DANMAS@aol.com wrote:
>
> In a message dated 98-09-01 14:21:11 EDT, Chris_Lillja@pupress.princeton.edu
> writes:
>
> > ... one electric turbo, coming up...
> >
> > http://www.turbodyne.com/
> >
> > 90 amps intermittent operation with electric bypass valves. Used mostly on
> > city buses as
> > far as I can tell....
>
> Chris,
>
> An interesting site, and an interesting concept. The 90 amp figure they quoted
> was for a 24v battery - that would be 180 amps on our cars. They also said in
> the tech section that the current draw was typically about 25% of the current
> draw for the starter motor on the same engine. Holy LUCAS, batman, those
> starters draw 360 amps!!! At 24 volts, yet. That's a BIG starter motor! That
> would be 720 amps on a 12 volt system!
I can speak from some experience that this system is undoubtedly used on
small buses, at best. As far as heavy-duty city buses (so-called ADB
-Advanced Design Buses) are concerned, such an item would be a waste of
electricity. All major heavy-duty engine manufacturers are now supplying
4-stroke engines with turbochargers only. The last heavy-duty
supercharger design still available is the Detroit Diesel 6V-92 (and
that is with mechanical supercharging), and that engine is only
certified for alternative fuels use--methanol or ethanol; new engines in
such drag are rare today.
Truth is, even 90A at 24V is a big drain for big buses, since they are
already consuming approximately 130A @ 24V for the a/c system alone when
the condenser and evaporator motors are on high speed.
The rough calculations presented by several folks for electrical power
to drive
a supercharger electrically are pretty much on target, except that the
losses may actually be higher than stated. Another consideration, not
stated, is that if the supercharger is to be driven electrically, how
_large_ is a 6-8hp 24V electric motor (6-8 hp necessary to produce about
5 hp at the compressor)? I assure you, it would barely fit comfortably
in the engine compartment of a Spitfire, even with the engine removed.
The 1 hp, 24V motor used to power the hydraulic power pack of some
wheelchair lifts on city buses is about 11" in diameter and 13-14" long.
One needs only to extrapolate a bit to see that it would be unfeasible
to install a compressor/electric motor combination in an LBC.
It's just more pragmatic and sensible to drive the compressor from the
crankshaft than to go to something more elaborate and much more
expensive for the sake of electrical drive.
Cheers.
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