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Discussion Starter · #1 ·
Hello all,

I just finished building a home made "mini" golf cart. I am having issues with the motor stalling though.
MOTOR Specs:
1000W - 48V Brushless Motor with gear reduction 1:5
Model: BM1412ZXF
1000W 48V rated controller
Full load current :28A / No load current: 5A
Rated Torque : 3.4 N.m
Rated RPM: 2850rpm motor / 570rpm shaft after gear reduction
SPROCKET:
Motor Sprocket: 20 T
Axle Sprocket: 41T
TIRES:
15" Tires
BATTERIES:
4x 12V 8Ah with 6-AWG Wires
LOAD:
~350lb Golf Cart + ~180lb Driver

Initially the motor came with a 14T sprocket, and I had 13" Tires installed. The golf cart was accelerating well but I had a max speed of 9mph. The top speed I am looking to achieve is about 13mph so i decided to change the motor sprocket to 20T and install bigger tires. That is when the issues began.

The golf cart stalls when I press the pedal throttle. It tries to start moving but it seems that the controller cuts off power to the motor. It feels like a lot of torque and instantly stalls. I have to let the pedal go and try again. Sometimes, if I press the pedal very slowly, it starts moving, yet it keeps stalling, thus never reaches max speed.
Surprisingly, I have no issues with reverse on flat ground, but sometimes the motor stalls when I try to go reverse over a driveway "curb" or in the grass.
It also feels like it generates a lot of torque once I initially press the pedal, (both forward and reverse), meaning no smooth acceleration at low rpm.
I understand that by changing the sprocket ratio to gain speed, I also loose torque, yet the motor seems to initially "kick" strong for a second, just before it stalls. Also it is good to mention that the motor does NOT get hot at all !!
I checked the batteries individually under load as well as a pack and they seem OK. They are 8Ah batteries, but once I get the golf cart fine tuned I will purchase good 35Ah batteries.

Now, below are my thoughts in regards to the cause of the issue and I will appreciate any support/suggestions based on your knowledge and experience.
A. The pedal might be defective (Chinese unbranded pedal)
B. The Controller is damaged
C. The sprocket ratio is way off the maximum capabilities of the motor

Possible Solutions that I am thinking:
A. Go back to 14T motor sprocket (or maybe try 16T), sacrificing max speed but gaining torque
B. Replace the pedal and/or controller (costly solution without solid confirmation that will resolve the issue)
C. Replace the motor and controller to 48V or 60V but 2000W. (costly and yet still unknown if the problem is the existing controller failing)
D. Over volt my existing 48V/1000W motor to 60V. (chance to burn the motor and also I will need to purchase a new controller since my existing controller is rated 48V 1000W). BUT I will appreciate your thoughts on this topic since I haven't over volt a motor yet.

I will appreciate any support/suggestions based on your knowledge and experience, in order to resolve this issue.

Thank you.
L-L
 

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You definitely need more torque, could be few reasons for controller to cut off, the draw of current or over heating, etc
 

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Discussion Starter · #3 · (Edited)
True, but the controller is not overheating, the 6AWG battery cables are not getting hot, and also the motor is not getting hot.
I am thinking to install a 48v-72V 1500W controller and hook it up to my 48V 1000W BLDC motor. Also reduce the motor sprocket to 14T instead 20T.
Initially I will try it with 48V battery pack and evaluate the performance.
If it stalls or if the max speed is too low, I will overvolt the motor to 60V and see if it gets any better.

Any comments/ideas?
 

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Going from 14 teeth to 20 teeth on your motor sprocket(plus the larger diameter tires) is a huge final drive ratio jump. Try increasing the number of teeth on the motor sprocket one or two at a time You're trying to use a relatively small, low power motor in an application that typically uses a much larger and heavier minimum ~ 2-3kW motor. You may be slamming the current limit on the controller so quickly that the motor, controller, and cables don't have time to heat-up.

Also, I just noticed you are using tiny, 8Ah LA batteries! That's only ~20 lbs of batteries. A typical golf cart uses ~100-300lbs or more of LA batteries. You have things way out of proportion here! As well as over-current controller shutdown, you probably have a steep voltage drop that triggers a controller low voltage shutdown. You can verify this with a voltage meter and an ammeter(a clip-on type will do for temporary use).
 

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Discussion Starter · #5 ·
Thank you electro wrks,
Indeed I am currently using small 8ah batteries. I take the extra weight of larger batteries under consideration though.
I just want to make sure that the concept will work before investing into 35ah+ batteries since good 35ah batteries are quite expensive. The small 8ah batteries I am using are brand new though and I checked the initial voltage drop of the entire pack as well as individually without noticing any significant drop.
Unfortunately, my YALU motor uses dual D-bore sprocket and I can't find different sizes in the US. I had to order the 20T from abroad (40-days to arrive). My only other option is 16T, again from abroad...meaning another month or so to arrive.
I will purchase and install a Digital Current/Voltage/ Power/Energy Meter though in order to have a better view of the actual measurements.
I agree that golf carts use 2-3kW motors, but this is a lightweight cart, similar to Cricket RX-5 which apparently uses 800W or 1000W BLDC motors @ 36V or 48V, thus the reason i am thinking to try my 1000w/48V motor with a 1500W/48V-72V controller, overvolting it to 60V and also go back to 14T motor sprocket instead of the 20T sprocket. I understand that overvolting will only increase the rpm and also help the motor to run at its max power. I don't think that going from 48v to 60v will damage the motor. Also the motor has a fan, so hopefully it will not overheat.

Any comments/ideas will be much appreciated.

L-L
 

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Discussion Starter · #6 ·
....Update: I reinstalled the 14T sprocket. It still stalls on initial acceleration but not as bad as with the 20T motor sprocket. If I press the pedal slowly, it does not stall and it drives to its max speed.
The weird part is that it runs just fine on reverse. Zero stalling on reverse.
 

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Check your voltage drop and current in both directions. Reverse function with some controllers limits power to reduce speed in reverse, as a safety feature. The motor ratings for the Cricket might be a continuous one. Your motor may have more of a peak rating.
 

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Discussion Starter · #8 ·
Update: I bought a 48/60/72V 1500W Controller and replaced my old 48V 1000W controller. Still the same 48V 1000W BLDC Motor with gear reduction 1:5 and motor sprocket 14T. NO MORE stalling !!! It seems that the controller did the trick.
Yet I only get 9 mph which is not what my goal is...but that was expected. The cart drives smoothly on the road and on the lawn. Both Controller and motor do not get hot.
I will try the 20T sprocket just to check if the motor will start to stall again. Since this controller is 48/60/72V, I am thinking to overvolt it to 60V to see the effect on the performance. I am not sure which test is better to try first...60V will result to more rpm, meaning higher speed but might result to stalling and pushing the motor to its max. On the other hand, 20T sprocket will result to higher speed but possibly causing the motor to stall. Any suggestions?

Thank you.
 

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Update: I bought a 48/60/72V 1500W Controller and replaced my old 48V 1000W controller. Still the same 48V 1000W BLDC Motor with gear reduction 1:5 and motor sprocket 14T. NO MORE stalling !!! It seems that the controller did the trick.
Yet I only get 9 mph which is not what my goal is...but that was expected. The cart drives smoothly on the road and on the lawn. Both Controller and motor do not get hot.
I will try the 20T sprocket just to check if the motor will start to stall again. Since this controller is 48/60/72V, I am thinking to overvolt it to 60V to see the effect on the performance. I am not sure which test is better to try first...60V will result to more rpm, meaning higher speed but might result to stalling and pushing the motor to its max. On the other hand, 20T sprocket will result to higher speed but possibly causing the motor to stall. Any suggestions?

Thank you.
Did you overvolt? / sprocket change again?
 
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