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

Members: 20

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 motor.

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 hydraulic brakes.

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.


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