Vehicle: Car: Battery
Petrol Alternator   (+1, -3)  [vote for, against]
Otherwise known as a generator

A replacement to the original alternator that came with the car, the unit is the same size and can be mounted in the same place. The only tricky bit of installation is to connect it to the fuel line.

The purpose of the device is to allow the car to use all of it's power to drive the wheels, rather than sapping some of it for the alternator. The generator would also be more efficient than using the engine. As it is connected to the battery, it can detect when the level of charge drops below a certain level and top up the battery. Depending on the type of battery being used, the unit can be optimised to charge the battery in its preferred way to maximise its life (some batteries should be kept full, others should be run down). It could also have a warning light to indicate when the efficiency of the battery has dropped below a certain level. Another benefit is that the unit could run without the engine running so you could recharge a flat battery or run electrical items without starting the car.
-- marklar, Aug 13 2007

So basically you just want to put an airplane style APU in a car.

Um. Why? The engine on the car is already running, so why not take the power from there?

Are you trying to gain a couple more horsepower at the top end? This does not seem like the best way to do it. A complete second engine (however small) versus adding a couple hp to the main engine.
-- Galbinus_Caeli, Aug 13 2007

[iron_horse] The clue is in the title (and it's not a seabird)

[Galbinus_Caeli] I agree that it would only be a couple of HP or MPG but I thought this would be an easy way to improve fuel efficiency and power output, compared to adding a turbo or fitting solar panels.
-- marklar, Aug 13 2007

modern alternators only draw power when required. The only savings would come from parasitc drag reduction on the belts and bearings and even those are nearly nil so the loss from the additional weight will eliminate the benefits.

Some Drag racers disconnect the alternator while at at the track and run only on batteries.
-- jhomrighaus, Aug 13 2007

Of course instead of gasoline you could just use waste heat and water (steam) to drive an alternator. But I suppose that's already been halfbaked.
-- acurafan07, Aug 13 2007

So, in the same volume as a belt-driven alternator, you are going to fit an engine AND a generator?? Better get out your magic wand, buddy, it sounds like a WIBNI to me. & never mind that the efficiency of gasoline engines suffers as the displacement is reduced.
-- afinehowdoyoudo, Aug 13 2007

[marklar] this marklar is complete marklar, what the marklar where you thinking when came up with this marklar? So the marklar in the marklar draws no power from the marklar by having its own marklar? And how much does this marklar weigh?
-- evilpenguin, Aug 14 2007

//run electrical items without starting the car// well, that pretty well describes me. I've got the microwave, slowcooker, GPS, laptop, DVD player, wireless router, and two rocket launchers in the mini-van. It would be nice to go out for the afternoon and not need to flag down a passing motorist to get home.

Besides, if I can rig it so I can pull out my key fob, press the button, and say "Perform APU prestart" to get it going I will be pretty much in geek heaven.

By the way - I'll tell you where to find the ideal powerplant for this gizmo. Next time someone parks a C-5 Galaxy on your street, walk over to the main landing gear. You will see two large threaded rods with a small hydraulic motor at the top. These are for the 'kneeling' function. Right next to one of the hydraulic motors you will see a gas turbine APU not much bigger than your hand. If that doesn't cause technolust in a halfbaker, I can't imagine what else could.
-- lurch, Aug 14 2007

I have actually suggested a stirling powered alternator in the past (in an anno). The point of this idea is that it is a small easy modification. I guess you could design a relatively simple stirling generator that would attach to the exhaust, but it would probably need to be specific to each model of car.

A gas turbine engine would mean adding a seperate fuel source. I was thinking of using an engine similar to those found in model aircraft.

// Better get out your magic wand, buddy // Is this going to be another anno that you delete now that someone has pointed out that it is wrong?

//the efficiency of gasoline engines suffers as the displacement is reduced.// [iron_horse] Do you know this or is it an assumption?
-- marklar, Aug 14 2007

marklar, sorry about the deleted anno. However it does seem like glossing over an important detail, not mentioning the engine. Yes, efficiency of IC engine does suffer as size reduced, owing to increased surface area/volume ratio hence a greater proportion of fuel mix is quenched near cylinder walls. Reference to magic wand may be facetious but justified in my view. kind regards, fishbone withdrawn
-- afinehowdoyoudo, Aug 27 2007

For example, the honda gx22, which would be about the right size for this idea, is about 7% efficient. Compared to approx 25% for a car engine, it seems preferable to use the existing arrangement, even after discounting the loss in the belt drive. Thats unless you really want to have standby power in the car.
-- afinehowdoyoudo, Aug 27 2007

yes, fixed loss happens no matter what the power level is. Every motor has bearings, oil, etc. In a car motor they are quite a measurable % of loss, in a giant power plant they are too insignificant to measure. This is why a single larger motor is always preferable, and why you would size it to be as close to full power as acceptable during normal operation. low rpm + full load = most efficiency.
-- AutoMcDonough, Mar 03 2010

i was badly disappointed by this idea.
-- WcW, Mar 03 2010

random, halfbakery