Increasing Range on a 36 Volt EZGO TXT PDS Golf Cart

Glen Batchelor

Active Member

The increase in magnetic force between the two coils is directly relational to the voltage increase. The 48V circuit is 36.4% higher in voltage and power so the motor speed is going to be 36.4% higher. Will it draw 36.4% more current or the same amount? Let's look at Ohm's law related to power, current and voltage. What's not taken into account in this circuit is increased magnetic resistance (flux) between the two coils due to a higher voltage being applied. The motor manufacturer records that as a percentage increase in usable power (max torque and rotor speed). In math, it looks like they are equal in current draw but you net a higher power output. In reality the flux increase will likely cause increase magnetic resistance and therefore an increase in current draw that can not be demonstrated here with a basic Ohm's law for power over voltage.

2.4HP = ~1790W
1790W * 1.364 = 2443W or ~3.2HP
36V * 1.364 = ~49V

P=IV
1790W = I * 36 = ~50A (1790 / 36)
2443W = I * 49 = ~50A (2443 / 49)

I'll try to video a test on my shunt wound motor this week.
 

gornoman

Well-Known Member
The issue is not how much power any given motor will produce across a variable voltage selection. The discussion is how much current it takes to perform a constant task vs different voltages. I’m sorry you can’t get past this point. Must be too busy trying to lick your wounds over being bounced off of a forum to think straight.
In one sentence you agree with me, and the next you hurl insults. Can’t fix stupid.
 

HotRodCarts

Cartaholic
When you were running at 20% and 40% at 36 volts and 48 volts the RPM of the motor was probably higher at those percentages with 48 volts due to the higher voltage. :twocents:

I would think in order to get a accurate difference in amp draw at both voltages you would need to be running the motor at the same RPM at both voltages instead of throttle percentage.
 

gornoman

Well-Known Member
When you were running at 20% and 40% at 36 volts and 48 volts the RPM of the motor was probably higher at those percentages with 48 volts due to the higher voltage. :twocents:

I would think in order to get a accurate difference in amp draw at both voltages you would need to be running the motor at the same RPM at both voltages instead of throttle percentage.

Even more accurate would be to run the cart to the same gps determined road speed under the same load. Thank you Rod for pointing out this major testing discrepancy.
 

Glen Batchelor

Active Member
Like I said you need to do a real road test due to coil-to-coil resistance. I was merely showing no load variances between voltages. Feel free to do a road test video.
 

Diode

Cartaholic - V.I.P. Sponsor
When you were running at 20% and 40% at 36 volts and 48 volts the RPM of the motor was probably higher at those percentages with 48 volts due to the higher voltage. :twocents:

I would think in order to get a accurate difference in amp draw at both voltages you would need to be running the motor at the same RPM at both voltages instead of throttle percentage.

If he had of tested this way the results would have been exactly the same, you need to remember the controller is putting out PWM signal to the motor, the motor only sees this as a lower or higher voltage so the motor would see 36 (lower because the motor would fly apart at full throttle) volts on both tests.
If he had a volt meter on the motor leads for this test the 36 volt reading would have been lower than 36 volts and the 48 volt test would have been lower than 48 volts the meter would read average of the voltage just like the motor sees.
You need to understand the same voltage is the same RPM, current will vary depending on load.
 

Diode

Cartaholic - V.I.P. Sponsor
If he had of tested this way the results would have been exactly the same both @ 36 volts what would you expect to change, you need to remember the controller is putting out PWM signal to the motor, the motor only sees this as a lower or higher voltage so the motor would see 36 (lower because the motor would fly apart at full throttle) volts on both tests.
If he had a volt meter on the motor leads for this test the 36 volt reading would have been lower than 36 volts and the 48 volt test would have been lower than 48 volts the meter would read average of the voltage just like the motor sees.
You need to understand the same voltage is the same RPM, current will vary depending on load.

Volts = Speed / RPM
Current = Torque / Runtime
 

Glen Batchelor

Active Member
The maximum speed of the rotor will be relational to the voltage. The current draw will vary based on net flux in the coils. You have two opposing coils that create magnetic resistance to each other which in turn affects the flux field for each individually. If you view the Alltrax monitor segments of the video you see that the free-wheeling controller output is all over the place but the battery draw is fairly consistent. This is because the controller is managing the current output(motor RPM/throttle ratio) between the shunt stator coil and the rotor coil. The gearing in the differential, wear spots in the bearings and axle/wheel inertia is likely causing dips and peaks in physical motor load as it runs the drivetrain. The motor RPM should be consistent if the controller has proper current feedback control. I will be happy to email Alltrax and ask how they manage PDS throttle/RPM ratio if you guys are that concerned about testing methods. PDS does not use a magnetic rotor sensor for feedback like DCS does. I will also ask them if 48V on that DCX400 will net more run time at a specific throttle setting.
 

HotRodCarts

Cartaholic
Back to the OP's question which was would eight 6 volt batteries have more run time than six 8 volt batteries. I think we can all agree that he would definitely get more run time with eight 6 volt batteries. :hattip:
 

Glen Batchelor

Active Member
Depends on the motor and batteries. Same amp/hour batteries and motor? I would think so just from a throttle usage pattern change. If you install lower amperage batteries with smaller cells, no it will be much less.
 
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