<VV> Electric fans, pusher or puller

[jvhroberts at aol.com]

 There's a fallacy based on false assumptions here. Locomotives and ships use electrical transmissions, and they are over 90% efficient. The battery doesn't enter into the equation here, as once the engine is running, the power goes from the generator/alternator right to the motor, the battery is there just to provide cranking power. 

All that being said, efficiency should be very good, with the right controls. Divorcing fan speed from engine speed allows the fan to operate at a far more efficient part of its curve. 

All THAT being said, the real drawback is lack of sufficient electrical power for any fan capable of doing a good job. 

Now, if someone wanted to use a 90 volt alternator going right to a 90 volt motor, separate from the rest of the car's electrical system, there's hope. Of course, the weight added will be substantial. 

So, as I often ask, what problem does an electric drive solve, and is there a simpler, less expensive solution to whatever the problem might be?

 

John Roberts
 

 

-----Original Message-----
From: kevin nash <wrokit at hotmail.com>
To: virtualvairs <virtualvairs at corvair.org>
Sent: Sun, Mar 17, 2013 1:08 pm
Subject: Re: <VV> Electric fans, pusher or puller







I've been reluctant to post on alternate fan drive topics because I've seriously 
grown tired of it and it seems like if anybody responds to it, no matter what, 
all it does is keep the discussion
going- however, this one time I'm going to make an exception, and try to explain 
the real reason why electric fans are a bad idea. No matter if they are pusher 
or puller, no matter if they
can generate the required cfms at the required pressure, no matter if they are 
heavy or not, the real reason that electric fans are a bad idea, is that the 
power path, is far too indirect and
inefficient to accomplish the desired goal. Consider the power path for any 
electric fan that's ever been tried is belt to alternator, alternator to 
battery, battery to motor, motor to fan, and
fan to engine. Each step along the way has losses involved, and although the 
individual losses might not be so bad, the accumulative effect is sizable.
These are the efficiency's that I will assume: Belt drive 95% alternator 70%, 
battery 85% motor 85% and fan is 85%-  Note what the accumulative loss turns 
into, assuming you are
going to allow 15hp to be used at the crank: Belt to alternator: .95 x 15= 
14.25hp alternator to battery: .7 x 14.25= 9.975hp, battery to motor: .85 X 
9.975= 8.48 hp, motor to fan=
 8.48 hp assuming direct drive, and fan to engine = .85 X 8.48= 7.2 hp. This is 
only 48% of that original 15hp, and is not even close to being enough air to 
properly cool an air cooled
engine, in all cases.  Although the 7.2 hp may seem like a deal given that the 
stock fan and drive uses approximately 8 hp at 4000 rpm, I assumed that the fan 
was 85% efficient,
but the stock corvair fan is only approximately .28 efficient at 4000 rpm, so to 
compare the stock drive vs the electric, I should use the same 85% for the fan, 
assuming that the engineneeds 1500 cfm at 8.5" of water pressure. I used the 
formula hp= flowXpressure/6356X fan efficiency, and I calculate that hp required 
is 2.36(!) hp. I neglected the fan belt drivein this but no matter, even 
including that the hp use is still less than 3hp. Testing the formula on the 
stock fan, using 27% efficiency gives 7.42 hp, so it is reasonably close to the 
measured 8 hp that gm states for the late fan. I used 8.5" of water pressure 
because that's what I've consistently measured in my own tests (so far), 
assuming that the damper doorsare blocked open. I've seen 11-11.5" water 
pressure at 4000, but only when the damper doors are completely closed. The 
point of all this is that there is much, much more to be gained by a more 
efficient fan (or gear down the stock fan and make up the low rpm co
 oling loss some other way that doesn't involveusing more power) driven by a 
belt than there is to using an electric set-up.Kevin NashEarly Turbo, Daily 
driver

 
 

 		 	   		  
 _______________________________________________
This message was sent by the VirtualVairs mailing list, all copyrights are the 
property
of the writer, please attribute properly. For help, mailto:vv-help at corvair.org
This list sponsored by the Corvair Society of America, http://www.corvair.org/
Post messages to: VirtualVairs at corvair.org
Change your options: http://www.vv.corvair.org/mailman/options/virtualvairs 
 _______________________________________________