Completed first ebike build but possibly having overheating issues with varstrom geared hub kit

[ManBroSON]

I recently (about 3 weeks ago) completed my first ebike build. I'm using a trek 820 with a varstrom 750 watt geared hub motor ebike kit. The varstrom hub motor is likely a rebranded bafang g0900. This is paired with a 20ah 52v UPP u004 triangle battery with unknown BMS, though I am guessing its likely a 30A bms since it was sold as a 1500 watt battery (1500÷52=28.9). The controller that came with the kit is only rated for 22amps peak. Still, I have been able to get 40mph unloaded speed, and max 34mph loaded on aflat ground on a full charge riding on a cool night fully tucked, though generally I get closer to 28-31mph max.


While initially satisfied, I would like to be able to cruise at a slightly higher top speed for longer. My 20ah 52v battery is massive and capable of close to 50 miles, possibly more, throttle only. However I have found that if I ride for over 20 miles throttle only, or even if I ride closer to the max speed for even a few minutes, if I release the throttle and then re-engage it, it stops giving power completely until I go down a PAS setting and then go back up a PAS setting. The battery thus far has never felt hot. There is no temp sensor in the motor or the controller, but so far I have only felt the motor get very hot (can't keep your hand on it hot), so I assume that is likely the issue, not the controller overheating.

This seems odd as the display is only showing that I'm pulling about 850-950 watts at max speed loaded, which isn't anything crazy for a 750 watt bafaang geared hub motor and is well below the rated 22amp peak of the controller at 52v.

I was considering upgrading the controller to a 30amp one for better loaded speed, but that will likely increase heat, so before I do that, is there any way to more effectively cool the hub motor?

I read you can add small amounts of ATF to geared hubs (50ml or so), though I dont really want to open up the motor.
If I was to add ATF, could I do so simply by unscrewing the brake caliper screws and injecting into those holes? I took one off and saw that it goes all the way through to a shiny metal surface that moves independently of the exterior of the hub, so does that mean it would allow oil to reach the motor and stators or is that just a motor cover?

If I don't opt for oil cooling, would adding heatsinks to the hub help at all?

Alternatively, could I just undo the 6 bolts for the brake caliper and effectively increase air cooling that way? I use v brakes with coolstop ebike brake pads anyway, so I dont need those holes, though I wouls worry about dirt and water ingress.

Thanks!

 

[E-HP]

I recently (about 3 weeks ago) completed my first ebike build. View attachment 388182I'm using a trek 820 with a varstrom 750 watt geared hub motor ebike kit. The varstrom hub motor is likely a rebranded bafang g0900. This is paired with a 20ah 52v UPP u004 triangle battery with unknown BMS, though I am guessing its likely a 30A bms since it was sold as a 1500 watt battery (1500÷52=28.9). The controller that came with the kit is only rated for 22amps peak. Still, I have been able to get 40mph unloaded speed, and max 34mph loaded on aflat ground on a full charge riding on a cool night fully tucked, though generally I get closer to 28-31mph max.
View attachment 388183

While initially satisfied, I would like to be able to cruise at a slightly higher top speed for longer. My 20ah 52v battery is massive and capable of close to 50 miles, possibly more, throttle only. However I have found that if I ride for over 20 miles throttle only, or even if I ride closer to the max speed for even a few minutes, if I release the throttle and then re-engage it, it stops giving power completely until I go down a PAS setting and then go back up a PAS setting. The battery thus far has never felt hot. There is no temp sensor in the motor or the controller, but so far I have only felt the motor get very hot (can't keep your hand on it hot), so I assume that is likely the issue, not the controller overheating.

This seems odd as the display is only showing that I'm pulling about 850-950 watts at max speed loaded, which isn't anything crazy for a 750 watt bafaang geared hub motor and is well below the rated 22amp peak of the controller at 52v.

I was considering upgrading the controller to a 30amp one for better loaded speed, but that will likely increase heat, so before I do that, is there any way to more effectively cool the hub motor?

I read you can add small amounts of ATF to geared hubs (50ml or so), though I dont really want to open up the motor.
If I was to add ATF, could I do so simply by unscrewing the brake caliper screws and injecting into those holes? I took one off and saw that it goes all the way through to a shiny metal surface that moves independently of the exterior of the hub, so does that mean it would allow oil to reach the motor and stators or is that just a motor cover?

If I don't opt for oil cooling, would adding heatsinks to the hub help at all?

Alternatively, could I just undo the 6 bolts for the brake caliper and effectively increase air cooling that way? I use v brakes with coolstop ebike brake pads anyway, so I dont need those holes, though I wouls worry about dirt and water ingress.

Thanks!

You're fighting a losing battle since the motor itself, per bafang specs, is only 80% efficient. That means you're trying to shed 20% of the power/heat from the motor that has no path for the heat to go. If you're feeling enough heat on the outside of the case to make it hard to touch, the motor is cooking itself inside. Cooling the case doesn't do anything for getting the heat from the stator to the case.
Check various geared hub motors using the Grin motor simulator to get an idea of what you're dealing with. A lot of the geared motors, when run at 52v 20A will overheat with full throttle, even on flat ground. Anything prolonged use over 100C and you're starting to have issues like cooked hall sensors and demagnetized magnets, so better to let things cool if you feel any heat from the case.

Motor Simulator - Web Tools - Resources

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

It would be best to enjoy the bike as is, and plan a better build, choosing the components to meet your requirements, for a future build.

 

[ManBroSON]

Can you please link the bafang resource you are citing for 80% efficiency of the bafang g0900? I cannot find that anywhere.

I cannot find an efficiency graph for the bafang g0900 or varstrom 750watt geared hub anywhere either and they are not listed on grin's site. I'm not sure which hub motors there would be considered similar so I don't know how to get a general idea. Maybe the bafang g60 is similar, but when I searched a comparison between the two, it seems that the g0900 is considered more modern with better torque and peak efficiency.

Since my peak unloaded speed is 40 Mph when running a 22amp controller with 52v battery, am I correct in assuming this potential yop speed wouldn't increase with more amps such as from a 30amp controller?

Obviously efficiency will drop steeply at some point as I approach the max speed, and that's what you were trying to show me with the link to Grin's motor simulator, however I do not know how to ascertain what that curve would be exactly for my hub motor.

 

[hillslayer@]

I am using the same battery with a 45 amp controller on a 1000 watt direct drive hub, which would still get to hot on hills if I didn't have a 250 watt mid drive to help it. Geared hub motor will maybe be alright if you don't have many big hills but your top speed is maxed out and I don't think you can go with a bigger controller without killing it.

 

[RunForTheHills]

Bafang Motor H840 RM G0900.750.D/DC

 

[E-HP]

Can you please link the bafang resource you are citing for 80% efficiency of the bafang g0900? I cannot find that anywhere.

I just searched on bafang h640 and one link was to the manual.
Here's the product page on a seller's website that lists the efficiency on a table.

bafang h640, bafang h640 hub motor, bafang h640 motor, h640 bafang, 750w bafang geared hub motor, 750w bafang geared rear hub motor, bafang h640 kit

Model No. H640 RM G0900.750.D-DC; Rated power 750W; Rated voltage 48V; Dropout 138mm; Weight 5.6KG; Certificates CE/RoHS. Applications E-Tour and E-MTB.

www.kinstar-ebike.com

 

[OlderGiantFan]

Since my peak unloaded speed is 40 Mph when running a 22amp controller with 52v battery, am I correct in assuming...

Nice looking bike, well done. Have you stopped and put your hand on the motor after a prolonged hi-speed run to see if it's getting really hot?

 

[ManBroSON]

Nice looking bike, well done. Have you stopped and put your hand on the motor after a prolonged hi-speed run to see if it's getting really hot?

Thanks! And, yes. If I cruise at like half throttle (350 watts), so about 20-22mph its fine. 3/4 (500 watts) throttle it gets warm after a bit, and full throttle (800-950 watts) on flat ground gets very hot to the touch (can't keep my hand on it hot) fairly quickly.

 

[ManBroSON]

Bafang Motor H840 RM G0900.750.D/DC

Yes, I watched this video. It is a bit confusing to me because there is a difference between my varstrom 750W hub motor and the bafang G0900 shown in the video. In my case, the cable comes out of the casette side (right side) instead of the brake caliper side, as you can see in the first photo I posted.

Not sure how this would affect the correct spot to inject a low viscosity atf, such as ATI Super F 0 weight, which is an ultra low viscosity ATF that is designed for racing applications and that doesn't degrade nylon (gears would be protected and probably better lubricated). I can buy a quart of it for 15 dollars, so this would be a relatively cheap upgrade potentially.

Ideally, based on the video, it seems like it would be best to inject it on the side of the motor that doesn't have the gears, so it could better access the stator.

I am also still unsure, based on the video, whether atf would penetrate into the motor if injected throught brake caliper holes in the plate.

 

[E-HP]

Sounds like a plan! It’s always best to shop around for the answer you’d like to hear.

 

[RunForTheHills]

Yes, I watched this video. It is a bit confusing to me because there is a difference between my varstrom 750W hub motor and the bafang G0900 shown in the video. In my case, the cable comes out of the casette side (right side) instead of the brake caliper side, as you can see in the first photo I posted.

Not sure how this would affect the correct spot to inject a low viscosity atf, such as ATI Super F 0 weight, which is an ultra low viscosity ATF that is designed for racing applications and that doesn't degrade nylon (gears would be protected and probably better lubricated). I can buy a quart of it for 15 dollars, so this would be a relatively cheap upgrade potentially.

Ideally, based on the video, it seems like it would be best to inject it on the side of the motor that doesn't have the gears, so it could better access the stator.

I am also still unsure, based on the video, whether atf would penetrate into the motor if injected throught brake caliper holes in the plate.

Did you read his write up?

1. Recommendations: Based on the teardown and parts availability, I recommend most users run this motor with its stock controller setup. Pushing it hard with aftermarket controllers (high phase amps) risks damaging the hard-to-replace gears, especially without thermal monitoring. This motor is best left to advanced users if modifications are planned.

 

[Apartunis]

Did you read his write up?

1. Recommendations: Based on the teardown and parts availability, I recommend most users run this motor with its stock controller setup. Pushing it hard with aftermarket controllers (high phase amps) risks damaging the hard-to-replace gears, especially without thermal monitoring.

52V times 22A would make the bike according to industry custom a 600W bike. I do not think he is overcooking it.

 

[ManBroSON]

52V times 22A would make the bike according to industry custom a 600W bike. I do not think he is overcooking it.

I was planning to potentially upgrade the 22 amp peak stock controller to a 30A one, such as the G062 controller, which is rated for 1000 watts and 30 +/- 1 amps continuous.

Not sure what kind of speed increase this would give, and I would definitely need to do some kind of cooling upgrade, given that the motor is already overheating on the stock controller when driven hard at max speed.

I suppose that, worst case scenario, I end up spending $85 on the new controller, $15 on the ATF, and idk if there are any compatible hubsinks, but possibly some money on heatsinking to attach to the hub with thermal adhesive, and after all that, I end up burning up the motor and smoking it. If that happens, I can just proceed with the suggestion from E-HP, and purchase a higher wattage rated direct-drive motor.

 

[hillslayer@]

52V times 22A would make the bike according to industry custom a 600W bike. I do not think he is overcooking it.

Ebikebuilder put a bunch of miles on it with a vesc controller and temp sensor. Was hitting close to 100c on around 22 amps so it overheats pretty easy, just not a good motor to mod .

 

[Apartunis]

Ebikebuilder put a bunch of miles on it with a vesc controller and temp sensor. Was hitting close to 100c on around 22 amps so it overheats pretty easy, just not a good motor to mod .

Maybe, I do not know the motor so I can not say. It looks like the same class as Bafang G020 which eats 26 battery amps on the stock plug without issues.

 

[ManBroSON]

Ebikebuilder put a bunch of miles on it with a vesc controller and temp sensor. Was hitting close to 100c on around 22 amps so it overheats pretty easy, just not a good motor to mod .

Do you know if there were any issues with the standard 9 pin connector? Some have suggested that it can melt. However, The bafang g0900 750 watt seems to use the same 9 pin connector as the bafang 1000 watt g062 which uses a 30A controller, so I think it should be fine?

 

[OlderGiantFan]

...and full throttle (800-950 watts) on flat ground gets very hot to the touch (can't keep my hand on it hot) fairly quickly.

Hmmm. Flat ground is where hub motors are supposed to excel? Good luck sorting it all out. And if it becomes too much, these do well on flat ground too, and exceptionally well on hills

 

[E-HP]

Hmmm. Flat ground is where hub motors are supposed to excel? Good luck sorting it all out. And if it becomes too much, these do well on flat ground too, and exceptionally well on hills

View attachment 388291

But it has to slow down on hills. I had bbshd’s try to race me for some reason a few times. I let them stay close on the flats, but when I get to the 15%+ hills, they need to downshift while I just keep cruising up the hill at 30+.
I like my mid drive shorter rides or climbing slow on dirt, so it has its purpose, but the hub gets a lot more use, and I don’t have to deal with all of that shifting.

 

[hillslayer@]

But it has to slow down on hills. I had bbshd’s try to race me for some reason a few times. I let them stay close on the flats, but when I get to the 15%+ hills, they need to downshift while I just keep cruising up the hill at 30+.
I like my mid drive shorter rides or climbing slow on dirt, so it has its purpose, but the hub gets a lot more use, and I don’t have to deal with all of that shifting.

Just so nobody gets confused remind us how many amps that hub motor pulls on a 15 % grade.

 

[E-HP]

Just so nobody gets confused remind us how many amps that hub motor pulls on a 15 % grade.

Depends on the speed. Unless the two systems are running at the same voltage, power is the better comparison, and it doesn't matter whether it's a mid drive or direct drive. More power will climb faster, by definition, since horsepower is defined as the energy required to lift 33,000 lbs by 1 foot in 1 minute. The small mid drive motor's strength is to still be able to climb a very steep hill, albeit slower than a motor with more power. I don't like riding around cars, but when living on steep hills, you can't totally avoid sharing the road with them, so sometimes you need to keep up with the flow.

 

[hillslayer@]

I will help you out

 

[E-HP]

I will help you out View attachment 388315

This is my bike, throttled to 30. A little less power required than the motor you modeled (3140W vs 3557W).




The BBSHD can do around ~30 on the flats, but has to slow down to 10 after downshifting on the hill.

 

[OlderGiantFan]

But it has to slow down on hills. I had bbshd’s try to race me for some reason a few times. I let them stay close on the flats, but when I get to the 15%+ hills, they need to downshift while I just keep cruising up the hill at 30+.

Well from your last post you appear to have a 3000W motor? No wonder you murdered the BBSHD lol. For the hills I always gear down anyway, simply to avoid stress on chain and sprockets. Most with mid drives do that I suspect. We could go faster but we'd be replacing chains every 3 months. I don't want a super powerful electric pushbike, just a pushbike that will allow me to ride a gut-buster route without cracking a sweat. I don't have any fixed in stone detest for conventional vehicles either and if I want to go faster I have a few motorcycles here that are a lot more practical than a beefed up pushbike

Reading around these threads I see clearly that many have a pathological avoidance of anything that burns gasoline. It's electric or nothing. But if that is the case then why the push to go faster and faster like the cars? It's not like you'll ever be able to go as fast as them anyway, not safely anyway. It sort of reminds me of Vegetarians. They detest meat in any form yet they are forever trying to make meals that 'taste' or 'look' like meat foods. Vegetarian hamburger paddies and sausages, vegetarian lasagna FFS. It all tastes gross compared to the meat based meals but they insist on serving it up. There are plenty of traditional vegi meals that actually taste quite nice, like Vegetarian falafel, a traditional Middle Eastern dish. Yum Yum



In 50 years we might well be limited to electric only bikes but until then I'm happy to go with flow, this is what I use for long rides in the hills. Sure it burns some oil product, just like the masses of heavy machinery that mined the Lithium rock out for the battery on my ebike.

 

[E-HP]

Well from your last post you appear to have a 3000W motor? No wonder you murdered the BBSHD lol. For the hills I always gear down anyway, simply to avoid stress on chain and sprockets. Most with mid drives do that I suspect. We could go faster but we'd be replacing chains every 3 months. I don't want a super powerful electric pushbike, just a pushbike that will allow me to ride a gut-buster route without cracking a sweat. I don't have any fixed in stone detest for conventional vehicles either and if I want to go faster I have a few motorcycles here that are a lot more practical than a beefed up pushbike

Reading around these threads I see clearly that many have a pathological avoidance of anything that burns gasoline. It's electric or nothing. But if that is the case then why the push to go faster and faster like the cars? It's not like you'll ever be able to go as fast as them anyway, not safely anyway. It sort of reminds me of Vegetarians. They detest meat in any form yet they are forever trying to make meals that 'taste' or 'look' like meat foods. Vegetarian hamburger paddies and sausages, vegetarian lasagna FFS. It all tastes gross compared to the meat based meals but they insist on serving it up. There are plenty of traditional vegi meals that actually taste quite nice, like Vegetarian falafel, a traditional Middle Eastern dish. Yum Yum

View attachment 388320

In 50 years we might well be limited to electric only bikes but until then I'm happy to go with flow, this is what I use for long rides in the hills. Sure it burns some oil product, just like the masses of heavy machinery that mined the Lithium rock out for the battery on my ebike.

View attachment 388322

I think the BBSHD is rated at 1500W peak. My motor is rated at 1500W continuous. I'm using less than 400W for the majority of my riding, at around 20-25mph. But if I need more power for hill or to speed up, I have it. If I'm riding 20 mph, I'm not going to slow down just because there's hill, like on a pedal bike. I'll adjust, just like car or motorcycle, to maintain my speed. (I can't recall the last time I had to shift my truck to low and slow down while driving on the freeway up a mountain pass. I just step on the gas a little.)

I have 300k miles on motorcycles, that included hundreds of close calls, and a few accident at speed. I always thought I'd be riding again after the kids were out of the house, but it never happened. I know I don't have the reaction time anymore to stay alive, but 20-30 mph on a ebike isn't a problem, and still a lot of fun.

 

[hillslayer@]

This is my bike, throttled to 30. A little less power required than the motor you modeled (3140W vs 3557W).

View attachment 388317


The BBSHD can do around ~30 on the flats, but has to slow down to 10 after downshifting on the hill.

Bbshd is only 30 amps your hub is 80 volts and 80 amps not something to compare to a low voltage mid drive.