Using a hub motor as a generator

edmontonbikes · Mar 9, 2013

Hello,

I'm working on an education & fundraising project that involves using a hub motor as a generator on a bike, pretty much exactly like what Martin described in this thread: http://www.candlepowerforums.com/vb...ycle-dynamos&p=3177070&viewfull=1#post3177070

The generator I have also outputs 24V.

My problem is figuring out an efficient (primarily from a financial standpoint--I'm actually not very concerned about energy efficiency) way of charging the 12V battery. I don't understand the circuitry surrounding the battery in the diagram Martin drew.

Could someone help explain or suggest a good way to do this?

Thanks!

charlie_r · Mar 10, 2013

Are you talking about the diagram in post 17?

If so, then let me see if I can help here.

Starting from the motor turned generator, the three wires are the main (normally) input wires to the motor. These are connected to 6 diodes to change what would be AC from the generator to DC that can be used to charge the battery. The positive output of this rectifier set goes to an ampmeter then through a 25A fuse,then to the battery. Connected at this fuse is s 1A fuse that feeds a voltmeter. The negative side of the rectifier set connects to the negative of the battery and the voltmeter.

I would highly recommend that you go here and read, starting with the volume 1. This will give you a better understanding what everything in that circuit is doing.

edmontonbikes · Mar 10, 2013

charlie_r said:
Are you talking about the diagram in post 17?

If so, then let me see if I can help here.

Starting from the motor turned generator, the three wires are the main (normally) input wires to the motor. These are connected to 6 diodes to change what would be AC from the generator to DC that can be used to charge the battery. The positive output of this rectifier set goes to an ampmeter then through a 25A fuse,then to the battery. Connected at this fuse is s 1A fuse that feeds a voltmeter. The negative side of the rectifier set connects to the negative of the battery and the voltmeter.

I would highly recommend that you go here and read, starting with the volume 1. This will give you a better understanding what everything in that circuit is doing.

Thanks; I just wasn't familiar with the ammeter and voltmeter symbols. I've never included them in my diagrams! They threw me. What does that "19.9V digital" mean? That his voltmeter reads 19.9V? Doesn't seem like a range, but that would toast the battery, no? My primary confusion in the circuit was charge control (or lack thereof)--I thought those mystery symbols had something to do with it, but if they're just meters, then obviously not...

charlie_r · Mar 10, 2013

A hubmotor, like any device with rotating magnetic fields will output a very large range of voltages. For example, and automotive alternator without regulation will output as high as 500V at normal operating rpms. Not saying it would last long if you were to draw any amperage at that voltage. One of the problems with driving any solid state device in the automotive electrical environment is the extreme range of spikes and droops that are normally present.

I'm guessing that at the speed the hubmotor was being driven that the reading on the digital multimeter was that high. As far as toasting the battery, I doubt that any damage would occur. A fully charged 12V lead acid battery will actually read anywhere between 13.2V and 14.8V, depending on it's construction and plate material. Charging a battery requires a higher than nominal voltage to do any meaningful recharge. At that level of voltage, the amperage would need to be limited, though.

Mattaus · Mar 10, 2013

Google search for some forums called endless sphere. You'll get everything you need and then some...

Sent from my Galaxy Nexus using Tapatalk 2

ianfield · Mar 11, 2013

charlie_r said:
A hubmotor, like any device with rotating magnetic fields will output a very large range of voltages. For example, and automotive alternator without regulation will output as high as 500V at normal operating rpms. Not saying it would last long if you were to draw any amperage at that voltage. One of the problems with driving any solid state device in the automotive electrical environment is the extreme range of spikes and droops that are normally present.

I'm guessing that at the speed the hubmotor was being driven that the reading on the digital multimeter was that high. As far as toasting the battery, I doubt that any damage would occur. A fully charged 12V lead acid battery will actually read anywhere between 13.2V and 14.8V, depending on it's construction and plate material. Charging a battery requires a higher than nominal voltage to do any meaningful recharge. At that level of voltage, the amperage would need to be limited, though.

A permanent magnet alternator is more or less a constant current source - assuming this hub motor behaves in a similar manner, the best way of protecting the battery is a hefty 15V zener diode.

Lucas used a large stud mounted 15V zener for regulating 50s.60s motorcycles - you don't need a zener quite as big for a hub motor turned generator, but the typical 400mW/ 1W wire ended types won't be big enough. the smaller end of stud mounted types might do - try it and see if it runs hot.

One possibility is the TL431 programmable zener/shunt regulator, it won't handle it on its own, but most manufacturers publish application examples showing how to boost it with a power transistor.

Using a hub motor as a generator

edmontonbikes

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edmontonbikes

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Mattaus

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