You answered the question yourself. Batteries have internal resistance. As soon as you start using them, they warm up, so the ambient temperature doesn't make much difference.

 

Ebike batteries are not the same as car batteries. Car batteries only discharge for a few seconds when using the starter motor, which doesn't give them enough time to heat up. After that, all the electrical power comes from the alternator. Ebike batteries give more or less continuous power until empty. How much they heat up depends on how much current you draw.

 

The good 18650s have an internal resistance of 50 milliohms. Lets say that an ebike averages about 4 amps (160w). The heat generated would be 0.8 watts per cell, which is 32 watts for a 40 cell battery. That's enough to gradually warm it up. When you go up a hill and use, say 10 amps or more, the heating would be 5w per cell and 200w total, which is substantial. That would be if it stayed cold, but actually, the internal resistance would go down when it warms up, so actual heat would be less.

 

Therefore, if your bike feels sluggish because you left it out in the cold, just run full power for a couple of minutes and then your battery will come to life.

That's certainly a good point regarding the usage pattern of car batteries being different to that of ebike batteries, but the rest doesn't match my experience.

 

I no longer store my bike outside, but when I did I regularly found that the battery gave considerably less capacity in the depths of winter than in warmer weather, maybe 25-30% less. At the time, my regular commute was about 20 minutes, so maybe this wasn't enough time for the battery temperature to rise sufficiently. My experience is with LiPo though, so perhaps the relatively low IR in either scenario (warm or cold) made little difference to cell temperature compared to other cells with lower C rates.

I was just looking at the spec sheet for Samsung 30Q cells. During the 10 amp discharge test, they heat up to 100 deg C!

My experience is with LiPo though, so perhaps the relatively low IR in either scenario (warm or cold) made little difference to cell temperature compared to other cells with lower C rates.

 

I haven't got a cell thermometer but I have touched my battery after a hard climb:

 

- The motor was hot, not burn your fingers hot but definitely beyond comfortably warm, I would have guessed 50-60°C (reminder get self an IR thermometer)

- The battery was not even slightly warm

 

Drawing 15 Amps continuous during a 20 minute climb from a pack that is capable of 25 Amps in reality or 100 Amps constructor, if I apply the ES formula, isn't going to create much heat. Charging at 1C they don't budge or maybe in the range of a couple of °C too little to detect manually.

 

I received a charger thermometer with my new chargers, where do you put that? For me the ideal place is in the centre of the battery pack but that is obviously impossible. They also have a logging function which I will have to get my head around when my life gets back to normal next month.

I was just looking at the spec sheet for Samsung 30Q cells. During the 10 amp discharge test, they heat up to 100 deg C!

 

Now there is a new invention to patent: "object serving to make a cup of tea while you ride" Or "water cooling mechanism for e-bike battery". Soon all those integrated down tube batteries will need external cooling fins, that will play havoc with your Cx ratio!

The Lightning LS218, which is the world's fastest production motorbike, and happens to be electric, uses a water-cooled battery.

http://www.evdrive.com/products/evd-motor-controller/

 

stick that on a mtb

Keep practising. Soon you'll be able to use a roadbike like me and do 0 Wh/mile, which saves a lot of messing about. No battery range anxiety either. Wind is also easier to deal with.

 

I've done 30 years of "normal" bikes, the ebike is a treat for the daily commute..

I average about 4wh/mile on the Gtech, proved it's worth again today riding into a hellish head wind..

I find that the effort to pedal my roadbike is the same as my (very efficient) electric bike on the lowest level of assist, which is about 60w. That's at the same speed and on the same hills. 60w at 4mph is 4 wh per mile, so that's the cross-over point, when a road-bike would be a more logical choice.

 

If you want a treat, not having to pedal too hard, you can't have 4wh/m, so the two shouldn't be put in the same context because it confuses some people, and in the worst case, they might buy a bike that isn't suitable. A statement like: " I normally use 3.5wh per mile because I like to pedal hard. On some days, I like a rest, so I don't pedal hard, which uses 10wh/ mile. Overall, I average 4wh/m", makes the situation much clearer.

 

The whole point of this thread was to provoke discussion on why statements about range and effriciency can be very misleading, in the hope that it will enable readers to make better choices.

 

Most people buy an electric bike because they want or need extra help when pedalling. Some don't want much, others can hardly pedal at all. Luckily, there's a choice of bikes that give different amounts of help. One thing is sure, though: You cannot have a lot of help and low power consumption. How much consumption you get is more or less directly proportional to how much help you get.

Hi Dave, I was interested that your bike seemed to have both a rear rack and rear suspension. That would be much kinder to the rear wheel/spokes than a hard tail.

 

I am also 100kg ish and carry heavy panniers on a rear rack and on my first electric assisted bike the Oxygen emate city that I used on rougher tracks than I should have this led to broken spokes.

 

On my sDuro yamaha Haibike I had a stronger rear wheel built to solve the problem.

 

I would love a good design for an off road commuter like me that allowed the combination of a full suspension mountain bike set up and a rear pannier rack.

Hi Dave, I was interested that your bike seemed to have both a rear rack and rear suspension. That would be much kinder to the rear wheel/spokes than a hard tail.

 

I am also 100kg ish and carry heavy panniers on a rear rack and on my first electric assisted bike the Oxygen emate city that I used on rougher tracks than I should have this led to broken spokes.

 

On my sDuro yamaha Haibike I had a stronger rear wheel built to solve the problem.

 

I would love a good design for an off road commuter like me that allowed the combination of a full suspension mountain bike set up and a rear pannier rack.

Get yourself on of these, or two if you want front carrying capabilities too!

We sell them, and they are very good...holds 25kg on top...nice drybags too.

https://www.thule.com/en-gb/gb/bike-accessories/rear-bike-racks/thule-pack-n-pedal-tour-rack-_-pp_100016

I don't have any problem with spokes on my bikes. It's possible that the rear suspension helps. I hadn't thought of that before, but I found that instead of building a stronger wheel, you need to build a weaker one. I think a stronger (stiffer) rim would help, but the main thing is the spokes. Most electric bikes use 13 gauge spokes, but I use 14 gauge that are thinner and more elastic. I reckon that the elasticity takes some stress off the elbow. Also, it stops the bottom spokes going loose when you hit a big bump. Each time they go loose momentarily, the nipple can unwind a bit. so the spokes gradually become loose permanently, which would cause complete failure if it wasn't sorted soon.

 

Breaking spokes is a bit of a mystery. I guess that there's lots of reasons for it. I had a very expensive Halford bike in 1989. I only weighed 75kg then, but I had loads of spokes that broke. Some of the traders tell me that they get batches of bikes where every one gets breaking spokes, but then the problem mysteriously disappears when nothing changed. Obviously something did change, but you can't see it.

 

Racks are a problem for bikes with rear suspension. If you attach them to the rear subframe, it increases the unsprung mass so your suspension doesn't work properly. I think most people use cantilever racks fixed to the seatpost, but you have to mount them high to allow for the wheel movement with the suspension. That can spoil the handling. Everything is a compromise.

I remember now that i had no problems with the spokes in the first rear wheel on my Oxygen.

 

However when the motor became faulty within the two year guarantee and Andrew at Oxygen sent me a new rear wheel and motor that wheel became a spoke breaker. However as I still had the old wheel I had plenty of spokes to play with!

For me the best part of the Gtech is the push away from the lights and help with the wind and hills.

 

I set off on it the other day without turning it on and it was instantly noticeable.

 

I did put this in my review and the reasons why I chose the bike (low maintenance singe speed, the hub motor is the perfect combination for a single speed imho).

 

Once up to speed it's easy to keep above the cutoff on the flat, but some days I slow down and let the motor do the work, especially if I've had a hard day at work!.

power: that's where the Gtech does not compare well to other bikes.

It's all a compromise really, the Gtech's weight is in it's favour to a degree but you need to pick the right tool for the job.

 

I do 3 mile commuting in traffic, lack of gears and light steering are an advantage in stop start traffic for me.

 

I could have quite easily bought a motorcycle to do the same job but enjoy cycling and decided to treat myself.

 

I think some people blur the lines between a cycle and a moped, for me pedal "assist" makes it a cycle?.

I was looking at the Juicy bike site and saw an electric scooter for £2,500 and instantly thought to myself I would never pay that much for an electric scooter.

 

Then I had a little moment and remembered that I had spent £2,000 on an electric bicycle!

 

It is strange how we rate things differently in our mind, justifying some things and not others.

3000w, 60v, 30ah and fully legal 30mph which satisfies a very different objective to our bicycles. Certainly not for everyone.

No criticism at all of the scooter or any of your products, or prices.

 

I was taken back at my subconscious thought process.

My bike is catching you D8veh, 60 miles+ miles and less than 20% battery used. And the range is getting better ( until I get a working display). 16ah of hobby King rules

I find that the effort to pedal my roadbike is the same as my (very efficient) electric bike on the lowest level of assist, which is about 60w. That's at the same speed and on the same hills. 60w at 4mph is 4 wh per mile, so that's the cross-over point, when a road-bike would be a more logical choice.

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It's interesting. When I got to around 5wh/m I switched back to an analogue mountain bike. Of course I still use the electric for transport and drunkenness, but for fitness/fun I now favour the manual.

 

Its a question I was asking a few weeks back. I didn't really get an answer.

 

So, I would conclude that at around 4-5wh/mile you may want to consider a manual.

 

Sent from my HTC 10 using Tapatalk

 

Of course I still use the electric for transport and drunkenness, .

 

 

What is not to like!

For most of my UK riding a normal mtb is a better choice but I had to leave my mtb in Austria. I didn't want to leave the Haibike unused until next summer. I am finding myself riding faster just to give the battery some work (unrestricted).

Edited October 2, 20169 yr by chris_n