March 2004 Labpacks Physics Equipment

March 2004 Labpacks We have two types of power supplies in the lab. They are called ‘Labpacks’ They allow you access to AC or DC voltage for experiments.

March 2004 The Dial Labpack

March 2004 The ‘Click’ Interval Labpack

March 2004 Which should I use? The dial type allows you to change voltage in very small increments. The ‘click’ interval type only allows you to alter the voltage by 2V increments. If you need fine adjustment choose the dial one – it has a built in rheostat OR use the click one within a potential divider circuit – see separate presentation

March 2004 Plug it in! The power supply has to be plugged into the mains socket. Carefully unwind the wire at the back of the labpack and plug it in. A socket is switched ‘on’ if the switch is down.

March 2004 Yellow terminals These give access to AC voltage. Each terminal swaps from +V to –V back to +V fifty times a second (mains voltage is at a frequency of 50Hz). These terminals are fine for lighting a lamp but should not be used for investigations into resistance. If you plug into these terminals you cannot use moving coil meters within your circuit – you would have to use multimeters on AC settings

March 2004 Red and Black terminals These give access to DC voltage. The red terminal is positive The black terminal is negative These terminals can be used for any circuit. If you plug into these terminals you must ensure that moving coil meters are connected the correct way round within your circuit You would have to use multimeters on DC settings

March 2004 The Green Terminal This is the Earth connection. You will rarely be expected to use this. Don’t worry about it.

March 2004 Reset Button The reset button is a safety device. If you overload the labpack by allowing too much current to pass through it (for example by shorting out a circuit!) it will cut the power off and this button will come out. You will hear a loud click when this happens. Wait for a minute, disconnect your circuit, and depress this button to reset the power supply. Next time, take more care!

March 2004 When the circuit is wired up correctly…. Turn the voltage dial to 0V ALWAYS START AT ZERO VOLTS AND STEADILY INCREASE THE VOLTAGE TO THE DESIRED LEVEL The red pointer is the one that indicates the ‘rough region’ of voltage supplied. The yellow one is for locking maximum voltage.

March 2004 The ‘lock’ If you cannot turn the voltage dial past a particular value, it may be because the dial is locked. The yellow marker is placed at the maximum voltage position and locked on place by the silver button. Turn this to release the dial.

March 2004 Then switch it on! At the top right hand corner of the labpack is a switch. Turn it on. A red light should come on. If it doesn’t check you have plugged the labpack in correctly and that the mains switch is down. If it is still off, there may be a problem – or the bulb in the switch may have blown…

March 2004 Putting the Labpack Away Switch it off (on its face and at the socket). Unplug it. Wind the flex neatly at the back. Carry it carefully to the trolley and stack it neatly. Take care these unit cost over £100!