18% hill - how much power? Which motor?

[paul-home]

I have an 18% gradient hill that is about 1/2 mile long on my way to work.
I have spent the last couple of years hauling a big heavy ebike up it.
It would be great to come up with a setup that could make climbing that hill easier.
I currently have a 9c front motor. With a battery putting out about 1000w at 58v, I have to stand on the pedals to get up the hill.
Does this mean I am just too heavy?? Should I get another job to avoid the hill?
Will an ecitypower 500w cute motor and a Lyen sensorless 12 FET controller get me up that hill?
Does anyone have any suggestions?

 

[swbluto]

It depends. What's your total you+bike weight and what speed do you desire? A higher amp controller would make the motor climb hills better, but typical non-brutish hub motors won't take to it kindly if it's a significant climb (Like more than 5-10 minutes to climb.). A smaller wheel would also help.

Based on the limited information so far, it appears a geared setup would be optimal, though it'll still be "slow" at 1000 watts but you wouldn't "have to" stand on the pedals. Appropriately setup, it'll still be faster than a typical hub motor.

 

[dequinox]

Yeah it sounds like in your case a non-direct hub motor would be best. You seem to have the voltage there... I have a chain-drive that only has 36v and it will eat hills without killing the motor thanks to the fact that it's an 8 speed with a granny gear. Look at other hub motors or an improved controller. There are some sales going on at e-bikekit for a $200 geared motor kit right now...though I don't know what the wattage is...

 

[paul-home]

My round trip is nearly 50 miles, the hill is in the last 3 miles so I am carrying a fair bit of battery weight, old Li-Ion 18650, 220 cells total. Still working after 2 years and a lot of miles.
I am about 15 stone, a consequence of finally stopping smoking after too many years!
I think the total weight is approx 19 stone, or 120 kg.
I don't care about whether the 18% hill climbing is slow, I just don't want to have to get off and push the bike up the hill, or arrive at work wanting to lie down!

 

[Russell]

You didn’t give any details about your present bike, motor or controller but I’ll assume it has 26” wheels that the 9C is a “9x7” model and the controller is a stock 20-25A model. If that’s the case then replacing the controller with a more powerful 40A unit will help somewhat provided your 58V battery can handle that current draw. If your present battery is not up to that task then you might as well stop and think about a new battery too since any solution is going to take a lot of current.

Climbing an 18% slope is a lot to ask from a hub motor, any hub motor. At a combined weight of 120kg it will take roughly 950W to the wheel to achieve a speed of 15 km/h up that incline. There are very few hub motors which can produce that kind of power at that low of an RPM in a 26" wheel. One that will is a BMC V2-T with a 40A+ controller with your 58V battery. A slow-wound 6x10 9C might also do the job but it's not modeled on the ebikes.ca simulator to check it out. It too would need a 40A+ controller to do the job. The 6x10 9C is also the cheapest choice and they are on sale at ebikekit.com. There’s no way a single little CUTE motor is going to do what you want but two might. Of course then you have the complexity of two motors, two controllers and you’ll still need a battery capable of delivering 40A+ total.

As others have said smaller wheels will allow any hub motor to spin faster and make more power at a lower bike speed. The downside of course is that there are few choices for adult bikes with 20 inch wheels and fewer I’d want to ride for 50 miles, save for maybe a recumbent.

External motors running through the gears might be the best solution unfortunately many of them compromise the climbing ability by eliminating the triple front chainring leaving you with only the rear cogs. An internally geared rear hub can be a solution but the wide range models are pricey.

As always there's a lot to think about!

-R

 

[jag]

Russell pretty much summed up the most relevant information above.

As a point of reference, I climb hills at about 10% with a 9C @ 2000W. This still requires vigorous pedalling.

When using the ebikes.ca simulator one thing to pay attention to is the efficiency of the motor:
The bad news is that when climbing at say 15-20km/h the 9C efficiency is only about 50% (set battery to 58V, current 40A). This means of 2000W in, 1000W turns into heat. The 9C tolerates this for a while, but probably not sustained. (At 40-50km/h speed the efficiency is 70-80% so more power to the wheel and less heat is generated.)

So just getting more current to your 9C might do the trick for a short steep hill, but not for long sustained climbing.

A BMC V2T motor is about 65-70% efficient at 15-20km/h and needs only 25-30A to generate 1000W mechanical power, but will give you slightly lower top speed. On the plus side you might be able to make do with your existing controller and battery. A v2S might also work, particularly if you upgrade the phase wires, though your controller might struggle with the higher phase currents at low speed.

Is there enough of a flat stretch in front of the hill that you can build speed and thus momentum? For a short hill this will help.

If your battery is not up to the current, and you are on a budget, you could add say 2series 2parallel (4 total) Dewalt toolpacks with the kfong boards. This will give you 53V nominal at up to 50A, and because the kfong board has a diode, current won't go backwards from your 58V main battery. (The main battery will just sag to 53V, and then the A123's in the Dewalt packs will start to deliver) http://www.toolking.com/dewalt-dc9280-28-volt-lithium-ion-nano-battery

 

[swbluto]

Based on your information and the previous responses, it sounds like an externally geared motor would be best for you. Geared hub motors may work, but they tend to be a bit on the expensive side for the kind of output power you're looking for.

The other plausible option sounds like a dual hub motor setup, but you'll need another hub motor, controller and you may need more batteries. You may also need new batteries depending on the output power of your current ones (The "laptop type" batteries doesn't inspire much confidence in regard to the amount of power needed for this application.).

I would seriously look at a cyclone or think about a RC setup-up. If you're price conscious or 'convenience-conscious', a cyclone would probably be best. (Or if you're technically 'advanced', an RC setup may be doable.)

For the cyclone, you may need a more powerful controller, though if you can get it geared correctly, it'll still haul you up with your current controller, it just won't be too fast. I may expect something in the 6 to 10 mph range with 58v and 20 amps.

If you live in a legally anal area where anything other than a hub motor would be quickly reprehended... well, that just sucks. It looks like dual hub motors with more batteries would be the only other practical option and, well, that introduces other complications.

 

[AussieJester]

I would seriously look at a cyclone or think about a RC setup-up.

+1 can be setup to climb steep hills and get you decent top speed on 48v setups.

Even with a single speed setup they have excellent hill climbing abilities, here's my buddy and ES memebers 1000w (Matt.P) with his 1000watt cyclone powered custom crusier tackling one of the hills around my area.

[youtube]44X6EI5W8kY[/youtube]

At the time this video was shot Matt was using an unmodified 35amp max cyclone controller with 48v 20ah Headway setup. Matt has soldered the traces and shunts and now gets 75amp
out of the controller, has significantly increased performance but as the video shows stock it has some climbing power without pedal assist!

Best of luck with your build...

KiM

 

[wasp]

I would seriously look at a cyclone or think about a RC setup-up.

+1 can be setup to climb steep hills and get you decent top speed on 48v setups.

Even with a single speed setup they have excellent hill climbing abilities, here's my buddy and ES memebers 1000w (Matt.P) with his 1000watt cyclone powered custom crusier tackling one of the hills around my area.

[youtube]44X6EI5W8kY[/youtube]

At the time this video was shot Matt was using an unmodified 35amp max cyclone controller with 48v 20ah Headway setup. Matt has soldered the traces and shunts and now gets 75amp
out of the controller, has significantly increased performance but as the video shows stock it has some climbing power without pedal assist!

Best of luck with your build...

KiM

+1

 

[liveforphysics]

If you're on a budget, lacing that hubbie into the smallest diameter rim you can find would result in a substantial increase in the hill climbing ability for minimal cost, and minimal added complexity (possible disk brake conversion needed).

 

[paul-home]

Thank you all for the advice, its very much appreciated.
If it weren't for this forum, I would have given up on ebikes a long time ago.

 

[dogman dan]

While a hub motor could be set up to take that hill, you'd then have a bike far from ideal for the rest of the ride. Definitely time to look at through the chain type solutions that can take advantage of the bikes gearing so you have low gear for the hills without losing top speed.

I find the small gearmotors I've tried start hitting the wall at 12-13% and dd motors tend to start bogging above 8-10%, so 18% is definitely out of the normal use range of just about all hubmotors.

 

[veloman]

http://www.analyticcycling.com/ForcesPower_Page.html

Input your total weight in kg and .008 for rolling resistence, .8 for effective frontal area. Then put in the hill gradient decimal.

.2 for 20% grade and so on

Gives you the exact power output you will need, sustained, to the back the hub, to climb that hill.

 

[curious]

20" wheel will help with torque but it will slow down normal riding for a given setup.

How about adding a second geared hub (freewheeling) and use it only on very steep hills as a booster ? It can be lightweight (as it will not work long enough to heat soak) and a slow one (the higher internal gearing the better).

Use your old controller to drive the geared booster hub and get something beefier/nicer for 9C. You can certainly push more than 1kW for a short time through 9C.

 

[Anonymous]

1200w cyclone. ebay it. I got a geared 500w and upgraded to 1500w geared, works flawlessly

I have an 18% gradient hill that is about 1/2 mile long on my way to work.
I have spent the last couple of years hauling a big heavy ebike up it.
It would be great to come up with a setup that could make climbing that hill easier.
I currently have a 9c front motor. With a battery putting out about 1000w at 58v, I have to stand on the pedals to get up the hill.
Does this mean I am just too heavy?? Should I get another job to avoid the hill?
Will an ecitypower 500w cute motor and a Lyen sensorless 12 FET controller get me up that hill?
Does anyone have any suggestions?

 

[GGoodrum]

I wouldn't give up on the 9C, just yet. You can run a lot more power through it than 1000 or 2000W. I have a 9C on a 20" folding bike that was using one of methods 100V/100A 18-FET controllers. I used an 18s2p 66V/10Ah LiPo-based pack, and the controller current limit was set at about 70A. 4500W will get me up any hill.

Anyway, with enough power, you can go up a hill fast enough that it doesn't have time to get too hot.

-- Gary

 

[swbluto]

^^^^^^^^^^^^
Very much depends on the hill. If they're "moderate" sized (Maybe 200 feet and less.), then that's likely true.

 

[dogman dan]

1/2 mile of 18% is pretty wicked. I probobally have 18% on the singletracks I ride in the mountains, but any more than I can take on momentum, and I end up walking the bike, using the motor to help me push it. Hard to even stand on those slopes with loose sand and gravel.

A half mile of 18% dirt would even challenge a gas dirt bike.

 

[Anonymous]

get a cyclone kit... that never gets warm on ANY hills... impossible to pedal hills are nothing now

1/2 mile of 18% is pretty wicked. I probobally have 18% on the singletracks I ride in the mountains, but any more than I can take on momentum, and I end up walking the bike, using the motor to help me push it. Hard to even stand on those slopes with loose sand and gravel.

A half mile of 18% dirt would even challenge a gas dirt bike.

 

[02jze]

x100 for cyclone kit. I have a 1200 watt kit and im over 100kg with out mny heavy bike and i only throw in light pedaling to get me up any hill i wish. Not as fast as matts in the video but i get there. That video makes me want to get rid of my heavy 48volts worth of slas and get some rc lipo packs.
Ill cruise around enjoying that power upgrade then do the controller mod.

 

[The Mighty Volt]

Just as a matter of interest.......a 20Ah battery at 72v is capable of a nominal Wattage of 1440w.

Now, if those batteries are A123, what is the true peak wattage that the unit is capable of?

I think some consideration must be given to the chemistry/brand of the battery and not just it's basic parameters {viz. Ah and Voltage}

 

[John in CR]

Just as a matter of interest.......a 20Ah battery at 72v is capable of a nominal Wattage of 1440w

Nominal Wattage??? I don't believe there is such a thing. A 72v20ah battery has a nominal capacity of 1440 watt hours, so you could theoretically run at 1440 watts for one hour or 2880 watts for 30 minutes.

 

[The Mighty Volt]

Just as a matter of interest.......a 20Ah battery at 72v is capable of a nominal Wattage of 1440w

Nominal Wattage??? I don't believe there is such a thing. A 72v20ah battery has a nominal capacity of 1440 watt hours, so you could theoretically run at 1440 watts for one hour or 2880 watts for 30 minutes.

With certain batteries, there is a nominal discharge and a peak discharge, no?