The “flywheel effect” and some theoretical questions….

[JRaf]

The flywheel effect.
Current multiplication
In an early service manual (1989) for solid state controllers EZGO Textron states that their newly introduced solid state controllers are able to generate more current than is actually available through the batteries through something they call “current multiplication” because the controller “acts as a DC transformer… ie., it takes in high voltage and low current, and puts out low voltage and high current… the result is a dramatic improvement in the vehicle’s efficiency; this gives greater driving range per battery charge.”
So my question is multi-part: Is this the “flywheel effect” that JohnnieB refers to? And is it correct to assume that in a resistor cart, there can be no greater amperage going to the motor than battery current? (If you have a 200 amp battery pack, you can get 200 amps max to the motor and never more?)
That would force me to assume that resistor carts were terribly inefficient. Not only were they incapable of delivering very high amperage, they were burning off power by dumping energy they didn’t always need into big resistors which turned that energy into heat instead of power. Do I have that right?
I don’t have a resistor cart, I’m just asking for my own edification. But following that, who were the first to put solid-state controllers into their golf carts? EZGO? Club Car? Someone else? Or did everyone hook into solid state motor controllers at the same moment? Was the solid state motor controller already a mature technology in 1989 when EZGO first introduced their solid state controller carts?

[Volt_Ampere]

Resistor carts are terribly inefficient. Mostly because they reduce the motor voltage when not at full throttle by putting the current through resistor banks. All that drop is turned into heat - lots of it. A modern controller uses switching circuits to pulse the current to the motor and that is far more efficient at part throttle. In a switching controller, it's true that the motor current can be different than the battery current. At full throttle, both a solid state and resistor cart produce the same motor current at roughly the same efficiency. But we don't operate carts at full throttle all the time.

[JohnnieB]

Originally Posted by JRaf

The flywheel effect.
Current multiplication
1. In an early service manual (1989) for solid state controllers EZGO Textron states that their newly introduced solid state controllers are able to generate more current than is actually available through the batteries through something they call “current multiplication” because the controller “acts as a DC transformer… ie., it takes in high voltage and low current, and puts out low voltage and high current… the result is a dramatic improvement in the vehicle’s efficiency; this gives greater driving range per battery charge.”

2. So my question is multi-part: Is this the “flywheel effect” that JohnnieB refers to?

3. And is it correct to assume that in a resistor cart, there can be no greater amperage going to the motor than battery current? (If you have a 200 amp battery pack, you can get 200 amps max to the motor and never more?)
That would force me to assume that resistor carts were terribly inefficient. Not only were they incapable of delivering very high amperage, they were burning off power by dumping energy they didn’t always need into big resistors which turned that energy into heat instead of power. Do I have that right?

4. I don’t have a resistor cart, I’m just asking for my own edification. But following that, who were the first to put solid-state controllers into their golf carts? EZGO? Club Car? Someone else? Or did everyone hook into solid state motor controllers at the same moment?

5. Was the solid state motor controller already a mature technology in 1989 when EZGO first introduced their solid state controller carts?

1. EZGO's explanation is closer to political speech than reality and more ad copy than technically correct. The controller's output is pulsed DC whose duty cycle varies between 0% to 100% and is pure DC at 0% and 100%. The voltage of the DC pules is equal to the input voltage, so there is no "Transformer" effect.

2. Yes. The attached page for the Curtis 1204/5 manual has a pretty good explanation of how the controller works and how the flywheel effect cause motor amp to exceed battery amps when pulsed DC is applied to the motor.

3. Yes. Motor current will never exceed battery current in a resistor drive, or in a controller drive at 100% duty cycle.

4. I don't know who was first.

5. The PWM (Pulse Width Modulation) theory used by motor speed controllers was known long before transistors were invented and I've seen pictures of PWM controllers with vacuum tubes, but solid state technology didn't get affordable enough to put into golf carts until the late eighties or so.

The controllers being put in carts these days have more computing power than the Lunar Lander had.

[JRaf]

So I imagine the reason 36 volt systems were originally used in golf carts was because it gave the carts enough power to drive two people and their gear over eighteen holes of golf. You probably couldn't use higher voltage systems because resistor systems were too inefficient, they needed the high amperage of six volt batteries, so the six by six systems were a common design. But once you had solid state controllers you could use lower amp batteries and get acceptable results with higher voltage and lower amperage, which gave us 48 volt systems. Does that sound right?
Now, with the introduction of lithium batteries, we're seeing practical voltages rise again with 72 volt systems. (And of course the lid's really off the jar when we look at high voltage battery-powered cars, but I digress.)
So, as lithium prices drop, and practical voltages rise, where are we going? Do you guys think golf cars in the future will be economically powered by 72 volt systems or are we going further than that? What's the advantage of an AC system? And why isn't AC available in a 48 volt cart?
And there's one important development I'm ignoring... the introduction of the "sepex" motors rather than "series" motors. What's the difference between the two, and what advantages does "sepex" bring?
Too many questions?

[Volt_Ampere]

There are plenty of 48V AC carts! Everyone makes them now. No brushes to wear out with AC motors. Higher voltage is more efficient - lower IR losses for the same power delivered. Electric cars are up in the 400 volt range for that reason. Sepex motors allow the separate control of Field Current vs Armature Current. This allows more torque / speed control vs a Series motor. This is an advantage with a modern controller that modulates both the armature and field current. Weakening the field as motor RPM increases can give you a higher top speed. Series motors still have their place in traction applications.

[JohnnieB]

Originally Posted by JRaf

1. So I imagine the reason 36 volt systems were originally used in golf carts was because it gave the carts enough power to drive two people and their gear over eighteen holes of golf.

2. You probably couldn't use higher voltage systems because resistor systems were too inefficient, they needed the high amperage of six volt batteries, so the six by six systems were a common design.

3. But once you had solid state controllers you could use lower amp batteries and get acceptable results with higher voltage and lower amperage, which gave us 48 volt systems. Does that sound right?

4. Now, with the introduction of lithium batteries, we're seeing practical voltages rise again with 72 volt systems. (And of course the lid's really off the jar when we look at high voltage battery-powered cars, but I digress.)
So, as lithium prices drop, and practical voltages rise, where are we going? Do you guys think golf cars in the future will be economically powered by 72 volt systems or are we going further than that?

5. What's the advantage of an AC system? And why isn't AC available in a 48 volt cart?

6. And there's one important development I'm ignoring... the introduction of the "sepex" motors rather than "series" motors. What's the difference between the two, and what advantages does "sepex" bring?
Too many questions?

1. In 1932, Lyman Beecher of Clearwater, Florida, invented a cart for golfers that was pulled by two caddies like a rickshaw. He later replaced the two caddies with steerable front wheels and added an electric motor. It reacquired the energy stored in six car batteries to complete 18 Holes of golf and car batteries at the time were 6V.

Basically, using a 36V battery pack was more incidental than designed and the objective was range rather than speed or torque. Mr. Beecher, a physically disabled person, simply used what was readily available to him to get the desired results of building a self-propelled cart to carry him and his clubs around a golf course.

2. You can build a resistor type drive for just about any voltage that can be used by a controller type drive. It is just that the resistor's Ohmic values have to be selected to match the pack voltage or it won't work quite right.

3. More than likely, speed was the objective. Applying a higher voltage to a motor causes it to spin faster with the same mechanical load applied.

4. Don't know where it is going. I'm sticking to a sepex drive with a 42V lead-acid battery pack.

5. AC motor are brushless and have higher max RPM, so numerically higher gear ratios can be used, giving higher torque multiplication over the RPM spectrum and less slowing on hills as well as better acceleration. (Yep, it is the RXV's 16.99:1 gears that gives it better performance than the DC carts with 12.44:1 gears. With the same gearing, DC carts might outperform AC carts.)

6. A DC motor can be wound to have high low-end torque at the expense of high-end torque (which determines max RPM for a given voltage applied) or be wound to have high high-end torque (high speed) at the expense of having low low-end torque. For series wound motor, the motor's torque/speed curve is set in stone at the factory.

Physically, the same is true for a sepex (separately excited) motor, but the torque/speed curve is actually determined by the relative strength of the magnetic fields produced by the stationary (Stator aka Field) windings and the rotating (armature) windings. By altering the amount of field amps, you can increase or decrease the magnetic strength of the stationary windings. thereby shifting the motor's torque/speed curve towards higher low-end torque or towards higher high-end torque on the fly. Basically, a sepex drive comes off the line with a high torque motor that transforms into a high speed motor as the motor's RPM increases.

[JRaf]

I had no idea RXV carts were all AC.
And since I'm obviously dumb, I'll ask another dumb question: Are their brushless DC motors? There are right? There must be. Of course there are. Right?
I think I have a rudimentary understanding of the difference between Series and Sepex. Thanks for that.
BTW, when I google "Sepex and series motors", the first link refers me to a thread in BGW featuring a detailed explanation of the technology written by: JohnnieB (and with an appearance by Volt_Ampere). So thanks for both of your patience on this and so many other matters. (I'll google more.)
Another question, and I don't think you'll know the answer: Since the introduction of solid state controllers (in golf carts) have we seen the number of electric carts sold risen... as opposed to gas carts?
Finally, I don't believe anyone, even JohnnieB will be able to resist the onslaught of lithium (or lithium-like) battery technology. At least once we figure out how to belay the recycling and safety dilemmas held therein.

[Volt_Ampere]

AC and brushless DC are basically the same. They use a synthesized AC waveform created by switching the DC around using an H bridge circuit. Most larger motors use Hall Effect sensors to determine the rotor position. The controller switches the H bridge transistors to drive the current through the windings in the correct direction to generate forward torque.

When I moved to Rio Verde in 2012, at least half of the carts were gas powered. There was a small gas station in Rio Verde then. That station went away and now you have to go 10 miles to get gasoline. I think that is the main reason we see almost all electric carts here now. Having to keep a gas can filled is a PIA. In the past year, many if not most of the new carts here are Lithium powered. I have been running a Lithium cart for almost 5 years now and I would never go back to FLA batteries.

[JohnnieB]

The only dumb questions are the ones not asked.

Yes there are brushless DC motors. They have armatures made up of permanent magnets, so no electricity is needed to develop the armature's magnetic field. They have multiple field windings that have to be excited individually and sequentially to make the armature to rotate, so the controller is more complex than controllers for brushed DC motors or AC motors.

I don't know about the ratio of gas vs electric carts, much less any changes in it.

My lead-acid batteries will be 9 year old next month and my plans are to replace then with economy grade 6V like Duracell (210AH) from Sam's or Super-Start (215AH) from O'reilly's this winter or next spring. I have a 42V pack with seven 6V batteries, so having less than the standard 225AH won't be an issue since my resultant range/runtime with seven 6V batteries will be greater than the standard sized 36V (8100Wh) or 48V (8160Wh) pack. (42V x 210AH = 8820Wh)

I'll be 79 in February and if I'm still kicking when my next set of FLA batteries need to be replaced, and the major bugs have been eliminated from Li systems, I might consider going to it.

[JRaf]

Mazel Tov, JB. I've heard 79 is the new 30.
I have nothing against flooded lead acid batteries. They don't catch on fire, they're 95% recyclable, require only the most humble care, and they're relatively cheap. (Of course they're heavy which makes them impractical for anything much larger than a golf cart.)