48V to 56V conversion ?

[PuttPutt]

Originally Posted by cgtech

Field windings don't match battery amps or armature amps, it's always significantly lower.

To measure dynamic tire size, I put a chalk line on the tire, point it straight towards the ground, and make a matching mark on the ground, roll the cart forward until the mark points at the ground agaln. Measure the distance between the marks and divide that figure by 3.14159.

Thanks I’ll try that tomorrow.


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[bronsonj]

Originally Posted by disland

@bronsonj what kind of top end speed are you getting with a 48V lithium and the 300AMP Alltrax.

I have a 300amp system club car but thought I would need to change out everything (controller, solenoid, motor etc) to go lithium?

Does it being a club car make a diffefrence in lithium performance?

It's been a while since I've been on the forum, sorry for the delay in responding.

My cart is sepex, I don't know if your cart is sepex or series. Both sepex and series get improved speed with higher voltage but the performance increase between the two types of systems is not the same.

I limit the RPM to 5800 currently and I will be turning that back to 5600 next time I connect it. I have 23" tires and clock in at 32mph. I have the 3 mode personality switch and in middle performance mode I limit it to 4800 and that's really about perfect for my lift and tire size. I feel confident letting any adult operate it up to that speed, I'd guess 24 or 26, but I haven't GPSed. In high performance mode the cart gets squirrly when it gets to 30mph and above.

The 300 amp Alltrax gave me the ability to program what V the cart stops at. With a lithium system you should have a BMS to cut power, but having the controller stop at a pre determined V is a good backup.

Lithium performance is due to no voltage sag and a lot less weight, all cart manufacturers benefit from that.

My setup has a max charge of 58.8v, but i don't charge that high for longevity. I don't know what a CC controller would do on 58.8v, it may let all the magic smoke out or it may work fine or may slowly die...

[PuttPutt]

Originally Posted by cgtech

To measure dynamic tire size, I put a chalk line on the tire, point it straight towards the ground, and make a matching mark on the ground, roll the cart forward until the mark points at the ground agaln. Measure the distance between the marks and divide that figure by 3.14159.

56 9/16

56.5625 / 3.14159 = 18.004 Wow 1/2 different than my first measurement.

[JohnnieB]

Originally Posted by PuttPutt

56 9/16

56.5625 / 3.14159 = 18.004 Wow 1/2 different than my first measurement.

Being a Techno-Nerd, I carry the method cgtech mentioned a step or two further.

Marking and measuring tire's BDC to BDC (Bottom Dead Center) is effectively the same, but I drive the cart for several tire revolutions, then divide the length measured by the number of tire revolutions before dividing by pi. Using more than one tire revolution reduces the errors caused by the chalk line thickness, parallax distortion and other sources.

As odd as it sounds, the effective circumference of the tire changes as weight is added or removed from the cart because the distance between the center point of the axle and the road surface get shorter or longer as the sidewall flexes more or flexes less. So measuring the circumference under actual driving conditions is slightly more accurate.

However, pushing and unloaded cart for one tire revolution is accurate enough for most purposes.

The magic number for a 18.004" tire with 12.44:1 gears in the differential is 232.255 motor revolution per MPH.

[cgtech]

Originally Posted by JohnnieB

Being a Techno-Nerd, I carry the method cgtech mentioned a step or two further.

I do too, but "one revolution" is still generally more accurate than tape measure on the side of the tire.

[JohnnieB]

Originally Posted by PuttPutt

Thanks JohnnieB
-----------------------------

1. I need to do some reading to understand what the field amps mean.

2. I don't understand why with a 500 amp controller I do not see any readings close to 500.

3. In the log files is current the same as amps? Battery current, motor current.

4. Cart used to hit 6000 rpm on level ground but not anymore.

5. Batteries are just under 100% on state of charge (after sitting a couple days off charger. is that enough to make 500 rpm difference?

1. First a little motor theory using a series wound DC motor. If the electromagnet created by the field windings (aka stator) is relatively strong relative to the electromagnet created by the movable windings (armature), the motor will have high low end torque, but will not reach high RPM. Conversely, if the electromagnet created by the field windings is relatively weak relative to the electromagnet created by the movable windings, the motor will have low low end torque, but will reach high RPM. Since the very same amps flow through the stator and armature in a series motor, whether it is a high-torque motor or a high-speed motor or something in between is cast in stone by the number of turns of wire used in the stator and armature winding at the factory.

The motor you have in your cart is a sepex (separately excited) and the field winding is excited (powered) separately from the armature. Again the number of turns of wire in the respective windings determine if it is a high-torque or a high-speed motor, but its speed/torque curve can be shifted towards either type by increasing or reducing the amp flow through the field windings. This can be done during operation via a process known as field mapping.

The field windings of a sepex motor contain a huge number of turns of wire, so very few amps can create a very strong electromagnet and maximum field current is typically 10% or less than armature current. Sepex controllers have two PWM (pulse width modulation) outputs, a high power one for the armature and a low power bipolar one for the field. (Reversing the direction the motor spins is done by reversing direction of current flow in field windings.)

In a nutshell, when more low end torque is called for the amount of field current is increased and when more RPM's are called for the field amps are reduced, effective transitioning from a higher-torque motor to a higher-speed motor on the fly.

2. The motor and the motor's RPM determine amp flow through the controller. All the controller can do is limit the number of amps a motor can draw.

If you put a loop of wire in a magnetic filed and run some current through it, it will move (motor) and if you move a wire in a magnetic filed a current is induced into the wire (generator). When the armature of a motor isn't moving (stalled) the number of amps it can draw is only limited by the DC resistance of the wires in the windings. However, when the armature starts turning, you have loops of wire moving in a magnetic field and amps are generated, which happen to oppose the the amps flowing to turn the armature. The net result is the faster the armature spins, the fewer amps the armature is capable drawing.

If you did a max acceleration effort from a standstill on a steep incline, or tried to pull a cabin cruiser out of the water, you might approach the 575A a XCT48500 is capable of passing when in peak amp mode.

3. Yes, current is another word for amps. In the data logs, the column labeled motor current is actually armature amps since field amps are listed separately.

4. I don't see anything that caused this. Maybe dragging brake shoes, gummed up bearings, cooler temperatures, lower pressure in tires.

Also, the XCT starts backing off on the duty cycle of the PWM output as the motor RPM approaches the max limit. Try upping the limit to 6500. That ought to tell you if the XCT is what is holding the cart back.

5. Maybe. Max motor RPM (max cart speed) is determined by applied voltage and the more amps drawn during acceleration to speed, the greater battery voltage drop. Battery voltage drops instantly when amps are drawn, but recover slowly, so for max speed accelerate slowly.