alternators on race cars

[Richy_Rich]

Here's a thought.... (might be a stupid one, not sure)

Basically your alternator is a bit like a big electric motor*, right? Now, if your series rules insist on you having one and you're not allowed a switch etc. How about just removing the stator (if that's what it's called) and cutting the windings on, say, every alternate, er, arm(?) Immediately you have a half power alternator.

Or is that totally wrong?

p.s. I haven't done this, but it'd be bloody hard to detect (and possibly do)

{added for clarification}* In design at least

[graham bahr]

interesting thought, would you end up with a half voltage alternator?

a more basic way to achive it might be using a loose or even greased? alternator belt.

i one saw a kit race kit car which had to have an alternator that worked ( well the charging lamp had to work) this was driven by an insideout V belt, the belt drove it just enough to make the charge lamp work but not enough to actualy produce a charge and create drag. it didn't look like its possible for a normal v belt to work when fitted almost tensionless inside out but it did

[Richy_Rich]

I really, really ought to know this having studied electronic engineering - but I don't.

However, I think what would happen is that you'd get the same voltage but at half the frequency (alternators produce AC), as this output is rectified to DC using diodes, it _might_ work ok.

Alternators might also be 3-phase, so it wouldn't be as simple as just cutting every other connection on the rotor. But I'm sure, if you care enough, there's some hackery you could do to effectively reduce the drag caused by inducing current somehow...

[dtype38]

Or just fit a tiny itty bitty alternator, with a great big pulley on it, so that it can only make enough power to run, say, your instrument lights. You could even use it as a belt tensioner for the water pump for good measure!

[Al Weyman]

I have a massive pully on one of my Chevys, Real Steel sell them and they fit a standard alternator, nice alloy one as well.

I don't think the analagy of an alternator being like an electric motor is correct. A dynamo is and if you power a dynamo it will turn as per a motor but an alternator works different and neds a positive power supply to activate its charging capabilitys. It is this low amperage wire one puts a switch in to simply turn off the generating of electricity and is why this works on an alternator and not a dynamo.

[zefarelly]

my alternator doesnt need a supply to make it work ? I know modern ones do and I think theyre bloody stupid, mines simple, turn it and it charges, end of , just one fat wire to the battery and a tiddler to the dash light. I can rev to 8k safely and the water pump goes with it. job done

[Al Weyman]

Thats a generator or dynamo then not an alternator, they fitted generators/dynamos to cars of your year Zaf, alternators came in a bit later, they are two different animals and an alternator definitely needs a power lead before it will work. I will check it out though and am prepared to be proved wrong.

[zefarelly]

ah . . .the alternator fitted to my car has a feed, from the dash light I guess, I'm not aware it needs that to actually work though.

[dtype38]

Would that be an internally or externally voltage regulated alternator?

Oh, and my little Brise thingy has three wires: charging out, 12v supply and ignition light connection... spooky

[Al Weyman]

Yes the chevy ones have three wires the later ones 2 and you can convert to a two wire configuration for hot roding neatness butthey reckon the three wire set up is better. Even with a two wire set up that main wire is live and as I said it needs a power to work how ever you get the power to it.

[zefarelly]

mines a 2 wire, I guess the ignition light is its supply, its internally regulated, I've never disconnected the small wire to see if it still charges, all I know is it works so leave it alone !

[graham bahr]

Originally Posted by zefarelly

mines a 2 wire, I guess the ignition light is its supply, its internally regulated, I've never disconnected the small wire to see if it still charges, all I know is it works so leave it alone !

assuming its a lucas acr it should still charge athough you will need a fairly big blip of the throttle to energise it in the first place. i've run my car for a couple of meetings now with out the charge lamp circuit connected ( the spade connector inside the alternator fell off) and my cars still charging and starting ok, which is handy cos the lttle varley battery i use dont hold much charge

[zefarelly]

mines exactly the same, a lucus ACR, the little varley is fine too, although helped by the new brise starter, it struggled with the old Lucus one in extremely cold weather ( ie freezing)

[graham bahr]

i plug a slave battery in for starting and trundling around the paddock etc, just to make sure the varley has always a good charge in it incase of a stall etc whilst on circuit

[zefarelly]

mine seems pretty self sufficient, I don't think I've had to do anything to it other than cross my fingers in the icy conditions at Aintree last November

[Al Weyman]

Hey what about this starting 5 times for the scrutineer then (or was it 7). :-)

[graham bahr]

the varley has never let me down, infact fully charged 10 starts on the trot aren't a problem, but repeated shunting around the paddock without actually running the car for more than a few moments takes out more than the alternator puts in, so it is possible to arrive on the grid with a battery in a low state of charge, in which case a stall on a hot engine may cause a DNF, so the slave battery is only a precaution

[graham bahr]

the slave is also usefull when keeping the varley topped up in the closed season, as your quite unlikely to damage it with overcharging (and its easily done) if the slaves also plugged in.

[zefarelly]

you could always put a solar panel on the roof :-)

when I build a new engine or I'm fiddling in the workshop I use a slave battery and a booster starter, leave the varley well alone

[grelley]

Unless I am missing something, the formula for electrical horsepower is watts = volts x amps, so a 40 amp alternator x 12 volts = 480 watts, plus a little friction/ inertia would be not much more than 500 watts or .66 kw. This would only be if the battery was very flat, and only for a short time. One of the main advantages of an alternator is that it will give full charge at low engine revs, so it is beneficial to gear the alternater down to engine speed or less. An alternator will only charge what is being consumed by the electrical system, so if you are only running an electric fuel pump and electronic ignition it will only be 2-4 amps.

[zefarelly]

all mine needs to run is coil/points ignition, a fuel pump and brake lights, the other lights are all there and work but I've never used them, in fact, tyres aside the cars road legal.

[maddogf3]

Thought this thread had stopped
Two wire alternators are known as "Machine Sensed" and anything with three or more are "battery sensed"
If the ign light wire is not connected or bust the alternator will not charge below about 3000 revs approx and will then charge normaly although i thought they stopped charging again if revs are dropped off . Dont see the point of not having a warning light circuit if you have a Alternator on the car Battery sensed as far as I know are just the same with revs .
Stick a voltmeter on the battery and you will soon see if it is charging or what happens when you rev it up from the voltmeter reading

[Dauntless]

In the USA there is no longer any debate about alternators on race cars. Several years ago one of our racing mags (Circle Track, IIRC) did a dyno test of a 'typical' 350-ish bhp carburetted SBC V8 equipped with a switch in the field circuit. After a thorough warmup they performed a 30-minute track simulation run with the switch on. Result: full power for the entire duration. Then they switched the alternator off and repeated the run. After a short initial slight rise they saw a loss of about 1bhp/minute for the 30-minute run. Several repeats had the same result.

You chaps who've DNF'd for flat batteries know this from grim experience...

[greenamex2]

Thanks for that Dauntless, it's nice to see one of my pet theories actually proved 'scientifically'!

[R59]

I've got one of the little Edge Performance alternators on my Chevy engine. It's three wire, battery, ignition, and light, but nowhere on the box, or on the paperwork that comes with it, or even on the suppliers website, does it tell me which pin in the connector does what. The output is a 6mm stud, that's simple. The other two are spade connectors, one is perpendicular to the other, for use with a bespoke connector shell.

Even without the ign/lights wiring attached, yes, it charges at 3000 plus.

Must get it sorted properly. Anyone got one, and have the terminal connections?

Rob.