PDS Selectable Chip

[JohnnieB]

If your friend's truck has oversized tires, his speedometer will read low.
The GPS system has the capability of being very accurate, but the receivers available on the civilian market can vary quite a bit in positioning accuracy.
The way they calculate speed is: You are at point A and then you are at point B and it took this much time to get there, therefore you traveled at X MPH between those two points.

If your GPS receiver has a screen that shows the satellite galaxy that is visible to it, it will probably indicate what the circular error is. (estimated positioning accuracy)
If it is 10', the speed will be fairly accurate, if it is 100', the speed won't be as accurate.
However, in either case, it will most likely be more accurate than the speedometer in a car or pickup.

I used a two 1x2 furring strips nailed to the asphalt of a backroad 20' apart and a stop watch to measure the top speed of my cart in Freedom mode.
I started and stopped the stopwatch when I heard/felt the front tires hit the strip, which more or less nullified my thumb's reaction time on the watch button.
I got a repeatable 18.2MPH on Carlisle Links 18x8.50-8 tires, inflated to 20.0PSI, which have the mounted height of 17.4".
With a 12.44:1 rear end ratio, the motor was spinning at 4,374 RPM at that speed.

With a GPS, I get from 18.0 to 19.5 MPH.

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I believe PDS controllers limit motor RPM to about 4,400 RPM in Freedom mode, which (Mathematically) would about 21 MPH on 20" tires and about 23MPH on 22" tires.

If you are not reaching those speeds, I suspect you are running out of Amps for some reason or another.

It takes more amps to turn bigger tires and PDS controllers are limited to 300A or 350A depending on the version installed.
Problem could also be resistance in the high current cables and/or connections.
Or it could be batteries are not capable of supplying the amps needed.
Maybe a combination of the three.

[bigpoppi]

Well, giving me yet another reason why I should have started from scratch, I thinks I'll be looking into some 2 gauge wires to start, figure start small, I'll be calling Scottyb for those, plus I'll be needing them when i get to 48v.

[bigpoppi]

Well, late yesterday, I took the cart for a spin, one to drain the batteries a bit, and recharge.. I hooked up the GPS and straight out running up and down my street with mild inclines and declines, 16 to 18 mph.... so, sometime soon, i'll be ordering the 2gauge cables.. if there could be another avenue to persue, let me know. speed sensor? cleaning of the cables? buy another cart??lol

[JohnnieB]

The easy one first.
The speed sensor is okay or cart wouldn't do 16-18MPH.

The high current passes through 10 cables, so there are 20 connections that need to be cleaned.
The 12 on the batteries are the ones most likely to be corroded, but they should all be spotless and tight
(Note: Max torque on the battery terminal nuts is 10 Ft/Lb)
Warning: Be sure to use two wrenches on motor terminals. Hold bottom nut from turning, or you mess up the connections inside motor

The two smaller cables between controller F1&F2 and motor F1&F2 don't carry nearly as much current, but make sure those cables are in good condition and the connections are clean also.

Attach a DVM between B- and M- on controller and monitor while driving.
When flat out, the voltage measured should be less than about 2V or so.
(Tech note: The voltage drop across the MOSFETs when conducting, is about 0.5V per 100A. Might be more, might be less, I can't find that spec for a Curtis 1206MX. or a 1206 of any flavor.)

If it is more than that, the controller isn't being turn on fully, so check out the ITS (Throttle), it might not be telling the controller to turn all the way on.

If it is 2V or less, attach the DVM leads across the various high current cables and monitor while flat out.
Any voltage drop at all measured across any of the high current cables is a power loss.

Why buy a different cart, you've got one of the best.

[bigstik40]

Something else to consider is how "free wheeling" your cart is. Some brake drag could easily knock off 2-3 mph. from your top speed. Another item to consider is how much air is in your tires. Harder tires will be faster (less rolling resistance). These will be the "free" miles per hour you gain. - RAY

[bigpoppi]

Well, today will be cleaning the terminals, checking the connections, and testing connections... while doing the open throttle checks, can this be done with the cart on jack stands, and is the ITS(throttle) , under the floor boards, so I might check and clean that? Also, seeing as I'm at work and the carts not here, are the B- and M- posts clearly marked?

Not to sound lost, but DVM=digital volt meter...... B-=Battery-... M-=motor-???? I'm guessing all is self explanitory and an easy layout....

Tire Pressure--- tire says to inflate to 35 lbs to seat the bead, 5lbs run operation, I just about a week ago bled my pressure down from 15 to 7lbs, I understand 'less pressure= more rolling resistance', but less pressure = more pleasurable ride...

Free wheelin, when I let off the 'juice', I don't notice any drag from breaks, speaking of last night, more of normal rolling resistance from low tire pressure...

I'll continue to persue my avenues, finding obstacles, asking you guys.....

Thanx Johnnie and Bigstik

[JohnnieB]

My bad....
On a PDS controller, the three big terminals on top of it are labeled B+, B- and A1 (A1 is the shorter of the 3)
Digital Volt Meter goes between B- and A1 (Might be labeled M1 on some PDS controllers)
The MOSFETs are electrically located between those two terminals.
They are turned on and off about 18,000 times a second and the ratio of how long the are on vs how long they are off (Duty Cycle) determines how much current is allowed to flow through motor. The longer they stay on during each pulse, the less the voltage will be across those two terminals.

When troubleshooting a non-running cart, this test is best done while on jackstands, but in this case, we are looking for something that happens under load, so it would probably be best to attach the test leads with alligator clips and monitor while driving, or have a passenger watch meter.

Also, you don't want to run the motor very long at full throttle with wheels off the ground.

Tire pressure. Kick the tires up to max pressure given on side wall and check speed.
Then adjust tire pressure for comfort vs speed. Like everything else about carts, it is a compromise.

[bigpoppi]

Can I use the DVM that Scottyb has on his posts?? the one that goes in the dash. if not, I have a voltage meter I can fab to hook to the terminals.. so ya! i have home work..

[ncfenceguy]

Just FYI Bigpoppi,
I've timed and tested 2 stock pds carts with the freedom chip,(not mine), fully charged (but not right off the charger) 2 and 3 year old batteries, stock tires w/15 psi on perfectly flat pavement. One was 18.9 mph and the other was 18.7. No aftermarket on either cart. No tires, lift,etc...

The PDS cart that I used to own in my avatar was 19.5 but it had harder low profile tires.

Scotty B. can hook you up with a PDS controller and wires that he says will be in the 23-24 mph range if thats your problem. I ordered those from him yesterday for a customer of mine (carts in my shop with a bad controller) and I can let you know how they work next week.

[bigpoppi]

Planning to get the #909 pkg from Scottyb, looking to add 2 batteries in spring and the 909 and 2 gauge cables... more torque and 24mph is what I'm shooting for.. so hoping that the 909 gets me there.. drove the cart 2 nights ago, batteries drained to 37.2, charged over night, back to 38.3 by morning..pulled the plug... checked this morning and still 38.3.. so they hold a charge, will take for a drive today and drain and charge.. trying to cycle the batteries more often.. adding pressure up to 15lbs in tires and will see what gps says tonight.. question on the discharging, will going below 37v, say to 36 v or 35v, hurt or do drastic damage to the batteries, i.e. if I run around all afternoon, and when I get home it's reading 35v and then I start charging...?

Just curious..