Electric Auto Association
East (SF) Bay EAA Chapter
Insights into Converting to Electric
Saturday, July 23, 2011
Location: Alameda Library, meeting room A, Alameda, CA
General announcements included letter of appreciation
from Castro Valley Science Fair to three members who brought their EVs
to the event (from March).
Announced next three events – EBEAA rally at Chabot College, Green Expo
rally in Richmond, and Silicon Valley rally in Palo Alto.
Speaker Eric Tischer presented a power point regarding his
Passat conversion. Eric began
his conversion career by changing out engines in two gasoline powered
vehicles to more powerful and robust IC engines. The first was a 73 MG
Midget that he upgraded to a 1.2 liter rotary and 5-speed transmission.
The second was a 75 Porsche 914 that he upgraded to a 2.7 liter water
cooled flat six.
He found a Siemens AC electric motor and gearbox on eBay for $900 CDN.
This gave him the inspiration to convert his VW Passat. Eric said the
Passat is known to have reliability issues with the IC engine, but
otherwise a solid vehicle. It took about six months to convert the
Passat. The Passat is reasonably modular, and items that sometimes
don't work when converting a modern vehicle to electric (like the
speedometer) work OK in the Passat.
He did not plan to use the Siemens gearbox, just the AC motor. As the
bearings on the AC motor were oiled by the gearbox, he had to change out
the bearings with permanently lubricated bearings. The union between
the AC motor and the Passat transmission was made with a taper lock
flange pinned and centered with a custom machined part to the output
gear on the AC motor.
The biggest challenge was the inverter. He found an inverter on eBay
for a 1HP motor for $35. He used the control circuitry to fire a new
high-power 6-pack IGBT. It worked OK for initial tests, but the way the
controller managed torque and speed was not practical for everyday
driving. As an aside, during the initial tests, the liquid-filled stock
motor mounts ruptured, probably due to the extreme torque put out by the
electric motor. He replaced the mounts with some custom-built units
which work well.
He found a more modern vector-control inverter to control the firing
rate of the IBGTs, and built a water cooling unit to keep them cool when
driving. The inverter output is scaled to fool the inverter logic board
to think it is still running a 1HP motor, and not the 100HP Ford AC
With the new inverter control, he is able to get regenerative braking to
work very well. It functions down to about 5 MPH (somewhat like a Prius).
It could work all the way down to zero MPH, but he disabled the DC
injection braking because it uses power - low speeds are handled by the
Thanks to the high RPM ability of the AC motor, (8,000 RPM) he is able
to get to about 80 MPH in 2nd gear, so he doesn't have to shift very
often – perhaps once or twice during his 45-mile commute from Dublin to
the Tesla factory. He travels on the freeway in 3rd gear. He uses a
clutchless link between the motor and transmission, and built a unique
speed matching profile into the controller logic that matches the speed
of the motor to the next gear when shifting. This reduces the
gear-grinding that is common in clutchless setups.
The original battery setup was 25 Optima 12v lead-acid batteries, but he
had since changed to 99 Thundersky 100 aH Lithium cells. The pack is
divided into thirds – 1/3 in the front, 1/3 where the gas tank used to
be, and the other 1/3 behind the rear seat. There is still room for
five people in the Passat.
Eric did not use a battery management system for the first year he had
the pack, but the monitoring and balancing on weekends took about two
hours every Saturday, so in order to not have to mess with the pack
every weekend he bought a mini-BMS for $12 a cell. He doesn't use the
balancing function, just the high-voltage cell cutoff for safety.
His DC/DC converter was originally an AC/DC inverter for 220 VAC. This
allows him to use up to 330 volts DC input by removing the original
input rectifier and connecting it directly via a surge suppressor.
In order to make the power steering work, he installed a DC hydraulic
pump from a Renault. The brake vacuum pump is DC as well.
He recently purchased an electric compressor for the air conditioning
system. It is a 4.4kW motor kit made by Master Flux, and has its' own
inverter board, and comes with the components to convert from the
belt-driven pump to electric. He plans to install it in a few months.