PDS questions - (Theoretical)

JohnnieB

The sepex motor used in PDS and DCS carts have a motor speed sensor that consists of a disk with eight magnets on it and a pick-up coil,
Therefore eight pulses per revolution of the motor is sent to the controller.

Theoretically, if two of the magnets were removed from the disk the controller would only get six pulses per revolution and think the motor was turning 25% slower than it actually was and limit the top speed to 24 rather than 18MPH.
Has anybody tried doing something like that?

Also, has anybody tried to run a tachometer from the pulse train from the motor sensor? An tach for a V8 for instance?

BGW

__________________
This advertising will not be shown in this way to registered members.
Register your free account today and become a member on Buggies Gone Wild Golf Cart Forum

madoc1

i don't pretend to know about those, but there was a thread in the extreme dc forum about a "speed disc" that someone was selling.

JohnnieB

Thanks Jim,

I saw a thread about a disk with fewer magnets being available for a Club Car, but it answered my first question.

scottyb

If this does work, you have to be very aware of the motor rpms. 24mph on stock tires would be about the safe limit but even holding that speed for more than 15 seconds could be detrimental, in my opinion.
The PDS motors are not real tough when compared to a series motor.
Keep us posted on this

gornoman

The speed sensor you describe cannot make the motor spin faster than it was designed/rated for. That design limit remains set in stone assuming the voltage remains constant. The sensor is used to regulate speeds BELOW the design maximum. Get it?

sonicj

if the controller is capping your speed at 18MPH based on the number pulses it receives from the motor, then yes, using a magnet with less poles will allow you go faster. if 18MPH is the top speed of the motor at X volts, then no, less pulses from the motor to controller will not make a difference because the motor has already reached its top speed for the given voltage & load.
-sj

JohnnieB

Having witnessed an armature explode from excessive centrifugal force, I have neither desire nor intent of exceeding design RPM.

I haven't researched the physical RPM limit of a stock PDS motor (Advanced Model DE2-4007) yet, but with stock tire height (18") and differential (12.44:1), it turns roughly 232.3 times per MPH, or about 4,182 RPM @ 18 MPH and about 5,725 RPM @ 24 MPH. Correct me if I'm wrong, but aren't people getting speeds in the low to mid 20's with stock motors turning stock height tires by upgrading controllers and/or upping battery voltage?

Granted, reducing the number of magnets on the speed sensor with not make the motor spin faster, however it will allow it to if the controller is limiting the duty cycle of the Pulse Width Modulated (PWM) DC being sent to the motor. I'll have to put an O'scope or Duty Cycle meter on it to see if this is happening.

Since the PWM is accomplished by on and off MOSFETs, the heat load in the output section of the controller should be about the same at a 75% duty cycle or a 95% duty cycle.
My guess is that the solenoid will be the weak link, but it might take out the controller also.

Actually, I probably won't try to increase top speed. About 18 is fast enough for an Old Guy like me.
What I want to do is increase the speed in the "Mild Hill" mode from 14 MPH up to the 18 MPH range while retaining the Regenerative braking.


As indicated in the title, this is still in the theoretical stage. I've got a lot of research to do before I do any experimenting.

Added: Hi SJ. Exactly what I was thinking. If the controller is limiting the RPM, lie to the controller.....

kgsc

OK, I'll bite. If you take the magnet out all together will that freak out the controller because it doesn't sense the cart moving? Also, if you do just take out half of the magnets will that mess with the regen or hill brakes(no pedal, cart moves, controller beeps and applies regen)

sonicj

you could build a divide by 2 circuit for like $1 using a CD4013 and a few caps. if you have a scope, i would do that first. what multi-meter do you have? some have a duty cycle function!

JohnnieB

Don't know since I haven't tried it, but here's what I suspect will happen.

If the Controller doesn't detect any movement (IE: No pulses from the speed sensor) it will think the motor is stalled and shutdown.

If the number of magnets is reduced, the various functions will still occur, but at a different speed. For example, if the cart rolls when pedal isn't depress the regen braking will limit it to 3MPH if half the magnets are removed or 2.5MPH if only two are removed, instead of the normal 2MPH.