This article is intended as a BASIC introduction to the concepts of Solar, and Inverters in an RV environment. It will not be going into detail, it is intended as a guide for people who do not understand the concepts, not as a how to of installing said items.
I am sure I will have missed relevant points, so I would welcome input from the many knowledgeable people on the forum, but PLEASE keep it at a general high level, do not include the detail, as it just confuses people who do not have a technical leaning.
Background
For many years caravans and motor homes have been built with two very separate power systems, a 240V (just like in the house at home) system to be used when the van was plugged in to a power pole in a caravan park. And a separate 12V (just like a car) system that could run a few essentials like lights and the water pump from a battery. The battery would then be charged by the towing car, or with a built in battery charger that came to life when the van was running on 240V power.
In the early days lights had both a 240V and a 12V globe (effectively two lights), but more recently the low power appliances lights, pump, radio, and television are designed to run on 12V only, with the battery being charged by the battery charger when sitting still in a caravan park (or plugged in at home).
Then along came a desire to use caravans independently (away from caravan parks) for extended periods, the batteries used to last one or two days, and the people were frustrated, they wanted to stay longer. The first solution was to add more battery, thus extending the amount of time people could stay, but batteries are heavy, expensive, and tend not to last very long when they are not looked after very well (the typical caravan battery).
People then flirted with generators, but again they were heavy, expensive, and smelly. Soon the people who parked and pulled out their generator were regarded as social lepers, but in the main they pretended they did not care that people shunned them, and went back to watching Home and Away.
Solar
When I started working for a company manufacturing solar panels they were incredibly expensive, now they are roughly a 20th of the cost they were then. Somewhere along the way someone realised the potential to fit solar panels to caravans, thus providing the ability for people to use their caravan independently (away from caravan parks) for longer, and if set up well potentially indefinitely.
How does solar do this?
Solar simply converts some of the energy in sunlight into electricity, and this electrical power is then used to charge the caravan battery.
What components does a solar system need?
If you have a solar system in your van, you will have one or more solar panel(s), some cable connecting the panel(s) to a special solar charger hopefully located near your battery, and some more cables connecting your charger to the battery. The function of the solar charger is to look after your battery, and to make sure you do not over charge it.
Now there are many different types of charger, but basically they all do the same thing, albeit in different ways.
Similarly there are many types of battery, each with its own capabilities and problems, but for the purpose of this document they are just a box to store electricity in.
So now we have a caravan with one or more solar panel on the roof, providing power to a charger that charges the caravan battery. We generate and store enough power during the day to power all the 12 volt items in the caravan (lights, pumps, USB phone chargers, radio, television etc. thus we can now camp independently for as long as we want.
Then along comes a hot day, and Mable asks George to turn on the Air conditioning, and the damned thing wont work!
The air conditioner like the washing machine, the microwave, the coffee maker etc all run on 240 volts, and we do not have a 240 Volt source (remember it is a separate system).
Inverters
This is where George goes out and buys himself an inverter, and gets himself into all sorts of problems, but before we talk about the problems lets look at what an inverter does.
An inverter takes a low voltage source, typically 12 volts, and converts that into 240 volts suitable to power the kind of devices you can plug in and use at home. Sounds great doesnt it ?
In principle yes, but in practice it brings with it a whole host of problems, mainly around the amount of power these 240 volt devices need to run, most caravan batteries are not large enough to run a device like an air conditioner for very long, and inverters that can handle a big device like that are typically large and heavy.
I hope this helps people to at least understand a bit of the background, and where those mystery devices fit in.
Many years ago I got a free 120W Projecta Inverter Can (drink can size) when I bought a 1200A jump starter. It was a good idea at the time as I needed to charge a laptop from the car. Laptops at the time were all > 12v and could not run from the 12V power outlet in the car. The inverter proved invaluable and were very popular. Nowadays most portable computing devices charge from the 12V socket.
Decided to test the inverter on the power outlet on the (fully charged) 1200A jump-starter. Ran a 12W fluoro for 24 hours and it was still on. Decided to try my 240v Dremel as I wanted to use it away from power. Lasted less than a minute.
Thanks Plendo, I found that article great, as I'm new to the whole solar, inverter thing I found this article really helpfull, and has encouraged me to learn more.
Thanks
Cheers
Greg
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Greg & Shas
"Take kindly the council of the years gracefully surrendering the things of your youth"
A nice little discourse about solar etc - may I add a bit about the batteries side of things
It's all very well having a solar recharging system and one or two house batteries ... but what can you do with them?
And how much battery power is really needed?
Conventional wisdom says that we only use 50% of a battery's power so that we do not stress the battery so as to dramatically cut short its life
So most people have 2- batteries in the van, so let's assume that they are each 100AmpHour batteries, 200Ah in all
Using the 50% rule-of-thumb, you have 100 AmpHours of battery power available
Now- if the device you plug in uses 1Amp, you have 100 hours available ... 2Amps gives 50 hours, 4Amps gives 25 hours and so on
To work out the "Amps" side of things, simply divide the Watts of the appliance by the volts (12v in this case)
Example-1
Look on the base of the TV - look up its power consumption in Watts - let's invent here and say 48watts [easy on the arithmetic]
So 48 / 12v = 4Amps ... and 4Amps = 25 hrs as per above
Example-2
Look on the base of your 240v toaster / jug / frypan to find its power consumption in watts. Again let's invent and say 2000watts
So 2000 / 12v = 166Amps ... ie: way beyond the power in the batteries, so it's a no-go job > ie: needs a Genny, or just say 'bugga that we'll use gas in the kitchen'
Example-3
Look on the base of the computer power-supply [the black box thingy]. It's a bit confusing here in that it says that on 240v it runs at 2 Amps, but the output of the power supply [black box] is now 20v x 4 Amps. So these are the numbers to use
Because it says "20v x 4 Amps" without the watts loading we need to do some backwards thinking
As "watts = volts x amps", so ? = 20 x 4, therefore it is 80watts
So- 80 watts / 12 volts = 6-2/3Amps [say 7 Amps] ... therefore it = about 14 hours of use from your batteries
Conclusions-
Well for many beginners it very often seems to be a bit of black magic - and not all of us are maths-geniuses
But after a while it does seem to fall into place a bit easier
The bottom line is that most small stuff in the van can run okay off the house batteries, but big stuff like cooking equipment, fridge & hair dryers don't do so
Plendo, good article, well written. Please keep this up.
Slightly O/T, what would you require to run a house on solar panels. The assumption is that you would have somewhere between 3.5kW and 5kW panels on the roof. Could you do it with a bank of batteries and an inverter?
Larry
Plendo, good article, well written. Please keep this up. Slightly O/T, what would you require to run a house on solar panels. The assumption is that you would have somewhere between 3.5kW and 5kW panels on the roof. Could you do it with a bank of batteries and an inverter? Larry
Simple answer is yes. A neighbour has two banks of solar panels. One bank feeds back into the grid as per normal. The other feeds a bank of batteries with an inverter. Not sure if that also feeds back into his house circuit (after his meter box) or if he has a separate circuit thru his house. Capital cost is huge for the batteries but with the buy-back from the electricity companies so low now (in Vic), his payback period is reasonable.
Thanks Plendo that simplified it nicely and well followed up by Ozzie Traveller on batteries also, like Nomes, I look forward to the inverter edition .
also on power cabling as the little that I know about wire 240 v is rated or sized different to 12 v which I find rather confusing as I would have thought a 2 ml wire should be called a 2 ml wire regardless of which system it is fitted to is there a conversion table some where ?
-- Edited by Woody n Sue on Tuesday 16th of June 2015 08:32:00 PM
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When the power of Love becomes greater than the love of power the World will see peace ! 24ft Trailblazer 5th wheeler n 05 Patrol ute and Black Series Dominator camper trailer ( for the rough stuff)
Thank you all for the kind words, it makes it worth doing when you know that people find it useful.
Thanks also to Phil for filling in the blanks around batteries.
Apologies to the people waiting for the inverter edition, the next one is solar panels and chargers in a bit more detail, then I will try to get the inverter section done.
What a great sub section,were very very new to all this .all the reading we've done its been daunting , hard as a novice to get our head around solar
And how much power we get to use when and if we free camp.
We picked out all our colors etc etc last friday ,they rang up today again to clarify a few things, so i told them to put another panel on the roof .
Now we will have 3/ 120 w panels 2 /100amp battery's , so hoping that would be ok to run / lights , tv , auto sat dish , vast , foxtel box, these would be on at night / occasional water pump ,
and may charge phone
Would i get away using these items, with the setup were getting ,or is this still to much power , if not we may have to lnvest in a generator .
comments please
Thanks
it certainly is daunting as you first start out, you are learning so much, and you always feel as if there is so much you just don't know. Don't worry you will be fine, just keep reading and absorbing as much information as you can soak in. There is a huge amount of experience being expressed in the pages of this forum.
Now to your set up, I assume from what you say your van is new, so it will have efficient led lights, thus your basic load (lights, pump, tv, phone charging) will not be an issue. I do not have any experience with the components of the satellite system, so I am afraid I would have to defer to others on that topic.
hi plendo and not to forget OZZIE
great articular that we could understand , i did read it 2 times lol. AND I WILL PROBABLY READ IT AGAIN
Our van will be a Supreme executive 2100. As in the small photo The more i read all these forums from what van to buy ,to solar panels etc, we upgraded most things,including the extra solar panel
Only one down side, $$$$$$$$$$ LOL
For many years caravans and motor homes have been built with two very separate power systems, a 240V (just like in the house at home) system to be used when the van was plugged in to a power pole in a caravan park. And a separate 12V (just like a car) system that could run a few essentials like lights and the water pump from a battery. The battery would then be charged by the towing car, or with a built in battery charger that came to life when the van was running on 240V power.
In the early days lights had both a 240V and a 12V globe (effectively two lights), but more recently the low power appliances lights, pump, radio, and television are designed to run on 12V only, with the battery being charged by the battery charger when sitting still in a caravan park (or plugged in at home).
To take you back further to the "dark ages" of last century, back then van manufacturers did not fit batteries to their vans. When i was ordering my van in 1996 it was hard to find anyone in the caravan industry who understood battery systems. During my investigations I educated a few sales staff. When I ordered my van I went down to the Spaceland factory to finalise negotiations. I spent quite a long time with the factory electrician (one of the management was actually a licensed electrical contractor.) I introduced him to the principles of DC-DC charging and high efficiency fluoro lighting (no LED around then.)
Last century vans came mostly without batteries and nearly all of them that did have batteries, the batteries were an after market accessory. In those days the separate 12 V system described above was powered from the tug. I remember well the 1972 Franklin van we used, spent many a week at a time living off the tugs battery with stop light globes for lighting that was not quite sufficient enough for reading.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
