That's an excellent point, wturber. And thanks, motomech, for providing some insight into it.wturber wrote:One point to consider is which of these motors is the easier to maintain or are they the same? Given the high mileage I suspect you'll put on these and that they use nylon gears, planned maintenance may be something to consider. For instance, simply changing the nylon gears out at set intervals before you have problems may be a good idea. That, or at least opening up the motor at such a time and evaluating the wear. Parts availability and cost may factor in as well.
The A/B variable in the following graphs is whether or not 200W of pedaling is applied. The only variable change between the graphs is that the current is ramped up in whole numbers from 15A-19A as the operating range approaches and then goes past the inflection point. You can see that:chas58 wrote:All out of box solutions will be to the right of [the inflection point].
Inflection point. On the red line (power output) the inflection point is when the controller hits the battery current limit, and current (and power) rapidly falls off after this. All out of the box motors cruise at speeds to the right of this point. This means that the controller is not maxed out (at maximum amperage), gives the highest speed for the motor, and generally prevents things from overheating.
So, for all off the shelf motors (except for very small ones) its near impossible to pedal hard enough to make the bike go faster. They cruise at speeds to the right of the inflection
point. Here power falls off so rapidly, while the aero effects raise so rapidly that no one can make much of a difference pedaling (on a higher powered motor at full power).
Again, the A/B variable in these graphs is whether not 200W of pedaling is applied, first with an example in the flats and the second on a 3% climb. You can see that:chas58 wrote:My bike doesn’t have enough current to get to its happy point (right of inflection point). It does about 20mph on its own, maybe 22 down wind in a tuck. I do about 25mph pedaling it. So, by adding 200+watt with my legs makes a big difference.
Pedaling makes a difference because the inflection point on my motor is 23mph – making it relatively easy to get from 20 to 23mph and a bit harder to go faster. And it keeps me in the safe zone to the right of the inflection point when I add 200watts. Ideally this is where you want to be.
But with a moderate powered motor running solo to the left of the inflection point, pedaling can make a big difference (if you can live with the drawbacks).
Now that I've settled on the Bafang CST and have a much better understanding of the operating regime (thanks!), I'd like to figure out which controller to use and how to use it.d8veh wrote:Good point. Controllers are generally rated at half the maximum current, so a 20 amp controller will run happily at 10A, but if you run it at 20A continuously, it'll over-heat. The current that it delivers depends on the motor speed, where the back emf prevents the full current when above the inflection point.
The KT controllers use current control, where the 5 PAS levels range from 10% to 100% of maxpower, so you can also prevent over-heating by using level 4, but of course you only get 12 amps instead of 20. If you're going to run a high kV motor, you need to consider how to help the controller stay cool.
Oh, bother, that's confusing!d8veh wrote:The poblem with the Bafang CST is to get one with the right speed. Make sure you know what speed you're buying because they don't normally tell you and there's a lot of different variants. Also the 250w, 350w and 500w versions are actually different, even though they look the same.
Assuming that I can indeed source the correct shred, would the KT controller work ok for the Bafang CST, instead?d8veh wrote:S09P and S12P are square wave controllers for sensorless motors. That only leaves the S12S . The PAS levels are current limits, so you select whatever power you want. Bear in mind that the S12S is quite large.
I knew that I would never, ever weigh in at 30 lbs., wihch is why I called it a "heavy 30^3."d8veh wrote:Your 30 pound target is now just a dream. With the additional weight of those items, you'll need a strong frame and wider tyres. I think you might have crossed over the point when you might as well get a DD motor, strong MTB, big battery, etc like all the others.
Are you saying to add solder to the shunt to decrease its resistance so that it'll handle more than 20A?motomech wrote:I run an Ezee V1 w/ an Elifebikes QQ 20 Amp controller that has been shunt modd'ed to 25 A. That's a 25 A peak only at start-up and in normal usage is more like a 17 A controller. It's kind of soft and if my bike was not 2WD, I probably would want a more powerful unit. But it's smooth, easy to modulate the throttle and provides good batt. economy.
So my proposal is, why not use the KT sine wave shunt modd'ed to 25 A on the BPM?
Yes, it would be under-powering the Bafang, given the conventional wisdom is the BPM should be paired w/ a 30 to 40 Amp controller. But, the Ebike CA sim. shows it would still get the motor up to the desired top speed w/out becoming Current limited.
I'm willing to accept this.motomech wrote:But the compromise comes to the fore as lazy aceleration to get there.
I know that they have, and I know that the Q128C is an improvement over the Q100, but, at least according to the model, the Bafang CST is even more efficient than the eZee or MAC, and they're both more efficient than the Q100. The efficiency gains of the Bafang CST over the Q100 are worth more than even an extra ten pounds. I wish that I had current data now, but I don't.chas58 wrote:Keep in mind that the ebike.ca simulator tested the Q100 a long long time ago. There have been changes to it since then, and the efficiency numbers may have significantly. We know the Q100H and Q128 are a lot different then they were back in those days.
So of pswpower's torque simulating controllers, they have a 17A/350W and a 20A/500W spec'd at 36V/48V, and they're listed with both the same dimensions and weight. Any reason not to get the 500W? (Efficiency penalty?) They would work with either the Q128C or the Bafang CST, right?chas58 wrote:For controllers: "torque simulating" controllers modify the current, the older design controllers are roughly like a throttle to limit power (i.e. speed limiting, but often use full current below max speed).
Translating the batteries that I'm carrying into a "power budget," I can only afford to average 750W, tops, so I can't afford to 20A+ constantly. I plan on running 10A with up to 20A on steeper or longer ascents.chas58 wrote:Rather than soldering the shunts, I would rather get a controller with the current I need, and then dial it back with the PAS settings. But again, your graphs showed 10 amp usage. If you are willing to sweat, you don't need a lot of current. The current is mostly going to get you low end torque anyway. Do you need that? The high current does not help you at all with speed - if you are traditionally to the right of the inflection point.
The huge FalconEV triangle bag came in, and even though all the batteries fit in the bag, they don't fit on the bike, so the CAAD4's out of the running.chas58 wrote:Personally I think a gravel bike is the best solution 32-45mm tires, (long, low, slack geometry) with alternates being a cross bike (more agile) or a touring bike. Gravel/Cross are built rather like a cross country mountain bike, but with more road geometry.
I agree with most of what you wrote above, and I think it's all good general advice. There's more considerations than the motor, though. A hybrid or road bike with thin wheels and forks is much easier to propel, once the speed goes over 20 mph. It's still an option to use the lighter motors with such bikes to get your high speed, but when you get to around 30 mph, pedal effort becomes less significant compared with the motor's power. Don't forget that some guys can average 30 mph without a motor at all, though for that, you need low resistance clothing as well as a low resistance bike.motomech wrote:Bottom line;Would it be too bold if I inquired what your profession is?
I have read here something along the lines of, The BPM (Bafang) is good up to 30 mph and above that, it's best to go w/ the MAC and believe this is about right.
26 to 28 mph avg.-Q128
27 to 30 mph avg.-BPM
30 mph and over- High-speed MAC
chas58 wrote:For controllers: "torque simulating" controllers modify the current, the older design controllers are roughly like a throttle to limit power (i.e. speed limiting, but often use full current below max speed).
These are the Sine wave ones. Torque simulation = current control, which they all have. There's a setting in the LCD if you want speed control, though I can't believe that many would want to use it.mystryda wrote:chas58 wrote:For controllers: "torque simulating" controllers modify the current, the older design controllers are roughly like a throttle to limit power (i.e. speed limiting, but often use full current below max speed).Help!?
I’m wanting to place the order for everything, but I just noticed that PSW’s torque simulator KT controllers are all square wave (linked above in the quote). Do I want that?? I thought that I wanted sine wave...