This is part one, of our five-part, Twelve Volt Series, where we discuss all the broad strokes to do with twelve volt wiring, solar and storage for four wheel drives.
If you’ve got a basic understanding, then you might want to skip this first article, or just use it as a basic recap. We’re not going overly in-depth for any of this.
Introduction to Twelve Volt Systems
“Twelve volt” is largely just the catch-all phrase, colloquially used to describe anything to do with a vehicles’ electrical system or accessories. All these concepts still apply equally well to a 24v vehicle.
What 12v Systems are Used for
Every vehicle comes with an inbuilt 12v system. It will have a starter battery, and an alternator to charge it when running. These are used to power everything such as headlights; radio; power windows; and all other stock components of the car.
We’re not too concerned with all the OEM/stock components of a car, as we’ll be adding secondary systems to run all the accessories we want specifically for four wheel driving and camping. These may include running a fridge; powering external lighting, such as those used to illuminate a cooking area etc; and even just charging phones.
It’s typically best to run all these from a secondary system powered by an auxiliary battery (see below), so that your accessories (fridge etc) don’t drain too much power from your starter battery leaving you stranded with a flat battery.
Therefore, our two primary concerns regarding the vehicles’ existing 12v system is that we want to utilise the alternator for charging our secondary battery, and we want something that’s going to stop us being able to drain the cars’ starter battery.
Common Applications
Most accessories won’t exceed the alternators charging capacity while the car is running. However, it’s common to use most of these accessories while the car isn’t running, which is when there’s a risk of draining the starter.
Such accessories include:
- Car fridges. These need to be run continuously, including through the night, if you want to stop your food going bad.
- Obviously used while camping and at night, when the car probably isn’t on.
- For running any standard home appliance/accessories that use 240v power. It’s becoming more common for people to purchase inverters, so they can run coffee machines. Save yourself the hassle and buy an AeroPress, or a French press, or a pour-over. If you do it right, you’ll get a better coffee than you ever could with a small 240v machine, and you’ll look like much less of a wanker in the process.
- 12v Induction systems are becoming more and more popular.
- Charging phones.
Components of a 12v System
Batteries
Battery capacity is measured in Amp Hours (Ah). One amp hour, is enough power to run a device that is drawing 1 amp, for an hour. Or, a device drawing two amps, for half an hour.
As we’ll see in the AGM vs Lithium section however, not every amp hour is comparable.
Starter Batteries
Starter batteries are used to start the engine and run all the stock accessories that the car comes with. Starter batteries are nearly always lead-acid and are designed for high CCA (cold cranking amps) output, not for deep-cycle use.
Starter batteries are easily damage, if allowed to be over discharged. If you want to repeatedly drain and charge a battery for powering accessories, you’ll require a deep cycle battery.
Auxilliary Batteries/Deep-Cycle Batteries
Deep cycle batteries are a type/class of battery, and auxiliary batteries are a use case, not a specific type:
Auxiliary batteries are when you install an additional battery to be used to power accessories and not for starting the engine. It just so happens that deep cycle batteries are almost exclusively used for auxiliary battery installations.
A deep cycle battery allows you to drain it further than a starting battery, without causing damage. They also will tolerate a greater amount of charge cycles over their lifetime.
Refer to the alternator section below, for the differences between dual batteries and auxiliary batteries
Types of Deep Cycle Batteries
Common types of deep cycle batteries include:
- AGM (Absorbed Glass Mat). AGM batteries are the most common style of deep-cycle battery used for as auxiliary batteries in four wheel drives. These are a lead-acid battery that utilise fibreglass between the lead plates. They are maintenance free.
- Gel batteries are also lead-acid batteries, but they utilise a viscous gel based acid and do not have fibreglass mats unlike an AGM. They are also maintenance free.
- AGM vs Gel:
- AGM is cheaper.
- They are both un-spillable and maintenance free.
- Gel batteries are more susceptible to damage from high discharge or quick charging (basically all high amperage use).
- Lithium-Ion. Lithium batteries are much, much lighter than lead-acid batteries; they can tolerate almost twice the depth of discharge that an AGM can, without being damaged; but they are much more expensive. They’re also more likely to catch fire, which we’ll discuss in detail in our dual battery deep dive, coming up next in the 12v series.
- AGM vs Lithium:
- AGM is much cheaper.
- Lithium is a lot lighter.
- 100Ah of lithium, is comparable to ~200Ah of AGM. As lithium allows roughly twice the depth of discharge compared to AGM, it can be thought of as having a 2 x coefficient compared to AGM when comparing amp hours. A 200Ah AGM battery, will let you utilise 100Ah worth of power, beyond which it will drop to a voltage low enough to damage the battery, whereas lithium will let you use ~90% of the specified amp hours.
Battery Charging
Alternator Based Charging
As mentioned, the alternator is a component of the cars engine that provides a charging current to replenish any battery power that was used to stat the car, or while it was off. It also provides the power that the engine utilises to run its electronic ignition.
An alternator – even though it is charging the battery – is not a “battery charger” according to a specific interpretation of the term. Battery charger sometimes implies that there is a regulated voltage or current (amperage) output, that is tailored to the charging level required by the battery. While an alternator does have a regulator, it simply limits the maximum voltage provided and does not adjust the charge, relative to the batteries own voltage (level of charge).
Because of this crude, limited functionality, there’s a few reasons why using the alternator to charge an auxiliary battery directly, is not the best option.
To clarify, you can add a second battery directly into the standard circuit that the existing starter battery is a part of. This will simply double your amp hour capacity, but is not an auxiliary battery in the sense that it is not isolate. If you run your accessories from this circuit, you will still drain the starter battery/s, it will just take a bit longer. As these batteries discharge and together at the same rate – thereby having the same voltage – no additional equipment is required for charging and they can both run directly off the alternator.
“Smart”/low-voltage alternators will be discussed in greater depth, in the dual battery article coming next in this series.
Automatic Battery Isolators
An automatic battery isolator, will typically have a voltage sensing relay that can tell when the car is running, or will have a relay that is switched from an ignition feed.
These will isolate the auxiliary battery – and therefore anything accessories that are wired to this battery – from the starter battery, when the car is off, but will reconnect them while it is running so the auxiliary battery can be charged by the alternator. This solves the biggest problem, of potentially draining your starter battery.
However, this solution will slowly degrade your starter battery. As the two batteries (starter and auxiliary) are being drawn from separately, they will be at different voltages when the car is turned back on and the batteries reconnected to the same circuit. Because of this, the alternator will draw a reading that is somewhat of an average of the two batteries, meaning that it will keep charging both batteries, even when the starter battery is fully charged. This overcharges the starter battery, and damages it.
If the automatic isolator, such as the Adventure Kings model, uses a voltage sensing relay, it will not work with a “smart”/low-voltage alternator. If it uses an ignition switch, or you make your own system with a solenoid, it will work with any alternator.
DC-DC Chargers
DC-DC chargers (or BCDC if referring to a Redarc model specifically), are true battery chargers in the sense that they will tailor the charge required, relative to the voltage of the battery in question. DC-DC just refers to the fact that they run off a DC power source (the alternator) and provide a DC charge to the battery.
A DC-DC charger also has an automatic battery isolator. Most models will have a voltage sensing relay, but will also have the option to run an ignition feed, which will override the voltage sensing relay. This allows them to be used regardless of the alternator type (smart or not).
Where DC-DC chargers differ from standard isolators (and where they get their name) is that they separate the charging current to the auxiliary battery. They provide a charging feed to the second battery, that is relative to it’s voltage/charge, but it also stops this battery from affecting the reading that the alternator takes from the starter battery. This prevents the alternator from overcharging – and therefore damaging – your starter batteries.
Most DC-DCs also have an inbuilt MPPT solar regulator, so it will simplify your wiring, should you choose to install solar as well.
240v AC Chargers (AC-DC Charger) & Trickle Chargers
AC chargers are simply just the battery chargers you plug into your mains power at home, to recharge your battery.
These days, many models are available that are designed to be permanently wired to your battery, rather than the type you may be more familiar with that uses alligator clips and is only used when you’ve got a flat battery. Most these models also have a trickle charger function, designed to keep your battery topped up, as lead acid batteries will slowly lose voltage from sitting unused, even if there is no current draw from it.
A permanently wired AC-DC charger is more often used in caravans and camper trailers that sit unused for extended periods of time. However, as 12v setups become more complex as the industry and practices evolve, it’s becoming more common to see these on 4WDs/canopies. They’re particularly useful if you have a touring car that’s nt used as a daily, if it doesn’t have solar or is parked in a shaded area.
Inverters
Strictly speaking, an inverter just needs to change DC (direct current) to AC (alternating current). However, for our use case – and probably 90% of all use cases – when we say inverter, we’re also referring to the voltage being increased. In the truly developed world – which does not include North America – we’ll be stepping up from 12v to 240v.
Inverters are just used so we can run standard electrical appliances designed to run on mains power, from our 12v battery.
Types of inverters will be discussed in more depth, in our upcoming dual battery article.
Solar Power
Solar Panels
Solar panels create electricity from sunlight, as you no-doubt know already.
You’ll see a few different types floating around such as monocrystalline, amorphous, or HPBC (hybrid, passivated, back contact).
Monocrystalline is the most common type you’ll see for 12v/4WD applications and there’s a lot of budget friendly options.
Amorphous can be found in some ultra-premium offerings, such as from Redarc, but I can’t figure out why you would pay so much money for a slight increase in efficiency. I think you’d be better off going for a slightly higher wattage monocrystalline panel.
HPBC is sometimes seen for semi-flexible solar panels. They can often be monocrystalline however.
Solar Regulators
Power comes out of solar panels, with no regulation. Depending on the level of sunlight and positioning, you’ll see huge variance in the voltage and amperage outputs from a solar panel at any given time. Regulators transform this output into an appropriate charging voltage/current.
Most regulators you’ll see in the 4WD space are PWM or MPPT regulators. They may also be referred to as Solar Controllers. We’ll discuss this in more detail in our upcoming solar article, but essentially PWM regulators are the cheapest option available and MPPT are more efficient, thereby giving you more charge for the same capacity of solar. As MPPT are the more expensive option, it’s common to see more functionality built into these regulators, which is more to do with economics than it is to do with technology.
Wiring and Connectors
Fuses, Relays and Circuit Breakers
These are terms that we commonly use when discussing auto electrical.
As you probably know, a fuse is a component you add in-line to a wire, so if that the current exceeds a designated amperage, the fuse will “blow”. This just means that the connection in the middle of the fuse breaks, disconnecting that cable. Most fuses will be found very close to the battery, so that if a wire gets damaged, the “short circuit” will occur after the fuse, so that the connection is severed. This prevents a fire, or just general battery damage.
Circuit breakers, much like the ones in your house, are a switch that turns off, once the designated amount of current is exceeded. Unlike a fuse, a circuit breaker doesn’t need to be replaced every time this happens, it can simply be switched back on. Circuit breakers are much more expensive than fuses (which are very cheap), and they’re generally bulkier, which is why they’re less common than fuses. They are becoming a lot more popular in pre-wired systems, such as 12v control/accessory panels.
Relays are very common in circuits that involve switching something. They are essentially a larger switch, that can be controlled by a smaller one. For example, headlight circuits will use relays. This allows for small guage wires (that can only handle a small current), to go to the light switch inside the cab. These wires will then be run back to a relay, that is closer to the headlights, that acts as a switch for larger cables that go between the battery and the headlights.
Anderson Plugs
Anderson plugs are commonly used for high current connections. They were most commonly used to connect caravans or camper trailers to vehicles, so that a charging connection could be established between the alternator and the caravan/trailer.
They are now becoming common to use for low current accessories such as fridges, as the connection is vibration proof, unlike cigarette-charger style accessory outlets where plugs can easily come loose. It is also now common to see them used for canopies on utes, to connect to the car.
Anderson plugs are most often seen in their 50 amp size, which can be thought of as their “standard” size, but are also available in bigger sizes that can handle up to 350A.
Andersons are usually grey, but can come in other colours such as red, that are designed only to fit that colour. For example, it’s common for red Anderson plugs to be used for connecting solar panel input. This prevents accidentally connecting a feed to a panel, which would result in unregulated power being fed into the battery or connected accessories.
Anderson plugs can also come in a 3 pin version, instead of the standard two. These are typically used for your positive and negative power supply, with the third pin connecting a switching feed, such as when you have a “smart” alternator and need an ignition switch to correctly control a DC-DC charger.
