Guest post from: Duncan Cumming
Electric Vehicles or EV’s are becoming very popular now either to buy or to lease via company car leasing firms. Electric cars use AC or DC motors. If the motor is a DC motor, then it may run on anything from between 96 and 192 volts (the difference between ‘Oww’ and ‘OWW, that really hurt.’)
Most DC motors that are used in electric cars actually come from the electric forklift industry. If it is an AC motor, then it will be a 3 phase motor running at 240v AC with a 300v battery pack = no eyebrows and spiky hair.
DC installations are less technical and cheaper too. A typical motor will be in the twenty to thirty thousand watt range, a 96 volt controller, by comparison will only deliver a maximum of four or six hundred amps. DC motors also benefit from the fact that you can over drive them for short periods of time – up to a factor of 10 to 1. This means that a twenty thousand watt motor will cope with one hundred thousand for a short period of time and deliver five times its rated horsepower. The good thing about this is that it is great for short bursts of acceleration. The bad thing is that heat builds up in the motor; if you overdrive too much then the motor will heat up to a point where it self destructs so, um, try not to do that.
AC installations allow the use of pretty much any industrial 3 phase AC motor. This makes it much easier to find a motor of a specific power rating, shape or size. The great thing about AC motors and controllers is that they often have a regen feature, which means that during braking, the motor actually turns into a generator and delivers power back into the batteries. Brilliant.
Now the not so brilliant stuff. The problem with any electric car is actually the batteries. How many problems do you think these batteries have? Go on, guess. Well, it’s six. And here they are:
One: They are bloody heavy. A typical lead acid battery pack weighs about one thousand pounds. About the size of a small dog. Secondly, they’re bulky too, measuring about six by eight by six inches – about the size of something that’s six by eight by six inches. Thirdly, they have limited capacity – typically holding about twelve to fifteen kilowatt hours of electricity – a range of about fifty miles. They’re slow to charge, with recharge times ranging between four and ten hours. They have a fairly short life – up to four years or two hundred full charge / discharge cycles. Finally, they can be pretty expensive too.
Despite those drawbacks, it looks like electric cars are going to be the way forward and technology is only going to improve of course.
For further information about electric vehicle batteries, read this.