HELP! 98 EZGO TXT 36v - Low Torque & Low Top Speed

[offthemap]

Originally Posted by JohnnieB

Sounds like you have a 36V Series drive with 22" tires and might be a bit on the heavy side. (Rear seat. winch, Clays basket, Etc.)

A typical 36V series drive on stock height (18") tires does about 14 MPH, so with 22" tires it should do about 17 MPH, mathematically.
Sounds like you have good batteries and good cables and you say it doesn't have brake drag, so I suspect you have tires whose max inflation pressure is 10 PSI or less.

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The percent throttle is actually the percent duty cycle of the PWM output to the motor.

When the Output Current and Battery Current read exactly the same amount, the controller is wide open.

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The number of amps a motor can draw depends on how fast the armature is spinning. I suspect the motor was spinning at 1500 RPM (about 8 MPH on 22" tires) when it was drawing 140A. Your stock motor might be able to draw all the amps the 400A controller will pass when starting from a standstill, but the amps will drop off fairly quick as the cart accelerates through walking speed and beyond.

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I don't like the battery that has a 5.9V reading while the others are all 6.2V or higher. A bad battery can cause problems like you are having.

Measure and record the battery voltages when they are fully charged.
Drive cart 4 or 5 miles, let the batteries rest for half an hour and then measure and record the battery voltages again. They should all six loose the same amount of voltage.

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When you do your testing with the laptop attached to controller, have Controller Pro save the data file on the laptop. Then it can be reviewed after the fact.

What do you mean by PWM?

So IF the 5.9v battery is bad/weak, it will restrict the motor from spinning at the proper RPM's to create the 400A draw that my controller is capable of?

What if the battery isn't bad? What restricts the RPM'S at that point? Insufficient voltage?

[cwayaustx]

The 5a charger throws a huge red flag to me. Everything else should be good to turn the tires uphill, no problem.Your top speed says you have a torque motor but your lack of torque says otherwise, then I see 5 amp charger... Your not getting a full charge.. add two more batteries and buy a delta-q 48v.. I watched a new one go on eBay for 156$ only because I didn't need another one..

[JohnnieB]

Originally Posted by offthemap

1. I understand that I shouldn't expect to gain any top end with my setup if I were to add the Axe 4844 right now, but is it normal for me to be seeing nearly 50% less speed on mild hills in my neighborhood?

2. What about the amperage readout? I NEVER saw it get above 140a at any point in my run. Therefore I'm looking at this as if my controller isn't capable of allowing/giving the 400 amps it's rated for. Am I wrong about that logic? (I hope I am!)

1. Slowing more than 50% probably isn't normal, but all DC cart motors slow when the mechanical load increases and going uphill increases the mechanical load. How much it slows depends on several factors.

To name a few:
Series wound motors slow more than SepEx (shunt wound) motors
Carts with taller tires slow more than carts with shorter tires.
Heavier carts slow more than lighter carts.
Carts with battery packs whose voltage drops further proportionally for the amps being drawn, slow more.

Have the laptop save the data so you (and others) can review it when you are not preoccupied with driving the cart.

2. When the Throttle% is at 100 and Output amps equals the Battery amps, the controller is passing all the amps the motor is requesting, so 140A is all that the motor is asking for.

How many amps a series wound DC motor requests depends on the motor's RPM and the voltage applied to the motor.

A series wound DC motor will draw maximum amps when stalled and minimum amps when spinning at its highest achievable RPM for the voltage being applied to it.

Look at the Battery Voltage column on the saved data log while going up hills.

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You can also monitor the voltage between the B- and B+ terminals on the controller.

You posted that the battery pack voltage dropped to 34.4 on mild hills, but what is the voltage the controller sees? If there are any bad cables, connections or contacts, the voltage between B- and B+ at the controller terminals will be less than what is measured at the main plus and minus terminals of the battery pack.

The find out how much voltage is being applied to the motor, monitor the voltage between the M- and B+ terminals on the controller.

If the voltage between B- and B+ equals the voltage between M- and B+ when climbing a hill with the throttle pedal on floor, the controller is not limiting the motor in any way.

[JohnnieB]

Originally Posted by offthemap

1. What do you mean by PWM?

2. So IF the 5.9v battery is bad/weak, it will restrict the motor from spinning at the proper RPM's to create the 400A draw that my controller is capable of?

3. What if the battery isn't bad? What restricts the RPM'S at that point? Insufficient voltage?

1. Pulse Width Modulation. The output of the controller to the motor is chopped DC. The transistors (MOSFETs) in the output circuit are turned on and off about 18,000 times a second and how long they stay on during each of those time periods determines how much of the electrical energy being applied to the controllers input circuitry is passed on to the motor.

2. The motor's RPM determines how many amps it can draw for the voltage being applied to it. A bad battery will reduce the voltage applied to the motor, so it will draw fewer amps for the RPM it is spinning at.

Your motor is only capable of drawing 400A when it is spinning below a certain RPM. If the motor is spinning above that RPM, it doesn't matter if the controller can pass 400A, 500A or 2,000A, the motor will draw less than 400A.

3. The torque produced by a series wound DC motor is directly proportional to the amps flowing through it and the amp flow is inversely proportional to the motor's RPM. Therefore a series wound DC motor will accelerate (increase in RPM) until the torque being produced by the amp flow equals the mechanical load (drag) being applied to the motor.

If the voltage being applied to the motor is decreased, the amp flow decreases (Ohm's Law), so less torque is produced and the motor slows until the torque being produce once again matches the mechanical load being applied.

If the battery pack voltage isn't dropping excessively, or the voltage between B- and B+ at the controller isn't dropping excessively, the mechanical load on the motor is excessive for the motor, or the motor is bad.
(Worn brushes? Build up of carbon dust inside motor case providing a bypass around motor windings?)

[offthemap]

Originally Posted by cwayaustx

The 5a charger throws a huge red flag to me. Everything else should be good to turn the tires uphill, no problem.Your top speed says you have a torque motor but your lack of torque says otherwise, then I see 5 amp charger... Your not getting a full charge.. add two more batteries and buy a delta-q 48v.. I watched a new one go on eBay for 156$ only because I didn't need another one..

I have been thinking this too.. but my pack reads 38.3v and it's been 32 hours since it was on the charger....?

[offthemap]

Originally Posted by JohnnieB

1. Slowing more than 50% probably isn't normal, but all DC cart motors slow when the mechanical load increases and going uphill increases the mechanical load. How much it slows depends on several factors.

To name a few:
Series wound motors slow more than SepEx (shunt wound) motors
Carts with taller tires slow more than carts with shorter tires.
Heavier carts slow more than lighter carts.
Carts with battery packs whose voltage drops further proportionally for the amps being drawn, slow more.

Have the laptop save the data so you (and others) can review it when you are not preoccupied with driving the cart.

2. When the Throttle% is at 100 and Output amps equals the Battery amps, the controller is passing all the amps the motor is requesting, so 140A is all that the motor is asking for.

How many amps a series wound DC motor requests depends on the motor's RPM and the voltage applied to the motor.

A series wound DC motor will draw maximum amps when stalled and minimum amps when spinning at its highest achievable RPM for the voltage being applied to it.

Look at the Battery Voltage column on the saved data log while going up hills.

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You can also monitor the voltage between the B- and B+ terminals on the controller.

You posted that the battery pack voltage dropped to 34.4 on mild hills, but what is the voltage the controller sees? If there are any bad cables, connections or contacts, the voltage between B- and B+ at the controller terminals will be less than what is measured at the main plus and minus terminals of the battery pack.

The find out how much voltage is being applied to the motor, monitor the voltage between the M- and B+ terminals on the controller.

If the voltage between B- and B+ equals the voltage between M- and B+ when climbing a hill with the throttle pedal on floor, the controller is not limiting the motor in any way.

Johnnie, you're the man! These are very specific answers that are helping me out tremendously. Thank you.

I think the reason I'm so interested in this cart is because I basically didn't know very much about DC electricity before I bought it but you guys have taken me to school on it!

So back to one of my original questions, could a bad ITS limit the amount of amps that the motor is "asking" for or drawing?

If I were to take my motor and send it to plum quick, would the re-work be something that would make the motor draw more amps (140a+) or would it just increase the efficiency of the motor to utilize the amps that are currently being delivered (140a)?

I think my answer to that question is that my amps won't increase UNTIL there is more voltage applied...

[JohnnieB]

Originally Posted by offthemap

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1. So back to one of my original questions, could a bad ITS limit the amount of amps that the motor is "asking" for or drawing?

2. If I were to take my motor and send it to plum quick, would the re-work be something that would make the motor draw more amps (140a+) or would it just increase the efficiency of the motor to utilize the amps that are currently being delivered (140a)?

3. I think my answer to that question is that my amps won't increase UNTIL there is more voltage applied...

1. Yes, or at least a bad ITS could limit the amount of amps the controller passes. However, when the Battery Current and the Output Current are equal, the controller isn't doing any limiting. Also, the Throttle% is going to 100% and if the ITS signal wasn't okay, it wouldn't be going to 100%.

Another indicator is the LED on the controller. If you can figure out a way to see the LED on the controller while you are climbing a hill, you will probable see it turn to yellow or orange, meaning the throttle is at 100% and the controller is not in current limiting.

You can also jack the rear tires off the ground (put on jackstands) and floor the pedal for a second or two. The LED should turn Yellow.

2. That is getting a bit into comparing apples to oranges. When PQ re-works a motor, it does not have the same Torque vs RPM curve as a stock motor, so the amps at the RPM at which your motor now draws 140A, could be higher or lower depending on they way they re-wind it.

If there is a heavy carbon dust buildup in the motor, cleaning it out will improve the apparent efficiency.

3. You will get more amps when you increase the pack voltage, but I don't think you are checking the amps in the RPM range that you motor can draw more than about 150A or so.

What is the cart speed when you see 140A going uphill?

Try this: With a fully charged battery, stop midway up a hill and monitor the amps (better still save the data log file on a laptop) while accelerating from a standstill with the pedal on the floor.

[offthemap]

Ok, I will run those two tests in a bit. I did just check all of the batteries individually and they came out to be 4 @ 6.39v & 2 @ 6.4v. So that's good news.