Thursday, July 21, 2011

Electrical Saftey in Battery Cars

Greetings from the Australian National University, where Professor Peter Zeller from Upper Austria University of Applied Sciences, is speaking on "Safety Aspects of Renewable Energy and Electrical Cars". The problem is that an electric car has a battery pack producing 100 V to 500 V which can deliver 10 to 20 kWh of energy. Rescue services may need to cut into a vehicle to after an accident, with the risk of electrocution or explosion of the battery. In addition the battery power is DC, not the AC which electrical engineers are used to controlling.

Simulating Short Circuits on Electric Cars

The Upper Austria University of Applied Sciences simulated the effect of a short circuit in an electric car, resulted in electrical arcing. Professor Zeller pointed out that such a high temperature arc will soon burn through the insinuation between the battery pack and the passenger compartment of a car.

There may be a very large fuse in the car, but this will offer limited protection. In theory a switch can be used to disconnect the battery, but the design of such a switch is problematic, due to the very high current involved. It occurred to me that for a safety switch a linear shaped charge might be used (explosives are already used in airbags and pretensioning seat belts).

An interesting point Professor Zeller made was that even the 48 volt systems used in new internal combustion cars are causing problems due to arcing and the problem is much worse with 100 to 300 volts in an electric car.

Photo-voltaic panel safety

There are similar problems with photo-voltaic panels on homes, with many electrical connectors exposed to the elements (as with the recent Queensland floods). Reports indicate that up to 80% of the solar panels installed on homes in Australia have faults.

Smart Batteries and Solar Panels

Professor Zeller's analysis is based on the assumption that the battery or solar panel creating the high voltage and current is "dumb". That is the cells are simply connected together in series to create a large battery (or solar array), which is then switched off as one unit. The other option would be to use an electronic switch on each battery, so that one large switch is not needed. This can be done easily where each voltage source has its own regulator (as for example where each panel converts low voltage DC to high voltage AC with a micro-inverter). If AC is used then the switching problem is much less.

No comments: