Bafang PAS Speed% setting

[DuncanC]

This is being reposted here at the suggestion of Al Hicks since the discussions here are more specific to the Bafang motors. I am gradually gaining a firmer toe hold on programming the controller for my Bafang BBSHD 1000 Watt using a 48 Volt battery. My current understanding is that the Speed% is a setting for the chain ring rpm (motor rpm) after which assist basically stops. Apparently the maximum rotational speed is a function of the battery voltage and is 150 rpm for a 48 Volt battery. However does the maximum rotational speed decrease as the actual battery Voltage declines over a ride or does it remain at a fixed value? I suppose bench testing the motor with a strobe would easily clarify this. So having recently acquired a strobe I think I’ll drop the chain off and at least see if the maximum chain ring rpm is 150. If that works out I’ll check the chain ring rpm’s of the other 8 PAS Speed% levels and see what values I get. If it works out I’ll post the results. Too, I can check the maximum Speed% after a long enough ride to drop the voltage to a level that will allow a measurable rpm drop? I do understand that the controller may function in a more complicated and nonlinear way with the Speed%, but at least this will add some data that should not be affected by any subjective experience gained from a ride. Wish me luck.

Best regards to everyone and thank you all for your many thoughtfully detailed explanations and guides all based on extensive experience and understanding.
Duncan

 

[DuncanC]

Okay then. I’ve come up with a way to trick the wheel speed sensor. Gimmicky but I think it will work. I’ll use my old record turntable at 33 rpm with one or more magnets on the platen to emulate a speed of 10-12 mph. I’ll simply use some machining dial mounts to suspend the sensor over the platen and magnets. Then I should be good to go. Wish me luck.

Now a question. I think it is accepted that the Speed% value is a percentage of the maximum motor or chain ring rpm. Correct me if I’m wrong. So that should result in a cadence limit above which assist stops. In that case why are the values so high in most of the published .el profiles. It’s doubtful many ride with cadences approaching the maximum rpm. The average cadence for efficiency is around 80. So it would seem sensible for purposes of feedback to set all of the Speed% of the maximum rpm to be no higher than you would expect or want to pedal. For cruisers that might be 80 to 85 rpm and for a max rpm of 150 that would be 53-57%. The end result would be the ability to select the necessary assist to maintain the most efficient cadence and get feed back when you exceeded it by having the assist reduce automatically. This is probably only something older riders would choose for a setup, but I’m going to give it a try along with softening the onset and stopping of assist with PAS and the throttle. The throttle will remain as the override of both assist and speed as “needed”. Why the stock setup increases the assist parallel with Speed% (cadence limit ) and up to such an extreme is really a question. Perhaps it is a hold over from when batteries had more parallel cells with great current but lower voltages so the max rpm was correspondingly lower.