We all know there is lots of work and R&D going on to develop better car batteries, working towards the goal of the all-electric vehicle which may complement or supplement the standard gasoline/diesel fuel car. I don't know if or when the breakthrough in batteries will come; or it may require some developments we can't presently envision (most radical improvements are that way).

But even if we do somehow get batteries which are nearly ideal (low cost, high energy and power density, lightweight, long life), and even if we don't worry about where all that electricity to charge them is going to come from, there's still one real challenge: getting the charge (current) into these batteries.

I'm a big proponent of what used to be called "back of the envelope" calculations, where you use rough but reasonable numbers to come up with a realistic estimate of a situation. It's a great way to avoid blindly believing your Spice model when says that you need a 10-zillion ohm resistor in your circuit, when the real issue is your model has errors or you entered some wrong numbers.

So try to do some basic analysis of the car situation, starting either at the sourcing end or the load end. At the sourcing end, figure you have 15- or 20-amp line recharging the batteries for "x" hours, and work over to the load: how long can this amount of stored energy run an electric motor of the size you think you'll need in the car? Or go the other way: if you have an electric motor size and run time in mind, how much energy does it require for the run, and how much charging will that require? (Remember: one horsepower is about 750 watts.) Of course, you should also use a derating factor of two (or 50%) to account, roughly, for the system losses between charging connector and actual delivered power. (For this first-level rough assessment, ignore any other loads the all-electric vehicle may have, such as a heater or air conditioner or multimedia system, but you know that they can only make things worse.)

I'm not going to go through the analysis for you, I assume you can do it yourself, I think you'll find it illuminating: it takes a lot of charging time at 15 or 20 A to deliver enough energy for most all-electric car scenarios. Petrochemical fuels have very high energy and power densities (with respect to both volume and weight) and so can move lots of energy fairly quickly.

And if you can't do the rough, first-order analysis yourself, you probably should do some basic reading-up on the relationship between current, voltage, power, energy, and work. Even if you are not involved with electric vehicles, those are fundamental relationships you need to be comfortable with using for quick estimates of your product and its power source. ♦