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Article by Val Rigoli ©, free advice freely given, my personal thoughts and advice gathered from in-excess of 40 years of practical hands-on experience, learned skills, and industry knowledge.
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Here are some useful RV electrical related facts!

  • Car cranking batteries are not designed for cycling, they are designed for CRANKING, and will perform very poorly and fail early if used for deep cycling purposes, this is a fact, would you buy a Mack truck to go shopping in, or how about Mini to tow a 30 ton load, different animals for different jobs :-)
  • On the other hand deep cycle batteries are designed for cycling, but should not be cycled below 50% of their capacity if you want them to last! 
  • Standard car and truck alternators are designed for various reasons to only recharge car batteries to 70-80%, and this normally works reasonably well, until it comes to charging our deep cycle storage batteries, so just when you need as much capacity as possible, as quickly as possible, it can take 8-12 hours of continuous engine running to achieve just this lowly 70-80% charge, and this is with very good cabling, so much worse with the regular poor wiring often found. Please check out my >>Dual Battery Systems article (click here)<< article for more info on this. 
  • Automotive battery chargers suffer from the same less than perfect regulation as car alternators, and achieve much the same results, so for a full and deep charge, 3 stage smart chargers are required (>>smart charger article here<<), a quality properly sized solar system will also give a full and deep charge. 
  • Auxiliary batteries that are mounted some distance away from the main battery (like in a caravan), must have very heavy connecting cable (minimum 13.5 mm² 6 B&S), or you will achieve much less than 70% charge, often less than 50%! ... It's a resistance over distance thing, the further the electrical current has to travel, the larger the cable/must be, or the voltage drops to an unacceptable level (>>article on wire and cabling  here<<). 
  • Gas/electric fridges when run on 12 volt draw a minimum of 10 amps, some up to 23 amps, in most cases the wiring fitted is far below what is required (voltage drop problem), 7.91 mm² (8 B&S) minimum cable size must be used here please, and extra few dollars spent here just the once will save you a whole heap of grief later I promise! 
  • Almost all of the 240 volt generators supplied in Australia are very slow and inefficient when it come to charging batteries via their 12 volt circuits, if using a generator it is much better and faster to use a smart charger of a reasonable size, connected to the 240 volt outlet (>>article generator charging here<<).
  • Voltage measurement alone on an un-rested battery gives you no real useful indication as to it’s true state of charge, purpose designed Battery Monitors are the only way to really know for sure how much charge you have left in your in-service batteries... Simply put they measure and tally up all current both drawn from, and replenished to the battery from all sources, so that at any time you can see on the display what you have left in your batteries, they give a multitude of other useful information too.......... That was the simple explanation, in reality the calculations these monitors do are far more complex, but the bottom line is accurate readings and information about the state of charge of your batteries that you can trust (>>article on Battery Monitoring here<<) 
  • When running a 12 volt compressor fridge, up to a 1/3 power saving can be achieved by running your fridge temperature at closer to 4.0 degrees in the fridge area instead of closer to 0.0 degrees temperature, in battery terms that’s a huge saving, trying to keep the beer extra icy cold will really chew through the batteries, of course if you do have heaps of spare power, then by all means crank the fridge up, or down I guess it is ;-)

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     Val Rigoli 

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