big trouble. If you’re uncertain where fuses or circuit breakers should be fitted, you need to consult an auto electrician.
There are several different battery and portable power pack types and the best of the conventional types cost plenty: budget minimum $500. (Lithium is even more expensive.) A cheap starting battery won’t run a fridge reliably or for long.
Incidentally, a starting battery that’s been used for heavy winching work needs to checked for condition afterwards, because extended winch operation that causes deep discharge is not recommended – even with the engine running at high idle.
A truck-rated starting battery is best for dual-battery winching.
Deep-cycle batteries tolerate overnight drain better than starting batteries, but unsealed lead-acid deep-cycle types need externally-plumbed ventilation and regular checking for battery condition – especially after long camping trips.
AGM batteries with 100 amp-hour ratings are heavy, but don’t need ventilation, can’t spill acid, are low maintenance and tolerate charging abuse better than gel types. However, AGM batteries don’t like heat, so an under-bonnet location isn’t ideal and won’t be warranted unless the battery casing is a special heat-insulated type.
Lithium-ion deep-cycle batteries are also heat-sensitive and we’ve yet to see one that’s warranted for under-bonnet installation.
No matter what isolator and deep-cycle battery you choose, you’ll still need to charge a single lead-acid battery – including AGM types – every day and a lithium every two days. Running the vehicle engine isn’t usually ideal.
You need some form of backup battery charging with every dual-battery installation, to make sure you won’t get stranded in the bush.
Solar power is useful, if the sun is shining, but can’t be relied upon in all locations at all times of the year. However, sunshine is reliable in the desert regions during winter and in monsoon-affected regions during the Dry Season.
A solar panel needs a controller that’s compatible with your battery choice and with your isolator system.
Beware the cheap solar controller
There are many different solar panels available these days and many on-line kits come with a solar charge controller as part of a package that’s usually around $120 or even less.
The charge controllers in these kits have a retail value around twenty bucks and should be treated with great suspicion. At OTA we bought one and fitted it to our LandCruiser 75 Series, in conjunction with a 130-watt solar panel.
The panel was connected to our under-bonnet second battery via the low-cost controller and we measured the input voltage at 14.4 volts. So far, so good.
However, even with the second battery fully charged the voltage remained at 14.4V, meaning the controller wasn’t dropping to recommended ‘float’ level, around 13.6V.
We checked the controller’s ‘diode’ capability by running the engine, so that the alternator charged the second battery at the same time as the solar panel was charging it.
The controller failed almost immediately and never worked again.
We replaced this cheap controller with a quality solar regulator – RRP around $85 – and it’s been functioning perfectly ever since. The regulator was programmable to suit standard lead-acid, AGM, Gel and Calcium lead-acid batteries. It also had a diode function that prevented alternator charge harming the regulator or the solar panel.
How Many Amps
It’s easy enough to calculate what size battery you need and how long you can expect it to last before recharging.
If we assume four hours of fridge operation each day you’ll need 300Watt-hours/day (75W x 4hrs). LED lighting and some phone and tablets charging is another 60Wh/day. That’s about the minimum power consumption a campsite can expect: 360Wh/day.
On the face of it the battery capacity needed is 360 divided by 12V = 30 amp-hours (AH).
However, lead-acid battery makers recommend no more than a 70 percent discharged level so, to have a 30AH daily supply, a non-lithium battery needs to be 100AH capacity. A lithium battery less than half that capacity can do the same job, but most buyers opt for a minimum 100Ah lithium battery, to increase fridge operating time.
Reducing your power consumption is one way of extending battery charge life. Our experience is that LEDs use much less power than incandescent or fluoro globes and we find that an LED light near the stove and food preparation area, in combination with LED head torches, provides ample camp lighting.
Lithium deep-cycle battery
Everyone these days is familiar with the rechargeable lithium-ion battery that powers most mobile devices, from phones to power drills, so it seems strange that it took so long for battery makers to produce a reliable, automotive deep cycle lithium battery.
The principal issues that delayed the lithium deep-cycle battery were safety improvements and development of a specific charging system. Well-publicised fires in aircraft using lithium-ion batteries had to be avoided.
Where the familiar rechargeable appliance lithium-ion battery is a lithium-cobalt type (LiCoO2) the automotive deep-cycle version uses lithium iron phosphate (LiFePO4) technology.
This LFP battery (Lithium Ferro-Phosphate) uses LiFePO4 as a cathode material, because it’s a more stable compound that resists breakdown much better than LiCoO2 if short-circuited or overheated. The LFP battery won’t catch fire in the way an LCoO can and also offers longer life, a better power delivery rate and a constant discharge voltage.
The downside is slightly heavier weight than an LCoO, but both types weigh only around one-third that of lead-acid batteries.
Also, where a lead-acid, gel or AGM battery should not be discharged below around 70-percent of its amp-hour capacity the LFP battery is said to be fine with discharge as low as 20 percent.
The LFP equivalent of a 120 amp-hour AGM battery weighs only 10-15kg – up to 23kg less.
Put another way, an LFP battery of the same weight as an AGM can produce constant power for up to four times as long.
On top of that, the LFP battery holds 12.8-12.5V until it reaches that 20-percent point, allowing the battery to deliver virtually full power until it is discharged, whereas a traditional battery loses voltage progressively as it discharges.
But there’s more: charging cycle life is said to be up to 10 times that of a traditional battery and charging times are typically 1.5-four hours.
However, before you rush out to buy a lithium replacement for your deep-cycle battery, there’s a catch. To avoid damage to the LFP cells that could be caused by excessive charging voltages, temperature-based voltage compensation, equalisation or continuous trickle charging, it’s vital that the LFP battery is connected to a purpose-designed charger. Lead-acid chargers cannot be used with an LFP battery.
The importance of a healthy starting battery
Regardless of the type of deep-cycle battery or power pack you choose, it’s vital that you have a healthy starting battery. Your alternator is programmed by the vehicle maker to recharge the starting battery and power the vehicle’s electrical and electronic systems.
It’s not set up from the factory to charge a second battery or power pack. To do that, the isolating system needs to connect to the starting battery and direct additional alternator charge to the second battery.
Any problem with the starting battery’s ability to absorb and maintain charge level can have serious effects. One we’ve experienced ourselves was a starting battery that became hot to touch and its case swelled visibly!
Another possible issue is that the alternator can’t charge both batteries properly, so the second battery might not reach full charge. The same issue can occur in systems with DC-DC chargers.
It’s been our experience that a starting battery starts to lose its edge after three years’ usage and can have serious capacity issues after four.
It’s tricky to diagnose a failing starting battery, because it may read 12.8 volts with no applied load and thus appears to be fine. Also, a failing battery might still have enough cranking amp capability to start an engine easily – especially in the case of today’s smaller-capacity petrol and diesel engines.
A simple way to test your starting battery’s capacity to bounce back from delivering healthy starter-motor amps is to check its voltage level while it’s actually cranking a cold engine.
After a normal driving day that should see the battery at full charge, park the vehicle overnight and then lift the bonnet and get out your multimeter next morning.
Select the ‘V’ mode on the meter and put the probes onto the battery terminals that should be reading 12.5-12.9 volts, without any load on the battery. If the battery’s overnight-rested voltage is less than 12.5 it’s a dud and needs replacement.
Have your better half press the starter, while you look at the voltage readout on the multimeter screen. You need to look carefully, because the voltage reading will drop momentarily as the starter motor engages and then the reading will quickly increase once the alternator does its thing.
The ideal voltage drop while cranking the engine is no less than 10 volts and more is better. If your starting battery voltage drops below 10 volts when cranking, it’s a dud and needs replacing.
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