What Are Advantages of 72v AC???

[konakid]

I bit the bullet and ordered a new Cushman Hauler Pro (built by EZGO). It has 72v AC power.

Perhaps not an easy answer - but the question is (maybe two questions) - what exactly does more voltage give you? Is it more power, or more range, and/or something else?

And how does the AC play into that question? In other words, what is the difference between 48v AC and DC? And what would be the differences between 36v DC and 48v DC?

And I guess I could then extrapolate the differences/advantages between 48v DC and 72v AC. Is one "better?"

And if anyone wants to offer an opinion - is there a "best" voltage and/or AC/DC configuration for your typical golf/utility cart?

[Gregorio]

Simply put VOLTS x AMPS = WATTS and 746 WATTS = 1 HP

Another simplification is that more volts for a given motor gives more speed and a little more power. More amps gives more power but a lot more heat.

When comparing a factory offering, there are a lot more things to consider such as cost and durability. I would expect that those are key factors in their decisions to go with one particular package over another.

Personally, I am liking the 72V AC packages more and more every day for all out power and speed....cost not being a factor.

[konakid]

Well then - something I didn't think of asking, and didn't think I was lacking information about would be this. What exactly are you doing when you step on the "gas" pedal? Are you supplying more volts?

[Gregorio]

Again, very simply put, the workings of the accelerator vary from brand to brand and generate a signal proportional to the angle of the pedal. The controller varies the voltage in proportion to the signal it receives from the pedal that is matched to the power curve of the motor. However in reality, it is doing a lot more than that but this is how a basic speed control works.

[Revolution]

The main advantage to an AC motor is the lack of brushes an comutator, the weakest part of most DC motors. The brushes add resistance and drag to the motor. AC motors don't need them.

The other advantage to AC motors is more efficient regenerative braking. They can regen brake with more control and to a slower speed than a DC motor.

The AC controller has to be more complicated in order to control the simpler AC motor, instead of the comutator controlling the magnetic timing of the motor in a DC motor the AC controller has to sense and adjust the power and the timing of the stator coils to turn the rotor of the AC motor.

The higher voltage does not mean higher power. The little motor in your vacuum cleaner runs on 120 volts, but it won't even make a golf cart roll. Voltage is the potential not the work.

To keep it simple a wire of a given size will only be able to supply a limited amount of current regardless of the voltage. A 12 gauge wire will safely supply 20 amps at 12 volts or 120 volts, but 12 volts X 20 amps = 240 watts and 120 volts X 20 amps = 2,400 watts, big difference there.

In golf cart terms a 36 volt cart with a 500 amp controller would be 18,000 watts. A 72 volt cart with a 500 amp controller would be 36,000 watts. They could both use the same size high current cables.

The main reason for higher voltage is for efficient power delivery. A 36 volt setup with the same power motor as a 72 volt setup would require high current cables twice as thick as the 72 volt.

[cgtech]

Its a little different from the DC "voltage chopping" systems we are used to where voltage alone dictates the amount of amps supplied. The AC system varies volts and frequency. The volts is similar to the DC system, but the sudo-sine waves (fabricated "on the fly"out of DC battery power by the controller) are continuously adjusted to modify torque characteristics (how often "per second" the power is applied, and what direction, this is key to the control of speed and regen braking) to accurately control speed. There are more technically accurate descriptions out there for this but this will get you started on the idea. As always, volts X amps equals watts, a 350 amp 72v controller can deliver much more watts to a motor than a 48v 350 amp system can. Watts "to the ground" equals performance, after the transaxle and gear ratio is done with it.

[cgtech]

Thanks "Revolution" for posting some more tech-side of it than the "easy-version".

[konakid]

Thanks guys - I can begin to see why the questions I asked do not have easy answers. But from what you have told me so far, can I assume the following?
1) The higher voltage AC systems have the most potential for both power and range. But are more complicated - so, more expensive to design, build, and maintain.
2) Therefore one person might prefer the simpler easier and cheaper to maintain DC systems if they do the job they need. While another person may wish the more "advanced" setup, regardless of the extra complexity and cost.
3) So if I started a poll to ask the preferred power system to power a golf cart, I would get varied answers and varied reasons for those answers.

[Revolution]

Maintenance on the AC carts would be the same or less than DC. The AC motor would need less for sure.

When AC systems are more reasonably priced I will jump on them.

For now both my carts are series DC, and go faster and do more than I really need.

[HiTechRedNeck]

Good answers all.
Let me answer from a users take away point of view.

Simplified below but true.

In a DC motor speed "rotational speed" of motor and therefor cart speed is determined by the Voltage and amperage applied to motor.


More voltage=more speed AND more voltage = more current"amps" AND more amps= more speed AND more power=more heat.

So more speed requires more power and more heat.

With AC motors.

At the "same" voltage and current, rotational speed of motor is determined by FREQUENCY of AC power applied.

Same is in quotes because i am speaking in relative terms. Increasing speed changes power requirements - just not in the same way (complicated math)
for ths discussion-- same works

This allows a controller to vary the speed of a cart without using more raw power.

The standard TXT has a 300 amp controller at 36v. 300x36=10800w
RXV's have a 200 amp controller at 48v.200x48=9,600w

An RXV is controller limited to 19.5mph while a TXT is hard pressed to go over 15mph.

RXV,s are FASTER with less power. Put the two side by side on a hill for a real demonstration of doing more with less.

Another point mentioned by others is maintenance.

Controllers are Electronic devices. The reliability of which depends more on the initial design of circuits and the quality of components than their complexity.

AC controllers are more complex than DC controllers, but The RXV controllers have a low failure rate. Every failure i have seen was caused by attempts to modify the wire harness to add accessories.

The increased complexity may also have real world advantages as the system provides thermal monitoring of motor and controller as well as low voltage protection lacking in some simple controllers.

DC motors hav an "Achilles heel", brushes.
these are mechanical wear points, generate heat and dust, and limit
the amount of power the motor can handle.

AC motors have no brushes. their mechanical weak link are the bearings.
Since the AC motors operate at lower power, they generate less heat and the bearings seem to last longer than with DC motors.

Again-- many details are glossed over.
But basic concepts are accurate.

Good luck!
please post review of 72v monsters actual performance in the real world !!!