General Category > Electric/Hybrid Car Conversion
Club Car with 10kw and 500A controller. Only 21mph??
Apcerame:
Attempting to dive into a friends golf cart. He purchased a 48V 10kW motor and a VEC500 controller. The cart runs good, a little jerky, but maxs out at 21 mph.
Looking at the motor specs, the motor should turn up to 6000 rpm.
I know speed will depend on gearing/wheel size. But is there anyway to check motor rpm? Like reading the position sensor of the motor with a dmm?
I’ve dug a little into the programming, is there any settings I should look at? What’s the max rpm the VEC500 can do?
Bikemad:
Hi andto the forum.
According to the dynamometer test data for the 10kW motor on 48v, it is only rated for 10kW@3,500rpm and the maximum recorded speed under minimal load appears to be 4,733rpm.
The GM 10kW motor can only produce 10kW of power at motor speeds up to ~3,515rpm, above this rpm, the maximum available power will gradually drop off.
If you look at the motor test curve you can see that the power output (Pout[W]) only increases as the rpm (N[rpm]) reduce.
Below 3,500rpm, the battery and/or controller's current limitation will determine the maximum power.
Your battery and controller would need to be able to supply at least 270 Amps to achieve a power output of 10kW, but the VEC500-48 controller appears to have a 200A maximum current rating. ???
Looking at the Dyno figures, I estimate that 200A would produce a maximum output of ~8.05kW@3790rpm.
If you want to gear it for maximum speed, and don't want it to climb hills, you will need to ensure that the rpm is ~3750 at the calculated maximum speed to enable the full 8.05kW of power to be available at this speed on the level.
However, if maximum hill climbing speed is more important, then you will need to reduce the gearing to suit the calculated maximum speed that 8.05kW of power can propel the vehicle up the maximum anticipated incline.
If more power is required at lower speeds for quicker acceleration (and the batteries are able to supply the required current) you would need to use dual VEC500-48 controllers (one for each of the two phase wire/Hall sensor sets).
Alan
Apcerame:
Hey Alan, thanks for the detailed response.
So if you don’t mind, I’m going to keep asking questions.
I understand AC motor theory and rpm being mainly based on frequency. I understand Rpm in DC motors is from voltage. And both on other factors engineered into the motor. I’m also familiar with VFDs on AC motors.
So in my head I’m thinking a brushless dc motor controller works a lot like a VFD, in that it is cycling/pulsing the stator currents. So the faster the pulses, the faster the motor spins.
Is this thought right? Thanks, Anthony.
Bikemad:
Hi Anthony,
Here's my interpretation, I think PWM is used to control the current and the three Hall sensors embedded in the stator simply control the switching of the individual phases relative to the position of the magnets on the rotor.
Although it may be possible to electronically alter the motor timing to some extent, the actual speed at which the switching occurs will always be directly linked to the rpm of the motor shaft/rotor, because if it was switched any faster (or any slower) the motor timing would instantly be lost.
The maximum unloaded speed of the motor will ultimately be governed by the battery voltage, and the rpm/volts ratio will be determined by the number of turns and the thickness of copper wire used for the stator coil windings.
At speeds below the motor's maximum rpm, the torque and/or speed can be controlled by adjusting the average current (and presumably the average voltage too) by using PWM control.
Here is my representation of a very simple MOSFET power circuit that could be used to control the DC phase switching if the MOSFETS were directly controlled by three Hall sensors.
Please Note: The Hall sensors and additional circuitry is not shown, this was done to keep the power circuit diagram as simple as possible:
If the Hall sensors switched the MOSFETS either 100% High or 100% low with no PWM control whatsoever, they would effectively function as an electronic commutator, and the motor would simply run at maximum power/speed from the fixed voltage battery.
However, if the fixed voltage battery was replaced by a variable voltage power supply, the power/speed of the motor could then be controlled by varying the supply voltage just like you can with a conventional brushed motor.
From my point of view, a DC brushless motor basically works in a similar fashion to a simple DC brushed motor except that it uses sensors and electronic components to switch the polarity of the windings instead of a mechanical commutator, and I'm pretty sure that the unloaded speed of both motors will still be directly proportional to the voltage being supplied.
Having said all of the above, my understanding of how a BLDC motors and controllers work is still quite basic ::) so please feel free to correct me if I've got it all completely wrong. :-[
Alan
TheKing:
Hi Bikemad
I hope you find the time to look at my case. I'm writing to you for the second time, the first time I had a burn controller ... so I had to buy a new one
I converted Daewoo Matiz from 620 kg weight .... with 10 KW BLDC Motor, 500A Controller from GM.
I put 4 155Ah lead batteries running on 48V
The vehicle works well on a flat road and on a downhill ... the problem occurs when I accelerate on low or higher uphill (or maintain speed) .... happens that the engine suddenly loses power (the controller shows flash off LED) but if I start driving again from the beginning the vehicle is running normally. Of course I lose the uphill speed and that is very inconvenient in regular traffic. Your opinion?
?hank you in advance
Jovan
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