It’s been far too long since I last posted, and it hasn’t been due to any delayed progress or not working on the Stirling. The last post (you can read it by clicking here) was showing off the fresh new interior shots of the chosen colour scheme of “whisper white” and “honeydew green” and contained a fairly lengthy soapbox rant about keeping the originality or departing from it.
It is now the middle of February, and we have come so much further. Upcoming posts will feature:
- The completed interior with the cupboards and interior painted and the linoleum laid
- What we have organised with the upholstery
- The addition of custom made Venetian blinds (these are now in and have truly transformed the van)
But this post is all about the electrical system. By far and wide it has been the most time and money consuming and frustrating part of the restoration because I have had to find a tradesman willing to do the work for a reasonable price and had to shop around to find the right components. But now that I look back on things, I realise I have learnt so much about caravan electrics that I am really excited to share with you all.
What are your energy needs?
My first piece of advice is to assess your energy needs and the way you want to use the caravan before you outlay one cent or one hour of time to the subject of powering up. Throughout Summer I have been mulling this over and over in my head, and then armed with the expectation of how we would use the van, I started to do some hard research and ringing around the local area to obtain pricing for a 12 volt electrical system.
As a family, we are more interested in what they call “free camping” in Australia. All over, there are state-based reserves and parks where you can just drive up and park your van or pitch your tent and camp for free. No reservations, no cost and no guarantees you’ll land a good spot. These free camps are generally pretty light on facilities – the last one had a long-drop toilet (BYO toilet tissue and torch for nocturnal visits), barbeque pits and rubbish bins. So, having decided that free camping was the way to go for us, I needed to kit the caravan out to be largely independent and capable of getting off-grid power. That approach may not suit everyone, though. If you prefer to use your caravan in paid parks with a 240 volt mains connection, you won’t need to look at a portable power supply, or not an elaborate one anyway. If you are opting for a straight 240 volt set-up, you probably don’t need to spend any time on working out portable battery powered needs.
I determined exactly what kind of set-up I would need based upon a reasonable assumption of my energy needs. I then learnt the ins-and-outs of working out the total amp hour demand of my combined appliances. So to explain this concept, I want to take you back to school and do a little classroom science lesson.
You need to work out the total daily energy demand, but to do that, you need to work out how to calculate the amperage (amps) which is the current that you need to draw. If electricity was equated to water, volts are equivalent to water pressure and current is equivalent to the flow rate. Electrical power is measured in watts. So if you were filling a bucket with water, and the amount of water was the power in watts, you can increase the rate at which the water fills the bucket two ways – firstly, by increasing the water pressure (volts) or secondly by increasing the flow rate of the water (current). By now you are probably starting to zone out and are thinking why do I even need to know any of this? The answer is that to determine the power requirements of your appliances, you will get different pieces of information and you need to render everything into amp hours (AH) to tell you how long you can run a battery for.
Power (P) = Voltage (V) x Current (I)
Watts (W) = Voltage (V) x Amps (A)
Here’s a basic example. I want to run a small electrical fan, so I want to work out the amps and then the total amp hours in a typical day’s usage. If the fan’s power requirement is 20W (it will use this over the space of one hour at maximum speed) and it runs off 240V, then it is as follows:
20W = 240V x ??? A
A = 20W / 240V = 0.0833
So my fan in question draws a miserly 0.083 amps per hour. To work out the amp hours, you need to realistically estimate the total running time of the fan during a hot summer day. If it runs on average 10 hours a day, then the total draw will be 0.83AH.
Drawing up a power table
Using the above methods, I worked out my energy needs by counting up the amp hours of my various appliances and putting them into a table.
||Amps (A) per hour
||Ave Daily Run Time
||Amp Hours (AH)
|2 compact fluro globes
|Two small LED globes
||5 x 2 = 10
|iPads and iPhones
|Inverter (even on stand-by)
So using the above table, I am able to calculate my daily energy needs as 45AH. Now that I know my daily needs, I am in a position to work out how much battery capacity I need, how long I can last without a charge and whether or not that motivates me to seek an off-grid power source.
In caravans, deep cycle batteries are the only way to go. Car batteries are designed to be continuously charged at 100% whilst running, so frequently draining a car battery will shorten its life span quickly. Deep cycle batteries allow for more frequent deep draining without impacting on the battery life. The general rule for deep cycle batteries is never run them below 50% capacity in order to extend their lifespan.
So knowing the capacity of your battery at 50% and the total AH in draw will tell you how many days you can last before needing a top up. With two 105AH AGM deep cycle batteries (which is what I purchased for the Stirling), I have 105AH at a 50% discharge rate. So with a daily energy demand of 45AH, I could last 2 and a bit days before I need a charge. For me, this was an unacceptable equation, because we will be looking to free camp for at least 5 days fairly frequently without re-charging at a park of 240 volt power source. This meant that I needed to consider an option to obtain off-grid power.
Off-grid power is simply energy derived from sources other than a 240 volt electrical socket. There are three main ways to obtain off-grid power:
- From your car
- Petrol generator
I considered each option in turn. If you are likely to drive from one camp to another each day, and you will be looking to drive for at least three hours every day, you can probably get most of your power needs via an Anderson Plug attached to your car. There are many factors to consider here, but if you were able to draw 10AH from your car, three hours driving each day would give you about 30 AH back. Of course, cars designed for towing and larger Anderson plugs will give you more. There are so many factors to take into account. Of course, a full day of travelling might give you up to 80-100 AH, which, depending on your power draw, may be sufficient for one or two days. For me, charging from the car was not going to provide all of my power needs because our style of camping is to make camp and stay in the same place for a few days. I was quoted somewhere around the $400 mark to install and set up an Anderson Plug charger on my car.
Solar panels are becoming cheaper. In a country like Australia, generating 6-7AH from a 120W panel across 8 hours will provide somewhere between 42-56AH per day. If you are the type of camper that likes to set up camp and stay for 2 or 3 days in one place, then solar is a great option. This is what I settled on because it suits my family’s style of camping. From my table above, anywhere above 45AH per day will see me in a constant state of full capacity in the batteries. I shopped around and found a 120W panel for $369, which was almost half the price of some others on the market.
Petrol generators are the final off-grid option. I priced a Yamaha model that would generate about 2000W and thus provide more than the sum of all my energy needs (at most, about 250W!). The cost was somewhere around $1,600. If I was running air conditioners, microwaves and TVs, I would have given more serious consideration to it, but given my power draw, it would have been overkill. There are a couple of options as to how you can approach generators. You can hook it up to a charger during the day for night-time power that doesn’t make noise. Or you can go battery free and run the generator straight into the mains connection point on the van and annoy the neighbours when you go to flick on a light at 2AM in the morning!
Solar was the choice
Read many forums dedicated to the topic of off-grid power and you get many different versions of success or failure with solar. I suppose I shall have to wait and see, but my manufacturers claims of 120W of panels generating 6-7AH proved correct on my amp-meter, and I took a number of averages across a hot summer day. There are probably huge discrepancies between the quality of panels. Mine is a portable folding unit that I can move around to face the sun, and is a reliable brand.
I have chosen a combination of two compact fluroescent globes (CFGs) – one for outdoor, one for indoor. They are moderately heavy at 12V / 12W therefore pulling 1AH. I have three more interior LEDs that draw almost no power.
The only other things running off power will be iPad and iPhone chargers, battery chargers and a fan and evaporative cooler that only takes 0.38AH. Even allowing for a massive over-estimation of the power usage of my inverter (600W Pure Sine Wave), I should comfortably sit at or below 45AH per day. So long as I can get the solar panels putting 6-7AH back in (the rule is around 20W = 1 amp), I will be fine.
And this is what it all looks like:
how it all goes together