2009 PDS cable question

[mutant]

not in a significant way....check alignment,low rolling resistance tires,check brakes for any dragging,ect....but those options wont make any large change-just maximize what you have....


think of a battery as a gas tank-more tanks-more distance driven...less tanks,ect.........

[scottyb]

Originally Posted by kgsc

Does your car burn more fuel at faster speeds ? Yes. Why, drag for the most part in multiple areas. Brakes, windshield, dog hanging out of the cart.. And if the op is getting those speeds there is some drag involved.

We can't know if the dog is long or short haired... that would make a difference Oh - and we don't know if he has his mouth open or closed........

Actually I was questioning your answer about the cart using more amperage at speed. Electric motors create a thing called EMF or back electromotive force. And the faster it spins the more EMF it creates which results in less amperage consumed the faster it goes.

[kgsc]

If the drag was the same at different speeds then yes once it was spinning faster the current will drop but in this case the faster you go the more energy it takes to keep the cart at that speed.

[scottyb]

Originally Posted by kgsc

If the drag was the same at different speeds then yes once it was spinning faster the current will drop but in this case the faster you go the more energy it takes to keep the cart at that speed.

I know that's not right. Wind resistance and wheel drag does not normally equal out what I'm talking about. I'll find some data for you.

[kgsc]

Or a real world test.. OP pull the chip and see if your range improves.. Simple test..

[scottyb]

That's what I suggested post #5.
But he would have to drive the same way and same place he does with the chip to get close to fair results.

[JohnnieB]

Originally Posted by thaduker

I also just ran a gps speedometer and the buggy topped out at 29.7, & pretty consistent speed of 26-27. I have read the speed chip allow the buggy to go 19 max. Is there anything I can do to get the charge to last longer?

What is your tire height and differential gear ratio?

With a speed chip, a stock PDS controller limits the motor RPM to about 4400 and with stock gears (12.44:1) your tires would have to be about 25" tall to get 26-27 MPH on level ground.

With tires that tall (or a combination of tire height and gear ratio), there is an effective torque loss of about 30%, so the motor's efficiency is probably down to 50% or less when running at or near top speed.

Driving slower and/or installing shorter tires would increase range.

[scottyb]

Real amp draw information from the Alltrax data log. Note this is a modified cart but the point I'm trying to make is clear.

At 4.5 to 8.1 MPH is 308 amps drawn
9.4 to 12.1 MPH is 211 amps
12.3 to 16.3 MPH is 189 amps
16.3 to 20.4 MPH is 161 amps
20.4 to 24.4 MPH is 126 amps
24.5 to 27.5 MPH is 99 amps

In this data file the amperage drawn was 1/3 at top speed than that of the low speed. A normal cart would draw only about 2/3rds of the amperage shown here.

[JohnnieB]

FWIW: Neither scottyb nor kgsc is wrong, but one is speaking about apples while the other is speaking about oranges.

The amp draw does decrease as motor RPM increase and the mechanical drag does increase as speed increase, however the decrease in amps vs RPM is fairly linear while the increase in drag is more or less exponential, so the net result is the fast the cart goes the less efficient it becomes.

Making matters worse, the final drive ratio for a stock PDS is 16.59:1 and to get 26-27 MPH with a stock controller, the final drive ratio has to be about 11.94:1, so the carts normal efficiency is compromised and when coupled with a battery pack whose storage capacity is only a fraction of the normal stock capacity, the impact speed has on the range on a single charge will be significant.

[kgsc]

The man in the foil hat has spoken. I 100% agree.