12V DC Deep Cycle 55 amp hour battery with electronic battery charge indicator, two 12-volt outlets and one 12-volt inverter outlet.

My Vixen cassegrain telescope uses around two amps of 12 volt electrical energy to drive the right ascension and declination motors. The telescope originally came with a small battery power pack which did not last all that long. Therefore, I decided to add more 12-volt capacity to the system. This is especially needed when using accessories such as heaters.

Firstly, the decision was what type of battery to buy and what capacity? After visiting the local battery specialist shop, I walked out with a 55amp hour deep cycle unit. This was apparently the best battery for my requirements as it could sustain repeated charging and draining and have sufficient power to last about 20 hours, give or take 5 hours depending on power consumption

Building a box around the battery was relatively easy. Made out of waste pieces of 10mm Medium Density Fibre board (MDF) that were glued and nailed together. The fitting of strong carry handles was important because of the battery box total weight, which is 20 kilograms. Also seen are the ventilation holes on the lid that allows the battery gases to dissipate.

In this image, you can see the piano hinge of the lid, the two 12V DC outlets and the inverter outlet (an inverter converts direct current into alternating current – DC into AC). I chose to use a unique inverter outlet so that there would be no possibility of the inverter accidentally connected to 240 volts AC. On top are some black strips of Velcro where the inverter is positioned.

In the image above, you can see the internal wiring, hydrometer for testing the specific gravity of the battery fluid and the electronic battery voltage level indicator fitted inside the small wooden enclosure with its top sealed with Perspex.

Another view looking directly down into the battery box. A note can be seen on top of the battery that describes the specific gravity of the battery fluid that should be maintained – in this case, it is between 1280 and 1240. This can be checked with the hydrometer, but not often necessary as the electronic battery voltage indicator does a very good job of letting you know the battery’s present condition simply by throwing a switch on the side of the battery as shown in the next picture.

Switching on the battery monitor lights up an LED display (light emitting diode) that is colour coded from orange to green and then red. This device is a Dick Smith Electronics item, called a “Car Battery Monitor – K4611”, which can be purchased for under $20. It comes in kit form, but is easily assembled with the instructions supplied. It has an adjustable trimpot included, so that if the green LED’s are illuminated, the battery has a good level of charge. If the LED goes into the orange section, its time to charge the battery – its that simple, you do not have to use the messy hydrometer to check the batteries charge level ever again. The photo above shows the LED’s illuminated, so the orange LED’s on the far left cannot be seen here. I have fitted the device in its own enclosure so that the corrosive battery gases would not affect the electronic components.

The above photo shows more detail inside the lid of the battery box. The white fuse holder, spare fuses and inverter connector.

The battery monitor circuitry is visible in the upper right hand corner of the lid with spare fuses to the top left.

All of the electrical components can be obtained at any good electronics store. I have used this battery pack for some years now and it has become indispensable and can easily be adapted to other power uses as required. The only minor problem with this type of system is the weight of the battery, remember - straight back and bend the knees.

Peter Sayers