Bafang G311 Suddenly Unresponsive, Need Help

[Odin Gray]

Hey there. I've been building a custom project using a Bafang G311 from Grin and a 20a Grinfineon controller/Sempu BB/Button Throttle with 48v battery and a 48v-12v regulator directly wired to said battery to power accessories.

I took it for its first test ride, and all seemed largely fine until the motor suddenly cut while hitting the throttle. It wasn't under a whole lot of load, and no weird noise, but it was as if someone had snipped it off. The Cycle Analyst does see throttle input and is sending 3.6v to the controller when I hit it. Everything else still works, reseating connections didn't change anything.

Variables I can think of:
- I extended the motor cable by cutting and splicing 13" of wire into the phase and hall wires and all that, but it seemed fine up until now.
-There was one instance of strain on the cable at the motor side when it inadvertently started slowly spinning and wrapping the cable around itself, but this was stopped pretty quickly. I noticed the Cycle Analyst saw no speedometer signal after this, but I didn't verify that it had one beforehand, either.
- It has some strange behavior sometimes when I turn the battery on: both the CA and 12v systems turn on and then quickly off again. Happens to the 12v whether the controller is on or not. Simply turning it off and on again fixes it and there's no problem past that point. Not sure if related.

I've emailed Grin about this, but I thought I'd throw it out there over here so I can get some insight about how to troubleshoot this. I've opened the motor before to paint the shell, but I'm not sure about accessing it wire-side if those terminals need to be re-soldered.

 

[amberwolf]

-There was one instance of strain on the cable at the motor side when it inadvertently started slowly spinning and wrapping the cable around itself, but this was stopped pretty quickly. I noticed the Cycle Analyst saw no speedometer signal after this, but I didn't verify that it had one beforehand, either.

That typically means that the hall sensor wires are damaged, which is a very common problem in the event of not using properly mounted torque arms to prevent axle rotation, and ending up with damaged axle-exit cable wires.

The wires could just be open circuit, broken, or they could be shorted against each other, the axle, or worse, phase wires. If the latter happens, or the phase wires short to each other, the controller is usually damaged or destroyed.

I would recommend first opening the motor, pulling the cable into the motor until the entire damaged area is inside the motor, then repairing the wires and reinsulating all of them, whether they appear damaged or not. Cutting the entire twisted section out is the safest bet if there is sufficient wire length to do so, and then splicing the remaining sections together, with good complete insulation on each wire to ensure they cannot short against each other or antyhing else, and then tie down that cable inside the motor. (don't pull it bakc out the axle--you'll just have to reconfigure stuff outside the motor to compensate for the shorter cable).

Then do a continuity test from inside the motor at every wire connection to the relevant contact on the other end of the cable, beyond the spliced-in portion of wire you added to extend the cables. This ensures you don't have any breaks in the wire there, either. You can also test for shorts by measuring every wire to every other wire, at either end of the cable. All the phase wires will read shorted to each other, this is normal. But all the others should read open-circuit.

Then close up the motor.

Then install at least one, preferably two, perfectly-fitting-to-the-axle torque arms, and secure them firmly and reliably to the frame, so the axle *cannot* twist in the dropouts at all.

After that, you can then retry the system. If it works, it was just a broken wire and you're probably all set.

If it doesn't, then there's two possibilities, and often enough it's actually both problems:

--the controller itself is probably damaged, and likely needs to be replaced (unless you are confident enough to replace FETs and possibly other small parts. Even if you do repair it rather than replace it, if the hall wires were hit with phase voltage, the MCU in the controller is probably damaged and that's not replaceable).

--the halls in the motor could be destroyed from shorting to phase voltage. There are tests for that on the Grin Tech website under Learn -- Troubleshooting.

- It has some strange behavior sometimes when I turn the battery on: both the CA and 12v systems turn on and then quickly off again. Happens to the 12v whether the controller is on or not. Simply turning it off and on again fixes it and there's no problem past that point. Not sure if related.

That usually means the BMS in the battery is shutting off it's output to protect itself from something. That could be a surge load charging the capacitors in the 12v DC-DC and the controller at the same time being just too high for it, triggering the BMS overcurrent protection, or causing voltage sag on the cells triggering BMS undervoltage protection.

You can look up "precharge" in the forum search, or on google, to find out how to add a precharge function to prevent that.

 

[Odin Gray]

Hopefully my controller isn't bunk, but the controller does supply power to the Cycle Analyst and appear to otherwise work normally.

Another comment on the battery BMS shutdown issue is that the 12v shuts down on its own, too, not just when the controller is on. My thought is that it's related to the 12v, so... I'm not sure.


Moderator EDIT: Apologies; I accidentally clicked "edit" instead of "quote", and ended up removing some of what you'd said.

I restored what I could of your post, but if you remember what you said you can just edit this post again and put it back in there.

 

[amberwolf]

but the controller does supply power to the Cycle Analyst and appear to otherwise work normally.

Unless this is an atypical wiring setup, and an unusual controller model, the controller doesn't actually supply power to the CA. It may pass it thru from the battery, but the controller itself could be a lump of charcoal inside and as long as the wires are intact inside the CA would still get power.

Another comment on the battery BMS shutdown issue is that the 12v shuts down on its own, too, not just when the controller is on. My thought is that it's related to the 12v, so... I'm not sure.

You said in the first post that the 12v converter is directly wired to the battery, which means that the controller doesnt' directly affect/control the 12v system.

But if the controller and/or the 12v system, which are both wired to the same battery output, draw too much peak current at battery turn-on, then the battery may respond to that by shutting back down. Turning it right back on would always work in that case, as the capacitors in the controller and 12v converter are already charged up, so no surge peak happens and the BMS doesn't panic.

But if it's been long enough after turn-off, the caps self-discharge and the surge happens again, and the battery could then shut itslef off again.


If the 12v converter just randomly shuts off now and then regardless of whatever else is happening, even though everything else still has power, then either there is a defect in it, or it's being overloaded by too much 12v stuff on it's output, or there is a wiring problem causing a short on the output or an open on the input.

 

[Odin Gray]

So, it seems like what I need to do is test for signal coming from the controller using a multimeter. If I'm getting energy from the phase wires when throttle is applied, and any other applicable signal across the nine conductors inside the cable, then I know the problem is likely happening in the motor or connection. If I'm not, I probably fried the controller.

 

[amberwolf]

First, you should to repair the cable itself, and do the tests already described.

If you don't do that, then any damage already done in the cable will prevent correct operation, and will also damage anything new connected to it--maybe not immediately, but at any time the already-damaged insulation fails between conductors.

The more times you apply power to the system with wire damage present, the more risk there is of component damage happening because of it.

The thing about a cable that's been twisted up is that there may be no visible damage, even if you open up the sheath and look at the wires inside. But there can be two different kinds of damage, either or both of which are present.

The first damage is thin wires that get their conductors stretched enough to break inside, while leaving the insulation appearing intact. This has no risk of destroying things.

The second damage is any wire that gets it's insulation pushed or pinched in a way that opens it up, because the conductor inside is pushed or pulled against another wire hard enough to force insulation away from both of them and allow the conductors to touch. This type of damage is generally not visible because the insulation is soft enough to "heal" as the wires are moved away from each other when it's opened up for inspection. To see it, one has to pry at the insulation to find the tears/pinches, and even that may not show the problem. But when the wires are bundled back up they may press against each other the same way again, and still cause the electrical connection.

When that causes two phase wires to touch, it usually results in greater drag on the motor (only in reverse manual wheel spin for geared hubs), but it might not be enough to notice when unpowered yet still be enough to allow current flow when powered, which would damage phase FETs.

When it causes a phase wire and any hall wire to touch, no visible symptom occurs, but electrical damage can be severe. If the phase is touching a hall signal, it may damage just the hall sensor itself, but it can also destroy the controller MCU as most are not protected against this. If the phase is touching the hall 5v, it can destroy everything attached to that, which includes the throttle, PAS sensor, ebrake sensors if they're hall type, the controller MCU and 5v power supply, and all of the hall sensors in the motor itself. If the phase is touching the hall sensor wire that is also used for the CA speedometer in a CA-DP setup, it will probably also destroy the CA itself, when battery-level voltage is passed thru 5v-level signal lines.


I've seen all of these failures occur to different people over the years, some of them myself.



It's also possible that no damage has occured, but since the problem started after the twisting, that's unlikely.


It may seem like a lot of work for a potential problem that you may not even be able to confirm exists visually with the wires, but it is a "better safe than sorry" fix.

 

[Odin Gray]

Still working on it. I opened the motor, I can't get any further in than I am to fix any wiring. I can't see any damage aside from some scuffing on the cable sheath.

Now, the controller's LED is flashing three times, which indicates that the voltage coming in is over voltage fault, according to Grin's site. https://www.ebikes.ca/product-info/grinfineon.html It's the 20a Grinfineon.

Both batteries give me the same problem. So, we have a controller problem, it seems. Damaged MOSFETs?

So, new controller. I'm worried the motor is damaged in a way I can't see or verify, and if I just buy a new controller, I could connect this motor and see the same damage happen again. What do you think?

edit: Also, I had removed the indicator LED previously and had to open and reconnect it to understand what it was doing, so that's why I wasn't able to immediately verify that. Lesson learned about removing indicator LEDs... I am using Grin's guide to testing MOSFETs to verify this damage now with a multimeter.

 

[Odin Gray]

UPDATE:

I followed Grin's guide, but was getting weird results through my multimeter. I used it to test a 10k ohm resistor and got... like 150 ohms. So I was thinking that it's busted, went and got a new one, found out I was right. I used this to test the phase wires against the negative battery contact on the controller. Two of the three give me the standard 5k ohms from the healthy MOSFET, but one of them is just straight shorted, indicating we have a blown MOSFET. I'm not experienced enough to know if this indicates only one is blown, or if I have to do more to find out about additional broken MOSFETs or parts, but I'm about to dig into that now.

It seems to me that the best course of action here is probably, if possible, to repair the controller, cut and completely redo my cable splice leading to the motor, and replace the motor core in case there's a short in there that's damaging my controller.

UPDATE 2:

I did do some testing on the phase and hall wires on the motor itself, and the speedometer, and it seems like everything is normal in the motor... So, I've ordered replacement MOSFETs and I'll carefully redo the cable extension I made, then see what happens, I guess. The motor core is completely disassembled, and there doesn't appear to be a way for me to completely replace the motor cable without removing the actual windings, which are on the outside.