There are several items around the house that can be converted with relative ease to run directly off the solar battery. The equipment I converted includes:

Standard/desk lamps;
AA/AAA Battery charger;
Smoke alarm;
LED based lighting;
Shelf lights;
Porch lights (changing from halogen to LED);
UPS (converted to run as an inverter - see next page);
Using automotive assessory chargers;
Adjustable output automotive accessory charger.

Lets take a look at each of these.

Standard/desk lamp conversion.
Conversion of the standard lamp and desk lamps were the easiest. Replace the mains plug with a cigar lighter plug and replace the 240V bulb with a 12V CFL bulb. Each lamp only took five minutes.

Not the prettiest of lights but this ancient desk lamp rescued from my loft already had an ES lamp fitting unlike most of my other bayonet-cap (BC) lamps making it an ideal candidate for conversion as I could only get the 12V CFL bulbs in ES form.



AA/AAA Battery charger.
The battery charger conversion was interesting. I recently bought a GP PowerBank charger (model GPPB80) to recharge my hybrid AA and AAA batteries. I have a mixture of Sanyo Eneloop and Uniross Hybrio Ni-MH batteries which are great. Unlike traditional rechargeable batteries these hybrid models come ready charged and can be used in low current applications unsuitable for standard rechargeable batteries. They have a long life (especially the Eneloop which are a higher capacity and ran my digital camera for ages before requiring a recharge). I figured I would get maximum benefit form my batteries if I recharged them from my renewable energy source and this job was made easier by the fact that the GP PowerBank is itself powered from a 12V mains adaptor. Conversion was simply a case of knocking up a lead with a cigar plug on one end and a DC jack on the other to replace the mains charger with a cable to interface it with my installation. Actually, my lead was itself salvaged from an old dead mains charger so I didn't have to buy the cable or DC plug, nor did I have to do any soldering on this end!



What surprised me about the PowerBank charger was the amount of current it uses, (probably because it charges batteries in fifteen minutes rather than trickle charging them over several hours). It's mains adaptor is rated at 3.3A on the DC side and I found it was problematic if I tried to charge more than two batteries at any one time from my solar battery. The limitation in my installation is the solar regulator and investing in a regulator with a higher output current rating may overcome the problem but for now I'm limited to charging no more than two batteries at a time and I'm better off doing it in the day (i.e. when the battery isn't being used to power my lights at night). Still, I can't complain, two batteries charged for free is better than none and because of the speed of the charger I can have four batteries charged in just half an hour!

Smoke alarm.
The smoke alarm wasn't part of my original plan - but while installing some of the wiring I noticed this one didn't have any batteries installed! It's a fire officers nightmare, and this model requires TWO 9V alkaline batteries (one for the alarm and one for the emergency light), so it gets through two batteries every year. As it was on the upstairs ceiling almost directly under the solar battery, it seemed a good idea to me to change its power source. As the solar battery produces 12V and the smoke alarm requires 9V, a slight conversion was needed. In my junk box was a recycled 7809 voltage regulator so I knocked up a quick stripboard circuit with connectors for a 12V input and PP3 snap-on connectors providing two 9V outputs for connection to the battery terminals of the smoke alarm.



If this were a normal smoke alarm I wouldn't bother with the heat sink but because it has to power the emergency light in this model, I figured it was better to have one as the higher current from the bulb may cause the regulator to warm up if it sets off for a prolonged period. The only thing to bear in mind is to wire the PP3 connector snaps in reverse (red to 0V, black to 9V). This is because the PP3 connectors are usually being connected to batteries - however in this case they are connecting to the smoke alarm as though they were the battery so you have to wire them in backwards to get the polarity correct.

Here's the regulator fitted into the smoke alarm.


Unfortunately I soon remembered why the batteries had been removed from this alarm - it has a habit of bleeping IN THE MIDDLE OF THE NIGHT for no reason! BAH!

Never mind, the idea is sound. Might have to buy a new unit though if it wakes me up one time too many!


LED based lighting.
I have several 'arty' LED projects around the place. As well as three sets of colour changing 'mood lights' I got from the Gadget Shop, there are several projects of my own making which serve no function other than to look pretty. Normally these run from mains transformers and in some cases are running 24/7. I've been feeling a bit guilty about their constant running for some time but their conversion to run off my solar battery was relatively quick and easy as they all either ran off 12V or 5V DC and my system produces both voltages (12V via the battery and 5V via the 7805 regulator installed in the control panel). The picture below shows an uplight I made a few years ago. It's a round piece of wood thats been subtly spraypainted running from silver one one side through a metallic red to a metallic gold. It has two CFL backlights that haven't yet been converted to run off the solar battery and a set of coloured LEDs on a binary counter that solwly pulses through it's binary pattern. A 330uF capacitor is used to slowly dim and raise the brightness of the LEDs as they pulse through their pattern which gives the whole thing a relaxing look - more relaxing now that I know it isn't burning up any resources unnecessarily! The metal bit in the middle is a key hook rack I got from Tesco years ago!


Shelf lights.
The shelf lights are another home made affair and are 100% recycled already. The bulbs came from an old Christmas decoration, the power supply once belonged to a HP printer, and the housings were, I am horrified to say, a classic piece of overpackaging from the clothing retailer NEXT.


The housings consist of a metal sleeve with a thick opaque acryllic insert. They look great, but believe it or not these were just packaging boxes for a set of cufflinks each! I hate to think how much effort went in to producing these boxes just for them to be discarded by most people. I actually bought the cufflinks so I could have the boxes (I rarely even wear cufflinks), but I knew the boxes would make nice lighting feature one day. They sat in a drawer for two years until I got around to fitting them into this Ikea shelving unit. Converting them to run of the solar battery involved changing the 34V bulbs for a pair of 12V bulbs I had in my junk box and replacing the old HP printer mains supply for a cigar lighter plug that would plug into one of my automotive sockets.

Porch Lights.
My porch lights use halogen 12V 10W bulbs and could be hung straight off the battery with no modification. The trouble is, although halogen is a more efficient incandescent bulb than traditional tungsten bulbs, it still relies on burning a filament to produce light which means a high current is drawn compared to other light sources such as fluorescent and LED. In this application, the doorway to my house is illuminated for visitors and the lights are controlled by a timer which is altered throughout the changing seasons to switch the lights on after dusk and off at about 22:30 when there are unlikely to be any further callers. In the depths of winter it can be dark by 16:00 hours so this would mean quite a large current drain on the battery. For efficiency, I have changed my porch lights from halogen to LED which gives me a similar light output but at a fraction of the DC current consumption.


Above: Before conversion and the last time these lights will be run from the mains and in their halogen incarnation.

To convert, I made new LED 'bulbs' that could run from 12V and would fit within the existing housings. Each bulb would contain 12 white LEDs with each LED rated at 7.2cd light output.



To further reduce the current consumption of the LED lights, each LED 'bulb' is fitted with an astable multivibrator - a circuit that switches on and off repeatedly (and explains the extra components mounted on the boards in the pictures above). The circuit diagram is below.


The white LEDs I used require a forward voltage of 3 to 3.4V and each light consists of twelve LEDs connected in four groups with three LEDs wired in series in each group. The astable multivibrator circuit 'flashes' the LEDs so that the group of six LEDs on the left in the circuit diagram alternate with the group of six LEDs on the right. The switching is done pretty fast using these component values which means the flashing action is just on the peripheral of what the human eye can see. That is to say, you might catch the flashing out of the corner of your eye but if you look directly at the lights they will appear to be steady on. Because the circuit effectively means only six LED's of the twelve are being fully powered at any one time, the current consumption is much reduced. Each unit is taking about 35mA from the battery when on - a definate improvement over the 1A consumption of each of the halogen bulbs they replaced. Notice the huge resistors in use on my bulbs - this isn't because of any heavy power dissipation, simply because they were the only 200 Ohm resistors in my junk box and have been in there since 1986! Nice to put 'em to good use at last. The capacitors are also recycled and came out of an old radio.


Here they are switched on after installation.

I won't lie - their light ouput is less than the halogen lamps but they still do a good enough job and, of course, now cost nothing to run. They look prettier too!




Automotive accessory chargers.
Not really a conversion this - just stating the obvious. Investing in automotive chargers can open up a multitude of devices for recharging directly off the solar battery if you wire in automotive sockets. This third party iPod car charger has a USB output allowing it to recharge all kinds of small gadgets with USB charge inputs and of course can also be used in the car to charge items for free.




Adjustable output automotive accessory chargers.
Another item of note is the adjustable output charger available from automotive suppliers. Like their mains counterparts they allow the input Voltage to be adjusted to a number of smaller Voltages suitable for running various items. They also have interchangeable plugs for connection to different devices. Mine is shown in the photo below. I got it from CPC and can power devices up to 2A. The only thing to make sure of is that the correct voltage and polarity are set for the item you want to use. Mine is currently employed in powering my kids Leapster .



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