Spring-loaded engine starter
 

The alternator sucks up lots of engine power, producing more electricity than the car needs. The reason it produces so much is because it doubles as a high power motor for getting the engine started in less than a second. If the alternator could be less powerful, it would be less of a power drain while driving.
So would it be possible to start the engine with some kind of powerful spiral spring, which would be wound by the alternator? The alternator could be less powerful since it would take its sweet time winding the spring, say 5-15 seconds. The spring could also be wound when braking. The spring could be slightly more powerful than a regular alternator, making it ideal for stop-and-start at traffic lights. Also, if your battery dies, the spring might still be wound up making starting possible. Or if it isn't, it could be wound up by a good old-fashioned hand crank. Just take the handle out of the trunk, pop it in a hole in your bumper, turn it 20-50 times and that's that.
I haven't fooled around with springs enough to know whether they can handle the load needed to start an engine, or how large/heavy they would have to be. Any comments?

Per pound, steel springs store less than 1% of the energy in a car battery, but they have occasionally been used to start aircraft and small engines. The usual difficulty comes if it does not catch on the first try. Compressed-air starters are lighter overall, effective, but less efficient. However, they can be charged up "for free" by using an air pump as a shock absorber.
It is very unusual for a car to have a combined starter and generator. The alternators are sized to replenish the battery fairly quickly after a cold start while running most of the lights and other accessories. Starter motors are built too light for continuous duty at regular power.

The alternator does not double as the starter. They are separate units. The alternator is a belt-driven item that hangs off of a bracket at the 'front' (opposite end as the transmission) of the engine and is driven by the engine. The starter is a smaller electric motor that bolts into an opening at the transmission end of the engine and engages with a large ring gear to spin the engine for starting.
I don't think you'll gain anything using alternator power to wind up a spring for starting. You're just adding another step, a.k.a. a source of loss. If you only wind up the spring manually, or through regenerative braking, then you're onto something. :thumbup:

Incorrect - the alternator only produces as much electricity as is needed... No more, no less.

The power is sucks up from the engine is the amount of power needed plus alternator inefficiencies.

And as already stated, your alternator does not start your car ;) Exceptions for a few vehicles that use starter generators...

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Spiral spring.... you probably mean power spring, like what's found in a seat belt or clock. You'd need one helluva spring - that's a lot of energy stored... And as said, it'd be quite heavy. Impossible? No... But as said, a battery has a much better energy density.

Correct me if I'm wrong, but I think with a conventional alternator most of the loss is actually coming from the drive belt and the cooling fan on the alternator pulley, not the alternator itself. The starter motor of course just sits there when it's not in use.

Stihl has chainsaws with spring starters, you pull the cord winding up the spring and when its fully coiled it releases turning over the engine. I've played around with one in the showroom and it seemed to work quite well. I don't know if it incorporates an auto decompression system as well.
It doesn't add much weight or bulk either.
Although springs don't store as much energy as batteries they sure can release it quicker! A typical spring on a strut seems to have enough energy to turn over an engine a few revolutions faster than most starters. The trick is harnessing it and reloading it.
Maybe for 1.0L engines all you need is to fit decompression valves to all the cylinders and then use a kick start off a motor bike.
Ian

IndyIan -

This makes me think there must be a regenerative braking solution that could be used for harnessing/reloading. You wouldn't use it for the "first start of the day", but you could use it for restarting from a stoplight. No idea how to do it, though.

CarloSW2

Naw, that's not the trick - there's plenty of mechanisms used every day for such purposes....

The trick is matching reliability.... How many cycles is a modern starter motor designed for? Half a million cycles? Maybe a million cycles? A former job of mine was inspecting/analyzing failed power springs connected to motors :thumbup:

Given the loads on a chainsaw (even a lawnmower) and how many cycle uses - it makes sense not to have an electric start - even moreso because the input is human power :thumbup:

http://dvice.com/pics/windupkey.gif

Springs aren't the way to go and neither is compressed air. You need gunpowder!! :D

Seriously, aircraft used to use the Coffman starting system because it was far lighter than the rest.

Coffman engine starter - Wikipedia, the free encyclopedia

Of course the neighbors might complain about you starting your car for a late night beer run. Of course the police might have a thing or to to say about you starting your car this way too.

However for the weight and thus efficiency a Coffman style starter and a box of blank shot gun shells will weigh far less than any other method except for push starting.

Ha ha! I remember that scene from The Flight of the Phoenix. That was a great movie.