Electric Conversions

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Contents

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Introduction

With its inherent simplicity with manual steering, manual brakes, manual transmission and air-cooled engine, the 914 is an ideal candidate for conversion to an all-electric vehicle. This primarily involves replacing the internal combustion engine with an electric motor and adding batteries and a motor controller to the vehicle.

With rising gasoline prices and the recent movie "Who Killed the Electric Car", many people have been inspired to convert an older vehicle to electric for fun, being "green" and to save gas.

Much of this Wiki entry covers specifics of the 914 electric vehicle conversion kits provided by Electro Automotive, as most 914 conversions have used these kits.

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History

While it is unclear when the first conversion of a 914 to an electric vehicle occurred, it probably used a DC motor with lead-acid batteries given the inherent simplicity of the DC technology. With the drastic reduction in the cost of compute power and electronics, AC induction motor systems are now more widely available for the 914.

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Electric Vehicle Architecture

Electric vehicles can be much simpler than gasoline vehicles and have the following basic parts:

  • Electric Motor - Generates the physical force to move the vehicle forward (AC versus DC discussed below)
  • Battery Pack - An energy storage device that provides the power for the electric motor (typically lead-acid, 120V or 144V)
  • Motor Controller - An electronic device that regulates the power from the battery pack to the motor to control acceleration
  • Charger - An electronic device that converts electric current from your house into power stored in the battery pack
  • DC-DC Converter - A device which transfers charge off the battery pack onto the 12V accessory battery to keep it charged (like the alternator in a gasoline car)
  • Battery Monitoring System (BMS) - Instruments and gauges that indicate the status of the battery pack to help the driver determine remaining range and health of the pack
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General Conversion Process

There are several typical steps to converting a 914 to an electric vehicle listed below. These are expanded upon in following sections:

  • Purchasing a 914 to convert
  • Purchasing conversion kit parts and batteries
  • Preparing the 914 for installation (fixing rust, suspension, brakes, transmission, dropping the engine)
  • Installing the electric vehicle kit parts
  • Tuning the system for driveability
  • Adding accessories (battery monitoring, LED lights, heater)


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What to Look For in an 914 When Converting to Electric

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Characteristics of Good Conversion Vehicles

  • Later model 914 with a side shifter
  • Structurally sound car for heavy batteries with little rust
  • Engine can be any condition (or non-existant)
  • Transmission must be good (or rebuilt)
  • Good paint job if you don't want to restore the car yourself
  • Flywheel and front motor mount are needed to attach the motor to the car
  • Functional 12V electrical system
  • Good brakes to handle the heavier car
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Finding Used 914s

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Paths to Electric Conversion

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Kits from Electro Automotive

The most common way people convert the 914 to an electric vehicle is through a kit from Electro Automotive. They provide both DC and AC motor kits that contain step-by-step instructions as well as all the required hardware from battery racks to motor, motor controller, transmission adapter, charger and gauges. The complexity of designing your own electric vehicle conversion system is high enough to cause many people to take this path. Several EV conversions have started with the ElectroAuto kit and then upgraded or modified the kit later with better batteries or other enhancements. See the link to Electro Automotive below.

Due to the recent enthusiasm in electric vehicle conversions, Electro Automotive is currently swamped with orders and has a very long lead time on delivery of parts. Some people have had to wait eight or more months to receive their kits. The DC motor kit from EA has been around for awhile and has most of the kinks worked out of it. The AC motor kit comes with the DC kit instructions and a document with changes for the AC kit. The AC kit is much newer and may have more issues with it. The reader is suggested to research the blog entries listed below for more information on people's experience with the ElectroAuto kits.

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Do it Yourself Approaches

This section needs input from someone who has tried to convert 914 without an ElectroAuto kit.

Here's a link describing why one person did NOT use a kit.

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AC versus DC Motor Conversions

There is much debate in the electric vehicle community as to whether DC motors or AC motors are a better choice for an electric conversion. Each has its own advantages and disadvantages to consider.

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DC (direct-current) motors

DC motor electric vehicle conversions for the 914 have been around for a long time (since?). They typically involve a large bank of batteries tied to a DC motor through a simple motor controller that acts as a rheostat. The electronics tend to be cheaper and the DC motors put out a high amount of torque at zero RPM, giving them advantages as drag-racing vehicles. The typical motor used in 914 electric conversions is the Advanced DC 9" motor. There are drop-in replacements such as the Warp9 motor as well.

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AC (alternating-current) motors

With the advent of cheaper electronics, generating the complex AC waveforms needed for an alternating current motor has come within reasonable range of DC motors. The inherent advantage of AC motors is that they tend to pull a constant amount of current regardless of RPM, making them more efficient, especially at higher RPM counts. Due to the electronic generation of AC waveforms, the motor controller can also run the motor as an AC generator and get regenerative braking which charges the batteries essentially for free.

The most commonly used AC motor used for 914 electric conversions is the Azure Dynamics AC24 motor in conjunction with its companion AC motor controller, the DMOC445. Despite the added efficiency and regenerative braking, the AC24 costs significantly more and puts out less torque at zero RPM than its older DC counterparts. Azure Dynamics recently released the higher power AC24LS motor to help with this torque difference.

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Motor Power Comparisons

These graphs show the torque and horsepower for the DC and AC motors typically used in 914 electric conversions. As you can see, the Advanced 9" DC motor has much more torque than the AC24 at lower RPM but tapers off more quickly as the RPM increases. The Azure Dynamics AC55 motor is also shown for comparison. The AC55 was designed for heavier vehicles that use lower RPMs. It has not been used yet in a 914 conversion, probably due to the fact that its minimum operating voltage is 312 volts and this would make the battery pack prohibitively large for the 914.

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Purchasing Batteries

If you purchase a pre-made kit, it will tend to require a specific type of battery. If you make your own, you can chose which batteries you use, given various trade-offs.

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Flooded Lead Acid Batteries

The kits from Electro Automotive tend to use the 6-volt and 8-volt deep-cycle golf cart batteries from US Battery. You can find ordering info here.

One of the advantage of the flooded lead-acid batteries is that they "boil" when overcharged. This tends to make battery equalization easier in that the batteries that are less charged finish charging while the fully charged ones boil. This does require the driver to fill the cells with distilled water every so often (try a garden sprayer); however, it eliminates the cost of a more complex battery balancing circuit (see battery management below).

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AGM Lead Acid Batteries

Due to the highly corrosive nature of flooded lead-acid batteries (think 914 hell-hole), many people opt to use Absorbed Glass Mat (AGM) batteries that don't spill any acid. These tend to be more expensive and may have issues with overcharging, but are much more maintenance free.

To extend their lifetime, AGM battery packs should ideally incorporate battery regulators or balancers. Some examples of regulators and balancers available for purchase or do-it-yourself include:

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Newer Battery Technologies

Cost prohibitive for the average consumer. Hopefully this will change soon.

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Preparing the 914 for Conversion

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Restoring the Structure, Fixing Rust and Paint

The car needs to be structurally sound to handle the extra weight of the batteries. Many times the 914 has significant rust issues near the battery rack in the "hell hole" that can compromise the structure. Assuming you want your car to look nice, getting the car painted and restored will also probably cost a bit. Some people pay a few extra thousand dollars up front so they don't have to spend the time on the restoration process.

After fixing all the rust, a good paint job is in order, possibly to a different color if you choose.

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Upgrading the Suspension

The additional 800 pounds of battery weight require that the rear springs and front torsion bars on the 914 be upgraded. These often come in the kit from Electro Automotive, but some people have also ordered them from (insert reference here with part numbers).

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Upgrading the Brakes

The lead-acid batteries that power the main motor typically add about 800 pounds to the weight of the car, so braking ability can be significantly compromised. Rebuilt or upgraded brakes are strongly recommended. See Braking_System.

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Dropping the Engine

Since you won't using gasoline anymore, dropping the engine out of the car is in order. See this article at Pelican Parts regarding dropping the 914 engine and transmission out. This process is made far easier with four 6-ton jackstands and two hydraulic floor jacks.

For the 914 electric conversion, be sure to keep the flywheel and front engine mount as this is how the electric motor attaches to the rest of the drivetrain.

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Rebuilding the Transmission

The 914 transmission has a long history of needing rebuilding. Whether you purchase a rebuilt transmission or try to do it yourself, the internal parts are very expensive and the labor costs can be prohibitive. A 914 transmission rebuild is a precision job requiring special tools and good expertise. Often times, buying a rebuilt transmission off the internet through Ebay or the 914world or 914club forums can save you a bunch of time and money. One well known transmission rebuild service on the 914world.com forums is run by "Dr. Evil."

Transmissions in electric vehicles often don't withstand a huge amount of torque relative to their gasoline counterparts, so special racing parts or performance modifications are often unnecessary.

More info at 901_transmission

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Fixing Everything Else

Waiting for your electric conversion kit parts to arrive is an ideal time to get the remainder of the car in operating order. Check out all your electrical accessories and make sure everything works. There are many technical articles at the Pelican Parts website regarding repair of commonly failing systems in the 914. Also use the forums at 914world and 914club to get help as well.

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Installing the Electric Vehicle Parts

Installation for the electric vehicle parts will vary greatly from car to car, especially those conversions which do not use a specific kit, which come with their own instructions. The intent of this Wiki section is not to describe the installation process in detail, but provide references to links and document common problems that are not commonly found elsewhere.

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Common Issues with the Electro Auto 914 DC Installation

Anyone?

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Common Issues with the Electro Auto 914 AC Installation

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Rear Battery Rack Interference

This blog entry covers some of the interference you may encounter when installing the rear battery rack. Some people just use a large hammer to bend the frame out of the way.

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DMOC445 issues

The folks at Azure Dynamics are very responsive. If you send them an e-mail with your DMOC parameter file and captured viewer logs, they can get back to you with technical fixes.

Azure sells a serial cable to interface to the DMOC445. You can make your own by adding 16 gauge wires with special crimp sockets to the 8-pin connector. The AMPSEAL crimp socket part number is 770854-3. The mouser.com part number is: 571-7708543

Several people have reported that they need to adjust parameters inside the DMOC to get it running properly.

Here is a blog entry which covers the EEXNoIgnSwitch and EE2ShaftDirection variables. These are often needed with the 914 AC kit just to get the controller to enable and get the motor turning in the right direction.

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Other Common Installation Issues

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Tuning the System for Smooth Driving

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Tuning the Cafe Electric Zilla Controller

Content needed here from people with Zilla experience.

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Tuning the Curtis 1231 DC Motor Controller

Content needed here from people with Curtis controller experience.

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Tuning the DMOC445 AC Motor Controller

This link covers the pedal settings for the DMOC445 which allows the shorter travel of the accelerator cable to send a 100% signal to the DMOC.

This link and this link cover adjustments to the torque slew curves to get acceleration and regenerative braking going more smoothly.

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Adding Improved Transmission Fluid

Consider replacing the fluid in your transmission with a performance gear oil. Electro Auto has suggested Royal Purple Max Gear 75W90 weight synthetic gear oil.

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Electric Vehicle Accessories

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Hooking up the Tachometer

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Tachometer kits for DC motor to drive the 914 tach

I think the Zilla has a tachometer output. How do other people attach their tachometer in a DC system?

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Tachometer for the DMOC445 AC Controller

Attaching the 914 tachometer to the DMOC445 is relatively straightforward. All you have to do is attach pin 25 of the DMOC445 to the tach input wire in the engine compartment and then adjust the EE1SpeedoDiv parameter. The DMOC445 also outputs two status signals which indicate the state of the controller. These can be hooked into the red alternator light and green oil pressure light with some simple transistor connections.

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Battery Monitoring and Management Systems

The complexity in a gasoline car is contained mostly in its internal combustion engine. The complexity in an electric car involves maintaining the health of the main battery pack. This has proven quite difficult as keeping track of the "state-of-health" for a long string of serially connected batteries can be challenging.

There are several methods of monitoring the battery pack for an electric vehicle. Some people use a PakTrakr which connects a wire to each terminal of every battery and sends the collective information back to a small LCD display in the drivers cockpit. Other people perform the measurements by hand with a digital voltmeter on every battery to see which ones are dropping faster than others.

Since this topic is not specific to the 914 electric vehicle conversion, here are some more references on battery management: (insert references here)

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Electric Vehicle Toolkit

The needs of an electric vehicle are different than the needs of a gasoline vehicle, so the emergency toolkit that you might take with you on the road may contain different items such as:

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Emergency Equipment
  • cable cutters - to cut the main power cables in a shorting condition
  • small electrical fire extinguisher
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Repair Tools
  • Haynes 914 manual for electrical diagrams
  • digital multimeter
  • wire crimper and extra pink,blue,yellow quick-connect crimps
  • two battery wrenches wrapped in electrical tape
  • electrical tape
  • extra cable lugs and hammer-based crimp tool
  • medium hammer
  • LED headlamp
  • extra fuses for everything
  • pre-made 24" battery cable with lugs (from NAPA)
  • #2 philips/standard screwdrivers
  • pliers
  • small utility knife to cut insulation
  • small 12V sealed-lead-acid battery to bootstrap the system if 12V battery dies
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LED replacement bulbs

Sometimes people upgrade their turn signals and tail lights with LEDs, thinking that they can prolong the life of their battery due the lower power needed by LED bulbs. One recent analysis (insert reference here) showed that the energy saved by using LED lights was approximately the energy used by traveling one block in the electric car. In short, the power needed by the primary motor far outweighs the energy used by the lights.

Of course, there are other reasons to use LED lights, such as faster response from your brake lights. Cars that have a weak DC-DC converter to charge the 12V accessory battery may also need LED lights to keep the 12V battery from discharging. If you do upgrade your lights to LEDs, you'll have to fix your flasher circuit to operate with the lower current (insert Randy's circuit here).

Here are some current measurements of various accessories before replacing the lights with LEDs:

  • key off - 10 mA
  • key on (motor controller idle) - 700 mA
  • parking brake flashing light - pulses of 300 mA
  • parking lights - 3.7 amps
  • parking lights and headlights - 9.4 amps
  • parking, headlights and fog lights - 17.3 amps
  • left and right turn signals - pulses of 3.3 amps
  • backup lights - 3.1 amps
  • parking, headlights and backup lights - 12.3 amps
  • brake lights - 3.3 amps
  • CD player - 1.0 amps
  • climate control fan (low) - 2.8 amps
  • climate control fan (med) - 4.5 amps
  • climate control fan (high) - 6.7 amps
  • defroster (hair dryer) relay - 200 mA


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Heater

With the gasoline engine gone, there isn't a source of heat for defrosting the windshield or heating the passenger compartment anymore. There are several options for heating the 914 without the gasoline engine. One of the more common methods is to use plumbing couplings and attach two variable voltage hair dryers into the heating system in the fuel compartment. Several conversions have used ceramic heater cores tied into the main battery pack.

Note that if you power a heater device from the main pack, you'll need a special high-current DC relay with a blow-out magnet. When a relay that is passing high current opens up its contacts, the high current will tend to form a plasma arc. If powered by AC current (say from your household wall outlet), the alternating current passed through zero volts 120 times a second, which will extinguish this arc. DC current never crosses through zero volts, so the arc needs to be "blown" out with a magnet. (insert link here with example)

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Real World Performance

Many people often ask electric 914 owners "How fast is it?" Since every car is different, please add your own 914 EV performance numbers to this table.

Owner Motor Pack Volts Top Speed 0-60mph sec. WHr/mile
TimK AC24 144 70+ ??? ~204
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Links

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914 Electric Vehicle Resources

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Existing 914 Electric Conversions with Online Resources

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online 914 resources

Many of the problems that happen during a conversion to an electric vehicle involve issues with the original car. There are many online communities that can provide support for the 914, including:

Retrieved from "http://www.roadglue.com/wiki/index.php/Electric_Conversions"
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