[Bafang + Nuvinci] Cargo bike seizes up in hills

[Winfried]

Hello,

Remotely, I'm trying to help a non-techie who bought a Dutch-made used cargo trike in good condition from a bike shop.

1. It has a Bafang M400 mid-drive (MM G33.250, 36V 250W 14A; It's in Europe, hence the 250W motor)), and a Nuvinci Optimized 330 gear hub with an automatic shifter + H3 controller.

She intends to ride her handicapped 30kg kid to school on 4-6% grade hills — so, not really steep, but not flat either.

The issue is that, when climbing, the motor just stops: The pedals won't go forward, but she can backpedal.

FWIW, she chooses the one dot mode on the H3 because the bike barely moves in hills when using the other two modes, especially the three dot mode (where you spin the most).

Could it be the 80Nm torque of the Bafang is fine, but a 36V battery isn't up to the task, and the controller shuts it off to preserve it? And/or something to do with the electric Nuvinci shifter?

2. As a lesser issue, when she recharges the battery — after letting it cool off as recommended —, the charger gets quite hot, although it came with the bike.

Thank you.

 

[indianajo]

More data is required. She needs to know, what is the voltage coming from the battery to the controller at the time of the failure. 32.4 volts or higher (20% charge) it is not the battery. 30.5 to 32.3 it probably is. As this bike is factory built, it may be quite difficult to modify the wiring harness to take this reading. Especially as when the bike is in motion.
I bought 2 batteries, both of which would run fine on flat ground but stall the bike on the first hill. Anything over 50 watts indicated would make the display blank and propulsion to stop. I didn't know if it was battery, controller, or motor?
When I suspected I had two bad batteries in a row from different vendors, I built a battery test jig involving a 10 ohm 500 w resistor, some alligator clip leads, and a DVM, to measure the voltage on the battery (sitting on a concrete step) at 5 amps draw (48 v battery). To draw 5 amps from a 36 v battery, you would want a 7 ohm resistor. Do this test outside on concrete, one does not want to set a fire.
I bought the resistors from apexelectronic.com and the alligator clip leads from partsexpress.com . These vendors will not help you much in Europe. And surplus house stock (like apex) varies from day to day. He doesn't mess with resistors anymore, surplussales.com and electronicsurplus.com do. Farnell has the resistors on 6 continents but you'll pay 3 to 10 times what I did for surplus. Do not set the resistor on a flammable surface, they get hot near rated wattage. I mounted my resistors on metal brackets standing above a metal plate.
Turns out one suspect battery was dropping to 11 volts when I tried to draw 5 amps out of it, the other 7. I got my money back for one battery but not the other as it took more then 31 days to acquire & build the test jig. It could have always been the motor or controller, but in my case it wasn't.
Note wire harness faults in the bike can cause low voltage at the controller that is not reflected at the battery terminal. Requires measuring voltage at both points during a failure to diagnose that problem.
Chargers that don't catch fire I suppose are in spec, although none of mine run that hot. I paid a royal $14 to $22 for my 2 amp chargers on ebay. I had to change the connector, nothing ever matched up to anything else. The charger I paid $60 for from luna was dead in the box.

 

[AHicks]

My bet - her impatience is costing her.

This doesn't seem to be working out well for her - "FWIW, she chooses the one dot mode on the H3 because the bike barely moves in hills when using the other two modes, especially the three dot mode (where you spin the most)."

She needs to let the motor take advantage of the lower gearing when in the hills. No, it's not going to be as fast, but at least she'll make it! When using the faster mode she's using, the (reatively low powered) motor isn't up to making the kind of power needed to climb the hill, so it's getting hotter and hotter until it quits.....

And a charger getting warm isn't to unusual.... HOT would be dangerous, but if she can pick it up OK, she's probably fine.

 

[kevinmccune]

Interesting, the only times I had an Ebike stop on a hill it was because the controller was too puny, I find if even given a full 250 watts I can make it up most hills( verified with cheap bikes) some of the more costly ones had tiny controllers that would shut off on moderately steep hills, one company scalped
Me for a better controller( told Me bike was overloaded) the other company graciously gave Me a better controller( guess who may get future business) in both cases the "hill problem" was corrected, one must anticipate doing a little hard pedaling as well. YMMV, some dogs are always dogs.

 

[Winfried]

Ah, didn't think of the controller. Thanks much for the input. She never could resume cycling, even after turning the motor off and on.

But we'll never know for that Dutch-made trike, as she finally got the LBS to replace it with a two-wheel Bakfiets, also with a Bafang mid-drive. Too bad no one was available around to simply swap the rear wheel for anything else, even a single-speed one, just to tell if the Nuvinci was to blame.

But again, the two-wheeler is also made for the Netherlands… so she might have the same issue (with a Nexus 7, though, not a Nuvinci/Enviolo). Stay tuned

--
Edit: I don't know if it means anything, but when the motor shuts off in a hill, the DP C07 display remains powered.

Could faulty connectors explain the bevahior — it's a second-hand bike? Since it's easy to do even without any tech skills, I advised checking them out with a flat screwdriver.