Leisure battery systems/ House battery systems/ Auxiliary power system

Leisure battery systems/ House battery systems/ Auxiliary power system.

Definition
Three names that usually refer to the same thing, an auxiliary power source with its own electrical circuit used for power whilst the vehicle is parked and not running. Not affecting the main starter circuitry

Raison d’être (reason to be)
This system allows power to be consumed without affecting the starter batteries. For instance you can use it to charge devices, run interior/exterior lighting and power appliances like fridges and still the vehicle would start on the turn of the key.

Type of battery
The start of a good system is the power source or battery. We have several options here, Lead acid, Gel, AGM (absorbed glass mat), Lithium Iron, 
Each has their pros and cons. Each will allow you to discharge at different rates before dropping below a usable voltage.
A lead acid battery will typically allow you to discharge to about 50% of charge, AGM battery can give as much as 80% discharge.

Size of battery, “It’s all about the amps”
The size of your battery will depend upon how much you are loading it, and the type of battery you use.
Time for a little maths. Watts = Volts x Amps.
Let me explain with an example. Something we all use is a  mobile phone. These charge via usb cable at 5v, now they differ in fast chargers and slow chargers. Normal chargers push out 1.2amps
So volts times amps, 5v x 1.2a = 6watts.
So if you wish to charge your phone it will require 6 watts per hour. Our vehicle is a 12v system not a 5v system though. So now we can calculate the amps usage per hour for our vehicle.
6watts divided by 12volts equals 0.5amps.
Your phone whilst being charged will draw 0.5amps from your leisure battery.
Two 18watt camps lights will draw 3 amps, per hour of use. (18watts divided by 12volts equals the amps)

Now we add these together. If I am parked up for 48 hours. I will charge my phone twice for three hours each charge and I will require lighting for 8 hours.
Phone - 0.5amps x 6 hours = 3amps
Lights - 3amps x 8 hours = 24 amps
So for this stay you need 27 usable amps of power.

Back to what we said earlier, a lead acid battery will only discharge 50% of its size. Its size being the AH (Amp Hour rating). So to have 27 usable amps in the battery you will require a 54ah battery.

Charging
There are several different types of charging system.

Voltage sensitive relay - this is a system that connects onto the main starter battery. When the battery voltage rises to a certain voltage the relay opens and connects the two batteries together, using the alternator to charge both batteries. This system can only be used whilst the engine is running and/or the starter batteries are above a certain voltage

DC-DC charging - This connects a 12v DC charger to your starter battery. This uses the power of your starter battery to power the charger. The charger then determines how much power/charging the leisure battery requires. Lots of DC-DC chargers have other options and features, for example solar input, trickle charging of starter batteries etc. This then depends on the alternator to keep the starter battery charged. This system can only be used whilst the engine is running and/or the starter batteries are above a certain voltage

Solar - This uses a solar panel through a charging system. This gives you the availability to charge wherever there is sunlight. Different panel and charge controllers will give different power outputs.

240v - 240v to 12v chargers will allow charging wherever there is mains power available. This cannot be used remotely.

Common Appliances

Fridge/cooler - Lots of people want to use a fridge or cooler in their vehicle there are a couple of different types, Compressor fridge or a cooler box.
Compressor fridges are one of the appliances that do not fit into my Watts = Volts x Amps
My fridge is a Dometic CFX 50, with is specified as a 52 watt appliance, which means this draws 4.3amps. Due to the way a compressor fridge works it is not working all the time. The fridge cools the produce inside down to the desired temperature, it then turns off until the temperature rises slightly. Then the cycle repeats. Depending on how much the lid/door is opened, how well insulated the fridge is, and how well stocked it is will determine how much time the fridge is on for.
Cooler boxes are a much cheaper purchase and they use a fan on-top to constantly turn and draw out the warm air from the box. This depends on having ice or similar to help keep your items cool. Because these run constantly these use a lot more power than a compressor fridge.

Inverter - 12v-240v inverter. This allows you to power 240v appliances off of your 12v leisure battery. The size of the inverter will depend upon the output required. Inverting your power is in-efficient. Approximately 20% of the power required will be needed in the conversion process.
Back to our phone charging, if you used an inverter rather than plugging directly into the 12v.

Kettle - I have seen a lot of people ask the simplest way or wiring a standard kettle into a vehicle. My personal opinion is DON’T. But I give you the option. You would have to use an inverter as shown above. Most kettles now run at 3000w so you would need a 3000w inverter.
3000w divided by 12v equals 250amps PLUS the 20% for the conversion equals 300watts, this is the equivalent of a winch!!!!!

Winch - Some people ask whether it is worth wiring the winch to the leisure battery system. You can use the leisure battery to assist the starter battery with this, some voltage sensitive relays have a controller that connects the two together on demand. But the leisure battery is not designed to take the loading of a winch.

Written By Douglas Falkner

 

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