New xct400pds

[scottyb]

7 CR220 arrive Tuesday.
This will allow me to make 36 and 42v tests.
42v PDS

[JohnnieB]

Originally Posted by cgtech

I bet the difference on the regen braking might be attributable to the xct having access to the tach sensor, where the dcx did not.

Here's what the Toolkit manual says about it on Pg-14 of 26:

Enable Speed Limit
This checkbox determines whether or not the controller will use the speed sensor to limit the RPMs of the motor. The controllers regen feature is based off the RPM of the armature, which is monitored by your speed sensor. If you choose to not use the speed sensor it will affect your ability to REGEN and the controller will not prevent you from over-accelerating while going downhill. What this basically means is that if you have a speed sensor, and don’t use it, you run a high risk of your motor coming apart if you’re not vigilant with it. Your motor should have a manufacturers recommended RPM rate, more than likely the Alltrax will already know what RPM it should be set for, but if you have to adjust these settings yourself we recommend calling our Tech Support for assistance or an Alltrax dealer.

Historically, the DCX controller was designed as a Plug-n-Play replacement for the unreliable EZGO DCS controller (Curtis 1206SX), which didn't have a speed sensor. At a later date, control wiring adapters were designed so the DCX controller could be used with CC, Yamaha and PDS drives, effectively turning them into a DCS drive system, but with a reliable controller.

The user could program the amount of regen braking, but operationally it simply turned on when you lifted your foot off the pedal. The amount of regen amps flowing into the battery pack was determined by the max voltage the motor could generate at the speed the armature was spinning at and the user programmed excitation as well as the pack voltage at the time. Since the pack voltage at the time was a major contributing factor, more intense regen braking was available with a 36V pack than was available with a 42V or 48V pack. Also, the cart speed at which the motor could produce a voltage higher than the pack voltage to get regen braking, varied with pack voltage, so the speed to with regen braking would slow a cart to was lower for a 36V system that it was for 42V and 48V systems.

Apparently, by knowing how fast the armature is spinning (Motor RPM), the XCT is able to adjust the excitation on the fly to generate the user programmable max regen current, so the intensity of the regen braking (Negative G-force) is about the same at 25MPH as it is at 15MPH.

However, that doesn't change the fact that the voltage generated by the motor has to be higher than the pack voltage for regen current to flow and generated voltage is determined by how fast the armature is spinning, and my cart is slowing rapidly rather than coasting at speeds less than what it was with a DCX controller installed, so I'm pretty sure there is more going on.

I suspect that Plug braking is also being incorporated.
In a sepex motor system, the fundamental difference between Regen barking and Plug braking is where the current generated by the motor goes.

With Regen braking, the electrical energy generated by the motor, is sent to the battery pack and is converted back into chemically stored energy.

With Plug braking, the electrical energy generated by the motor, is converted into heat that is dissipated by the controller, or by other means.
(Sidebar: The RXV electrical braking system dumps the current the batteries can't handle into an external resistor that is designed to dissipate a lot of heat.)

There are three programmable sliders that appear to control the XCT's electrical braking functions (Max Regen Armature Amps, Max Regen Battery Amps and Plug Braking Current), but I have yet to find out or figured out what, exactly, each one does or how they interact.

[scottyb]

I notice that with all 3 of the XCT's electrical braking functions (Max Regen Armature Amps, Max Regen Battery Amps and Plug Braking Current) at default setting my PDS cart comes to a complete smooth stop. I'll drive a little more today and see how effective it is down hill

[JohnnieB]

Originally Posted by scottyb

I notice that with all 3 of the XCT's electrical braking functions (Max Regen Armature Amps, Max Regen Battery Amps and Plug Braking Current) at default setting my PDS cart comes to a complete smooth stop. I'll drive a little more today and see how effective it is down hill

I'm speculating of course, but the amount (intensity) of regen braking when you lift your foot going downhill will probably be the same as it is on level ground, but it may still stop the cart, only it'll travel further before stopping.

By tweaking the three settings mentions we ought to be able to tailor the regen braking for our personal taste and the specific cart's requirements.

On the other hand, I suspect if you go downhill with your foot on the floor, the XCT will reduce the duty cycle of the PWM to zero when you reach the max RPM you've selected and then use regen braking as required to keep it at that RPM.

Had the XCT been available a couple years ago, I'd probably still be running a stock PDS motor.

[yurtle]

Doesn't the stator have to be fully powered in order for the rotor to generate electricity? I'm not all that savvy about generators, but if you have a weak field, won't that affect the amount of juice fed to the batteries?

In other words, if the batts are pretty weak, even going downhill for a while will only do so much?

[scottyb]

Back door exchange with Alltrax about the throttle settings revealed throttle % should be 25 not 80 as these early models were sent.
So tone it down Johnnie and see what you get. I hope to have some program time later on myself.

[JohnnieB]

Originally Posted by scottyb

Back door exchange with Alltrax about the throttle settings revealed throttle % should be 25 not 80 as these early models were sent.
So tone it down Johnnie and see what you get. I hope to have some program time later on myself.

That is an interesting tidbit of information. I'm going to reset it to the default settings, then adjust the Throttle rate to 20% and the Speed curve to something akin to a logarithmic increase, and then start tweaking from there.

---------
A plastic spiderweb with a bunch of mounting holes in it arrived today, but it'll probably be Thursday or Friday before I can use it to remount the XCT.

For those that are not aware of it, there is a raised area on the EZGO heatsink that the PDS controller was mounted on. (See attached picture)

Without using the mounting adapter, it is next to impossible to mount the XCT controller flat against the heatsink surface. I put a washer between the XCT and the heatsink to offset the raised surface, but could only get washers under the top bolts and didn't want to run the risk of flexing the base of the controller, so I only fastened it down at the top.

.

[JohnnieB]

Originally Posted by yurtle

Doesn't the stator have to be fully powered in order for the rotor to generate electricity? I'm not all that savvy about generators, but if you have a weak field, won't that affect the amount of juice fed to the batteries?

In other words, if the batts are pretty weak, even going downhill for a while will only do so much?

The stator (field windings) has to be powered, but not "fully powered".

In very general terms:
* The amount of field current determines the maximum number of amps the armature can produce.
* The voltage produced is determined by the armature RPM, fast it turns, the higher the max voltage.
* The actual amount of current flow is determined by the difference in the battery voltage at the time and the maximum voltage possible at the RPM the armature is turning at.
* When a higher field current is applied, more amps can be produced, which in turn, raises the pack voltage higher.

If the batteries are high enough to move the cart, they can produce enough filed current to slow the cart going downhill. In fact, the lower the pack voltage is, the more regenerative braking you have for a given field current.

Apparently, the XCT varies the field current while in the generator mode to dynamically alter the amount of regen current as the cart slows, but I don't have a saved data log after I got my regen barking to work, so I can't tell for sure. In fact, I'm not entirely sure if it is the Armature or the Field that produces the regen current, again the logs should tell me.

Basically, I'm just starting to scratch the surface on how the XCT works.

[scottyb]

What did you calculate was the max safe ground speed for the stock motor on 18" tires?

[JohnnieB]

Originally Posted by scottyb

What did you calculate was the max safe ground speed for the stock motor on 18" tires?

About 28 MPH, which is about 6,500 RPM at motor.