Acacia - Electric Car Project

Last updated Saturday, 14-Aug-2010 11:06:22 EST

Status: Deferred Phase - This project has been deferred until the technology catches up.

I intend to keep adding information to this web site in order to formulate a workable design for an electric vehicle. The problem that I am finding is that there are so many options, interdependent variables and design constraints that any one component selection can lead to a dead end. Because of this, I am planning to develop a software application that can guide people through the process and take all of the variables into consideration. Please check back again to find out more.

Project Goals

This project seeks to analyse the costs and other issues associated with building an electric vehicle to use on Australian roads.

You should be able to use the formulas on this page to build your own electric car.

Collapsible Regions (please click for details)

What is an electric car?

A vehicle powered is propelled by electic motors.
A vehicle that uses electrical energy stored on-board.
A vehicle that depletes its energy store until recharged.

Why an electric car?

Avoid the use of petroleum, its unpredictable prices and its future declining reserves. Never have to visit the fuel statuon again!
Transfer the carbon back to the power stations where it can be disposed of or recycled economically.
Make use of solar energy alternatives.
Enjoy a quieter ride.
Do what the auto makers seem to be avoiding at the moment (until they have exhausted the current technology revenue stream).
Only pay about 2 cents/km compared to 10 cents/km for petrol based vehicles.
Eliminate oil changes, starting problems, water pump problems, ignition problems.

Why EV is Still Archaic? From my research to date it has become obvious that the current state of EV technology is still resting in the dark ages, particularly in the area of energy storage.

Why would you want to pay $5,000 for a set of batteries that will wear out in 2 years?
If you use any more than 20% of the battery capacity before recharge, the life span drops drastically (read up on depth of discharge and cycle ratings on batteries). This means that you must carry 80% of you battery bank along for the ride and never use it.
The more load that you pull from the battery bank, the less total energy you can draw from it, again forcing EV builders to oversize the bank. The factor may be as high as 60%.
Electric motor technology is basically unchanged since the first motors were invented back in the 1800s with efficiency only around 90%, meaning another 10% is added to your battery bank size.
Your battery bank will likely be connected in series, meaning that the failure of any single cell will render the entire battery bank dead (weakest link wins).
When you add up the losses, recharge costs, battery replacement and motor maintenance, EVs cost more that an ICE to operate.
In order to provide adequate range and power, the EV weight will need to be at the limit of the vehicle's carrying and braking capacity. All this extra weight is distributed in a different way to the vehicles design, leading to handling problems and a number of dangers in collisions including volatiles, acids and high voltages.
You might get some extreme acceleration, but this could damage the vehicle and without very clever control logic, you will quickly overheat the batteries, controller and or motor. Under these conditions you will likely hit a sudden limit relating to under voltage, over current or over temperature on one of the components, causing a sudden and dangerous change in vehicle operation.
If everyone recharged their EV each night, the power grid could not cope with the additional 40% loading.

The Ideal EV Technology So what would be the ideal combination of technology that will give us the quantum leap in cost and performance that we are all hoping for?

Energy Storage - ideally will be light (50kg), support infinite recharge cycles, allow full discharge and will not be handicapped by high demand capacity limitations. Self monitoring and self healing cells would ensure that the death of any single cell minimally impacts the bank. At present, Ultra-Capacitors have some of these characteristics, but their voltage, weight and price make them impractical for the forseable future.
Motor - ideally around 98% efficiency, with optimised regen capability and built-in instrumentation for temperature rise and current and torque. The torque and speed characteristics should match direct drive requirements for a motor vehicle, allowing the gearbox to be eliminated.
Controller - should include voltage, current and temperature protection for the motor and energy store. It should ensure that all energy in the store is provided to the motor. It should include the functionality of the main contactor, reversing contactor and support fully isolated interlock circuitry and collision detection/response facilities. It should provide auxilary supply to other circuitry. It should automatically handle regenerative braking. It should have instrumentation outputs for the driver. It should monitor and control recharge and maintenance of the energy store.

+ Safety - The No. 1 Issue

Probably the most important aspect of this project is safety, and this should be factored into every design decision.

Safety Considerations - You should consider safety points listed below, as many of these may not be expected.

Isolate High Voltages for Occupants - High voltages should be isolated from users by maintaining an isolated control system with it's own battery. All control of high voltage components such as the power and reversing contactors should be done using relays with appropriate isolation ratings.
Include Interlocks - Interlocks that stop the vehicle from operating when turned off, when charging, when the drivers seat is empty, when seat belts are not used can all make the EV a safer item to use.
Cabling - Include appropriate cable sizes and insulation so that any potential fault currents can be carried without anything melting, overloading (contacts) or catching fire is essential.
Voltage Spikes - Whenever coils are switched in control circuits (i.e. contactors), the collapsing magnetic field can cause very high voltages to be generated which can be a safety risk to people and to equipment. The generated voltage spikes can damage electronic equipment and cause flashovers with potential for subsequent high current arcing and melting. Always include flywheel diodes of sufficient ratings to quench these transient conditions.
Electrical Protection - Ensure that all cables are protected with appropriately rated fuses or current limiting devices (such as the motor controller). You should also be aware that in AC and DC circuits containing capacitors (like the controller), very large inrush currents may occur at power-up that exceed normal operating currents. Include additional components to pre-charge these capacitors and/or ensure that the fuses can handle these types of load without blowing or degrading prematurely.
Insulation - Ensure that all high voltage AC and DC cables and terminals are covered with insulating material and that warnings are displayed in prominant locations so that mechanics are aware of the hazards in front of them.
Reversing - Ensure that the maximum reversing speed is say 5 percent of the forward speed by adding appropriate control circuits. Remember that the electric motor will run just as quickly in reverse as forwards, so imagine the horrifying consequences!
Free-Wheeling - If you take your foot off the throttle while moving, some controllers apply PLUG BRAKING which makes the motor stop extremely quickly and could cause accidents. Ensure that the control circuitry does not permit plug braking to occur. If the motor is automatically switched off using special control microswitches etc (i.e. High Pedal Disable), ensure that any auxillary equipment still works such as the vacuum pump if you need this for power assisted mechanical braking.
Warnings - Always pass on any detectable warnings from the controller or sensors to the driver. They should see some indication (lamp etc) if the battery is running low, the limit speed or current has been reached or the controller is overheating for example. These warnings will allow the driver to change the way they are driving to handle the condition(s).
Control Circuit Failures - Consider what would happen if any driver control input or sensor input either open or short-circuited. These should fail in a safe manner and if this is not possible, the driver must have a way of disabling the vehicle. This situation could also occur in the event of failure of electrical protection circuits, causing cable melting and potential for fire.
Charging - Consider the volatile gasses that may be released when charging. Will these accumulate where they will present a risk of explosion (Hydrogen gas from Lead-Acid batteries). Ensure adequate venting, eliminate potential ignition sources such as static electricity, motor armatures etc. If it does ignite, how will the pressure and fire be handled?
Collisions - If the vehicle is involved in a collision, it will likely have a different weight distribution with a concentration of mass in the battery bank. In such circumstances, you should ensure that the batteries will not rupture or release/spill corrosive or flamable chemicals, and if this cannot be totally avoided, ensure minimal contact with occupants. You should also consider the safety of occupants and rescurers and ensure that an inertia switch is installed that isolates the high voltage battery bank in the event of a collision.
Loss of Auxillary Supply - You might think of the auxillary supply that powers the radio as unimportant. This is not the case as it powers all of the important equipment like power steering, power assisted brakes and headlights. Ensure that the auxillary supply is reliable, self resetting and includes fail-safes such as backup batteries if necessary. It should be switched on and available even if the motor is not running.

+ Electric Vehicle Links

+ Prototype Design

Let's get straight to the point and list some components and iteratively refine the selection and specs based on the requirements and research further down this page.

Approach - After reviewing Government regulations, it appears that the simplest approach is to take a commercial internal combustion engine vehicle and do an EV conversion. In most Australian States and Territories, an engineering certificate covering only the alterations and a check with the local registration authority gets you on the road with a fully registered electric vehicle. This is much simpler that starting from scratch and you already have most of the equipment installed and working before you start.
Where to Start? - This web page outlines an iterative design that make initial assumptions, fleshes out details and back-tracks to refine other associated details. I have attempted to break the design into logical top to bottom steps that should provide a template for others looking to do an EV conversion. All figures quoted show the calculations that lead to the value and links to supporting information are included whereever possible. Your selection of components will likely lead to a very different EV conversion.
Keeping It Efficient - Keep the tires pumped up, recharge often and clean out the boot.

+ The Vehicle

EV Vehicle Wish List - The following criteria will help find a suitable ICE vehichle on which to perform an EV conversion. The money that you invest in converting this vehicle to electric is likely to exceed $10,000, so deciding on a vehicle that you are not embarrised to drive is important.

Age - Get the newest vehicle you can afford because it will be lighter and the accessories will still be in working order.
Weight - Aim for small, but remember that you still need sufficient towing capacity (brakes) to carry and stop hundreds of kg of batteries.
Gearbox - A manual gearbox is best because you will probably find a suitable gear and lock it. The clutch will be removed, so we dont care if it is shot. The gearbox will be used in the EV and it is important that this is still in good condition with no oil leaks. Before you convert the vehicle, try changing gears without using the clutch at various speed by matching revs. If this is difficult or impossible, you may not be able to change gears while moving in the EV.
Drive Type - If the car is front wheel drive, you will need to retain the gearbox to power both wheels. For rear-wheel drive vehicles, you have the option of removing the gearbox all together and directly connecting the motor to the drive shaft however the gear ratio will be like 4th gear and may not provide sufficient low speed torque.
Engine - If the engine is shot, the owner won't beleive his luck that you will remove the vehicle at no charge. The engine power rating is a good indication of the peak electric power that will be needed in your EV, but most of the bits that need service/repair including the engine will be removed in the conversion.
Clutch - The clutch will not be used so its condition is not important. It is important to note that having a clutch is not recommended in an EV with a series motor as the motor can be run so fast that it can self destruct with no load.
Air Conditioning - This will be removed as it imposes unnecessary load on the EV.
Power Assisted Brakes - These are usually assisted by the vacuum from the ICE. To complete the project, you will need to add an electric vacumm pump so that the brakes work.
Power Steering - If you can get a vehicle without power steering, this is a great advantage. Power steering is usually assisted by a hydraulic pump, driven by the ICE. To complete the project, you will need to add an electric hydraulic pump. This pump is expensive (>$1000) and will consume a large portion of the auxillary supply, also forcing you to pay more for this as well.
Body - Needs to be strong enough to support the battery bank. Skip rust buckets.
Propulsion - The ultimate would be to use 2 of these EM Drive modules. Feed 1kW into the first magnetron to lift up to 3 tonnes of car off the ground, and send a couple of watts to the other for acceleration and braking. We should be able to use a 600W magnetron from an old microwave oven since our car will be less that 3 tonnes. The EMDrives become less efficient the faster they go, so you would need to keep the speed under the speed of sound. They need the microwave cavity to be superconducting to get the Q value up to 6.7x10^6 which means liquid nitrogen.

The Vehicle to Convert to an EV - If we start with a 1990 Ford Laser these seem to be as common as mud, have 5 speed manual transmission (recommended) and no power steering. The air conditioner will be removed, but the demister fan kept. If you choose another vehicle, it will probably be a similar size/weight. The following ICE statistics for this vehicle will provide a useful benchmark for the final EV conversion.

Kerb Weight - 960 kg with ICE, so pesimistically lets assume that it will be 1200 kg after EV conversion. ICE and extras approx 250kg, add 50kg for motor and 300kg for batteries.
ICE Capacity - 1.6 litres.
ICE Power - 53kW.
ICE Torque - 120Nm.
Power/Weight - 18W/kg.
Towing Capacity - 500kg - which really indicates how much extra weight (like batteries) that the brakes can reasonably stop.
Transmission - 5 speed manual transmission, so we should be able to find a suitable gear that will cover zero to the required maximum speed with adequate power.
Cost ($) - $0

+ The Motor

Motor QuestionsWhat is max power it can handle and for how long? Can it run in reverse? Does it provide regen? What's max RPM? How do you cool it? What do you do if it overheats while you drive? Will you even know if it is overheating? What is max RPM before commutator bars start arcing or lift? What's the warranty period? Will the motor shaft fit perfectly in the gearbox and is it the correct length? Does it have the other end of the shaft exposed for powering other equipment?What is the design life for the motor bearings and is this life dependent on average speed?
Choose a Motor - Now that we know the weight of the vehicle, this article suggests that a 60 kW motor will provide good performance in hilly terrain for a vehicle between 1250 and 1600 kg, so we have some room for error.

There are a number of types of motor, with the ultimate being a 3 phase AC synchronous motor that can also be used for regenerative braking. These are expensive, and in this project we will use the more common and cheaper Series DC motor.

It is understood that regenerative braking adds about 10% more range to stop-start trips. For the moment, lets choose a 203-06-4001 8 inch dia motor.

Type - Series DC Motor, meaning that the field is connected in series with the armature.
Voltage - 72-120VDC.
Power at 120VDC (fully charged) - 16.2kw (21.7HP) continuous, 18kW (24HP) for one hour, 27.6kW (37HP) for five min, 61.9kW (83HP) peak.
Power at 96VDC (depleted charged) - 14.2kw (19HP) continuous, 15.5kW (20.6HP) for one hour, 16.2kW (21.7HP) for five min, 50.7kW (68HP) peak.
Size - single shaft, motor body is 200mm diameter and 370 mm long.
Torque (Nm) - 13Nm at 120A, 111Nm at 500A (linear Nm = [A-60]/60) - see the torque curve for more detail. This fits well with the 120Nm available from the ICE (when it was new).
Weight - 50 kg.
Current - 800 ADC at maximum load of 61.9kW.
Insulation/Temperature - Class "H" insulation meaning 180 deg C temperature rise inside motor.
Shaft - 28.5 mm diameter with keyway. Requires custom adapter plate to attach to gearbox shaft.
Cost - $2,420.

+ The Controller

Controller QuestionsIs it waterproof? Is it certified for automotive environments? Can the high voltage terminals be enclosed? Can you add extra cooling? Can it reverse the motor without and extra contactor? Can it limit motor RPM to the safe level? Can you monitor temperature limits? What happens if it is overloaded or shorted?
Choose a Controller - Now that we know the type, voltage and current rating of the motor, a suitable controller can be selected. The Curtis> 1231C-86XX Series Motor Controller has a suitable power rating and functionality. The manual provides a lot of useful information and sample circuit diagrams for the main circuit and auxilary control circuits.

Voltage - 96-144VDC.
Rating at 120VDC - 500ADC max, 500A 2min, 375 5min, 225A 1h, 0.3V drop @ 100A, undervoltage cutback at 64V.
Suitable for - Series Wound DC motors.
Frequency - 15 kHz (normal) down to 1.5kHz (low throttle).
Current Limiting - A built-in acceleration rate circuit maintains a maximum rate of power increase to the motor. The standard setting is such that with the throttle full on, the controller requires approximately one second to reach full output. This feature contributes to smooth, gentle starts. It also ensures that the maximum current will be limited to the 500 ADC limit and will reduce if controller thermal limits are reached.
Protection - Thermal protection and compensation circuit provides undertemperature cutback, constant current limit over operating range, and linear rollback in over-temperature. Thermal protection and compensation circuit provides undertemperature cutback, constant current limit over operating range, and linear rollback in over-temperature. No sudden loss of power under any thermal conditions. Frequency shifting feature provides improved control of current limit at low duty cycles.
Standby Current - 30 mA.
Heatsink - The controller should be fastened to a clean, flat metal surface that provides an adequate heat sink.
Precharge Resistor - 750 ohm, 25W. This is needed to limit the power-on inrush current to the internal capacitors in the controller.
Under Voltage Limit - 64V then power output is reduced.
Throttle Resistor - 5 k ohm with 1 k ohm parallel resistor in reverse to limit maximum speed.
Reversing - Requires an external double pole contactor and control circuitry to reverse the motor field connections.
Power Limits - The controller will automatically limit the output current to 500A, meaning that the maximum motor power output of 800A will not be acheived, effectively limiting motor power to about 38.7kW. This will help limit battery discharge and motor heating under full throttle conditions. The maximum power will also be limited by the internal resistance of the batteries and the impedance of the cabling between the battery, controller and motor.
Design Issues - Despite the thermal protection of the controller and current limits, it appears that it will still be possible to run the motor at a high current for extended periods which exceeds the motor thermal rating limits. As such, additional thermal monitoring of motor temperature rise will be included in this project and act to reduce motor power to match the rated limits.
Cost - AUD$2,420.

+ The Energy Storage

Choose the Energy Storage - Lets work through the requirements and calculations

Sizing Calculations - here are the assumptions and detailed calculations.

Required Range - 100km - distance before having to recharge.
Required Speed - 80km/h - the speed limit on most Canberra roads.
Measured Cruising Power (W) - 7000W = 350V * 20A - was measured in this paper on an electric vehicle travelling at a constant 60km/h.
Required Power (W) - 8100W = 16200W x 50% - let us start with half the continuous motor rating as being a reasonable power output that ensures the motor and controller thermal limits are not exceeded. This compares well with the above figure and provides a margin for variations.
Average Current (A) - 67.5A = 8100W / 120V - i.e. the average current draw from the battery bank into the motor via the controller.
Required Energy (Wh) - 10200Wh = 8100W * 100km / 80km/h
Required Energy Capacity (Ah) - 85Ah = 10200Wh / 120V.
Depletion Time (h) - 1.25h = 100km / 80km/h - the time to travel 100km at 80km/h.
Maximum Bank Weight (kg) - 500kg - this is the maximum capacity for the selected vehicle.
Required Energy Density (Wh/kg) - 20.4Wh/kg = 10200Wh / 500kg - i.e. the minimum energy storage per kg that the battery bank must provide. This will help determine the type of batteries that will work for us.

Choose Storage Type - next we need to determine the type of battery bank to use.

Maximum Bank Internal Resistance (ohms) - 0.24ohms = 120V / 500A - for maximum current supported by the controller. This is the maximum allowable internal resistance of the battery and connecting wiring to acheive 500A to the motor.

Type $ per Wh Wh/kg MJ/kg Wh/liter

UltraCapacitors $120.00 0.89 0.0032

Carbon-zinc $0.31 36 0.13 92

NiCad $1.50 39 0.14 140

Lead-acid - AGM $0.25 41 0.146 100

Lead-acid - Gel $0.25? 41 0.146 100

Lead-acid - Flooded $0.17 41 0.146 100

NiMH $0.99 95 0.34 300

Alkaline long-life $0.19 110 0.4 320

LiPo

Lithium-ion Phosphate $1.80

Lithium-ion $4.27 128 460,000 230

Conclusions - Lead-Acid batteries provide double the required energy density and have the lowest cost of all the storage types listed in the table above, so this is what we will use.
Estimated Cost - $2,550 = $0.25$/Wh * 10200Wh.

Lead-Acid Battery Calculations - If we use a Lead-Acid battery bank, the following calculations apply.

Type	$ per Wh	Wh/kg	MJ/kg	Wh/liter
UltraCapacitors	$120.00	0.89	0.0032
Carbon-zinc	$0.31	36	0.13	92
NiCad	$1.50	39	0.14	140
Lead-acid - AGM	$0.25	41	0.146	100
Lead-acid - Gel	$0.25?	41	0.146	100
Lead-acid - Flooded	$0.17	41	0.146	100
NiMH	$0.99	95	0.34	300
Alkaline long-life	$0.19	110	0.4	320
LiPo
Lithium-ion Phosphate	$1.80
Lithium-ion	$4.27	128	460,000	230

Lead-Acid Batteries - Check out this great article on lead-acid batteries theory and practical issues. I would highly recommend reading this article in the same series on Sizing a Lead-Acid Battery Bank.
Type AGM Deep cycle lead-acid. Deep Cycle batteries have thicker lead plates that make them tolerate deep discharges better. Typically, the amp-hour capacity of a battery is measured at a rate of discharge that will leave it empty in 20 hours (a.k.a. the C/20 rate). If you attempt to discharge a battery faster than the C/20 rate, you will have less available capacity and vice-versa. This article explains the differences between "Flooded Wet Cell", "AGM - Absorbed Glass Mat" and "Gel" lead-acid batteries. We will choose AGM due to safety (cannot leak), can be mounted on their side, do not require a sealed and vented box, allows very high charge and discharge rates (5 times flooded rate) and is maintenance free.
Battery Discharge Voltage Limit (%) - 50% - of battery voltage before recharging.
Battery Capacity for 3C Discharge Rate (Ah) - 167Ah = 500A / 3 - Thundersky say their batteries are capable of discharging 3C meaning that the maximum current that they will provide in Amps is their Ah capacity times 3. This matches well with the previous value of 170Ah.
Capacity Reduction Factor (%) - 60% - of the C20 value quoted by battery manufacturers for a 1.25h 50% discharge. This means that we will need to increase the required capacity because we are discharging the battery in only 1.25h and we suffer a reduction in capacity due to chemical processes in the battery.
Revised Battery Capacity (Ah) - 142Ah = 85Ah / 60% - due to the higher 1.25h discharge rate compared to the manufacturers quoted C20 rate.
Battery Weight (10 batteries) (kg) - 50kg = 500kg / 10 - maximum of 50kg per battery.
Battery Weight (20 batteries) (kg) - 25kg = 500kg / 20 - maximum of 25kg per battery.
Cell Requirements (10 batteries) - 10 x 12V, 142Ah, deep cycle, connected as 10 in series - note that each series connected battery must have the capacity of the whole bank in order to acheive a 120V 142Ah bank.
Cell Requirements (20 batteries) - 20 x 12V, 71Ah, deep cycle, connected as 2 parallel connected banks of 10 in series.

Type Brand Model Voltage (Vdc) C5 (Ah) C20 (Ah) C1.25 (Ah) Dimensions (mm) W (kg) $

AGM Trojan 24-AGM 12 61 80 48 260x168x241 24 $??

AGM Trojan 27-AGM 12 76 100 ?? 306x168x239 30 $??

AGM firststart FS-12V 75A/H 12 65 75 xxx 259x168x226 23 $279

AGM firststart FS-12V 90A/H 12 76.5 90 xxx 305x168x226 28.9 $309

AGM firststart FS-12V 150A/H 12 xxx 150 xxx xxx 45 $479

xxx xxx xxx xxx xxx xxx xxx xxx xxx $??

Selected Battery - If we select the firststart FAGM FS-12V 90A/H battery due to the cost, capacity, type and size.
Bank Configuration - In order to minimise initial costs, we will use a bank of 10 batteries connected in series. The capacity will be 90Ah, weight will be 289kg and will require a acid proof ventilated box 1240x1200x250 mm. This will allow for an extra parallel set of 10 batteries later if the 60% capacity reduction factor noted above is realised or more range is required. Initially the storage will be configured as 2 rows of 5 batteries with room for another 2 rows later.
Cycles - 1400 cycles at 30% DOD, 700 cycles at 50% DOD, 300 cycles at 100% DOD. Note DOD=Depth of Discharge. We will aim for 1400 cycles by recharging at 30% DOD on average.
Expected Life (yrs) - 2 yrs - The manufacturers warranty (design life is quoted as 6-8 yrs) - Battery manufacturers define the end-of-life of a battery when it can no longer hold a proper charge (for example, a cell has shorted) or when the available battery capacity is 80% or less than what the battery was rated for. Note that further down in the Charger calculations, we determine that the life should be around 8 yrs.
Internal Resistance (ohms) - 0.0251 ohms = 10 batteries x 0.0052 ohms/battery / 2 parallel banks. This is much less than the maximum 0.24 ohms, leaving room for lead and controller resistance.
Cold Crank Amps - CCA (A) - 900A (5s) - the maximum current for 5 sec at 0 deg F. This means that the bank should be capable of much more than the 500A controller current limit.
Terminals - M6 screw in internal thread with brass posts.
Self Discharge (%) - 3% of capacity per month at 25 deg C.
Cost - $3090 = 10 x $309. Add freight. GST is included in this price.

Type	Brand	Model	Voltage (Vdc)	C5 (Ah)	C20 (Ah)	C1.25 (Ah)	Dimensions (mm)	W (kg)	$
AGM	Trojan	24-AGM	12	61	80	48	260x168x241	24	$??
AGM	Trojan	27-AGM	12	76	100	??	306x168x239	30	$??
AGM	firststart	FS-12V 75A/H	12	65	75	xxx	259x168x226	23	$279
AGM	firststart	FS-12V 90A/H	12	76.5	90	xxx	305x168x226	28.9	$309
AGM	firststart	FS-12V 150A/H	12	xxx	150	xxx	xxx	45	$479
xxx	xxx	xxx	xxx	xxx	xxx	xxx	xxx	xxx	$??

Ultra Capacitor Calculations - Just for interest, lets analyse the practicallity of using ultra capacitors for the primary energy store.

UltraCapacitors - On first glance, you might question why you wouldn't use a capacitor instead of batteries. Well there are a lot of reasons! They don't really have a cycle limit, allow extremely fast charge/discharge and will outlast the vehicle. Ultra capacitors consist of activated carbon sheets separated by thin non-conductive membranes, immersed in an organic electrolyte. Charging the capacitor moves cations and anions to opposite carbon layers. Because this movement is not a chemical process it is easily reversed with no detriment to the capacitor. Thus, the capacitors can be repeatedly charged and discharged with no deteriorization. Voltage = Current x Time / Capacitance. The voltage is proportional to remaining energy and decreases to zero. Energy = 0.5 x C x V X V. See this paper that demonstrates the use of a 7 Farad ultra capacitor bank to supply peak currents and limit battery peak loads. The disadvantages (as you will see) are cost, size and hence weight using the current technology. The voltage also reduces linearly, meaning you will need more complex controllers.
Proposed Capacitor Size - 1000F (Farad), 2.5V, 2.7V max, 3.2kg.
Capacitor Count - 48 = 120V / 2.5V - sufficient for a 120V nominal, 130V max bank.
Bank Capacitance (F) - 20F = 1 / (48 x 1/1000F)) - the total capacitance of the 48 capacitors when connected in series.
Energy Storage (J) - 144,000J = 0.5 x 20F x (120V x 120V).
Energy Storage (Wh) - 40Wh = 144,000J / (60 x 60).
Bank Cost - $4,800 - based on $0.10/F x 1000F x 48.
Conclusion - Although the bank is much lighter than batteries, it has 0.4% of the required capacity at a 50% higher cost. Not really practical. To provide 10400Wh would cost $1.25 million and weigh in at 11.5 tonnes - Arhhh!.

Lithium Iron Phosphate Calculations - Just for interest, lets also analyse the practicallity of using these cell types.

About LiFePO4 or LFP Batteries - See Wikipedia.
Required Rating (Ah) - 90Ah - same as for calcs above.
Selected Battery - The Thunder Sky LFP090AHA LiFePO4 3.2V 90Ah AUD$141.90 inc GST, 2,000 cycles to 80%DOD, 3,000 cycles to 70%DOD, 61x143x220mm 3.3kg
Battery Count - 38 = 120V / 3.2V.
Weight (kg) - 125kg = 38 x 3.3kg
Bank Cost - $5,392 = 38 x $141.90.
Conclusion - Although the bank is only 50% or the weight of lead-acid batteries, it is $75% more expensive for the same capacity and cycle rating as AGM lead-acid batteries. May be worth considering on the next battery change.

+ The Charger

Charger - Now that we have determined the size of the battery bank, it is possible to choose a suitable charger.

Charger Notes - Clearly, a normal 240AV/12VDC charger is not going to do the job, except to charge an auxilary battery. We want to plug into a normal single phase 240 VAC powerpoint. The Zivan NG3 Charger (below) will do the job and can be included in the vehicle as it is only 9kg. Batteries start to gas when you attempt to charge them faster than they can absorb the energy. The excess energy is turned into heat, which then causes the electrolyte to boil and evaporate. Self discharge can be between 8 to 40% per month so trickle charging should be maintained when the vehicle is not in use.
Recharge Frequency (days/c) - 1.5days/c = 100km range for 100% DOD x 30% DOD / 20km/day.
Vehicle Usage (days/wk) - 5days/wk.
Cycles each week (c/wk) - 3.33c/wk = 5days/wk / 1.5days/c
Battery Life (yrs) - 8.1yrs = 1400 cycles / (3.33c/wk) / (52wk/yr). This sounds OK and fits well with the design life of 6-8yrs.
When to recharge - Lead-acid cells should be fully recharged after each use. The greater the DOD (depth of discharge), the shorter will be the battery life (number of cycles). We will recharge each 30km on average or each 1.5 days of use.
Required Battery Charge Profile - 14.4-15V at 22.5A (max) for 4h, 13.6-13.8V (float). See battery spec.
Required Charger Ratings - 144-150V at 22.5A (max) for 4h, 136-138V (float).
Selected Charger - The Zivan NG3 Charger (below) will do the job and can be included in the vehicle as it is only 9kg.
The Zivan Charger - On-Board - $1750 Zivan NG3 Charger 12 to 144V and 15-19A DC output and 1 phase 240 VAC input - 9kg. Protected against overload and short circuits. See the NG3 Manual
Charging Time (h) - 4.7h = 90Ah / 19A.
Efficiency (%) - 85-90%. This means that a 30% charge of the battery bank will release up to 342W = (100% - 85%) x 19A x 120V of waste heat for 1.4hrs = 4.7hrs x 30%.
Installation - This charger will be mounted inside the vehicle as close as possible to the batteries with heavy cabling to reduce losses. It includes cooling fans and must be mounted with the correct orientation with ventillation to avoid overheating. The optional thermal sensor should be included to ensure that battery temperature limits are not exceeded during charging. A relay should be included on the 240VAC side so that the motor control interlock can disable the motor when the charger is turned on.
Safety Issues - Plugging your EV into a 240VAC supply has the risk of the vehicle being energise and requires safety measures including double insulation from the vehicle body, earth leakage protection at the powerpoint (not in the vehicle) and fusing at the powerpoint.
Cost ($) - $1,750

+ Power Steering Pump

+ Vacuum Pump

+ Auxillary Supply

Auxillary Supply - All of those accessories such as headlights, wipers, washers, horn and radio will need to work in the EV.

If we use the old 12V starter battery from the ICE, this can be recharged when the battery bank is re-charged, but when used for lights, it will deplete quickly leading to dim lights and a radio that doesn't work.

The battery could be recharged by mounting the ICE alternator on the motor shaft, but considering all of the mechanical and electrical losses, this is a very inefficient way to charge a battery.

Another option is to eliminate the 12V battery and just tap 12V from the 120V battery bank, but this potentially overloads one of the batteries in the bank, reducing its life and limiting output from the entire battery bank. Tapping off the main battery bank is also dangerous because it means that the high voltage bank is not isolated from the chasis.

The common solution to generating an auxillary 12DC supply is through the use of a 120VDC to 12VDC electronic converter, and this is what we will in this project.

Requirements - The DC/DC converter must be able to supply the peak needs of the accessories, convert efficiently and operate down to low battery bank voltages (at least down to 65V where the controller cuts power).
Power Budget - This table lists the estimated power requirements for the auxillary supply.
Starter Battery - Why would we still need a starter battery? It should be noted that the estimated peak load is many times higher that the estimated average load, and it is very important that the peak load be met without tripping or damaging the DC/DC converter, otherwise the auxillary supply may not be available. For example the driver has the headlights on and turns the steering wheel - not a good outcome! Also note that the higher the capacity of the converter, the higher will be the cost. For these reasons, we will select the smallest converter that will supply the average needs, and use any spare capacity to supply a seperate battery. This battery will then supply the peak power needs as they occur. This will minimise the cost and provide a level of safety and assurance that the important auxillary equipment keeps operating under all conditions.
DC/DC Converter - 400W 120V/12V Converter. We will use a xxxxx converter.
Battery - 12V, xxxAh = (xxxW peak x xxxh) / 12V.
xxxx - yyyyy.
Cost ($) - $1,750

+ Financial Analysis

+ Electrical Design

This section provides details of the electrical components in the EV conversion including power, control and instrumentation.

+ Power Circuit Design

Power Circuit Diagram - This circuit diagram (below) is largely based on the circuit provided in the Curtis controller manual. The components are explained below.

240VAC Supply - Requires a xxxxA 240VAC powerpoint with an earth leakage device. The protective RCD (Residual Current Device) can be purchased from most electrical retailers and will trip the 240VAC supply if it detects that there is any return current in the earth wire (indicating a fault in the power lead or vehicle AC wiring).
AC Power Lead - yyyy.
AC Fuse - Optional - used to protect the charger.
Charger Relay - This relay closes contacts when the charger is turned on. These contacts are used in the control circuity to disable the main contactor.
Metering AC Power - Optional - used to assess overall efficiency.
Earth Leakage Relay - Detects shorts of either +ve or -ve high voltage DC to the vehicle chasis and is used to disconnect the battery bank.
Charger - yyyy.
Battery Fuse - Protects faults in the "Main DC Breaker", controller and motor..
Batteries - yyyy.
-ve Connector - This is the main connection point for the high voltage negative cabling and must be isolated from the vehicle chasis.
Main Contactor - Used to isolate the batteries from the controller and motors. Extra contacts also disable the controller so that it will not activate plug braking (KSI turned off).
Pre-Charge Contactor - Closes on as soon as the vehicle ignition switch is turned and is used to charge the internal capacitors inside the controller through the 750 ohm resistor (which limits the inrush current). This contactor must remain closed for at least xxx seconds before the Main Contactor is closed.
Main DC Circuit Breaker - Used to enable the controller and motor circuitry. Includes a "Pre-Charge Resistor" to limit power-on inrush currents to the capacitors inside the controller.
Controller - yyyy.
Reversing Contactor - yyyy.
Motor - yyyy.

+ Control Circuit Design

Throttle - The throttle circuit includes a variable resistor to set the motor speed and sensing/control relays.

Throttle Potentiometer - This is a 5kohm linear wire wound potentiometer, with the minimum throttle at the lowest resistance.
Throttle Disable Relay - The throttle disable relay contact is installed as an emergency measure to short the throttle resistor to force the motor controller to stop. These contacts are closed when the interlocks relay is open.
Reversing Relay - These contacts are closed when the vehicle is moved into reverse. They act to place a 1kohm resistor in parallel with throttle and will limit the maximum motor speed in reverse to a fraction of the forward speed as a safety measure.
High Pedal Disable - When the throttle is at the zero position, the high pedal disable contacts are openned. This is used in the control circuit to stop the motor from being energised.

Control Circuit Diagram - This circuit diagram includes all of the sensing, control and interlock circuitry for the EV converion. Each part is explained below.

120V/12V DC/DC Converter - yyyy.
Aux Charger Fuse - yyyy.
Aux Battery - yyyy.
Aux Load Fuse - yyyy.
Hydraulic Pump and Contactor - Not required in this project. Note the heavy wiring that will need to handle 100A at 12V if this component is required for power steering.
Vacuum Pump and Contactor - yyyy.
Aux Fuse - yyyy.
High Pedal Disable - yyyy.
Forward/Reverse Switch - yyyy.
Forward Relay - yyyy.
Reverse Relay - yyyy.
Aux Relay - yyyy.
Main Contactor - yyyy.
Forward/Reverse Contactor - yyyy.
Hydraulic Contactor - yyyy.
Vacuum Pump Relay - yyyy.
Interlocks Relay - yyyy.
Interlocks - yyyy.

Inertia Cutoff Switch - yyyy.
Seat Belt Switch - yyyy.
Seat Switch - yyyy.
Key Switch - i.e. Ignition switch.
Earth Leakage Relay - yyyy.
Master Switch - yyyy.

Sensors and Instrumentation - yyyy.

Battery Voltage - yyyy.
Charging Current - yyyy.
Battery Current - yyyy.
Motor Temperature - yyyy.
Controller Temperature - yyyy.
Battery Temperature - yyyy.
Throttle Position - yyyy.

Interlocks - yyyy.

Charging - yyyy.
Change direction - Ensure that throttle and wheel speed is reduced to zero before direction is reversed.
High Pedal Disable - When the throttle is in the minimum position, turn off the main contactor.
Reverse Speed Limiting - When reverse is selected, limit maximum speed to 5 percent of full speed.
Disable Motor - When operator microswitch is open, key switch is off, vehicle is charging, battery compartment or motor compartment is open or gear is not engaged .....
Driver Seat Occupied - yyyy.
Driver Seatbelt Fitted - yyyy.

Limits - yyyy.

Motor Temperature Upper Limit - Action is to reduce power by 20%.
Controller Temperature Upper Limit - Action is to reduce power by 20%.
Battery Temperature Upper Limit - Action is to reduce power by 20%.
Motor Current Upper Limit - Current is limited by the controller to 500A.
Controller Current Upper Limit - Current is limited by the controller to 500A.
Battery Current Upper Limit - Action is to reduce power by 20%.
Battery Voltage Lower Limit - Motor current will be reduced by the controller if the battery voltage drops below 64V.
xxxx - yyyy.

Contactors - yyyy.

Main DC Breaker - yyyy.
Forward/Reverse - yyyy.
Heater - Should use some form of heat exchange from motor.
Vacuum Pump - For power assisted brakes and heater controls?
Headlights - yyyy.

+ Mechanical Installation

This section provides details of the EV conversion steps.
Note Because of the high voltages and currents involved, the work listed below is Dangerous and you should take all reasonable steps to ensure your safety. Never connect the battery to the rest of the circuit without access to a disconnect switch that is capable of disconnecting a short circuit (900A+).

+ Preliminary Bench Testing

+ Remove ICE Components

+ Mount the Electric Motor

+ Install the Battery Charger

+ Install the Controller

+ Install Battery Bank

+ instrumentation Design

+ testing Design

+ registration Design

+ ontheroad Design

Misc Parts - From Basicly Natural P/.
Motor - 203-05-4001 from Electric Vehicle Motors Series Wound DC motor, 8 inch dia, peak = 62kW (83 hp) contiuous 21.7 hp 120V, 110 lbs AUD$2420. See Choosing an EV Motor
Curtis Controller - $2420 from Bylong, Curtis 1231C-86XX Spec Series Motor Controller - 96 to 144VDC, 500 Adc (max) PDF Spec, Manual.
Soliton1 Controller - from EVNetics $3750 - 300 kW Series Field DC Motor Controller inc 8V to 340V battery input 800-1000A spec and Ausie Dealer .
Circuit - from EV Power.
Vacuum Pump - $440 VBS Vacuum Pump Kit - required to run power assisted brakes and heater controls. 12VDC, 30ADC, 2.6kg, 2 sec to full vacuum.
Energy Monitor Gauge - Thundersky BMS $3590 - computer, LCD multiple voltage, temperator and current inputs.
xxxx - yyyy.
xxxx - yyyy.
xxxx - yyyy.
xxxx - yyyy.

Auxillary Support - all of the following items are taken for granted in a petrol based vehicle and are supplied from excess mechanical or electrical energy from the petrol engine. In an electric vehicle, additional electric motors and/or power supplies are needed.

Steering - yyyy.
Braking - yyyy.
Head/tail lights - yyyy.
Heating - yyyy.
Cooling - yyyy.
Windscreen washing - yyyy.
Entertainment - yyyy.

Department of Infrastructure, Transport (DoTARS) - See Vehicle Certification in Australia.

In Canberra - Rego ACT. Also see Light Vehicle Modifications in the ACT if you want to convert a conventional vehicle to Electric.

Registration 20% concession - This means that you pay 20% less on the cost of the registration component but must pay the full fee for Compulsory Third Party Insurance, Road Rescue Fee, Road Safety Contribution and Short Term Registration Surcharge (if applicable).
Requirements - All electric powered vehicles must be inspected at the Dickson Test Station prior to establishment of initial registration. An electric powered concession is not available on hybrid vehicles..
Engineering Certification Report - Vehicles will be inspected against the relevant ACT Road Transport Laws...must be presented with a suitable engineering certification report that includes at least an engineering report that covers all modifications, relevant NCAP checklists. .

Ideas

I would be interested in any other ideas or variations on this project.

TBD - .

Click here to check out the list of other projects.

You may also like to click here to check out the list of Artificial Intelligence projects.

If you would like to get any further information on this or any of the other projects shown on this web site, please send an email to Acacia Lateral Technologies. or place a comment in our Guest Book

You might also like to submit your idea to our Free Ideas page for the benefit of other like-minded soles.