Preliminary design notes

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Motor Selection

Seems most build over the years used DC motors (see all the builds on http://www.evalbum.com/).  Features of these motors:

  • Shunt wound:
    • Constant speed regardless of load
    • Low starting torque
  • Series wound
    • Poor speed regulation
    • High starting torque
    • Not very rugged, high current might burn out motor over time (2/18/2020 update: many people claim these are beasts, and can be pushed hard and last forever)
  • DC motors in general
    • Very high torque at low rpm, but drops off rapidly as speed increases
    • Smaller and lighter
    • Less costly systems
    • Regen not available
    • Larger DC motors - more torque and power, but less speed

 

More recently AC motors are becoming more popular.  Along with Tesla more home builds and conversion companies are selling AC kits.  Features of typical synchronous reluctance AC motors:

  • Hi power through entire speed range (even at zero speed)
  • Very rugged
  • High efficiency
  • Ability to use decel regen to charge battery
  • Costs are coming down for AC systems

 

Due to the info above, plus my day-job experience with AC motor control, I've decided to go with AC on this build.  Motor kit being considered: https://www.thunderstruck-ev.com/hyper-9-is-integrated-system.html

Controller manual for reference: https://www.go-ev.com/PDFs/HyPer_9HV_IS_User_Manual_REV08.pdf

Motor Decision Update (2/18/2020):

AC (or even new DC) is just way too expensive for this car.  To go with a new AC motor (like the Hyper9), I would really be forced into Tesla batteries as it does not make sense to me to buy a $5k motor/controller and have inferior batteries.  So the cost was going to balloon to over 20k I think.  Just not worth it on this particular car me thinks.

So, cheap is the decision.  Used motor, controller, and lower end batteries (like Leaf) is the plan.  See Final Motor Selection.

Motor / Controller Manufacturers & Distributors

 

Battery Selection

Most builds have used many (dozens?) standard 6 or 12 VDC lead-acid car or marine batteries wired in series to power the EV.  They are heavy, have quite low AH capabilities, do not perform well under heavy loads, but they are cheap! On the opposite spectrum, are Tesla designed Lithium-Ion batteries.  They have very high AH, relatively light weight, and are in a good form factor for an EV.  Downside -- expensive and required liquid cooling!!!

Example configurations:

Type Configuration  VDC AH KWH Approx Weight (lbs) Approx Cost Note
Led Acid  8 @ 12 VDC 96 22 2.1 600 $800 Heavy, terrible performance
CALB LiFePO4 30 @ 3.2 VDC 96 180 17 400 $8000? Pricey, prolly better off with Tesla for the $
Tesla 18650 4 @ 24 VDC 144 255 37 330 $9000 King, but too much $ for this little car
Chevy Volt 7 @ 48 VDC 336 45 15 ? $5600 Reviews say solid battery engineering, voltage issues suck, and somewhat pricey
Nissan Leaf 3 sets of 7 @ 48 VDC 144 132 19 210 $2400 Degrade very quickly (possibly due to no built-in cooling), but cheap and readily available.  Good physical size for mouting.

 

Expensive, but going to look at the Tesla modules here.  Used units are readily available.

2/18/2020 Update: While it looks like Tesla is the performance king, and Volt right behind (although have to dealing with config that's not ideal), I'm going cheap here, and going with Nissan.  Don't need a lot of range, heck even 10-20 miles would work for me, 30 would be ideal, but this seems doable with even badly degraded Nissan's.  We'll see.

 

Tesla Battery Physicals

Each module is about 27" wide, 12" deep, and 3.1" tall (Detailed drawing: https://evwest.com/support/Tesla%20Model%20S%20Batt.PDF) Units can be stacked.  The space behind the back seat is 36" wide, 13" deep, and 13" tall with the stock rear seat location.  Should be enough space for 4 batteries stacked in a battery box.  Might even get in sub-woofers in that space as well due to the tapered seat allowing more depth at the bottom.  See hand sketches.  Need to model this enclosure probably after receiving batteries.

Other features to research:

Inertia switch to shut down electric system upon accident.  Sounds like a good idea.

 

General Controls Concepts:

AC Controller Notes:

The HyPer 9 controller listed in the motor kit above includes a good amount of digital and analog io (both preset, and configurable).  This would allow for basic IO control via a PLC/HMI or physical buttons/switches/gauges.  It also includes CAN Bus connections to connect to other CAN enabled devices (for example a CAN enabled HMI: https://www.digikey.com/product-detail/en/grayhill-inc/3D50VT-100/GH7769-ND/5823341 -- little pricy tho ~800 plus software I think).  Not sure I can connect the CAN network to a PLC and get full use of the data.  Need further research.

DC Controller Notes:

Zilla

Solitron

  • Seems out of business 

Netgain

Zeva (a new Australian company)

BMS

Motor to Transaxle Connection:

A supplier with a nice diagram of their connection method.  Looks like ~1k to buy the unit. 

https://electroauto.com/catalog/adaptors.shtml 

Can-Ev makes as well: https://canev.com/product/vw/

Will probably just design myself, and have fabb'd locally.