Question about electric motor wear

[Tummy]

Hello everyone.

First of all, excuse me for my bad english.

Today I finally started to put a motor on my bycicle. Its really a dream come true. I feel that I'm finally old, handy and smart enough to do it. And I have vacation now so I have lots of time.

But I have a question. Will the motor wear faster if im riding at lower speeds where the motor is for example at 1800rpm but still push 24V trough it? I ask this because if you have a motor and put electricity on it, but you make it so it can't spin, It will wear and break after some time. But will this still happen if you let it spin, but there is to mutch resistance to make it spin at it max speed?

here are the specifications of the motor:
2900 RPM
190watt nominal power
24VDC input

 

[anickode]

It really quite depends on what the motor was designed for, and whether or not it can sufficiently cool itself at lower rpms, but still full load.

Chances are, if you have things set up so the motor cannot hit full speed when supplied full voltage, you need to reevaluate your gearing. If you gear it so that the motor is able to hit full speed, and the top speed of the bicycle is not fast enough for you, you need a larger motor. Forcing the motor to do more work than it is capable of will burn it out faster.

It seems to me that most bicycle motors are in the 500 to 1000 watt range. I don't know much about motorizing bikes, but it seems to me your motor might just be too small to get the results you want.

 

[Tummy]

Thank you for your reply, I apriciate the help!

The motor is from a bus, it's function is to profide the enigine of the bus with enough air. I don't think it is built for low RPM with normal voltage because the work it is designd to do is very consistant. I'm struggeling with the exact problem you discribed. If I make the gearing easier the bike goes very slow and if I make it to high the motor won't be able to pull it.

Here in the Netherlands electric bikes are restricted to 250W max power. I'm gonna make the weel of the motor directy to the weel of my bike and acording to my calculations it should hit 29KM/h at full speed with a diameter of 50mm. I can change te diameter to change the gearing ratio.

But maybe if the enigine is just not powerfull enough I can use 2 or even more for 380w+. But It could be overkill because my grandma has a bike with 250w and it does weelies at full power from a standstill . keep in mind that is with gear 1 and 2 out of 8. And I can't make a machanisem that shifts, only one permanent gear ratio.

I think that i'm gonna try it with one motor first and if it hasn't got enough power I will put a second one on it.

 

[anickode]

If it is a blower motor, it might burn up quickly anyway, as they frequently have no internal cooling mechanism, and rely on the fan-forced air flowing past them to keep them cool.

Also remember that every stage of mechanical connection adds an efficiency loss, with some types harming performance worse than others. That is why most e-bikes these days are using brushless multiphase hub motors to maximize efficiency.

 

[Tummy]

Yes that's true, I made it so that it can get as mutch wind as possible.

But my dad came up with another idea, he said that I shoud call a garage where we frequently bus stuff and ask if they have a spear starter motor. They are like 600-2200w so it should be enough and they have loads of torque. I called them and they have some but I need to wait until the boss gets back to ask him. And I also need to make an entirely new system to hold the motor. And I need a new gearing system.

But vacation is still 3 weeks so I should have enough time

 

[anickode]

Starter motors are a poor choice. They have extremely low duty cycles, meaning they are meant to run a few seconds at a time, then stop. They do not usually have bearings, but rather bushings. They are also typically sealed with no ventilation or cooling, so they overheat and burn up from prolonged use.

24v diesel starters can draw upward of 1000 amps, depending on the size of the engine (like the big ones you'd find in a bus).

Perhaps a better alternative if you do not want to buy a proper motor is to research converting an automotive alternator into a motor. They can be adapted with relative ease, and run with a brush less motor contoroller.

 

[Tummy]

I just looked it up and that's a pretty good idea. But I still need a controller.

I'm going to the garage first and see what they have for me, the lady called me back and said they had something bu didn't say what. She said that I can some today.

I'll keep you posted on what they give me

 

[Tummy]

okay I just went to the car garage and they have a "dynostarter" for me. It's basicly a starter motor and a dynamo in one unit, so it can sustain the load with the power of a starter motor. I can pick it up tomorrow with a working battery. It will me around 900watt.

Ik think we solved all the problems with this, and it doesn't even need a controller or anything.

 

[anickode]

okay I just went to the car garage and they have a "dynostarter" for me. It's basicly a starter motor and a dynamo in one unit, so it can sustain the load with the power of a starter motor. I can pick it up tomorrow with a working battery. It will me around 900watt.

Ik think we solved all the problems with this, and it doesn't even need a controller or anything.

You need some sort of controller unless you only want to go full speed all the time.

 

[Functional Artist]

You need some sort of controller unless you only want to go full speed all the time.

He'll still have (2) speeds
...full speed & coasting speed

Yup,
...you'll still need a speed controller

 

[Tummy]

Yea, I know what you mean. But what I was trying to say is that I don't need a controller that sends electricity in a specific way. I only need one that changes the Voltage/amperage, and that's mutch simpler than these kind of things (see image)