Taking steep hills with a hub motor

Ohm_slaw

10 µW
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Nov 11, 2018
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6
Location
Northern Los Angeles County
I have a CA3, Phaserunner and a Bafang G062 1000W hub motor. My battery pack is rated at 48V 30A with Samsung cells.

I am pulling some steep hills and at some points the bike does not have enough power and slows down. I notice that as it slows down, the delivered wattage drops, which seems odd to me. I am doing whatever I can to give it all the current I can, but it does not respond. Why does the wattage drop?

If I give it a rest, it comes back rather quickly.

Is something getting hot and kicking in current limiting?

In other threads I read that keeping speed up around 10 MPH is important to avoid this sort of motor “bog down.”
 
More like 15 mph bro, unless you are riding a 20" motor wheel. Your wattage might be dropping as the motor approaches melt temp. But I doubt that is the cause.

At full speed cruise, your wattage should drop a bit, then increase to max as you start the hill. As the load increases, you often do see a drop in wattage, with most batteries.

I suspect you are not seeing a wattage drop at all. Well you are, but its not because wattage drops when you hit the hill. What you are seeing, is your battery voltage sagging like grannies tits. As your battery chokes out, its voltage drops 10v or so. Which slows you even more than the hill.

50v x 20 amps is 1000w But 40v is only 800w.
 
Pulling that kind of power regularly, for more than a few seconds, is an invitation to a burn down/long walk home. There is little doubt you are going to start burning parts eventually. That motor is only able to produce the power you're talking about for a minute or so and will then need a cool down period before you do it again.

If you need that kind of hill climbing power, you should consider a mid drive. There's no driving technique that's going to change that.
 
Ohm_slaw said:
Is something getting hot and kicking in current limiting?

In other threads I read that keeping speed up around 10 MPH is important to avoid this sort of motor “bog down.”

I try to keep the motor running over 14-15mph; 10mph is way too low.

If the CA is controlling, then it rolls back power on high temps (thermal rollback), assuming your motor has a temp probe, or on low voltage, assuming you have the low voltage rollback setting turned on.
Do you see either a T or a V flashing when it happens?
 
Get a thermistor installed in the hub motor and have a controller that can read it and save your motor.
I should have done that with my mxus 45H 3kw hub motor, and it would have been saved from melting. That hub motor was heavy a.f. and I never used it to its potential, I actually used it quite under its potential but I am pleased with the 5T? or 6T? (Might be better off with higher Turn Count motor like 8-10T, I never use the top bit of 52V for speed, just hills, but 36V I use all of it most of the time for flat cruising and hills.) Leaf 35H 1.5kw hub motor I have now as its much lighter then the 45h hub motor and has suited my needs.
- I just need the power for the hills for whatever mood I am in, whether I want to pedal, break a sweat and lose extra pounds, or be a lazy frock and not pedal as I used to be. Even a half assed, half pedaling, half not pedaling + diet = lost a ton of weight. With zero p.a.s., only throttle and the cruise function of the cheap generic controller. I found I just needed a pleasurable ride, having all the gears working properly, 3x8 has cheap chains, derailleurs and gears I have no need to afix more expensive parts like 1x12, and it doesnt really matter as ebikers like us generally only use 3 or 4 gears. For myself I like the option of having cruising gears with low cadence, having the choice to switch gears for a higher cadence but also that 2-4% of the time I run into a big hill I can go 22-24 crank gear and 34 rear gear for hill climbing. All other hills the middle 38 crank + 34 rear is fill as most hills are short so I can just power up, speed up to them and throttle on up them. However there are some 15' zig zags up the hill which slows me right down but 38 crank 30-34 rear is fine.



In general, taking steep hills with a hub motor just requires lots and lots of watts.
I have played around with low power, wimpy, low wattage setups and it was not pleasurable because I preferred not to pedal at that time.
At some point, there is a huge huge difference with increasing wattage, not pedaling and going up hills.
That all depends on your total weight, the kv of the hub motor, diameter of the wheel, and the power (battery + controller)




Mid drives are not needed for the majority of cases.

It might be the case for the scared people or those who buy and get ripped off by OEM low power wimpy ebikes and who have a certain amount of hills, but one or two hills using a hub motor that you can run up to it with speed, have good gearing, and sufficient watts (not 250W, not 500W but be an illegal criminal go to jail do not pass go scared mofo type 1200-1500W ---- Just ride with common sense, and courtesy)
 
markz said:
Mid drives are not needed for the majority of cases.

It might be the case for the scared people or those who buy and get ripped off by OEM low power wimpy ebikes and who have a certain amount of hills, but one or two hills using a hub motor that you can run up to it with speed, have good gearing, and sufficient watts (not 250W, not 500W but be an illegal criminal go to jail do not pass go scared mofo type 1200-1500W ---- Just ride with common sense, and courtesy)

Did you get your licence back after your DUI?

You sound like a zealot on your unregistered, unlicensed and uninsured motorcycle.
 
Ohm_slaw said:
I have a CA3, Phaserunner and a Bafang G062 1000W hub motor. My battery pack is rated at 48V 30A with Samsung cells.

I am pulling some steep hills and at some points the bike does not have enough power and slows down. I notice that as it slows down, the delivered wattage drops, which seems odd to me. I am doing whatever I can to give it all the current I can, but it does not respond. Why does the wattage drop?

If I give it a rest, it comes back rather quickly.

Is something getting hot and kicking in current limiting?

In other threads I read that keeping speed up around 10 MPH is important to avoid this sort of motor “bog down.”

Sounds like sag or temperature, but I'll ask anyway. Is phase current sufficient. If you are getting slow enough and into the initial power ramp you will see a power drop.
 
To expect performance and reliability when steep with a hub build does require power and speed, way above what you’ve got.
30+ lbs DD hub, 150+A controller, and the batteries to match.

Either you climb slow with a mid drive small motor, or you climb fast with a powerful hub motor. Simple as that.
 
MadRhino said:
To expect performance and reliability when steep with a hub build does require power and speed, way above what you’ve got.
30+ lbs DD hub, 150+A controller, and the batteries to match.

Either you climb slow with a mid drive small motor, or you climb fast with a powerful hub motor. Simple as that.

Nobody has the same definition of steep, but when I think about steep, I think about mountain biking where power is less of a factor than balance and traction. I know even with a lot of assist, I'll still jump off the bike around the same points due to loss of traction or flipping over backwards. Momentum does help in some cases though.
 
TDB said:
Sounds like sag or temperature, but I'll ask anyway. Is phase current sufficient. If you are getting slow enough and into the initial power ramp you will see a power drop.


I don’t know how to check phase current.

I’ll look at the voltage while it’s happening see if it’s sagging. If so, I’ll drop down the max current.
 
Thanks for the comments. My previous bike had a mid motor so I was used to slowing down in hills, but I can see from these comments that this is not a good strategy with a hub drive.
 
TDB said:
markz said:
It might be the case for the scared people or those who buy and get ripped off by OEM low power wimpy ebikes and who have a certain amount of hills, but one or two hills using a hub motor that you can run up to it with speed, have good gearing, and sufficient watts (not 250W, not 500W but be an illegal criminal go to jail do not pass go scared mofo type 1200-1500W ---- Just ride with common sense, and courtesy)

You sound like a zealot on your unregistered, unlicensed and uninsured motorcycle.

He's a big big man, like me. 1500W for us is just like 750W for a regular size man, or 500W for a wee Vladdy Putin. The law doesn't acknowledge us, but that's okay; we can acknowledge ourselves.

When I encounter a properly steep hill, I have to pedal my 1500W front hub bikes like I'm running from wild dogs, lest they peter out and stall.
 
Ohm_slaw said:
TDB said:
Sounds like sag or temperature, but I'll ask anyway. Is phase current sufficient. If you are getting slow enough and into the initial power ramp you will see a power drop.


I don’t know how to check phase current.

I’ll look at the voltage while it’s happening see if it’s sagging. If so, I’ll drop down the max current.

Maximum phase current is set in your controller.
 
Others just mentioned it, but I was about to bring up weight. If Ohms-law is slowing to 10 mph, either it IS steep, or its moderately steep and the load on the bike is heavy.

Typically, a geared motor such as he has does fine on hills that slow it to 10 mph, if the hill is short enough. So I mean 10-15% grades, for a 200 pound dude pedaling fairly hard in a 10 mph gear. This is just fine if the hill is one mile long or less, even if they repeat with a bit of coast down the hill time on the other side. I weigh 200, and have done years of riding a similar motor on single track trails that are moderately steep for the most part, and tend to have lots of 5% or less grade riding between the steeper bits. The hard parts are shorter, less than a mile usually.

Really steep shit, like the mule trails the national forest built in the 30's, will melt my big motor. I ride those on a 250 cc motorcycle now.

Where he will be in danger of melting the motor is if the hill slows him to 10 mph, and its 3 miles long at that much steep.

All this is possibly solved easily by pedaling hard as he can up the 10 mph hills, so he gets up them closer to 12-13 mph. But like the motor, a 3 mile hill that steep may be too long to avoid overheating himself as well as the motor.

If things are that severe because of above 10% grade, his weight, or a combination of the two, then he needs a mid drive, or a more powerful motor, or a second very small geared motor in the front wheel to assist only when it's that steep.
 
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