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My M600 (46.2) 48V motor shuts off at 42V. How do I fix this?
- Thread starter mux0l0v
- Start date
The M600 is Bafang's mid-drive motor - 95Nm, up to 750W depending on implementation, and considerably more DIY-friendly than anything Bosch or Shimano will let you near with a soldering iron. It's the motor of choice for custom builds and open-source tinkerers, which is probably why it attracts the crowd it does here.
@mux0l0v - is there something specific you're trying to sort? Wiring, display, power issues? I've got pinout documentation sources and a fair bit of community knowledge on the M600 if you've got a particular problem to dig into.
@mux0l0v - the short answer is that 42V on a 48V system isn't actually a bug, it's the motor doing its job. 54.6V is a full 48V battery; at around 42V, it's nearly completely empty.
So the cutoff is working as intended. The question is whether it's cutting too early.
Our community knowledge flags that firmware 46.2 specifically is one of the more aggressive derating versions - it starts throttling power from 40% SOC, which many riders find excessive. If your battery is genuinely reading 42V at the pack terminals (not just under-load sag), then it's a very flat battery, not a malfunction.
However, if it's cutting at 42V indicated while under load, voltage sag is likely the culprit.
A Bafang motor under hard load can sag enough to trip the cutoff even when resting voltage is considerably higher - which is not confidence-inspiring mid-trail.
The controller sees the sagged voltage and pulls the plug. Two things worth checking:
• Check resting voltage - turn the motor off, wait 30 seconds, measure again. If it bounces back above 43-44V, it's sag, not genuine empty.
• Firmware update - for the newer M600 hardware, 46.2 and 46.3 are the available versions, and 46.3 or a modified version is generally better-behaved. The BESST tool is your friend here; the Bafang Go app will likely misidentify your controller and push the wrong firmware, so avoid it.
What does your display show for battery percentage when it cuts out?
@mux0l0v - the community knowledge on this is pretty clear, and it's not great news for doing it cleanly.
Bafang bakes a fairly conservative "low cutoff voltage" into the firmware itself. The standard BESST tool doesn't expose a UI element to simply dial the LVC down - it's hardcoded into the firmware binary, not a configurable parameter you can tweak.
The route people have taken to get below 42V is flashing a modified firmware. There's an experimental firmware on the OpenSourceEBike GitHub project with a lower low cutoff voltage, described as still within safe battery specifications but giving more usable range.
That project also has an open-source alternative to the BESST tool - it supports CAN-bus motors including the M600, though not all features are implemented yet.
Worth being realistic about the trade-off though: 38V would be a more permissive cutoff and is still technically within battery specs - cells can go down to around 35V combined before genuine damage - but 42V exists partly to protect longevity.
If you're running a quality third-party pack and are comfortable accepting slightly faster cell degradation, the community consensus seems to be that 40V is perfectly survivable.
The practical path: OpenBafangTool on GitHub is your best starting point for the M600 on newer hardware. Bafang themselves won't help - the community has been asking them to lower LVC for years and they refuse, citing battery safety.
You're in DIY territory here.
Good. There are two practical routes here and the search results give us what we need on both. @mux0l0v - two routes to 39V, depending on whether you want a firmware flash or a hardware workaround.
Option 1: K1 Flash (firmware) K1 Flash is compatible with all Bafang CAN bus motors with the 5-pin "house" connector, and supports the M600 specifically.
It comes with a large firmware library on SD card and you edit an AutoSet.txt file on the SD card with your preferred settings.
The key point for your use case: there's an experimental firmware for the old M600 rev.A without power limitation at low battery level, with limitation only starting at 10% SOC.
Your 46.2 firmware puts you on rev.B, so check with them whether the equivalent exists for your revision before ordering. k1ebikes.com is where to look.
Option 2: K1 BlackBox Racing (hardware intercept - no firmware flash) This is the cleaner option if you're wary of flashing.
The K1 BlackBox Racing device lets you set the Low Voltage Cutoff and discharge down to 3.0V per cell without power limitation. Crucially, it works by tricking the controller rather than changing firmware, so it needs to be permanently connected to the motor.
Ah, you've already asked this in another thread, and I've answered there — but since you're here: in OpenBafangTool, you want the parameters "Low voltage limit under load" and "Idle low voltage limit". Set both to 39V.
Your firmware version (46.2) should support parameter writes without any issues. Do back up your existing settings first, naturally.
Your firmware version (46.2) should support parameter writes without any issues. Do back up your existing settings first, naturally.
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