# Electrical and Electronics

Electrical and electronics engineering disciplines are concerned with the study, design, application and diagnostics of equipment, devices and systems which use electricity, electronics, and electromagnetism.

We tend to think of electrical engineering as that associated with high voltage AC and DC systems in the home, electric cars, factories and distribution systems. Electronics is associated with the operation of discrete components such as capacitors and transistors, designing and engineering them into circuits.

#### Ampere-Hour

An alternative unit of electrical charge. Product of the current strength (measured in amperes) and the duration (in hours) of the current. The quantity of electricity (capacity) of a battery or cell is usually expressed in ampere hours.

Symbol: Ah

One ampere-hour = 3,600 coulombs.

Batteries – have an Ampere-Hour (Ah) rating. A discharge rate is normally included with this to signify the maximum current that the battery can be discharged at and achieve the rated capacity.

As an example a battery with 60Ah C/20 has a 60Ah capacity when discharged at the capacity divided by 20 which equals 3 Amps in this case.

milliampere hour (mAh) – One thousandth of an Ampere-hour (Ah), this is commonly used when stating the capacity of rechargeable batteries used in mobile phones.

#### Heat Sinks and Cooling Fins

The fundamental aspects to consider in heatsink design are:

• Surface area – you want to maximise the surface area as this is where the thermal transfer to the coolant medium takes place.
• Aerodynamics – the coolant medium needs to be able to easily flow around the heatsink
• Thermal transfer – heat flow within the heatsink needs to be good to get the heat out to the fins and so maximise the use of the large area.
• Contact – you need to maximise the contact with the part needing to be cooled and maximise the efficiency of the contact. This also needs to be maintained over the lifetime.