For your hybrid application, I'd go with the AC. One word: regen --
without it to recharge the battery, "hybrid mode" is of little
benefit;
better to just disengage the motor altogether.
I get decent performance out of my Porsche 914 with a single 9" DC
motor
in 3rd gear (although it tops out around 65MPH). It even starts and
drives
OK in 4th, but the clutch begins to slip. The lower gear ratio
Netgain
suggests will keep motor speed down, making it easier to to push
current
when the engine is spinning the crankshaft at higher speeds.
However,
running slow comes at the expense of the torque multiplication in
your
gearing; ultimately, you'll be running the motor hot in a
low-efficiency
region. My Porsche performs as it does because I have a 170V pack
and a
1000A Zilla, but each of those drives up the cost & complexity. At
lower
voltage, I'd be much more dependent on the gearing to have any power
at
speed, and at lower currents, I'd be much more dependent on the
gearing to
provide starting torque. And when I actually use 2nd-4th gear, it's
a lot
more fun/powerful throughout.
The AC has a better torque profile for a fixed (albeit higher) gear
ratio.
However, given the rating of the motors, you'll probably need two
AC-51's
to get decent performance unless they're upstream of the
transmission.
As for the hybrid mode, I would strongly encourage you to take it
incrementally, because the controls will be a challenge and you
don't want
to be kept off the road while you figure it out. The vacuum sounds
like a
good idea, but my gut says you'll need inputs from the throttle too.
You'll almost certainly require a control processor (possibly
Arduino,
possibly more powerful). Step 1, IMO, is to make the car work with
an EV
mode and with an engine-only mode where the electric motor just
spins
freely. Once you have that working, you can tinker with hybrid
control
schemes all day long. Frankly, I think it will be a game of
diminishing
returns. Since you're using the existing engine instead of an
undersized
one that relies on the electric boost, and since your motor is fixed
on the
driveshaft (meaning you can't regen without also burning energy in
compression braking), I think the fuel efficiency gains will be
limited. I
would say you should think of it more like a Honda
Civic hybrid than like a Chevy Volt/Prius, except it will have the
ability to fully disengage the engine for EV-only drive.
-Ben
On Jul 23, 2014, at 5:02 PM, Ben Goren via EV <ev@lists.evdl.org>
wrote:
I know the question of AC and DC motors is a controversial one, and
probably done to death. But if all y'all might humor me, I'd
appreciate a
bit of guidance on this.
To recap, I have a chance to buy a 1964 1/2 Mustang in good shape
for
not much money. The goal is to get something not unlike the driving
experience of a Volt, with an all-electric range of roughly a couple
dozen
miles and a "traditional" Prius-style hybrid range limited only by
the gas
tank. The thought is to replace most or all of the driveshaft with
one or
more electric motors.
I've now spoken with somebody at both HPEVS and Netgain.
The guy at HPEVS wasn't exactly enthusiastic about the plan, but
thinks
it can be done. He recommends a rear differential ratio in the 6:1
range to
make an AC-51 not be miserable. That would require a new 9" rear end
for
the car and a custom transmission geared appropriately taller to
keep the
combustion engine happy. He doesn't know much about people doing
direct
drive or hybrid stuff with HPEVS motors.
The guy at Netgain was most encouraging, and has done something
nearly
identical to what I have in mind. He didn't recommend any gearing
changes;
indeed, he suggested that a higher ratio (3:1 or higher) might be
better
than stock, instead of the other way 'round. He had many very
helpful
suggestions, such as ways to couple two motors or to get the
electric
motor(s) to supply most of the power at low speeds and little power
at high
speeds, thereby maximizing overall gasoline economy.
It seems the beaten path for this type of project is therefore a
Netgain
DC motor...but I still like the regen capabilities of the AC motors
and the
reduced maintenance.
I'm aware that only limited efficiency gains are available with
regen,
but I have a secondary concern. When running in hybrid mode, once
the
batteries get depleted, the car would become a pure-gas vehicle.
It'd be
nice to instead use the combustion engine to just barely recharge
the
batteries enough to still provide acceleration assist -- the same
way the
Prius and the Volt do things. With regen, that should be
straightforward.
Without, I'm left thinking of kludges such as using the combustion
engine's
12 volt system to trickle-charge the electric motor's batteries, and
I'm
not so sure that's even safe, let alone possible. However, as a
practical
matter, this might not actually be a concern if a full battery
charge would
be comfortably ample for a full day's worth of hybrid-mode city
driving.
So...I'd appreciate a bit of insight on all this. Would a pair of
AC-51s
be as happy in a direct drive application as a pair of WarP 9s,
despite the
HPEVS guy's lack of familiarity with the matter? Am I worrying too
much
about regen and brush maintenance? Is there something else I should
be
worrying about instead?
Thanks much,
b&
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