I’m beginning a new project and this one is a touch out of the ordinary for me. I know absolutely nothing about cars, but I’m going to be taking an old 1976 Ford Mustang II, modernizing it, restoring it, and converting it to electric power or die trying.
My first objective is to establish the technical requirements for my project. The purpose of this vehicle, once built, is going to be taking me to and from work on a daily basis; however, I would like to maximize the vehicle’s acceleration where possible in order to yield a more pleasurable driving experience.
Dialing in the Project Requirements
My daily commute is 16 miles each way. I want to have at least a 30% mileage buffer but would prefer a 50-60% buffer due to additional battery drain caused by auxiliary systems like HVAC, the stereo, power steering, etc. This all totals out to:
This means my minimum range is 42 miles, and my target range is between 48 and 52 miles from. The next step is to determine how much power it will take to drive my car each mile. This metric is known as Watt-hour per mile or Wh/mi. This number can be extremely difficult to determine prior to producing the finished product. It is further muddled by the driving efficiency over speed curve. That is to say my base requirement is a function of the vehicles weight and aerodynamics, but my electric motor will also have a different efficiency based on the speed I am traveling at and the gear ratio of the vehicle’s transmission/rear axel. This means that I have to begin making assumptions and over-engineering my system in order to develop an adequate product.
The most important controllable variable in this equation is the vehicle’s weight. 1973-1978 Ford Mustangs had a gross curb weight of anywhere between 2600 and 3400lbs based on the year model and trim package. By ditching the major vehicle components required for an internal combustion engine (ICE), we shed a bunch of the car’s flab. My donor car is a 1976 notchback body style 2.3L v4. This makes it a muscle car wussy! Fortunately for me, it also makes it one of the lighter Mustang IIs weighing in at 2600lbs. The vehicle also suffers from some rust and is in need of a facelift so I will be constructing my own paneling out of fiberglass and carbon fiber. These modifications should allow me to shed additional weight over the existing sheet metal.
This is of course just the vehicle’s weight without the new electric drivetrain and batteries to propel it forward. Once I factor those pieces in the car will be much heavier, though still lighter then it was as a stock ICE. Since we won’t know how much battery we need until we solve for wh/mi and we need the to know vehicle performance data in order to calculate that we will make some assumptions. Wh/mi for most light vehicles tends to be around 250-300 and for small trucks it is 350-400. I was able to find that amp draw for a small miata is 90amps at 50mph. We will use this number as our low end. For our high end, since the Mustang II will be much heavier we will assume 170amps at 70mph. For all of these calculations we will assume a 144V battery system, though our file setup might differ. We’re just eyeballing and overestimating here.
The last thing we need to do is solve for our power requirements. In order to preserve the lifespan of our batteries we must factor in a depth of discharge (DoD) limit. If we deplete our cells by greater then 80% it will greatly shorten the life expectancy of the EV. This means that we will need an additional 20% on top of our power requirements. For this conversion I will be using lithium ion batteries (LiFePO4). However, if using lead acid batteries it is important to also factor in the Peukerts effect. This effect causes lead acid to output at only 55% efficiency meaning that we need almost twice as much power for the same effect. All right! Power is in watts so let’s solve for it!
|Value||Power Requirement||DoD Factored|
|Minimum Power @ 50mph||10811.84||12974.208|
|Base Target Power @ 50mph||12475.2||14970.24|
|Top Target Power @ 50mph||13306.88||15968.256|
|Minimum Power @ 70mph||16219.84||19463.808|
|Base Target Power @ 70mph||18715.2||22458.24|
|Top Target Power @ 70mph||19962.88||23955.456|
This means that peak power for my rig is 24,000 kW. Now it’s time to take a look at equipment and gauge the kind of power I am going to see.
I want my “muscle” car to handle with the same level of growl you would expect out of a small block v8 like the 302s Mustangs are famous for. A little bit of tire squeal is appealing, especially on a bad day! In EV speak we have a couple values to work with. What is somewhat counter intuitive, is that they are each predominately controlled by different components of the car. That means that horsepower isn’t as simple as a big motor.
|Volts (V)||Horsepower (Top Speed)||Battery Pack -> Motor Max|
|Amperage (A)||Torque (Acceleration)||Motor Controller|
|Amp hours (Ah)||Range||Battery Pack|
An electric car is a system. High voltage means high top speed, but only if both your motor controller and your electric motor can support it. Your controller can always output the max amperage it is rated for; however, the voltage sag that it can place on your batteries if they aren’t rated for it can be catastrophic. What is similar to an ICE vehicle is that the more fuel (Amp/hrs) you pack into it the farther it can go in one straight shot.
I found that I could get a really good deal on certain pieces of equipment by buying used. Since EV components are typically rated to work for a long time without breaking I felt safe buying certain parts like the motor and controller second hand. The current rig I am planning to build with associated specs is:
|NetGain WarP 9 Motor||156V continuous||Should handle like a small block v8 when fed properly|
|Manzanita Zilla 1KHV||1K Amps/300V||HV controller is powerful enough to handle dual WarP 9s if I upgrade in the future|
|PWN Real Force||3.2V 100AH/170V||Not sure about these yet…|
Reading around online I’ve found that the WarP 9 should be able to run at 170V fairly stably given that it is still run within its holistic power guidelines. The controller is also capable of adjusting the true voltage/current seen by the motor thereby shielding it from the battery pack. This means that as long as my pack is not over 300V it should be within limits, but in order to hit near max voltage for the WarP 9 (to maximize the top end speed) I will need to be careful about choosing batteries with too much AH opting instead for higher voltage (more on this in a future post).
OMG!!! What did I sign myself up for!
That is the general details regarding my conversion project. I decided to just jump right in and start working on this car because I’d otherwise never actually get around to it. The most difficult part of the project might not actually be the EV conversion. I have three major goals in mind:
- Make a cool electric car
- Make said car actually look cool too
- Create a sick car computer system to jam out and hack the planet!
I’m not too worried about that last part… it’s my forte; however, that second bullet might give me some trouble and will be the focus of my next post. I want to make the whole thing look very different than stock. This is going to involve a LOT of fiberglass and carbon fiber fabrication work! I have NO idea what I’m doing, but I can’t wait to get started! I’m glad to have you along for the ride. Please comment below if you have any questions or want to provide suggestions/encouragement. Most importantly please comment if you think I’m and idiot and have a better idea or a flaw to point out! You’re dumb and this is why are the best comments out there!
P.S. Sorry about the exclamation marks… I get excited