Sunday, January 30, 2011

Fried brain

After my two weeks or so up at Coronation I have decided to get serious about updating my camper trailer to include some electrical components. Currently I run my fridge from a dual battery system in the car, topped up with a solar panel, but there are a few problems with this.

Firstly, the fridge sits in the car, in the sun, meaning it has to work harder to keep things cool. It's in an insulation bag, and I've also given it an extra foil reflecting blanket (an old windsceen shade), but the fact is it's a pain to have to keep walking to the car for fridge supplies when you are camped up in the same place for weeks.

Secondly, my solar panel, an excellent quality Solarex 60W, is far to inadequate for the task of keeping my auxilliary battery topped up, especially if I run a fluoro light as well. Which means I flatten my battery in 2 days, not good for even a good deep cycle battery.

Thirdly, and the most important factor, my cabling is far too thin for the job required, meaning I lose most of the voltage before it even gets to the battery from the solar panel. Not only that, the cable connecting to the fridge also loses voltage, meaning the fridge cycles more often, for longer, draining more power. And I paid to have that cabling put in!!

Apparently this cabling mismatch is not uncommon. Whilst researching solar panels on the internet, I've come to the conclusion that pretty well every one of those portable setups being advertised at ridiculously cheap prices on ebay and elsewhere comes with cabling too small for the job. Which means built-in inefficiency from the outset. But now I'm onto it I shan't be fooled!

So after more research - including talking it over with friends and acquaintances, buying a book specific to the topic, looking for info at the hopelessly inadequate local library, and of course hours trawling through internet sites - I rang the 12 Volt Shop in Perth to have a chat with some real experts. And they suggested going even thicker again on the cabling!!!

The cabling problem arises because the descriptions of cable size are not uniform. I need 4 B&S cabling, which is 25sqmm copper wiring, not size 4 autocabling, which is 2.5sqmm of copper. BIG DIFFERENCE!! Guess what I've got??

The reason the cable has to be so thick is because of the distances it must travel to power or charge things. From the battery under the bonnet to the car fridge is approx 4m, which is 8m conductor length. And there's similar distances again for the trailer. Less resistance in the cable over such lengths means less voltage drop. The bigger I go the better. And who knew you were getting a tutorial on basic 12 volt electrics?

So I've decided to both upgrade the wiring in the car - probably by a professional - and completely wire the trailer with it's own standalone system that can be charged by either solar when camped for long periods, or the car alternator when travelling or if solar is inadequate. And I'm going to do the trailer myself.

Most fortuitously, I've found a charger that is both a top quality solar regulator and a voltage step up charger, meaning that I can get very efficient battery charging all in one unit. It's about the price of the solar regulator I was looking at buying, but without quite as many monitoring functions, but does 2 jobs in one. Am very pleased with this find, and it's not even Chinese!!

I've worked out my power requirements - the fridge, some simple fluoro lights, a water pump and occasional battery/laptop charging - and worked out what size battery I need and how much solar wattage is required. And the 12 Volt Shop chap told me I was spot on!! I have built in a fair amount of redundancy, and have allowed room to expand so I'm pretty well ready to start spending.

But not quite yet. I've just been forced to buy some new sails, after my 4.5m kind of disintegrated on me last week, so I am holding off on any big purchases - like solar panels and batteries - for a month or so till my bank balance looks a little healthier. And I've a trip to Perth in March for a conference, so I think I might hold off till then and have a real proper chat with the guys in the shop before I purchase my cable.

So after putting this down in my blog for posterity, having drawn a bunch of circuit diagrams, saved squillions of articles on my harddrive, and effectively fried my brain (I'm even staying awake at night thinking through circuitry options!), I'm putting the paper bits into a little manila folder and packing them away. It's time to let all those ideas coalesce and for me to do something more immediate.

Like the laundry!!

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