Alternator Questions

[dimi trip]

Hi everybody,

I am Dimitri from Belgium and, altough i am a real petrolhead (sorry), became very interested in this forum recently.

I am going for an engine swap in one of my oldtimers. It is a europear Ford, so not a big V8, but efficiency of the standard 2-litre engine is poor.

My best option for this car was a 2.9 cosworth V6. It is far more efficient with double horsepower and in standard form only a slight increase in fuel consumption over the previous engine. But that is not enough!

I have allready the parts for a large list of mods. Not only mileage related, but most of them are:

Aero mods. The car has a typical european coupé-body (fastback), so not bad to start with. But, as most 70's cars, drag is to high. I am planning:
• Lowering by 40mm (economy and performance reasons)
• Making an air dam in front
• Underbody panels (most gains are to be expected here. The car underbody had theaerodynamics of a brick)

Gearbox mods:
• Switching from auto to manual box
• changing the fifth gear for a higher ratio one
• lightened flywheel (more for performance reasons)

Final drive mods:
• Using a higher ratio diff (power of the engine should be fine with it)

Wheels:
• Changing steel by alloys
• Low resistance tyres
• Pressure monitoring system (believing in an effective gain here, as i am to lazy to check pressure regularly, even when the compressor is next to the car)

Lightening:
• Removing parts that are not neccecary (spare tyre, jack,...)
• Replacing rear window and rear quarter windows by perspex

Engine:
• Removing Airco
• Removing power steering
• Replacing waterpump by an electrical one
• Replacing mechanical Fan by electric fans

Electrics:
• Replacing all available bulbs by LED
• Replacing Headlights by H.I.D
• Replacing dash by lighter and one that draws less current
• Keeping Cruise control from the new engine
• Installing trip meter



Maybe forgetting things, but that is about the list i'm starting with. As you can see, some of the mods are also performance-orientated. I like cars with power. But instead of tuning the engine by giving it more air and fuel, i went for the other way. Expecting some gains without touching the engine itself, and that way, affecting economy in the positive way

I am thinking of the last thing i can do to make a noticable difference. The alternator. But my lack of fysics keep preventing me from getting good ideas.
I have read many topics about removing the alternator. But that is no option for me. The engine will run, even without a battery. But i am not going to risk the electric waterpump to fail.
Only option is to make the alternator as efficient as possible. I looked on the web for smart alternator controllers, but could'nt find any. So i kept thinking, and have an ideas so far, but don't know if they can be made to work.

Replacing the crankshaft pulley by one that has a freewheel integrated, and replacing the alternator pulley with one that has enough mass to function as flywheel. Now switching the alternator field wire (as seen in other topics) to charge only when throttle position is, lets say, below 1/4th.
When departing, the alternator sees no load, and when slowing down, it has the stored kinetic energy from the flywheel to keep spinning. With my driving style (doing many engine breaking when shifting down) the alternator gets a free shwung from the engine (a slight form of regen breaking i guess).
Now... the original alternator is 90A, but has to feed a load of gadgets in the original car (the kind of car that has every electric accessory you can imagine). My car only has lights, heater, dash and the stuff needed for the engine (including water pump and dual fan).
I guess, in standard setup. A 70Amp alternator would be more than enough for me, but if running this setup, it won't be charging constantly. Is it wise to use a larger (for example 150A) aternator so it can charge the system in less time?

Do you guys think it works? It seems like a noticeable amount of captured wasted energy. But i have absolutely no idea how to calculate the extra consumption from the extra rotational mass.
I do believe it must be possible with the right battery/alternator setup it is possible to shift the alternator load for 80% (if the alternator field is only controlled by throttle position, couse it is still charging at idle) or more (charge when throttle position going downwards/charge when throttle position is at zero but car is moving).

d

[pete c]

I believe a simple switch to allow for intelligent alternator use is the way to go. No need for added gizmos such as clutches and flywheels. The engine itself is the flywheel.

[dimi trip]

The engine is designed to drop revs as quickly as possible... applying brake on the alternator, so i don't believe it acts as a flywheel in this case.

I would consider a simple switch if:
- i would be using a belt driven water pump.
- i could easily charge my battery at night (car is in a busy street without power outlet)

It would be to easy to forget the switch (like the many times i forgot to switch off the choke). With the possibility to overheat the engine in my case.

and... where would the gain come from if manually switching on and off? Are you really just switching the alternator on every time you use the engine for breaking? Couse that is the only time you can use power that is lost otherwise. And your allready using it in a standard setup. The real gain in that setup is by using the alternator as 'emergency unit' and using cheap electricity to charge batteries.

Point is to use the power from engine braking to spin a flywheel, and use it to produce much more electricity (because it will stay spinning without applying a load on the engine) than possible with a conventional system.

flywheel and clutch are very common, and the setup is easy to fabricate. (having a lathe to fabricate pulleys)
Using a centrifugal clutch (like in a chainsaw for example) would even make it possible for the engine to spin freely (without power loss caused by the added flywheel) at idle and making the clutch engagement smoother. And acts also as a freewheel when engine revs drop.