Getting to know your voltmeter function
A voltmeter measures the batteries potential in volts. A deep cycle AGM battery is considered fully charged at 12.8V when measured at rest and dead flat it reads around 10.5V. When charging, a battery will read higher than 12.8V, often up to 14.5V. Regularly discharging your battery to 10.5V will result in a drastically shortened life.
It’s recommended to discharge to no lower than12.2V. You may notice your fridge starting to cycle more frequently at this voltage hinting towards the depleting charge, therefore its decision time.
The most accurate time to measure voltage is when the battery is at rest, without any load. This is usually in the morning, assuming a cool climate when there has been little electrical demand overnight.
How many batteries work best?
Logic tells us two batteries are better than one if you are doing more than weekend trips, as it maintains a reserve for those times of high usage or low recharging. There won’t always be sun to drive solar and you may be camping in a national park which prevents generator use, so extra battery reserves will go a long way to power your devices.
You may need to consider reducing your power usage and to do that you need to understand how much each item consumes.
A deep cycle battery is typically measured in Amps, such as 100Ah. It is important to note, you can only safely discharge an AGM battery to around 50% of its capacity, which means a 100Amp battery only has 50 Amps utilisation. If a fridge draws 2 amps per hour (Ah), the battery will only last just over 2 full days (48hrs). Put like that, it’s easy to appreciate why you need more than one battery!
Have Your Alternator Tested Free
We will test your alternator, battery and starter motor free of charge.
How to Calculate Power Useage
Understanding power usage is helpful for understanding how much you need to replenish each day and how long that could take. There are four methods for calculating power use.
Formula: Watts / Voltage = Amps. If a fridge draws 24W, divide by 12V = 2 Amps per hour. A fridge/freezer will cycle on and off as required so will only draw 2 Amps while running. If an LED light draws 6W, it will draw 0.5A per hour.
Battery Management system:
The battery management system shows the current draw on the batteries at any given time. By switching on your devices one by one, you can see how much power each one draws. This is by far the easiest method to figure out best power use patterns.
With your list of devices and the power drawn by each, you can begin to estimate how long your batteries will last without any additional charge. Ideally you will be harvesting some power each day to replenish what you use.
Battery Charging Methods:
Most campers these days come with a 240V charger to renew the battery to 100% charge. It does this using a stepped charging profile, gradually reducing the incoming charge as it nears full charge. Generally, the charger size is equal to 10% of the total size of the battery, so a dual battery bank of 200Amps would need a minimum charger of around 20Amps/hr.
Tow vehicle alternator via an Anderson Plug:
The plug allows connection of best fit (max size) cables from the vehicle battery via a circuit isolator to prevent accidental discharge of the vehicle battery. Its best practice to run both negative and positive connections to eliminate any possible voltage drop by tapping into the vehicle body parts for a negative return circuit connection.
Charging with a Portable Generator:
A camper plugged into a generator should utilise the camper’s on-board 240V charger to increase the rate of charge. Most generators deliver around 8 amps per hour, whereas a 240V charger of 20A capacity will do the job much quicker.
Battery Management Systems:
One method of taking the guess work out of battery management is to install a premium battery management system. The Redarc Manager30 fitted to the Pioneer Mitchell is one such system. It consists of a 30A 240V charger, 30A DC to DC charger, multi power point tracking (MPPT) solar regulator, LCD screen and monitoring software to help manage the state of charge.
The LCD screen shows a range of information, from a simple fuel gauge and percentage charge, to the current discharge rate, time until empty, the current recharge rate, time until full, and a maintenance log to see the state of charge over hours, days and weeks.
Unlike a voltmeter, which only measures surface charge, the Redarc system uses a current shunt to accurately measure the state of charge in real time. The Redarc system also has a voltage sensor which acts as an isolator, to prevent accidental discharge of the towing vehicle’s starting battery if left connected.