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Lost at sea diaries
Jonathan Hare's diary about the challenge for the Lost at Sea programme, from the BBC/OU series Rough Science 5
We are all working together on making survival gear for someone (Kate) if they fell overboard. The idea is to make a life-jacket with various additions that might make it a really great bit of safety gear. We each have a part of the challenge and my part is to make some lights that can be powered from the sea.
Day 1
Show the possibility of making batteries from screws and pencil leads (or from carbon rods from old worn out batteries). The power from a battery is derived from chemical energy and we intend to use sea water (which technically is called the electrolyte). I demo a six cell battery made up from six screws, six carbon rods. I used an ice cube tray as this has a number of compartments that can be used to hold the six trays of sea water to form each cell separately.
I got some small LED lights from the radios and these will be used as the lights for the life-jacket. The screws and rods are fixed in pairs to a piece of wood, six of the ice cube trays are filled with sea water and the rod pairs are dipped in. These are then wired up, like a daisy chain (in series) to make a battery of six connected sea water cells.
Day 2
Six cells easily light an LED. However we want to light more LEDs and also if possible use the energy more effectively so that we get a bright flash. This will be much more noticeable out at sea.
The way to do this is to use a capacitor. These can be found in the radios. A capacitor is a device used to store electricity. It does not create electricity like a battery it simply stores it. If we take the example of household water pressure being like the electrical force in a battery, then the capacitor in this example is rather like a water tank – it stores water but does not create it.
What we do is charge up the capacitor (fill the tank) and use this stored energy to pulse across the lights. This way we make use of the batteries' ability to supply a constant low level power to the capacitor but also the capacitor's ability to supply short pulses of high power. We are not getting something for nothing because the overall power is the same, we just use the capacitor to allow us to deliver the power in a different way. I find a couple of 100 microfarad
capacitors from the radios, which I add together - they look like they will be ideal.
Make up a ‘halo’ of 4–6 LEDs so that when the person is in the water a light can be viewed from any angle the rescuers may be coming from.
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Content last updated: 26/01/2005
