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Selecting the Best Battery Voltage for Your Camper
By Tim McDonald
Article 0001 Published 6/27/2024 Viewed 219 Times Updated 6/27/2024
  Common Voltage Systems Available
   There are several battery voltages to use when designing a system for your camper. This article will focus on camper vans but it can be applied to other RVs and campers as well.
   Probably the most commonly used voltage is 12V and for a good reason, this is the voltage already used by the vehicle itself. In simple systems, this probably would be the best solution. But in most other systems, there are other voltage choices that probably would be better. Other voltage configurations are based on multiples of 12V. These include 24V, 36V and 48V. Of these, the most popular is probably 24V with 48V gaining in popularity; however, 36V is seldom used.

   When needing more power for operating appliances, especially over a longer cable distance, using higher voltages have an advantage. This is due to the fact that higher voltages will deliver the same amount of power using lower current. The current is mostly what determines what gauge (size) of wire you need to use. Higher voltage with lower current also means you will have less power loss. Plus, being able to use smaller gauge wire, means lower system cost and lower weight. With a simple system, this may not amount to much, but as the complexity grows, it becomes more important.

   On most camper van builds, I gravitate towards using 24V. This will keep our current flow to half of that of 12V. But, we will still need 12V and 120VAC for many items. For 12V items, I will use a 24V to 13.8V DC-DC converter rated at 40A. This will be used for lighting, vent fans and other relatively low power items. For higher powered items, I will use 120VAC and sometimes 24V. The current flow for 120VAC will be about 1/10th of that for 12V for the same amount of power delivered.
  ABYC Wire Sizing

   The American Boating and Yacht Counsel (ABYC) has a wiring standard E-11. A wiring chart can be found at www.BlueSea.com/resouces/1437 . This is a good resource to use for determining the recommended wire gauge to use. There are two columns on the left that list lengths of wire for critical (no more than 3% voltage drop) and non-critical (no more than 10% voltage drop). Since a wire run is a loop (power to on positive and power return on negative), you will need to double the physical length of cable for looking up in chart. I explain this and how to use the chart in a youtube video.
  Auxilliary Power Unit

   I typically bundle the LiFePO4 battery cells, Battery Management System (BMS), 3KW Sine Wave Inverter, AC charger, Solar MPPT charger and a 24V to 13.8 DC-DC Converter all into one package which I call an Auxillary Power Unit (APU). This keeps the inverter close to the battery to minimize power loss.
   The package is completed by including a microcontroller, display and keypad. The microcontroller communicates with other controllers in the van using PCAN (Purrfect Campers Area Network) which is a specific CAN Bus protocol very similar to OBDII used in all vehicles today. This allows the APU to be monitored and controlled with a PCAN tablet or it can be controlled using it's own keypad. With all that said, the APU can be removed from the van and used as a stand alone power source since all of it's external connections easily unplug from it.
   A really cool feature of the APU is, once you select automatic mode, it will turn the inverter on whenever there is no shore power and there is no power from the V-inverter (I'll discuss the V-inverter a little further down in this article).
   Taking a look at the wiring diagram for the APU, the orange lines represent the solar power coming in. The red lines are the 24V bus. The blue line is for 13.8V out. The yellow lines are 120VAC. The black lines are ground. The small unlabeled square boxes are for relays/contactors. Their main purpose is to prevent charging when the battery temperature is near or below freezing. They will instead divert power from the charging source (solar or ac charger) to a heating pad to warm the batteries. Note that this uses power from the charger sources and not the battery itself.

  V-Inverter

   One thing you will notice, is the APU doesn't have DC-DC charging from the engine's alternator. This is done using a different method you probably haven't seen before. I use a V-Inverter which is usually a 12V to 120VAC 2K watt sine wave inverter placed under the driver's seat and is connected to the van's battery. It is switched on automatically when the van is runing and the alternator is putting out at least 13V. The advantages of using this method include less loss of power through long runs since the APU is generally located at the back of the van, 120V is available in the van without consuming power from the APU, and reduced system cost since we only need to run a 12 AWG power cable between them.
  
  Transfering Power



   In the Omnia, the 120VAC power sources are all controlled using the Power Management System (PMS). It uses small transfer contactors to control which source to select from. An alternative option is to use a transfer contactor with a 120VAC coil to swap between sources. Transfer contactors are important to prevent one source from feeding power back to another source.






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