Installation of BMW throttle body and its connection to the Soliton 1

The BMW throttle body is directly connected to the driver's accelerator pedal on the floor.  It has a cable linkage that moves the vane within the throttle body and simultaneously rotates an attached three wire rheostat (throttle position sensor).  If a voltage is applied across the potentiometer, then a movable wiper will output a voltage that is dependent upon the position of the wiper. 

The Soliton 1 can accept a 0-5 volt DC signal when applied to the terminal labeled "Throttle", where +5 volts is considered to be "full throttle".  The Soliton 1 can accept signals from other potentiometer type devices such as a Hall effect device, the Evnetics throttle transducer, and in principle even the BMW throttle body potentiometer itself.  This last solution has merit in that the throttle body potentiometer can be salvaged from the donor car's engine at no additional cost and the cable linkage is already established between the pedal and the throttle potentiometer!  The cruise control actuator is also connected to the throttle body, thus it may be possible in the future to also include the cruise control option in the final EV conversion.  

Evnetics Throttle Body



Picture of the Evnetics throttle assembly.

When using the Evnetics throttle body (picture above) the red wire is connected to the Soliton 1 terminal labeled S5V, the black wire is connected to the Soliton 1 terminal labeled SGND, and the white wire (wiper) is connected to the Soliton 1 terminal labeled THROT.  During operation the throttle body output was measured to be 0.396 volts DC when at 0% throttle, and 4.346 volts DC when the throttle was at 100%.  Calibration of the throttle is completed according to the instructions provided on page 23 of the owners manual (  http://www.evnetics.com/downloads/Soliton_Manual_1v4_rev2.pdf  ). 


BMW Throttle Body and Potentiometer

One of the biggest challenges regarding using the BMW throttle body and potentiometer is determining where and how to mount the oddly shaped mechanism.  To further complicate the task, the cable feed from the accelerator pedal only extends from the firewall about 17 inches into the hood area.  One possible solution is to use the driver side engine mounting bolts to secure a platform that is elevated above the mounts and sufficiently close to the firewall that no cable modification is required.  The mounting surface described in a previous posting was predrilled and the holes tapped to accept 1.5" long hex head 1/4" 20 bolts (picture DSC04253).

Picture DSC04253 which shows the mounting surface measurements and the four holes that were tapped to mount the throttle body.  

Picture DSC04254 of the secured OEM throttle body on the mounting plate.

Picture DSC04257 view from the top of the mounted throttle body and mounting plate.  The multiple red (temporary) butt splice electrical connectors at the top center of the picture were used to connect the three wires from the BMW OEM throttle body to a three wire cable that was connected to Soliton 1 terminals SGND, S5V, and THROT.  For simplicity, in this picture the cruise control cable has been removed.  On the left side of the picture is what remains of the original OEM wiring harness that remained after the ICE was removed.  These wires are gradually being separated out and those that are not necessary to the build are being eliminated. 

The BMW throttle body uses a three pin female socket (picture DSC04262  ) and the corresponding OEM plug that was retained from the donor car wiring harness is shown in picture DSC04261.  

Picture DSC04262 of the connector located on the side of the BMW throttle position sensor.  Pin 1 is to the far left, pin 2 is in the middle (wiper),  and pin 3 is to the far right.

Picture DSC04261 of the connector salvaged from the ICE donor wiring harness.  Pin 1 is to the far left and is attached to the brown output wire, pin 2 is in the center and is attached to the brown/black output wire (this is the wiper) , and pin 3 is to the far right and it is attached to the  red/yellow output wire.

To connect the outputs of the BMW throttle position sensor to the Soliton 1, the Red/Yellow wire (pin 3) is connected to the Soliton 1 terminal S5V, the Brown/Black wire (pin 2) is connected to the Soliton 1 terminal THROT, and the Brown (pin 1) throttle position sensor wire is connected to the Soliton 1 SGND.   During operation the throttle body output was measured to be about 0.643 volts DC when at 0% throttle, and about 4.368 volts DC when the throttle was at 100%.  Calibration of the BMW throttle was then completed using the same process as was used for the Evnetics throttle body.  Additional test drives of  the 1992 BMW 325i EV conversion has shown that the accelerator (or "gas pedal") now behaves in the same way as the original ICE donor car !!

On first attempt it was interesting to discover that when the connections between pins 1 and 3 were reversed, the car's accelerator pedal behaved quite differently.  If the car's accelerator pedal was fully pressed to the floor, the motor was off, and when the foot pedal was fully released, the motor was at maximum acceleration!  It would be a stressful driving experience if all cars on the road were to use this inverted throttle configuration !!!

Butt splice connectors were initially used (picture DSC04257) when wiring the test circuits, but the trial and error process was made easier when fully insulated 0.250 Tab male and female terminals were used instead (picture DSC04264). 

Picture DSC04264 of the disconnect 0.250 tab disconnect terminals (female on left, male on the right) that were used.