🚀 go-pugleaf

In article <30DEC199200153934@pierre.mit.edu>, chuck@pierre.mit.edu (Chuck
Parsons) writes, in part:

>  People have been considering this problem from the standpoint of
>how much energy a gas powered car uses and missing a few points.
> 
> First a car engin is only about 25% efficient under good running conditions.
>electric systems can be 95% efficient. 75% efficient should be redily 
>obtainable so divide gasoline_energy by three.

	uhmmmmm.  The 25% figure is FUEL IN to SHAFT HP OUT.  The commonly
	quoted figure for a combustion engine (VWs had 25 HP, Corvettes had
	300-400HP, etc, is SHAFT HP OUT)  (I am NOT getting into losses is
	gearing, tire friction, etc.)  So the comparision of 25 HP electric
	to 25 HP gasoline is correct, no 75% derating applies.

	The "only uses 25HP" we have seen going by over the past few days is
	_also_ valid, since the usual design approach leaves a substantial
	reserve between _average_ load and _peak_ available HP, for passing,
	etc.  Electric motors have a small advanatage, as they have, control
	gear permitting, substantial short time overload capacity.

	I reccomend "The Electrical Engineers Handbook", the one I have is
	Fink & Beatty, McGraw-Hill.  Handy graph of energy densities for
	various systems:
		NiCd peaks at 40WH/KG
		Lead Acid  at 50WH/KG
		NaS	   at 400WH/KG
		Combustion engines over 4000WH/KG
	Similar figures for a flywheel system should be available from
	proponents.  To each must be added containment figures.

	(At the risk of restarting the flame war, consider the collision risks
	of NaS...  A battery, tho, has an advantage ofver a flywheel:  since
	the storage is chemical/potential, rather than kinetic, once the battery
	has disassembled the release of the stored energy stops.  One then has
	lots of lead (perhaps) or sulphuric acid or maybe 500C mix of Na and S
	lying about the street.)
	
thanks
dave pierson			|the facts, as accurately as i can manage,
Digital Equipment Corporation	|the opinions, my own.
40 Old Bolton Rd		|I am the NRA.
Stow, Mass, USA	
01775				pierson@msd26.enet.dec.com
"He has read everything, and, to his credit, written nothing."  A J Raffles