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Old 10-18-2021, 04:35 PM   #11
Lee0smond
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Default Re: 48V Conversion - No Speed Gain

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Originally Posted by scottyb View Post
D&D is pretty adamant that many of their motors will gain 1-2 mph when going from 36 to 48 volts. They should know they built it? Call them and ask. Let us know what they say
I'll reach out to them.

Just didn't seem right to see 0 speed gain and 0 torque gain going 36v to 48v.
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Old 10-18-2021, 04:51 PM   #12
JohnnieB
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Default Re: 48V Conversion - No Speed Gain

You've got an Alltrax SR controller, so if you have a laptop or similar device, record a data log and post it here.

Use the continuous sampling rate.

The .csv cannot be attached to a BGW post, so zip it and attach the zipped file.

The data log will tell us the battery voltage getting to the controller (B- to B+), the voltage going to the motor (M- to B+), the % throttle and a ton of other info. (Battery amps, motor amps, etc., etc.)
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Old 10-18-2021, 05:52 PM   #13
Lee0smond
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Default Re: 48V Conversion - No Speed Gain

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Originally Posted by JohnnieB View Post
You've got an Alltrax SR controller, so if you have a laptop or similar device, record a data log and post it here.

Use the continuous sampling rate.

The .csv cannot be attached to a BGW post, so zip it and attach the zipped file.
Ok, Zip log attached.

This log is started on flat ground, got up to 18MPH, eased off throttle to take a turn, then back to 100% throttle up a hill at 12MPH.
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File Type: zip Alltrax - Log Test.zip (1.8 KB, 0 views)
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Old 10-18-2021, 05:54 PM   #14
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Default Re: 48V Conversion - No Speed Gain

Am I reading it wrong or does my current look REALLY low?
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Old 10-18-2021, 05:58 PM   #15
Volt_Ampere
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Default Re: 48V Conversion - No Speed Gain

I would say your current looks normal. My full throttle runs on my cart run about 70 to 80 amps. You are hitting high current during accel which is normal. You are getting battery voltage on the motor which is as much as the controller can give you. With a series motor that is all you get. No field weakening like you get in a sepex motor.
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Old 10-18-2021, 06:03 PM   #16
Lee0smond
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Default Re: 48V Conversion - No Speed Gain

Ok. Appreciate the insight. Just disappointing to have 0 impact from the upgrade to 48v. Oh well. Live and learn.
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Old 10-18-2021, 06:37 PM   #17
JRaf
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Default Re: 48V Conversion - No Speed Gain

Wait a minute!
That log is so interesting. But shouldn't the voltage be up above 51? Resting pack voltage? It never gets higher than 49.9.
And, if I'm reading it right, he's getting 320 amps peak into the motor, which seems huge. (The most I've been able to measure with stock Curtis controller and stock motor is 150 amps full blast up a hill... at a blistering 8mph... not that I'm complaining.)
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Old 10-18-2021, 07:13 PM   #18
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Default Re: 48V Conversion - No Speed Gain

The max battery voltage at the controller was only 49.9 and it quickly dropped down to 41.8V when the battery amps hit 270A near the start of the run. This indicates the batteries have a very low capacity or not very well charged.

I'm pretty sure an Interstate GC8 is a 8V-170AH battery, which is what is typically used for a 48V pack and has about the same storage capacity as the standard 36V pack.

New batteries only have about 75% of their rated capacity until they are broken in (two dozen cycles or more), so that may be part of the reason and it is getting cooler, which is another reason for low capacity.

Charge the pack over night and restart the charger in the morning for another cycle. Then do another data log.

The throttle is reaching 100% and when at 100% both battery and motor voltages are the same, as is battery and motor amps, so the controller is passing all the amps the motor can draw at the RPM it is turning with the motor voltage being applied.

If the battery voltage as measured at the controller (B- to B+) can be raised, the motor will speed up some.
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Old 10-18-2021, 07:23 PM   #19
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Default Re: 48V Conversion - No Speed Gain

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Originally Posted by JRaf View Post
Wait a minute!
That log is so interesting. But shouldn't the voltage be up above 51? Resting pack voltage? It never gets higher than 49.9.
And, if I'm reading it right, he's getting 320 amps peak into the motor, which seems huge. (The most I've been able to measure with stock Curtis controller and stock motor is 150 amps full blast up a hill... at a blistering 8mph... not that I'm complaining.)
Due to the flywheel effect, motor amps can be, and most likely will be, higher than battery amps when the PWM is at less than 100% duty cycle.

If you want to measure peak motor amps measure the amps coming out of the controllers M- terminal.
Attached Images
File Type: jpg PWM waveshape at motor.JPG (182.4 KB, 0 views)
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Old 10-18-2021, 07:26 PM   #20
Lee0smond
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Default Re: 48V Conversion - No Speed Gain

Quote:
Originally Posted by JohnnieB View Post
The max battery voltage at the controller was only 49.9 and it quickly dropped down to 41.8V when the battery amps hit 270A near the start of the run. This indicates the batteries have a very low capacity or not very well charged.

I'm pretty sure an Interstate GC8 is a 8V-170AH battery, which is what is typically used for a 48V pack and has about the same storage capacity as the standard 36V pack.

New batteries only have about 75% of their rated capacity until they are broken in (two dozen cycles or more), so that may be part of the reason and it is getting cooler, which is another reason for low capacity.

Charge the pack over night and restart the charger in the morning for another cycle. Then do another data log.

The throttle is reaching 100% and when at 100% both battery and motor voltages are the same, as is battery and motor amps, so the controller is passing all the amps the motor can draw at the RPM it is turning with the motor voltage being applied.

If the battery voltage as measured at the controller (B- to B+) can be raised, the motor will speed up some.

The interstate GC8 batteries are 8V-170AH, correct. 6 x 8v. Batteries were fully charged (charger shut off).

I've only gone through 2 recharge cycles. I knew batteries had a break-in period, but I did not know that they only have about 75% capacity until broken in. I'll keep an eye to see if things change over time.

Also, my batteries are rated at 2.47 absorption per cell, and the charger came preset for 2.40v/cell. It does have an option to increase to 2.45V for charging setting, is that recommended? or is the 2.4v better for longevity? does it actually make a difference?
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