VW Beetle Conversion

VW Bug conversion to electric

SHIFT EV is converting this 1970 VW beetle to electric power for a couple from Washington state.

Design goals:

  • Desired range: 150-200 miles from fully charged.
  • Acceleration: Better than stock
  • Instrumentation: Stock speedometer, fuel gauge to display correct State Of Charge (SOC).
  • Charging: SAEJ1772 Level 1&2 (110VAC and 220VAC)
  • Heat: PTC (electric) heater, Operated by stock heater controls

Evaluating battery type and capacity we have to consider the energy consumption rate for typical driving. Many bugs have been converted in the past with efficiency claims between 200 and 300 Watt-hour per mile (Wh/mi). Many variables contribute to this efficiency such as weight, tire type, motor efficiency, speed, etc. To determine battery capacity we'll take the upper and lower end of our range goal, and multiply them by 250Wh/mile.

(250Wh/mi) x (150 miles) = capacity of 37,500Wh, or 37.5kWh

(250Wh/mi) x (200 miles) = capacity of 50,000Wh, or 50kWh

With target battery capacity understood, we then look at available motor and controller/inverter solutions that provide good efficiency and power per dollar for this application. We narrowed it down to either an HPEVS ACXX or one of the NetGain Hyper9's. Ultimately settling on the Hyper9. That locks us into a maximum and minimum voltage range that our batteries must provide.

 

Tesla S or X Battery Module

After reviewing a few types of batteries in different scenarios, the Tesla battery modules used in the Tesla Model S and X are a good option for this build in several ways.

 

  • Slightly used Tesla S and X battery modules are 5.2kWh (depending on some model variants). 5.2kWh x 10 modules = 52kWh of capacity. That's 2kWh more than we'll need.
  • They have a high energy density, meaning they're more compact relative to many other batteries.
  • They're capable of more than enough power that our system will draw 750A.
  • As long as healthy modules are purchased, they're a good value at around $230/kWh on today's market.
  • We can accomplish our drive systems maximum and minimum voltage range
  • With 5 modules wired in series, the full and empty voltages fall within the operating range of our motor controller. To use all 10, we'll run two strings of 5 modules this way, in parallel. During discharge, one string will its + and (-) outputs in parallel with the other string. To avoid hazards is critical to have a BMS that properly monitors and manages the two strings and decides whether each string is allowed to connect the DC output bus that is used by the motor controller or any other loads. For more on this surprisingly complex topic, start with this document by Orion BMS.

With the high-level system decisions finished, we move into how we're going to properly and elegantly fit and wire these parts in the space we have. Beginning with the battery pack spaces.

Adjustable test fit jig for battery box concept
Mockup of a proposed battery box design, to confirm fit of the complex battery box shape.

 

Front view of SHIFT EV's 5module VW battery box -front
Front box in place. Fitting the stock-sized spare tire is a bonus.

SHIFT EV 5module VW battery box - rear
Five-Module battery box for the rear.

 

SHIFT EV's 5module battery box - rear-2
Five module battery box resting in place. It will move rearward a bit more on final assembly.

Preparing parts for powder coat

 

Opening Tesla battery pack to remove modules.

 


Modules exposed.

 


Modules extracted, stacked on a pallet behind the empty battery tray.

 


Some other useful parts are recovered from the Tesla pack, but most of it (metals) goes to our local recycler. 

 


10 Tesla S modules will go into the beetle (16 modules are pictured).


This week we worked out the specific placement of components that are not mounting directly to the battery enclosures. To do this quickly, we took measurements and printed off several sheets of the orthogonal views above, and begin sketching out scenarios.

A bit of non-EV conversion effort is occasional restoration work. The thick dirt had built up over decades. The painters didn't remove the heat and sound deadening material, so underneath lies a bit of clean-up. This clean-up was made sense to do now because wiring and access will be difficult after the conversion.

These tail-light grounding connections were previously corroded due to being buried under dirt (mud in winter). Also, you can see the engine rubber seal bits that were left have been cut off clean at the gasket attachment point. Once we know how we want to seal up the final engine bay, we'll see if we need to remove that bead or finish things in a better way.

Another shot shows the blue paint on the otherwise black rubber engine bay seal. What's left of it.

The Engine bay cleaned up. transmission adapter plate fit-tested, and ready to receive the motor (which hasn't arrived yet).

Other things worked on:

  • Updates to wiring diagram to reflect this build.
  • Located all non labeled wires (16) and isolated them with tape for a 12v power-up test. They'll need to be traced and decide what to do with them later.
  • Powered up 12v systems & verified what works:
    • horn
    • brake lights
    • turn signals
    • headlights
    • headlight dimmer switch
    • speedometer light
  • windshield wipers
    • What didn't work:
    • dome light (switch)
    • glove box light not working
    • didn't check courtesy light switches (door switches), hood light, trunk light, or license plate light.


      The charge inlet is installed in the stock fuel location. It was a bit of work to trim out the old gas tube and weld in the backing plate deep enough for the inlet to not block the original fuel door. It's a nice subtle finish and accepts large J1772 connectors.
       
      The motor, controller/inverter and wiring harness arrived and we've installed the shaft coupler and the trans adapter plate. It is staged for the KEP performance clutch, pressure plate, lightened flywheel, and related small parts that arrive next week.

      This is the fuel display tester driving your stock fuel gauge. The circuit cycles the needle from empty to full to be sure it works, and to verify how we need to build the circuit for the BMS to send proper State Of Charge (SOC) signals to it.

      The rear battery box is powder coated and sitting in place without batteries.

      The front battery box is powder coated and sitting in place without batteries.
      Wiring schematics are being updated for your motor and controller. Once that is done (enough), we will begin pulling the wiring for most components through the chassis. Chris has already been studying and preparing for the best routes on this build.


      Since the last post, the high voltage cables have been pulled from the front to the rear.

      The sound/heat deadening matt was removed from the trunk because we need to mount some parts to the steel wall in the trunk (plus it just didn't look good).  It will look a bit like we're going backward for a few days, but the new finish plan will be much better. Next week you'll begin to see why.

      The upper-left image was after Chris installed the shaft adapter so that it can accept the new lightened flywheel. It's browned because it must be heated to about 400F to expand and slip onto the motror shaft. It cools to a zero clearance fit.

      The lightened flywheel was even further lightened because I couldn't resist cutting off the ring gear that your old electric starter motor will never engage with. Removing this took two pounds off. Doing this will not have a detectable affect on balance.

      Other things done included sorting out the trunk's old wiring and pulling many out that will not be used. Also, fuel lines and emissions parts, and tubing was removed. Space was made under the hood to mount the charger by re-aligning the right front brake line. The holes for the DC-DC (on the front battery box) were tapped for assembly. Next week we begin assembly of the modules into the boxes.


      New Flywheel assembly, a KEP Stage II pressure plate, and a four puck clutch on a lightened flywheel - plus starter ring gear removed.


      Completely controlled by wire, the charger was mounted in the old fuel compartment space. All of its connectors extend to the drivers' side for easy access.


      With the motor installed, the clearance behind it looks good. It is hard to imagine that the engine compartment was barely long enough to get this assembly into place. The motor had to be staged at the proper angle as the car was lowered down over it to get the motor/clutch assembly started around the transmission input shaft. The motor was simultaneously inched forward to clear the rear body panel. For much of this maneuvering, there was less than a 1/4" of clearance between the body and the motor until the splined transmission shaft lined up with the splined hole in the motor coupler. Then the motor assembly slid forward over the transmission shaft and stoped against the adapter plate. Notice 1 of 3 bolts is missing from the back of the motor on the middle photo. That's because there wasn't enough clearance between that bolt and the body.


       
      These images show the front box in position with the DC-DC converter, BMS, and main contactor with a high voltage fuse. We are verifying fit, final wire routing, and service access before the final installation of the battery modules into the box. Re-routing of some under-box wires and the hood-release cable were things we knew were needed. We also decided the 12V fuse panel will be relocated so that its backside wire connections can be accessible in the future for serviceability.  I didn't get an image of the template and location yet, but I'll post it next week.


      The 12V fuse planel landed here. Easy to reach and still in the standard VW configuration. There will be other cosmetic panels covering up the less than pretty backside of the dash that is normally exposed. 

      This was a super short work week for me and the crew, so there's not much visually to show. However, I have a question for you to think about over the weekend. I realize interior work was to follow the conversion project. However the dash is in pretty rough shape as seen below. It can only be removed with the battery box out of the way. The box can be removed by the other interior restoration folks, but I'm wondering if you would rather have the issues below addressed now? This will avoid having someone else pull that pack for access later.


      And finally, I have a suprise that is 16% bigger. Bigger than what you ask? Bigger capacity, of course. I recently bought TESLA battery modules from a Tesla P100D. Thes have more cells in each of the same sized modules. Externally, only the coolant plumbing is a little different. Otherwise the same external dimensions. They came from a Tesla that was purchased for reverse engineering by a TESLA competitor. The car wasn't wrecked and had been driven less than 5000km. I would like to mount these into your Beetle instead of the P85 pack above. I hope you're excited about that.


      The images above show the rear battery box coming together. The top-left and the two bottom-right images show the box sitting upright. The rest show the box tipped on it's back while making a revision. The base bolt holes (originally slots) were where we planned to bolt the box to the floor. The revision is the addition of the rivet-nuts being fitted and fastened to teh base. This will ease assembly, reduce parts and be a bit more strong.

      To install the new BMS, we need to wire the new cell tap wiring harness and cell temperature wiring harness to each battery module. We must replace the stock PCB (green) with a reliable connection method. The stock PCB precisely positioned the cell tap connectors (red) to minimize movement and stress on the connecting flex circuits (blue/orange) coming from the cells. The white connection mates to the new BMS cell temperature harness. Its position is more flexible. The black connector is where the Tesla wiring harness was to connect to the module.

      Top left & right are the first draft of a 3D model and its 3D print process set-up. That draft was used to quickly check for interferences when in position on the module. The bottom left and right images show the latest 3D model and printed part with connectors in place. The channel guides keep wiring organized and the small slots are for zip ties to secure the wiring. In the past, we have installed aftermarket PCBs (not pictured) sold for this purpose, but they would cost >$300 for this 10 module pack and require more labor time to install because of connector issues of their own. The 3D printed solution cost is $0.50 each, which eliminates the need for the black 10 pin connector and allows visual confirmation that connectors are properly seated without removing the fixture.

      The old dash panels, switches, glove box door, etc. have been removed.

      Much of lasts week was spent researching the best PTC components to assemble a 5kW to 6kW heater system suitable for the NW climate that will fit in the available spaces without crowding the passenger compartment. Most heater system parts have been ordered. The under-the-hood ductwork will be ordered when we see what parts and shapes we need to mate to on the dash kit ducts.

      Wheels are in! We didn't make them, but it's always nice when big shiny parts arrive for a project.

      The tires are mounted on the wheels with chrome valve stems and caps. this will look really nice when they go on the car next week.

      This week I uncrated all the Tesla P100D modules. I'll spare you the booring images of that process.

      The rear battery box is bolted together except for the side walls. Modules were inserted, and the fit was as good as we had hoped. BMS cell taps and temperature wiring is underway. Then we'll make the high current series cables and install them between modules. The final steps will be plumbing, leak testing, and cell tap harness testing.

      This image shows the black 3D printed board using scavenged connectors from a TESLA slave board. The green board is a TESLA slave board (which we don't need) that we are testing the idea of using its connectors without removing them. We're looking for the most stable way to make our connections considering serviceability, visual inspectability that connections are seated completely and a few other things.
      Dash parts are ordered, Stereo will be ordered as soon as I get a confirmation link back.
      That's it for now. Please let me know if you want to see something specific.