Burn the motor while pedalling too hard?


New Member
My bike commute is 115 km roundtrip which takes me little less than 4 hours per day, I do this 4-5/week and have done so for 4 years. In winter ( lives in sweden) I switch to MTB and the trip takes up to 6 hours especially if there is lots of snow. To reduce the time in winter I just ordered a 250w front wheel with 36v 10ah litiumbattery. 3 questions:

-instructions says toppspeed is 25km/h. Will that increase to 35 km/h or so if I add my usual peddaling power?
- how will the battery handle swedish winter? (Minus 10-15 celsius)
- is there any risk of burning the motor if I pedal to hard?

115kms is roughly 71 miles, so to be honest i think you`re wasting your time with a 250w front hub motor and a 36v/10aH battery. In minus 10-15C you`ll be lucky to get 20 miles,


you`re going to do a heck of a lot of pedaling!
Right now i am peddaling all of it so any assist is of help. How much would the battery output change in minus 10 comped to plus 20? 25%? 50%?
I don't have the math answer with regard to affect of cold on the battery, but I have a question. Is this pedal assist or is the kit you ordered throttle only? The reason I ask is that even though you might get fairly limited range with a 10AH battery, especially in the cold, if you can force yourself to limit using the throttle for only the times when you really need it (hills, or when you get a bit tired), and do so while still pedaling, that can go a long way towards extending range. In other words, since you are already pedaling the whole way now, you are right to assume any e-assist will help you out a bit, it's just a question of how judiciously you use it so that it lasts the whole way. The same can be accomplished with pedal assist, assuming you have an easy way to turn off pedal assist when not needed, but the temptation would be to keep pedal assist turned on, hence running the battery down faster. Simple throttle only when needed is probably the best way to extend range as long as you always keep pedaling.
Thanks, thats great info. The kit has both pedalassist and throttle but sounds like throttle is the way to go. Have to try to keep the battery as warm as possible.

Anyone know if there is a risk of burning the engine, like in very steep uphills or if going downhill very fast with full throttle?
I think controllers for the European market will quit sending power to the motor when the wheel is turning at the speed limit. So if you are pedalling and want to go above the governed limit, I believe you will be supplying all the energy. I will see what my own e-bike does. I've pedalled faster than its speed limit but thought the motor was still helping.

My goodness, a six hour commute in the snow on a bike. We weaklings in the USA would complain bitterly about an unexpected two hours in a car because of snow. This while holding our coffee cups at our warm desks.

If you go throttle only up a hill, and the bike drops down to slow walking speeds, then you're burning up the motor.
I don't know what kit or motor you have, but it should cut out (intentionally) before it gets overheated. Usually it will kick in again pretty quick, especially in cold weather. I've actually had this happen a couple of times with my Hill Topper kit going up steep hills. It does this to avoid damage. I think it's pretty common functionality, but I admit I do not know if it's universal.
With the mid mount Bafang motor I have, apparently what heats it up is the problem is not enough pedaling. Slowing rpm and increasing load heats up the motor . Apparently an aquarium thermometer can be used to keep an eye on temps. http://electric-fatbike.com/2015/06/07/installing-a-temperature-sensor-in-the-bbs02-unit/

Not sure how that would work on a hub motor.

You would want to get an extra charger, or pack along the one you have, so you can charge at work.

I was thinking of making an insulated battery cover for mine, there is a purpose made neoprene one for Bosch batteries, but it is expensive.
Once you reach the upper speed limit of the motor, the motor stops working and so at that point you would be providing all of the power through pedaling. You can go as fast as your legs will carry you, but the motor is not helping.

I think the suggestion about mostly using throttle mode is probably a good one for someone who is as active an fit as you are. You could just use the throttle judiciously on uphills and when you need a little boost. Then always take the battery indoors with you to keep it as warm as possible, and also recharge the battery at work. A nice way to use the throttle also is for starting from a dead start. It takes a bit of a push to get a bicycle going, so when I come to a stop, I use the throttle to get the bike going and then start pedaling again once I am in motion. This seems to be a good place to supplement my own efforts to conserve my own energy.
A torque sensor setup, with the torque sensor adjusted so it only helps you when you exert extra effort (hills) is the most perfect ride I can imagine. It's fabulous.
@Ulvåsa , hub motors cut out from heat overload if a hill is too steep for the size motor you're using or you're not contributing enough pedaling or the battery can't provide adequate power to the motor. The last occurs if the battery is nearing empty or is a smaller voltage and amp hour set up that just isn't powerful enough to do what the motor needs. The cut out is a safety default so none of the components are damaged. Really cold temperature, like freezing and below is going to be an issue for all of the better know Li Ion battery chemistries other than Li Titanate and ebike batteries aren't being built from that at this time. Friday, I spoke with Kyle Wilson, part of the technical team at BionX in Canada and he laughed calling the -10C temp shirt sleeve weather for them! Figured that they wouldn't be intimidated by a little cold weather :D. A number of their team do commuting and recreational winter cycling (not quite the commute you do, though!) and the most important recommendation was to keep the battery indoors where it would charge and stay warm until time to ride. Protect the battery connectors with the battery removed to prevent ice or moisture accumulation. And finally, use your system, whatever brand in at least the lowest level of pedal assist. Keeping current flowing through the battery all the time will help to keep the battery a little warmer and a cover for the battery unit is also a smart idea. Given that you're a strong rider and not really needing too much assistance, the folks at BionX indicated that just using your system on throttle only would let the battery cool down more, thus a lower temp which would reduce range and functionality of the motor system.
My understanding is that on a BionX kit, they have a feature called "Mountain mode" which essentially overrides the temperature sensor and allows the motor to get hotter than the system would ordinarily allow. BionX FAQ section describes it this way:

The Mountain Mode optimizes driving performances in alpine terrain. Ideally, the Mountain Mode should be activated right at the beginning of a long uphill in order to take advantage of the optimized performance. The Mountain Mode is activated via a software update by your local BionX dealer. To engage, hold the + button from any level of (A) or (G) for 2 sec. The four assist levels will flash, MOUNTAIN will appear briefly. Press – to disengage. The Mountain Mode sustains your power up to the top of the hill. It is not a “level 5” of assistance, but a different setting.
Other things to consider from my recent experience:
A dir drive motor will provide some noticable rolling resistance when not powered, and if you are trying to pedal the bike with NO battery power.

A gear hub motor has a coasting feature which allows you to pedal with less resistance. Meaning you can ride the bike like a normal pedal bike once the batt is done.

A couple options:

1) TINKERING... if you are patient, and handy with tools.... then you can do the research on your own and build something for this application.
2) Purpose built, or custom build..... You can work with a reputable shop to spec something out..... it should at least work on paper.... RE AH's, mileage, Speed, etc...... they can help with this.

I suspect with the right tuned PAS (pedal assist) that sips ah's......... you can achieve your goal. I'm thinking a dir drive hub motor, a large AH battery (in an insultated bag/case), and a tune-able programmable controller that allows you to fine tune PAS to a low level for a long time.

The things that seem to eat battery life: 1) throttle use..... heavy, 2) all throttle up hills, 3) fat tires, 4) low tire pressure, 5) starting/stopping rapidly, 6) no pedal assist.... etc...... When I want to run a long distance I will use my throttle(s) judiciously...... only applying enough e-power to assist at the minimum and work my legs to the maximum.... I decide at the start of my trip if this will be a 20MPH trip, or a 17MPH hour trip......... or a 14MPH trip............... then I pedal and thottle to maintain that max speed. I can tell you a 25MPH trip will be MUCH shorter than a 17MPH trip.

Yes, all true, but Ulvasa's primary issue is the very cold temps over an extremely long commute.
Man are all Swedes this tough? Hope we never play them in football.

Ulvasa I have no idea why you choose to commute this way, but if you're really capable of 115km/4hours = 29 kmh, a legal eBike will slow you down, since they are limited to 25 kmh.

I don't know if the Swedes allow a higher speed with ebike if pedal assist is used.. You should find out.

Anyway here are your coldweather problems:
Lithium Ion can operate down to -40c (According to battery university).. I would have a custom pack built that has good cold weather cells.
Drastically reduced battery capacity at cold temperature. Expect half the range at -20c compared to optimal conditions 20c
Reduced discharge capacity of cold temperature.
Can't charge a very cold battery at all until it warms up.

So you would need to buy a battery that can take you 115km on a single charge, at 25 kmh, under perfect conditions. Then buy a second charger so you can charge at work, assuming you will only get 50% range in cold weather.

You would need to let the battery warm up before you could charge it.

My guess is that you would need a battery around 36v 30 ah. Or two batteries 36v 15 ah each.

You should also fashion a thermal blanket around the battery pack. I would also suggest a thermal warmer, the kind hunters use.