PDS Cart Poor Torque, New Motor

[pastor@southwestbaptist.o]

If HP is only connected to voltage, then amps and a higher amp controller only contributes to acceleration and takeoff? Seems like a upgraded controller is sort of an unnecessary item unless ones wants to take off faster.

From everything I have read on this site, an upgraded controller is supposed to help with steep grades and pulling heavy loads. If it is just voltage, then would the only cure for poor performance on grades be increased voltage?

[davewil@mc.net]

The cart speed is fine on level ground, about 20 mph. But this new motor is supposed to have huge torque. 12 hp at 36 volts, more at 48 volts.
If maximum current of 178 amps seems OK, as some are suggesting, why in the world would a 400 or 500 amp controller be needed?

Is slowing down from 20 mph to about 8 mph on moderate hills "normal" for a cart, especially one with a high torque motor?

SepEx Motor with Regen
12-hp@1300 rpm @ 36 volts
Double Brush set (8 brushes total)
High torque motor
Requires upgraded controller like the DCX500
For maximum performance, safety, and durability, a minimum of 4 gauge cables throughout the cart & heavy duty solenoid are required.
19 Tooth Female Spline
10" housing length, 12" including the sensor.

[davewil@mc.net]

Originally Posted by cgtech

what you guys are failing to consider is that any motor at a speed above a couple hundred rpm can not take the controllers full amp output. also, controllers dont "push" amps into the motor, they only allow the motor access to whatever amps it can use for its current load, up to the max limit of controller output. the only time you will see motor amps that are equal to the controllers max output is during the first few feet when doing a quick full throttle launch from a complete stop. a motor cruising at full speed usually has a amp load around 85a.

A cart cruising at full speed on level ground may only use about 85 amps, but when it gets to a hill it will use a lot more. Another post incorrectly stated that hp is purely a function of voltage. That is incorrect. It is voltage and amps:, here is the formula.
(Volts x Amps x Efficiency)/746

When the throttle of the cart is 100%, the voltage to the cart is about 48 volts. But the amps, and therefore the hp, increases when you go up a hill. Just like a regular car needs more power, hp, to go up a hill.

So the question remains, why is the current only going up to about 178 amps when going up a moderate hill that is greatly slowing down the cart?
If that is the limit the motor can draw, why do motor manufacturers talk about big torque increases going from a 400 amp controller to 500 amps.

At 48 volts X 178 amps X 80% typical motor efficiency/ 746 = 9hp, far below the motor rating of about 16 hp at 48 volts.

[JohnnieB]

The number of amps a series motor draws depends on how fast the armature is spinning and the amount of voltage applied, however the number of amps a sepex motor draws depends on how fast the armature is spinning, the voltage applied to the armature and the amount of field current. With both type motors, the difference between a 400A and a 500A (or a 1000A) controller only exists below the RPM at which the motor is capable of drawing the max amps of the lowest amp controller.

At 8MPH on stock height (18" tall) tires with stock (12.44:1) differential gears, you motor is spinning at 1858 RPM, which is apparently above the RPM that there is a noticeable difference between a DCX400 and a DCX500.

Dropping from 20 MPH on level ground to 8 MPH on a moderate hill (14° or less) is dismal performance, especially with at 48V. The 20 MPH top speed may be about right for a very high torque motor, but the 60% drop in speed isn't.

Your data shows the Battery Amps equal to the Motor amps when the throttle is at 100%, so the armature was drawing all the amps it was capable of drawing at the RPM it was spinning at and the voltage being applied. You also stated the voltage applied to the motor (between A1 & A2 ???) was 46V under heavy load. That indicates the controller is functioning normally and the battery pack as well as the high current cables are doing their jobs adequately.

That leaves Field Mapping. FM#55 is for a GE D1162 motor. You might get better performance from FM#49, which is for a EV7-4001 motor running at 48V.

Best to call Alltrax and find out what the correct Field Map for your specific Make/Model motor is. There may be more than one that will work, some will work better than others in your cart since most carts with after market motors have taller than stock height tires and tire height affects field mapping requirements.

Also, try the cart with Turbo turned off. (Or turned on if it is off)

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FWIW: HP doesn't mean diddle squat, except for advertising and bragging rights, it is how much torque the motor produces at what RPM that counts and how many amps a motor draws determines how much torque it produces.

The amps a motor is capable of drawing decreases as the RPM increases, so the amount of torque generated also decreases as the RPM increases. A series wound DC motor will accelerate until the torque it generates equals the mechanical load imposed upon it. Basically, a carts top speed is the motor RPM at which the torque produced equals the drag of the cart.

When a cart starts climbing a hill, the drag increases, so the motor slows down until it is again capable of drawing the amps needed to produce the torque required to equal the cart's new amount of drag.

A sepex motor works about the same way, except they don't have to slow as much with the same amount of field current for torque to equal the increased drag and the field current is variable (field mapping) so they can be made to slow even less with proper field mapping.

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BTW: The formula you gave is for electrical HP. Mechanical HP is Torque times RPM divided by 5252.

Your motor is rated for 12 HP at 1300 RPM, so it produces about 48.5 ft/lb of torque at that RPM.

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Also, with stock height tires and gears, you probable won't see the motor drawing 500A unless you do a max effort takeoff from a standstill on a steep hill. Or at least that was the only way I could get my motor to draw 500A when I was running a DCX500.

In addition, change the sample rate to continuous when logging data. That will give you about 3 or 4 samples a second and a much better picture of what is happening with your motor, battery and controller.

[davewil@mc.net]

I have emailed Alltrax with the data log and all the cart info. I will report back what they say. Sure would be nice if a different field map would fix the poor preformance.

[davewil@mc.net]

No response from Alltrax today, will resend email to them tomorrow.

[jjance]

You need to call. Alltrax doesn't accept email.

[scottyb]

I get Alltrax email just about every day, so I'm sure the system is working.
Maybe you have the wrong email, I will ask which address you should be using.

[jjance]

I guess they changed that. Up until recently they had a notice that said. Due to being bombarded by junk mail they wouldn't accept email.

[scottyb]

Alltrax emailed me back about their email response......
General tech support is helpdesk@alltraxinc.com answered by Ron
and I use whopper@alltraxinc.com answered by Will