Hybrid Lovers Read This and Lament

Hi!

cross-posting removed

Bill Putney

A combustion engine would be a poor choice for a starter, on account of being unable to deliver torque from standstill. Where electric motors tend to become too big when they are made big enough to start huge combustion engines, I think the usual choice is to start the huge engine with compressed air. That's how they do it in Diesel locomotives, at least.

The starter for a pbuttenger car engine usually delivers around 1 bhp, let's say 1,500 watts (approximately, a couple hundred either way don't matter). If I'm not totally off the tracks, that would be around 1,000 amperes at the D-cell's 1.5 volts. That current is needed for a few seconds to start a car, which means that you need something like 1,000-3,600 amp-hours, or 0.28 amp-hours, to do that. A good-sized modern rechargeable battery will give you a couple thousand mAh, so in theory it should contain enough juice to start a car.

However, you cannot extract those couple thousand mAh anywhere near fast enough even to spin up a flywheel (which has its own losses from friction during the spin-up time), let alone to start the car directly. Batteries don't like being drained quickly, and give only a fraction of their nominal power when mistreated that way. You might be able to compress enough air from the juice of a couple of small batteries to start the engine that way, but if you're prepared to have a compressor and compressed-air starting system on board, it would be much easier to compress said air with the car's own supply of energy prior to shutting down the engine instead. It would, however, make a fine emergency starter: all you need is a foot pump and a little time, and off you go. Wait, am I hallucinating, or do I really remember that sometime in the early days of the horseless carriage, some engines really were started like this?

Yours, Erik. -- "People who're going to be using electricity for heating, anyway, might as well leave their PCs on all the time, since they're just as efficient at warming up the air, but do something useful with the power as well."