DIY Electric Car Forums banner
1 - 1 of 1 Posts

· Registered
72,624 Posts
Discussion Starter · #1 ·
Your posts are very painful to read. I assume English is not your first

In your last post it seemed like you were advocating a series setup
where an electric motor ran a compressor which then ran an air motor.
Most of us see such a thing as ludicrous because every conversion costs.
Compressing air is one of the lowest efficiency tasks out there. The
best I have seen with mechanical compression is 23% eff.

so lets do the real math.


lets use 80% eff for getting power out of the battery, even assuming a
lead acid battery with pukert effects this is probably low.
lets use 95% eff for the controller. We know this is pretty accurate by
looking at the amount of heat generated vs the power going in.
lets use 90% eff for the electric motors conversion to mechanical energy.

lets use 25% eff for the air compressor. Without cryogenics, this is
about the best you can do mechanically.
lets use 25% eff for the expansion motor. Again, we are using air and
you will see drastic temperature changes which indicate
lets assume the expansion motor can be used as a compressor for
regenerative braking.

typical EV
.8 * .95 * .9 = 68% eff ; I would say this is conservatively low, even
for a home brew DC conversion(only saying that we use whats avil in DC
conversions, not that dc is inherantly less eff than AC systems) If we
use advanced batteries and desinged for EV AC systems in a designed for
EV vehicle, I see no obstacles to achieving .95*.95*.95 or about 85% eff.

Your suggestion
Lets assume that running at a constant rpm doubles the eff. (1/2s the
battery->controller->motor->compressor->expansion motor
.9 * .975 * .95 * . 25 *
.25 = 5% eff The compressors kill us.

Even if we say you have managed to come close to an electric motor and
get 90% eff on the motor and run the batteries direct to the motor

battery->controller->motor->compressor->expansion motor
.9 * 1 * .95 * . 25 * 1
= 21% eff The compressors still kills us.

This is dangerously veering off topic, So I would like to end this
conversation on line. If you have any real method of mechanically
compressing a gas at over 25% eff, Id like to hear about it off list.
Ignoring the fact that it would solve one of the fool cell advocates
problems, it could make us a mint revolutionizing the industrial air
compress market.

For subscription options, see
1 - 1 of 1 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.