practical field weakening

[offGridDownUnder]

I need to spend time with diagrams and reading to understand the technicals of field weakening beyond the basic idea of advancing the motor phase. This means explanations in math aren't useful, and aren't what I'm asking for. I won't learn much if your answers are phrased this way and you expect me to figure it out - I haven't studied yet, and I want practical advice for this now.

I have a 8T GMAC, a V5 Baserunner, a CA3 Analyst, 48V nominal battery that can provide 40A peak, but probably never has needed to, and a final gear reduction from the motor to the wheel of 60:26 (the 26 is on the motor). I've applied up to 25A of field weakening current in the Baserunner with the trike on a stand, and the indicated top goes up to 50+km/hr. With no field weakening, it is at 27km/hr with that gear reduction.

I have already just read that I should not do this on the stand, but only with a physical load. No smoke has been released, so I'm preparing for tomorrow on the road.

Like the fellow said in the movie: "I'm fuzzy on this whole good/bad business. What's bad?"

As I play with the field weakening current, what do I watch for to decide on what is best? I understand that I will get good torque at low speed, and higher possible rpm at top, but less torque at top. That's fine with me, I'm making a truck.

What's bad? Amps too high? Which amps?
Temperature too high?
I already won't accept not being able to go up steep hills even if only at low speed - I can do this now, and anything that prevents that is 'bad' in my reckoning.

What do I try and what do I watch for to decide what is the optimum setting?

 

[offGridDownUnder]

I need to spend time with diagrams and reading to understand the technicals of field weakening beyond the basic idea of advancing the motor phase. This means explanations in math aren't useful, and aren't what I'm asking for. I won't learn much if your answers are phrased this way and you expect me to figure it out - I haven't studied yet, and I want practical advice for this now.

I have a 8T GMAC, a V5 Baserunner, a CA3 Analyst, 48V nominal battery that can provide 40A peak, but probably never has needed to, and a final gear reduction from the motor to the wheel of 60:26 (the 26 is on the motor). I've applied up to 25A of field weakening current in the Baserunner with the trike on a stand, and the indicated top goes up to 50+km/hr. With no field weakening, it is at 27km/hr with that gear reduction.

I have already just read that I should not do this on the stand, but only with a physical load. No smoke has been released, so I'm preparing for tomorrow on the road.

Like the fellow said in the movie: "I'm fuzzy on this whole good/bad business. What's bad?"

As I play with the field weakening current, what do I watch for to decide on what is best? I understand that I will get good torque at low speed, and higher possible rpm at top, but less torque at top. That's fine with me, I'm making a truck.

What's bad? Amps too high? Which amps?
Temperature too high?
I already won't accept not being able to go up steep hills even if only at low speed - I can do this now, and anything that prevents that is 'bad' in my reckoning.

What do I try and what do I watch for to decide what is the optimum setting?

Specs as above.

Summer here. Ambient temperature was 26C - 30C, weather sunny, 15km/hr + winds (often headwinds).

I tried Field Weakening values entered via the Phaserunner Suite software of 20A, 15A, 10A. No anomalies were detected, no resets required, no smoke released. Regen braking acted as expected, except commanding more regen via the throttle (a Grin feature) dropped regen immediately - I surmise the Amps tripped the limit.

Highest speed on level under motor power was 40km/hr at 20A. Other settings produced ~37km/hr and ~33km/hr respectively.

Highest motor temperatures recorded were just below 60C. I did not try climbing for 20 minutes as I had no such hill.
Highest A was 22.86. W-h/km reports 9.0, and I used the throttle hard some times.

This arrangement will accelerate uphill (if below it's top speed) which matches my expectation I can pull a trailer uphill at a steady speed. I'm going to swap the GMAC out and put a Shengyi SX2 Fast wind in next - Grin's simulator says at the speeds and ratios I run the extra power of the GMAC has no effect. I want to see how it actually behaves.

 

[trep420]

Thank you for this, I am interested in trying to adjust my field weakening amps but also had no idea how much I should try.

 

[alfy22]

hi @offGridDownUnder and @trep420. Just found this post and i am also interested in trying field weakening with My shengyi SX2 standard wind (paired with baserunner v6 and a 36V battery) but not sure which current to start with. Do you have any advice to share? Thanks

 

[offGridDownUnder]

Do you have any advice to share?

Nothing based on much experience. But I have some thoughts about what I would do.

I'm not riding much these days, as I have made the fatal error of moving to a location with no sympathy or usable roads for cyclists. I am planning my revolution, but in the short term must find a vehicle to haul my trike around in - neither are quick solutions, as I did not plan my retirement around a fossil fuel machine. I am rooting for the collapse of civilization.

I am not running my ShengYi - I did but now have replaced that with a Grin V3 All-Axle rear with a 22:48 drive reduction which tops out at about 35km/hr in a jurisdiction which does not permit power above 25km/hr (if you can pedal that fast, you're ok). This arrangement does what I do want, which is to scoot up steep hills carrying large loads without breathing hard.

Your battery is 36v. Find out the maximum amps you can get - which component is the bottleneck? Battery itself, Baserunner, motor.

The first question is "Does this have an effect?" For this, I would choose a day I can spend a few hours riding, then ride with no setting for long enough to be used to the ride - 15 minutes, half an hour? Try to throw in any particular interests - the hill, the long stretch, whatever.

Try adding half of your maximum amps. I tried large values, as noted above. Then do a 'binary search' - cut the value in half, and try that. Until you find some setting that makes some difference, you haven't learned anything. Cast about for the value that makes a difference, then try more or less to have the difference go away. That experience can lead you. Somewhere between "I didn't feel a thing" and "Oh, shit!" lies your sweet spot.

It's like base-jumping, without the likelihood of imminent death.

Points if someone else gives better advice. Try that.