Electrical Supercharger

[Seth Allen]

On Thu, 8 May 1997, Steve Meade wrote:

> Date: Thu, 8 May 1997 19:55:30 -0700
> From: Steve Meade <smeade at deltanet.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Electrical Supercharger
> 
> 
> 	I noticed a while back (over a year ago) there was a discussion about
> electrically powered superchargers. I was wondering if anyone actually
> followed through on plans and tried it. To me, there are several advantages
> to electrical power over the traditional crankshaft power:
> 
> 	1. Cost (electric motors are less than blowers and don't strain engine as
> much)
> 	2. Placement -- the placement isn't dictated by crank positioning.
> 	3. Ease of installation -- no need to completely tear apart front of
> engine
> 	4. Adjustability of boost -- a simple 2-d rpm and boost mapping system can
> be made
> 
> 	However, I was thinking of the extra energy losses by using an electrical
> blower. In a regular system there are only two possibilities for energy
> loss:
> 
> 	1. Crankshaft attachment scheme / gearing (if any)
> 	2. Impeller / screw losses
> 
> 	An electrical system incurs three energy losses though:
> 
> 	1. Alternator inefficiency
> 	2. Electric motor inefficiency
> 	3. impeller / screw losses
> 
> 	I was wondering whether or not a system could be developed to produce 3psi
> or so. That would be enough to satisfy my performance cravings for now.
> About how much power could one expect from just a couple of pounds of
> boost? Remember, the blower wouldn't consume any extra power off the engine
> if using the stock alternator. On my car, a BMW 325is (relatively little
> displacement of 2.5liters) a regular supercharger kit costs around $6K! As
> you can imagine, I would be very willing to accept a fraction of the power
> boost for a small fraction of that cost. Also, designing the system myself
> would be fun. 
> 
> =-=-=-=-=-=-=-=-=-=-=
> Steve Meade
> smeade at deltanet.com
> 

I have wondered myself if this could be done, but with a roots style 
blower at about 60% efficient, a lot of current will be required.  Just a 
guess, but if it take 5hp to compress the ait divided by the efficiency 
(60%) that means 6.3 hp, or 4750 watts, or about 400 amperes at 12 
volts, or about what it trakes to crank the car.  Maybe with two or three 
batteries and a more efficient centrifugal blower (80%ish)?  I may be off 
onthe hp requirement, but I bet that I am not off by an order of 
magnitude.  You would need a lot of fets in parallel to drive that motor, 
or run up the voltage and take a loss there.

Maybe my math is wrong, but there must be a reason whay it hasn't been done.

Seth