[thingstodo]

I have likely confused many people about what I'm trying to do. I know that I use a lot of acronyms and that makes it harder to follow. So I'm going to step through the parts and pieces that I have collected and try to explain what my goal is. Then I'll back up a bit and explain how the tests that I'm doing fit into the system.

The 40 Horsepower (HP) General Electric (GE is just a brand name) electric motor is an AC motor like you'd find in many mills and other industrial installations all over the world. This one happens to have a rated voltage of 575 Volts of Alternating current (VAC) three phase. Connected to a motor starter that uses the normal 60 Hertz (Hz) electricity from the grid, the motor will spin at 1770 revolutions per minute (rpm), driving a load of about 120 foot-lbs. Foot-lbs is a measurement of the force that the motor will 'push' at a distance from the center of the motor shaft. At this load, the motor will draw about 38 Amps (A) current. If the load is lower, the motor will spin slightly faster, but will not exceed the 1800 rpm that the electricity is 'driving' the motor at.

The Variable Frequency Drive, or VFD, is not exactly a controller like a Curtis or a Soliton. As designed, the input is 60 Hz three phase, or three wire, electricity. The VFD uses diodes and electric filters composed of capacitors, inductors and resistors to make that input electricity into Direct current (DC), similar to the battery current. It then uses power electronics (transistors or IGBTs) to 'make' a rough version of AC that is fed to the motor. The Frequency (f) of the AC is what speeds up and slows down the electric motor. There are many ways to 'tell' the VFD what speed you'd like the motor to turn. Most VFDs have a 'keypad' mode where you type in a number from 0 to 120 or 200 and the VFD speeds up the motor, then controls it at that speed. It is also common to use a 0 - 5V signal to change the speed. So the VFD takes care of the 'throttle' or gas pedal part, and it has a lot of parameters, or numbers that you can change, to allow you to specify how fast you'd like to motor to speed up, slow down, how much current it can put into the motor, when the motor will overheat and should be shut down ... there are many modern VFDs that have 600 - 1000 parameters. I don't use the AC part. The batteries connect up to the 'middle' of the VFD, where the AC has been converted to DC. The DC batteries are connected in series, or the + of battery 1 to the - of battery 2, the + of battery 2 to the - of battery 3, and so on, to add up the required voltage and the VFD works as it would in a mill. It is NOT intended to be used in the way that I am using it ... but it works.

A Programmable Logic Controller or PLC is an industrial computer that is used to control many groups of motors in modern industry. I'm using an older model to take all of the inputs - accelerator, brake, motor speed, battery pack voltage, motor and battery current, and a few dozen more ... and drive the VFD, drive gauges on the dash of my truck, log data, and keep me safe. Many of the dashboard gauges accept a voltage output that I can approximate by turning the PLC outputs on and off quickly, called Pulse Width Modulation or PWM. The programming language of the PLC allows me to do many things that used to require relays and timers. My main reason to use the PLC is to over-ride the speed signal to the VFD under certain conditions. And the PLC allows me pretty much full access to anything that I want to log, or record. I plan to log as many things as I can so that when something goes wrong, I have as much information as possible to figure out what went wrong and how to fix it. So the PLC is sort of my controller, but the combination of the PLC and the VFD is what a Curtis or a Soliton does. I have looked at what optional inputs there are in the Curtis and the Soliton. I'll check out any other controllers that I can find information on to assist me in determining with what options I want to use. Again, we'll see.

Getting back to my testing. I have parts of a VFD that is large enough to drive my 40 HP motor, and that is the end game - check what the 40 HP motor will do. But it is difficult to test. I don't have a bank of batteries large enough to drive that motor for any realistic testing period. I have 240 VAC to my house like everyone else, so producing 575 VAC or 750 VDC is difficult. So I'm doing some testing with a smaller 5 HP motor, and I'm using equipment that can be driven with 240 VAC and batteries that I have. These motors are called T frame motors and they have specifications that are published by a standards organization - NEMA. Any particular motor from a name brand can exceed those specifications, but they must meet the minimum. And a lot of the specifications deal with the shaft size, the distance between the mounting bolts, the size of the mounting bolts ... the mechanical details that let you buy a replacement motor from another vendor when the first motor fails.

If the NEMA specifications gave me the information that I want, I would not need to test. But the specifications were developed for use in industry, years ago, so they don't include quite enough information. Because T frame motors have certain specifications, I'm testing a smaller one so that I can apply that information to the larger one. For example, I'd like to know what the maximum torque is that my motor will produce. That is the central factor that determines how fast it accelerates, and is the difference between driving a big golf cart that takes 4 minutes to get to 60 mph and driving the original Internal Combustion Engine (ICE), where it took about 25 seconds to get to 60 MPH. Will it perform better that the ICE and get to 60 mph in 15 seconds? likely not without a transmission. If the acceleration is too low I have a problem to solve - I may have to get a bigger motor, or use a transmission, or something else. If NEMA listed that torque, with the current that is required to produce that torque, I would not need to test. The graphs that are published show about 220% torque as a maximum or 'breakdown' torque. There is no mention, that I can locate, of what current is required to produce that torque, nor what slip rpm it is produced at.

Another factor is how much current the motor takes when it is accelerating at it's maximum. I need the battery bank to be able to supply that current, and the VFD to be able to put out that current, and the cooling system to be able to get rid of that heat so things stay running and are reliable.

So that's how the 5 HP torque testing fits into the truck design.

The Direct current to Direct Current (DC/DC) converter or Direct Current to Alternating current (DC/AC) inverter that I've been playing around with is an attempt to boost the voltage from my battery pack up to the voltages that the VFD can use. The 575 VAC VFD will run with a minimum of 750 VDC, but that's 60 batteries at 12.8V each. The weight is just not practical. If I can take a larger battery, like a fork truck battery, and boost the voltage from 12VDC to 140 or 150 VDC, then I can wire those 140V outputs together in series to get the voltage as high as I need it to be. The efficiencies I've seen so far make me think that this loses about 10% of the battery power as heat. That's a pretty steep cost, needing an extra 10% battery power. I doubt that this is a practical solution, but I will check it out since I want to learn and most of the parts have been surplus, ebay, or free. I want to explore some options before I begin to sink large amounts of money into this project.

So that's how the DC/AC inverter (The higher voltage DC portion is between the 12V DC input and the 120VAC inverter output) helps make my truck move.