Removing Starting Torque Limits?? Sabvoton SVMC72150

[Degreeless_Engineering]

I have a Chinese Stealth Bomber and I want more starting torque(specs below). I've ran through the mobile and mqcon app and have done about everything that can be done to increase performance based off the information provided by "Kathy" in an older post. However, the starting torque still ramps up slowly until at speed. The bike performs fine otherwise, I would just like more punch. Is there a way to adjust or remove this feature using an alternate program? Thanks for your help!

Purchased in 2022
72v 45ah battery
SVMC72150 72v/150a DC/350a Phase Current
150a BMS
12000watt hub drive

 

[amberwolf]

For reference I'll quote my reply to a point in your other post here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=116098&p=1745536#p1745536
in case it's helpful to this thread at some point, given the various mechanical issues seen in the many variations on "Chinese Stealth Bomber" clones and clones of clones of clones of clones....

I'm sure it's also not healthy for a hub motor to receive that much power from a dead stop.

If the motor and it's torque-transfer mechanism to the frame are properly designed and made for the torque level required, then there's nothing unhealthy (for the motor) about putting the designed level of power thru it at any point.

But...most hubmotors are not well designed for their torque transfer mechanism, using just the tiny axle flats to do this, and most of hte axles are not well made of sufficiently strong materials either, making it even worse...the motor itself doesn't usually fail, but rather the axle itself, usually at the point where the flats end at the shoulder--shearing off rotationally is the most common failure mode.

If the axle itself is well made and so is it's attachment to the motor core supports, and the rest of the motor is also well-made, then the next typical failure point is the dropouts or other torque transfer mechanism, such that the axle spins within them, tearing them up and sometimes damaging the axle, but more often just ripping up the wiring as it tangles around the now-spinning axle...and the damaged wiring often shorts internally between phases and sometimes to halls or other signals, and taht usually destroys the controller, and sometimes other parts on the electrical system.

 

[amberwolf]

I have a Chinese Stealth Bomber and I want more starting torque(specs below). I've ran through the mobile and mqcon app and have done about everything that can be done to increase performance based off the information provided by "Kathy" in an older post. However, the starting torque still ramps up slowly until at speed. The bike performs fine otherwise, I would just like more punch. Is there a way to adjust or remove this feature using an alternate program?

The most likely thing is that it's just the way the firmware in that specific controller model and version is designed, most likely to protect it's own hardware (I would guess as a reaction to failures caused by design problems or the use of cheaper parts than originally designed for, etc).

If the controller manufacturer can supply you with alternate firmware you can flash to it that removes the limitation you could try it, however you should note that "Sabvoton"s have been noted for sudden deaths, and as referred to above I suspect the limitation you're running into was put in place to help prevent that.

Alternately you could replace the controller with one that meets your specific feature and function requirements. (would need to know those before recommending anything).

Another possibility is the controller is reducing current draw in response to voltage sag of the battery--it's not uncommon for the cheap batteries often used in these bikes to be unable to easily supply the current demanded at high loads. Do you have a wattmeter you can install between battery and controller to monitor current, power, voltage, for realtime and max A and W, min V? If not, we can make some recommendations depending on whether you would want to permanently mount it or just use it for testing/troubleshooting.

 

[dominik h]

Also quoting myself from the other thread.

I measured phase current at 0RPM, it takes a little time to reach full phase current, but it gives full phase current.
I thought it starts with reduced current, as it feels like more tourque at around 20mph/30kph. But the first two seconds after a stop feel to slow.

The Sabvoton has no temporary boost or a start boost function like other controllers might have.
It gives 350A peak Phase Current a 0 RPM.

I changed my 5kW motor to an 8kW with a lower KV and the now it feels like more tourqe from 15mpH /25kph ,but I must now use weakening field to get a top speed around 97km/h before it was 103 km/h without weakening field.
0-80kp/h times dropped from 12.2 to 11.5 seconds.

It needs more phase current for a faster start, and the SVMC72150 does not offer more.