Gas To Electric Conversion Experience At CIT-Day 2
Learn The Electrical Theory And Simple Equations Required For Electric Car Conversions And How To Test A Series Wound DC Electric Motor
Electric Motor Inside Bracket - Part of Day 2 activities
The 2nd day of the Gas (Petrol) To Electric Conversion Experience started off from where Day 1 ended with some theory:
- electrical theory;
- electronics theory; and
- wiring theory.
The practical side included:
- testing the Series Wound DC Electric Motor;
- working on the Electric Motor bracket; and
- laying out the Electric Motor with bracket inside the buggy.
Electrical Theory
With Electric Car Conversions, there are certain things to keep in mind when it comes to Electrical Theory. This article will focus on using the International System of Units (SI system also known as metric system) because it is easier to do calculations particularly when translating electric power to mechanical power. When the final answer for figures related to power and torque need to be converted to imperial, a conversion calculating website can easily work out that final converted figure.
Volt
This is the Electromotive Force (EMF), which is electrical pressure. In other words, how much work measured in watts (W) is required to per charge measured in coulombs (C). In other words, how much work is required per unit of charge.
Equation symbol is V. Unit of measurement is volt (V).
Ampere
This is a measurement of current which is the flow of electrons going through a conductor. (It should be noted that conventional current flows in the opposite direction to the flow of electrons.)
Equation symbol is I. Unit of measurement is Ampere or Amp (A).
Resistance
This is a measurement of electrical current drag.
Equation symbol is R. Unit of measurement is Ohm (Ω).
Ohm’s Law
Ohm’s law states that voltage and current are directly proportional and inversely proportional to resistance. This is represented in the equation V = IR .
So how do we apply this?
Say, voltage is increased whilst current remains constant, then the current will increase.
If voltage stays constant, but resistance is decreased, then the current will increase.
Quantity Of Charge
The quantity of charge is a measurement of the 1 amp (A) of current in 1 second (s), measured in Coulombs where 1 Coulomb is equivalent to 6.242 x 1018 electrons.
Equation symbol is Q. Unit of measurement is Coulombs (C).
The relationship between quantity of charge, current and time can be summarized in this equation: Q = It
For example, this means if a current of 10 amps flows for 2 seconds, then the quantity of charge that has flowed is 10A x 2s = 20C which means 20 x 6.242 x 1018 electrons have flowed.
It should be noted that when dealing with batteries for Electric Car Conversions, the units used for charge is Amp Hour (Ah) instead of Amp Seconds or Coulombs (C).
Energy And Work
Energy is the ability to do work and there are different types of work such as Electrical Work, Mechanical Work and Thermodynamics Work.
Equation symbol is W. Unit of measurement is joule (J).
Mechanical work can be summarized using this equation: W = Fs where W is work measured in joule (J), F is Force is measured in Newtons (N) and s is Distance Traveled measured in meters (m). Note: Force (F) = ma where m is mass measured in kilograms (kg) and a is acceleration measured in meters per second squared (ms-2) which means the unit of measurement Newton (N) is equivalent to the kgms-2.
Electrical work can be summarized using this equation: W = VQ where where W is work measured in joule (J), V is voltage measured in volts (V) and Q is charge measured in Coulombs (C). Note: Q = It (where I is current measured in amps (A) and t is time measured in seconds (s)) so Electrical Work can be re-written as W= VIt.
By using the SI system, it is easy to work out the relationship between mechanical work and electrical work.
Power
Power is energy or work done divided by time. This can be summarized in this equation: P = W/t where P is power measured in Watts (W) or joules per second (J/s), W is work in joules (J) and t is time in seconds (s).
Mechanical power can be summarized using this equation: P = W/t = Fs/t
Electrical power can be summarized using this equation: P = W/t = VIt/t = VI
Using ohm’s law where V=IR, then the electrical power equation can be rewritten as P = W/t = VI = (IR)I = I2R
By rearranging ohm’s law V=IR, it can be rewritten as I=V/R which means the electrical power equation can be rewritten as P = W/t = VI = V(V/R) = V2/R
This means power P = W/t = VI = I2R = V2/R
It should be noted that electrical energy over time that gets converted to heat energy over time, like when current flows through a resistor, is known as I2R as that is power loss.
Power rating of electrical equipment = maximum power dissipation. Exceed this rating and the equipment is cooked.
When doing your Electric Car Conversion, power ratings, voltage ratings and current ratings of motors, controllers, wires and various components are critical things to know to help ensure a safe and reliable Electric Car.
Electronics Theory
Batteries
A battery is an energy source made of 2 dissimilar metals immersed in an electrolyte. Conventional current flows from the anode (positive electrode) to the cathode (negative electrode). There are various types of batteries which could be used for an Electric Car Conversion such as:
- lead acid;
- Lithium ion;
- Lithium Iron Phosphate (LiFePO4); and
- Nickel Metal Hydride (NiMH).
Fuel cells could become viable in the future.
Electrical Symbols
There was a quick run down on electrical components and their electrical symbols. This becomes important when understanding how to wire up the controller and other associated parts.
Wiring
Wires are a form of electrical conductors. Copper is the most common material used in wires as it is a good conductor and fairly robust. With conductors, the relationship between length and resistance is that the resistance is proportional to length.
A shorter conductor means less resistance whilst a longer conductor means more resistance.
The relationship between cross sectional area and resistance of conductors is that resistance is inversely proportional to cross sectional area.
A larger cross sectional area means lower resistance whilst a smaller cross sectional area means higher resistance.
Temperature also affects the resistance of conductors and that is dependent on the temperature coefficient of the conductor. If using copper wires in your Electric Car Conversion, selecting the correct wire or cable thickness will is much more critical than worrying about the temperature coefficient.
The wiring standards which we will follow will be in compliance with AS/NZS 3000:2007.
Testing The Series Wound DC Electric Motor
Testing the Electric Motor was one part of the practical session of the day. As the Electric Motor was a Series Wound DC Motor, it means when no load was applied to the motor, it could run the risk of speeding up to destruction. To test the motor, only 12 volts was applied to it.
Working On The Bracket For The Electric Motor
Post Bending Work Required To Make Motor Fit
Electric Motor Bracket Welded Up, but further work still required
The bracket for the Electric Motor was made up. It was outsourced to someone else. When dropping the Electric Motor into position, it was discovered that the motor would not fit in. The bracket had to be bent out a bit which involved hammering and using a hydraulic jack. It took a while and a couple of people were involved in the process. The next hurdle was that there was some interference between the face of the Electric Motor and the bracket so some material on the bracket had to be ground away.
Lesson learned: When welding up brackets, ensure that things don’t go out of shape. When angles have to be 90 degrees, ensure that they are 90 degrees after welding.
Grinding Slot To Accommodate Electric Motor
Fellow Student Grinding Electric Motor Bracket
The slots for the Electric Motor were not wide enough. This was due to the face of the motor having a bump. It was not a major problem and in fact it is better to have extra material which you have to grind away, then too little material. If you take away too much material, then that causes more problems. When getting brackets fabricated, it is best to take your time. Cutting away too much material can be an irreversible mistake, hence, why in our situation, it was better to have more material which we would slowly remove, then check to see if the motor would fit in.
Lesson learned: Before grinding access material, measure, check, mark it on the material, grind and check regularly to ensure it is on track.
Drilling Holes To Into Bracket
Crazy Al Drilling - Bad drilling technique demonstrated with drill not straight and back not straight.
Holes had to be drilled into the bracket so that the Electric Motor could be mounted. The original bracket when this motor was used in a forklift was used as a template in marking the holes. The holes in the template were 12mm in diameter. With the template in place, a fellow student told me to use a 12mm drill and drill just a little bit to mark out the holes. I thought that was a great idea. We did not have to use a center punch and we were able to mark out the holes very accurately.
The next step was to drill a pilot hole using a 2.5 mm drill, followed by drilling a bigger hole that was 2 to 3 mm bigger in diameter. We continued this process until we created 12mm diameter big holes.
In the photo on the right, I did not use correct drilling technique. I should have had the drill vertical and I should have had my back straight.
Lesson learned: Keep drill straight. Keep back straight. Use drilling lubrication.
Laying Out Electric Motor With Bracket Inside Buggy
Electric Motor Inside Bracket Loosely Bolted Up. Notice space between bottom of Electric Motor and bracket to that bolt and nuts can fit and so a spanner can fit as well.
Electric Motor Inside Bracket Inside Buggy
After grinding and drilling the bracket to suit the Electric Motor, it was time to bolt it up and see how it fits inside the buggy. This would not be a permanent bolt up as we would need to get shorter bolts and there was the issue of the drive train. Also, the bracket would have to be fastened to the buggy which means that some more holes in the bracket would need to be drilled. This layout is starting to look a bit like the layout of the Mitsubishi i-MiEV Electric Car.
Lessons Learned From The Second Day Of The Petrol (Gasoline) To Electric Conversion Experience At CITace?
The main lessons learned were:
- Use SI units when doing calculations for your Electric Car Conversion. It will simplify things later on. When the final result needs to be in other units, you can do that conversion at the end.
- Have the above formulas handy and know how to use and apply them. This will take the guess work out of a lot of your work.
- When fabricating brackets for your Electric Motor, have the Electric Motor available to the fabricator so they can do the final grinding and drilling. This will save you a lot of time.
- When testing a Series Wound DC Motor with no load, use a low voltage and do not do it for too long, otherwise you risk having the motor spin to destruction.
Summary
Day 2 of the Gas (Petrol) To Electric Conversion experience was a continuation of Day 1. Electrical, electronics and wiring theory as required when doing your Electric Car Conversion was taught. The practical side involved working on the bracket and testing the Series Wound DC Motor. Day 3 will involve theory that covers how to wire up the Motor Controller and working on the drive train.
This is Crazy Al signing out.
P.S. Please book mark this post and check out day 3 of the Petrol (Gas) to Electric Conversion Experience.
