Which e.bike?

[Eaglerider]

I've had a Freego Eagle for two years and been very happy with it. It's done around 2600 miles. I have the 16a/h battery and it's still going strong. Last week I completed a 43 mile trip including climbing from sea level to the top of Beachy Head and back and still had power to spare. I was 15.5 stone when I bought it, I now weigh just 13 stone. You need a big battery, but as others have said you will find you won't use the throttle much at all for road use.

When I bought mine, I tested it back to back with a Wisper 905 sport and the Eagle won, just. There is really no substitute for trying them all for yourself. Take a day out, visit several stockists and then decide. Comfort is a major consideration, if it hurts you wont be riding for long.

 

[John F]

How do I know my motor will not overheat on a hill then? (I'm 95kg)

you don't have to worry about the weight. The frame won't break, but you do have to worry about the motor. Most will over-heat under the stain of your weight on any sort of hill. Those ones i mentioned will cope, but not many others.

 

[Deleted member 4366]

The slower a motor goes (at full throttle) the lower the efficiency becomes. So, travelling at normal speed of about 12 mph it will be about 70% to 80% efficient in converting battery energy into motion. When it gets down to 6 mph, it will only be 50% efficient, so the other 50% will be converted to heat, i.e. about 7.5 amps at 36v or 270w. The faster you can keep it going by pedalling, the more efficient it will be. Motors with high torque can go up hills faster so they run more efficiently.

Here's a typical efficiency curve for a low-powered motor. If you go to the website, you can pay with the parameters to see the effect. All the graphs assume no pedalling.

 

[John F]

That's a fascinating chart thanks. I'm beginning to get the picture. Interesting web site too, particularly about batteries.

I'm still worried about possible motor damage though. I would have thought that the electronics would have prevented this? (As I understand it my draws a max of 14 amps?)

The slower a motor goes (at full throttle) the lower the efficiency becomes. So, travelling at normal speed of about 12 mph it will be about 70% to 80% efficient in converting battery energy into motion. When it gets down to 6 mph, it will only be 50% efficient, so the other 50% will be converted to heat, i.e. about 7.5 amps at 36v or 270w. The faster you can keep it going by pedalling, the more efficient it will be. Motors with high torque can go up hills faster so they run more efficiently.

Here's a typical efficiency curve for a low-powered motor. If you go to the website, you can pay with the parameters to see the effect. All the graphs assume no pedalling.

 

[trex]

How do I know my motor will not overheat on a hill then? (I'm 95kg)

put your hand on the motor.
anyway, crank drive motors don't overheat and don't break spokes.

 

[John F]

Ok, I'll take thermometer out on my next ride!

Why don't crank drive motors overheat?

put your hand on the motor.
anyway, crank drive motors don't overheat and don't break spokes.

 

[trex]

ha ha.. only joking.
My motor only gets warm - never too hot to touch.

 

[Deleted member 4366]

Everything's protected against too much current. The only real danger is over-temperature. If you run some controllers at their maximum for too long, they can get hot, but most are protected with a thermistor, which tells the CPU when it gets too hot, so the CPU will shut it down. Most motors aren't protected against over-temperature. Running them at high current is not a problem as long as you have the speed to keep the efficiency high, but as the speed drops off, so does the efficiency, and up goes the heating effect. I've been on this forum 3 years today, and I can't remember anybody getting a burnt out motor on a standard bike. Even when you hot-rod a bike by turning up the current and voltage, provided that your aware of this effect and don't labour your motor up hills, it'll still be OK. Increasing the current can make a bike climb faster, so its efficiency is higher, and so is less likely to over-heat, plus it could even use less battery for the same hill whilst going faster, which sort of defies logic.

One thing that is bad for everything is stalling the motor completely. The torque goes very high, so you can damage the gears inside the motor. You can see how torque rises with decreasing speed on those graphs. Also, a stalled motor can damage the controller.

To summarise: As long as you don't stall your motor, you've got little to worry about.

 

[John F]

That's reassuring thanks.
In a nutshell then, make sure you are in a nice low gear at the start of the hill, and give it some pedalling!

Everything's protected against too much current. The only real danger is over-temperature. If you run some controllers at their maximum for too long, they can get hot, but most are protected with a thermistor, which tells the CPU when it gets too hot, so the CPU will shut it down. Most motors aren't protected against over-temperature. Running them at high current is not a problem as long as you have the speed to keep the efficiency high, but as the speed drops off, so does the efficiency, and up goes the heating effect. I've been on this forum 3 years today, and I can't remember anybody getting a burnt out motor on a standard bike. Even when you hot-rod a bike by turning up the current and voltage, provided that your aware of this effect and don't labour your motor up hills, it'll still be OK. Increasing the current can make a bike climb faster, so its efficiency is higher, and so is less likely to over-heat, plus it could even use less battery for the same hill whilst going faster, which sort of defies logic.

One thing that is bad for everything is stalling the motor completely. The torque goes very high, so you can damage the gears inside the motor. You can see how torque rises with decreasing speed on those graphs. Also, a stalled motor can damage the controller.

To summarise: As long as you don't stall your motor, you've got little to worry about.