Bafang's BS vs. Reality

[Papa]

A neighbor swung by my place the other day, toting his deceased RadRag... (or whatever it's tagged) in the bed of his truck. To anyone with a nose, it was reasonably clear the Rad's motor is a crispy critter. Pulling numbers, the motor appears to be a Bafang G60 500W 'rated' hub motor. He realizes a motor replacement is mandatory, so he begins quizzing me if an upgrade is possible. After checking later that night, I see Bafang offers both a 750W, and a G062 (1000W?), both appear to be bolt-in's (more or less). But before I started hammering my plastic on the replacement, I decided to run some numbers on Justin's Simulator.

Ya know.... I just don't see spending an extra 150 bucks for the measily wattage increase is such a bargin. Thoughts?

 

[amberwolf]

What specific conditions and usage killed the one he has?

Knowing that will help figure out something that can handle that. it might not be more power that's needed, it might be a different configuration of the same power.

 

[Papa]

What specific conditions and usage killed the one he has?

His 16yo son!...
.... and his explanation doesn't point to a 'problem' with the bike. The way I see it, boosting HP could easily result in skin loss.

 

[Epithemeus]

The way you've got the simulator set up isn't really a fair comparison. You've got them both with the same controller set up so the same amount of power going into it. As you've discovered the power limit of a motor is really about how much heat it can handle before becoming a toaster. Do the same simulation you've done but with a 10% grade, you'll see that the g60 overheats in about half the time as the g62. So the g62 can handle a fair amount more power.

So if the bike had had a g62 instead it would potentially have been able to survive the load. (Can't say that for sure of course without knowing the exact load) It very well could be worth the extra $150 to give more breathing room though. Really the best upgrade would be a thermistor in the motor and a controller that can limit power based on temperature, that's more difficult though.

 

[Papa]

Appreciate the feedback - that's exactly what i was seeking. As requested...


Yes, as expected, temperatures on both motors increased. However, note the 25 minutes to 'overheat' for the 500W G60... that's a 10% 'nasty' for 8.4 continuous miles (without stopping). Is that being realistic for a mostly off-road vehicle? Note too, the G62 is also toast 16 minutes later... not at all what I would call an acceptable buffer zone for the claimed 1000W and 150 bucks additional cost. Thoughts?

 

[neptronix]

equalize the speeds to within .1mph, so the RPM lines up as well as possible. You can put a decimal in the percent field, btw

In this case, i would bet the difference between these motors gets a lot smaller.

 

[Papa]

equalize the speeds to within .1mph, so the RPM lines up as well as possible.

Like this?...

 

[Epithemeus]

You need to adjust the throttle level as well as the speed. Checking the little checkbox for "auto" by throttle level will adjust the throttle automatically to match where the speed slider is. Though it's not always spot on, so I did it manually (hopefully you can read my crappy screenshot from my phone) It seems like the g62 is a pretty good improvment (45 minutes instead of 25) G62 (1000W) Fatbike Motors Makes sense given what this blog post says, wider motor = good. Though of note, you'd likely need to swap out the connectors, the grin versions use different connectors for sure, not sure about the rad whatevers.

Given they've already fried one motor though you very well could be right about it not being enough no matter how big a difference it makes. I dunno, I understand motors better than people

 

[Papa]

Somewhere among my digital travels, someone stated that despite the obvious rotor width difference, the magnets were the same dimensions (image was included). But I failed to bookmark it. Still looking.

 

[offGridDownUnder]

best upgrade would be a thermistor in the motor and a controller that can limit power based on temperature

Does the mention of temperature in the simulator mean there is a thermistor in the motor? The Grin pages I found for the motors do not say.

 

[neptronix]

Ahh this explains the efficiency difference, although it's rather small.

G62 looks like more of a fun time; but seems equally poor in the heat shedding department ( this is really the achille's hell of geared hub motors )

Somewhere among my digital travels, someone stated that despite the obvious rotor width difference, the magnets were the same dimensions (image was included). But I failed to bookmark it. Still looking.View attachment 343966

 

[Papa]

Yet another difference I just remembered: (quotes below from Grin)

G60 has Z910 connector "...30-40 amps of max..."
G62 has L1019 connector (12g) "...shown to be reliable for up to 100A..."

Yes, I realize the Rad's connectors are different

 

[Epithemeus]

Does the mention of temperature in the simulator mean there is a thermistor in the motor? The Grin pages I found for the motors do not say.

No they don't seem to unfortunately. I'm assuming they had to add a thermistor themselves for the simulator profiling. Not a particularly easy mod either.

 

[amberwolf]

Does the mention of temperature in the simulator mean there is a thermistor in the motor? The Grin pages I found for the motors do not say.

No, it means that thermal testing was done on that motor (not just a simple thermistor added in one spot; they have some info around here and on their site about that testing) so they could build a thermal model of it (as well as the electrical one).

Motors with no thermal info in the "overheat in" section have no thermal model.

 

[Papa]

Source: youtube.com/watch?v=uSSOwjQw3gI&t=293s

*** Note rotor width comparison ***

G062 !000W - Cable exits brake rotor side
G060 750W - Cable exits cassette side

 

[Papa]

Grin/Bafang MG62 - 1000W - 6.5T - 8rpm/V - Fatbike 170mm

 

[Papa]

UPPER IMAGE - Bafang G62 1000W from Grin ebikes.ca. LOWER IMAGE - Bafang labeled G62 1000w unknown origin.