In order to answer the above question you first need to know:

• How much power are you using on a daily basis, and…
• How much time do you have to replace it?

Naturally, your camping fridge uses different degrees of power throughout the day. This is because ambient temperatures can radically fluctuate between morning and night.

It also has a lot to do with opening and closing the fridge, which you’ll presumably do more often during the course of the day, than you would at night

However, typically speaking, most 12V camping fridges use between 30A/h and 40A/h over a 24-hour period.

Depending on daylight conditions, as well as your geographic location, most campsites have anywhere between 2- and 7-hours of usable solar input.

Considering an 85W panel produces approximately 5A per hour (in ideal conditions), you would need at least 7-hours to replenish the 35A you’ve removed.

That said, in order to account for non-ideal conditions such as dew and partly cloudy weather, it’s best to upsize the panel to a 120W or 150W unit. What’s more, upsizing your panel will help to produce enough energy to power additional camping accessories such as LED lighting, and/or a cellphone charger.

Of course, the above calculations are radically simplified in terms of fridge size, performance, operating conditions, and how often you’re reaching for “one last beer”.

That said, it’s not uncommon to find campers using panels that are up to 300W in size. However, bear in mind that your regulator would need to be rated to this capacity, and that such a panel would be impractically large in the case of a non-flexible unit.

FREQUENTLY ASKED QUESTIONS

1)   Does the quality of the panel make a big difference?

Yes, panel quality can significantly affect the performance and efficiency of your solar setup. Panels are typically divided into two main options: Monocrystalline and polycrystalline. Monocrystalline panels are generally more expensive and better performing due to their structure being made from one large crystal. This is in contrast to Polycrystalline panels which are made from lots of smaller crystals.

It also means that Monocrystalline panels produce more energy in relation to their size. 

2)   Does the quality of the regulator make a big difference?

This will depend on several factors, but generally speaking MPPT regulators are better performing and more costly than PWM regulators.

3)   Does my battery type make a big difference?

Yes, battery chemistry (and size) can play a significant roll in the performance of your solar setup.

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Is it time to ditch your lead-acid battery for lithium-ion technology?

While some overland travellers have migrated away from lead-acid batteries in favour of Lithium Iron Phosphate (LiFePO4), others are not yet convinced of the economics.

Although it may be true that the higher costs of a LiFePO4 auxiliary battery make it harder to justify in a vehicle-based application (where the system is only used a few times a year), there are significant recharge benefits to switching to a LiFePO4 dual-battery setup.

Economics aside, the real question is: How much better performing is LiFePO4 when compared to lead-acid batteries?  And, does that performance justify the higher upfront costs?

BATTERY TESTS

Boasting a range of DC-DC chargers that are all lithium, AGM and wet-cell compatible, National Luna recently tested three battery options that are commonly used within the leisure market. We conducted these tests by discharging each battery type by 70Ah, and then recorded the recharge performance using our 25A and 40A DC-DC chargers.

As shown in the graphs below, the LiFePO4 battery features a longer ‘Bulk’ charging stage in relation to its shorter ‘Absorption’ stage. This is thanks to lithium having a better ‘Conversion Efficiency’, which means the LiFePO4 battery reaches its full capacity in a far shorter period.

In contrast, the recharge performance of the wet-cell and AGM batteries is hindered by a disproportionately short ‘Bulk’ stage, in comparison to a longer ‘Absorption’ stage.

What’s more, the extra 15 amps of the NLDC-40 help the LiFePO4 battery reach a full charge in less than 2-hours. Needless to say, a rapid recharge cycle is supremely practical in terms of driving times and how you plan your road trip.

PROS & CONS

Of course, only you can decide if the above data justifies a migration, but aside from the rate of recharge, there are several other pros and cons to consider.

LiFePO4 PROS:

• Charges faster
• Significantly lighter (important for portable systems)
• Can be deeply discharged without greatly affecting battery life
• Has a longer life span

LiFePO4 CONS:

• Heat sensitive
• Costly initial expense
• Requires a unique charging algorithm
• Cannot be charged directly from your vehicle’s alternator
• Can have a much lower current limit, making it unsuitable for high-current applications, i.e. winching and engine cranking

SUMMARY

With the above points in mind, it’s clear that the decision to adopt LiFePO4 technology has less to do with economics, and more to do with the convenience of having a fast-charging dual-battery system.

That said, it’s really a personal question of whether the performance benefits of a LiFePO4 battery are enough to overlook the initial costs of the newfangled technology.

However, it should also be noted that the integration of a solar panel will also greatly influence your decision, as well as your camping habits: Do you typically drive long distances between camps, do you move around a lot, or do you tend to stay in one campsite for a few days?

What’s more, not all DC-DC chargers support lithium technology, so make sure your DC- DC unit is lithium compatible before you make any changes to your dual-battery setup.

Brought to you by National Luna

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The 4×4 travel market has no shortage of hot debates and shootout tests. Whether it be vehicles in a comparison, or tyres, suspension, fridges, winches, or even camping pots for that matter, people want to know what works “best”.

However, there’s one subject that many overland travellers are generally keen to steer clear of, and that’s the topic of batteries and split-charging systems.

So why is the topic so controversial?

Well, it has a lot to do with varying vehicle types, alternators, preferred battery locations, power needs, and of course, different driving times / distances. There are so many variables to consider that it’s almost impossible to say: “This dual-battery system is better than that one”.

With this in mind, we laboratory tested various dual-battery kits, along with various battery types, to determine which setup performed “best”. However, rather than deliver a conclusive result, the tests highlighted just how complex the subject really is.

The following graphs highlight what we found in terms of when a solenoid system works best, and when a DC-DC system should be the preferred choice.

SOLENOID TEST

The above mentioned tests concluded that in certain instances, if your vehicle’s alternator output delivers a constant voltage of 13.9V or more, then a 20A to 25A DC-DC system will actually slow down the recharge process. In fact, above 13.9V, the solenoid system radically out performs (within the first few hours of driving) any 20A to 25A DC-DC charger on the market, regardless of what type of battery you use.  

As shown in the graph above, the solenoid system (blue line) rapidly outperforms a 25A DC-DC setup (red line) within the first 3-hours of driving. You’ll also notice that at this voltage (13.9V), the solenoid system doesn’t quite make it to full capacity (98% charged).

However, in saying that, it will also take the DC-DC system more than 5-hours (driving time) to fully recharge the battery.

This explains why so many dual-battery systems work well within the first year or so, but as time goes by, the system becomes less efficient. The reason for this is because the performance of the battery is declining with each partially recharged state. This is especially important for wet-cell batteries.

That said, it’s strongly recommended that an Intelligent Maintenance Charger be used (after your trip) no matter what type of system you use. The mistake many of us make is to believe that a few hours drive home will do a sufficient job at recharging the auxiliary battery, when in fact, the battery still needs a maintenance charge in order to reach a full (storage friendly) state.

DC-DC TEST

The graph below highlights the obvious advantage of a DC-DC setup once the alternator’s output is as low as 13.5V.

Although the solenoid switch is still outperforming the DC-DC system within the first 2-hours of driving, the bigger issue is that the solenoid noticeably fails to fully recharge the battery (even after 8-hours), and the best it can do is an 86% recharge state.

If you continue driving for more that 2-hours the DC-DC system starts to drastically outperform the solenoid switch.

To further complicate things, the tests showed that your chosen battery type (wet-cell, deep-cycle, AGM and lithium) played a fundamental role on how well the DC-DC system worked.

Put another way: If your DC-DC charger is unable to change its charging profile to suit certain auxiliary battery types, it could potentially ruin your battery.

What’s more, because DC-DC systems are heat sensitive, once engine-bay temperatures reach 50ºC+ (a very normal under-bonnet temperature), many DC-DC units shut down. Which is why it’s often best to install your auxiliary battery and DC-DC system in the boot of your vehicle – away from heat. Incidentally, solenoid switches don’t have the same problem.

SUMMARY

• If your vehicle’s alternator delivers a constant voltage output of 13.9V or more, a solenoid switch is the preferred choice.
• If your vehicle’s alternator delivers a constant voltage output that’s less than 13.9V, a DC-DC charger will do a better job at restoring the auxiliary battery’s (near) full capacity.
• No matter what dual-battery system you install, it’s advisable that an Intelligent Maintenance Charger be used to service the auxiliary battery and restore it to full capacity after each road trip.
•  Aside from the 13.9V threshold, the tests do highlight a growing need for DC-DC chargers within the modern-vehicle market and their increasing use of variable voltage alternators.
• Most high-end DC-DC systems include other functionalities such as solar compatibility and lithium-ion support. So if either of those features is important to you, then a good quality DC-DC system is the obvious solution.

Brought to you by National Luna

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