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Running Alternator Off Half-Shafts
scootz - 23/12/08 at 07:57 PM

Saw this on a Formula racing car at the weekend... is there any benefit (other than space-wise)?

Does the 'normal' Alternator to Pulley assembly sap more engine power than driving the same Alternator off the half-shaft?

blakep82 - 23/12/08 at 08:00 PM

mmm all well and good on a race car i think which is constantly moving, but imagine being stuck in traffic, like i was in the floods on friday nite, took me 2 hours to move 2 miles, with that progress your battery would be dead i think

my car kept overheating....

scootz - 23/12/08 at 08:03 PM

Ah... good point!

I'll get me coat!

blue2cv - 23/12/08 at 08:07 PM

You'll probably find that the alternater on driveshaft trick is an easy way to get over the problem of extra battery drain (inj pumps etc) when using the racers total loss electrics

DIY Si - 23/12/08 at 08:08 PM

Also, good luck getting the gearing right for it! Would you want peak voltage at 30, 40, 60, 100 mph?
Either way, not a brilliant idea unless racing. Even then, you might get away without running one at all!

rusty nuts - 23/12/08 at 08:17 PM

If space is a problem it may be possible to run a drive shaft from the engine to drive the alternator like the Focus diesel?

britishtrident - 23/12/08 at 08:26 PM

I am pretty you will find it was fitted purely to satisfy the scrutineers --- it must have been running in a class that required a generator to be fitted.

Most single seaters run toothed belt water pump drives (idea is the pump turns more slowly to reduce the drive power required and reduce cavitation) which make driving an alternator in the conventional postion difficult.

In the old days you used to see cars in some classes with a bicycle dynamo (unlikely to actually be connected of course) that could in theory be swung down to run on the outside of the fan belt



[Edited on 23/12/08 by britishtrident]

JoelP - 23/12/08 at 09:14 PM

quote:
Originally posted by DIY Si
Also, good luck getting the gearing right for it! Would you want peak voltage at 30, 40, 60, 100 mph?
Either way, not a brilliant idea unless racing. Even then, you might get away without running one at all!



Wouldnt the regulator sort that out, to regulate the voltage?!

within reason i mean, obviously you'd have to make it spin a lot faster than the driveshaft.

[Edited on 23/12/08 by JoelP]

Canada EH! - 23/12/08 at 09:24 PM

They used to do that in NASCAR, but now with all the fans and pumps for brake and driver cooling the small alternators that ran off the drive shaft are not adequate. They mounted the alternator on a bracket off the differential. It would be hard to keep the belt on the pulley on a half shaft, more up and down movement.

ss1turbo - 25/12/08 at 11:35 PM

I'm thinking that driving an alternator off the drivetrain would be more power sapping - as it would take the same amount of power to drive it, but you're adding your transmission losses as well. May be only a few percent, but most of the time those last few percent of power from the engine cost the most.. OK we're only talking Watts for power (say 50, 0.05kW), but that could thoertically mean the difference between 1st and 2nd in a race..