High School project - electrical power generator

I don't have any personal experience with these. Check out the linked videos for details about the internals of these.

Looking at the specs on ebay, the smaller unit looks like it will only put out about half a watt. The larger is close to 5 watts at full speed, but how well you can utilize that depends on the voltage you need.

splinter said:

When i multiply the capacity by 1.4 (why 1,4? loss of current?) and divide it by the output current i know the time it takes to charge the battery pack.

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Hi splinter,

You ask why 1.4: it is convention to specify an alternating voltage or current, in terms equal power (heating effect) to a DC voltage or current.

The mains voltage in Belgium is 240V RMS at 50Hz which will have the same heating effect as 240V DC. RMS stands for root mean square.

The relationship between the peak value of an AC voltage or current is RMS value * ( the square root of 2).

Thus, RMS * 1.414 = peak value of RMS AC.

In the case of your mains supply, the peak value of the sine wave = 240V * 1.414 = 339.36V and the peak-to peak voltage is twice that, to include negative and positive excursions of the sine wave = 678.72V.

The consequence of all this is that if you connected the bridge rectifier of post #5 to your mains supply (you would need diodes with a PIV of 407V or more) you would get 339.36V - (2 *0.4V) = 338.56V across the reservoir capacitor. The (2 * 0.4V) loss is for two Schottky diode forward voltage drops.

End of lecture.

spec

Hi Splinter, you can also use small steppermotors salvaged from an old printer or photo copier. They output between 6 and 18 Volts depending on their speed. Freely available from dumpsters or on the side of the road.
Low power output but enough for your projects.
Connect a bridge rectifier and a Capacitor and they are ready to use.
Some have a nice gearbox on them as well.

Hi S,
Does your school have an oscilloscope? (Two input)
In your initial question you ask if more than one alternator could be run together. If you get two alternators, and show their outputs on the two oscillator inputs, you will see their sign waves. Most likely they won't be in time, so they could not be added together. However if you had two stepper motors connected with say a toothed belt, and timed, they would show both sign waves together. These could be added together,and would give more current. (Anyone correct me if I'm wrong)

C.

camerart said:

Hi S,
Does your school have an oscilloscope? (Two input)
In your initial question you ask if more than one alternator could be run together. If you get two alternators, and show their outputs on the two oscillator inputs, you will see their sign waves. Most likely they won't be in time, so they could not be added together. However if you had two stepper motors connected with say a toothed belt, and timed, they would show both sign waves together. These could be added together,and would give more current. (Anyone correct me if I'm wrong)

C.

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Just a small point camerart,

you could add as many generators, of all kinds, as you like by having a separate bridge rectifier for each dynamo.

Even AC and DC generators could be mixed, although only a single diode would be required for D C generators.

spec

spec said:

Just a small point camerart,

you could add as many generators, of all kinds, as you like by having a separate bridge rectifier for each dynamo.

Even AC and DC generators could be mixed, although only a single diode would be required for D C generators.

spec

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Hi S,
I think generators are DC, correct? and alternators as AC, correct?
Are my comments correct, when talking about Alternators and Stepper motors?
C.

camerart said:

Hi S,
I think generators are DC, correct? and alternators as AC, correct?
Are my comments correct, when talking about Alternators and Stepper motors?
C.

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Yes, camerart, you are correct on all counts.

Alternators produce AC and dynamos produce DC. A generator is the generic term for both alternators and dynamos, but the word generator may also apply to an engine and generator, as in generator set (or petrol electric set and diesel electric set)

Bicycle alternators are called dynamos for traditional reasons: in the old days cyclists would probably not have been familiar with the word, 'alternator'.

Stepper motors make particularly good alternators because they have at least two stator windings and multiple poles on the stator. Stepper motors would be quite efficient too, because of their fine tolerances resulting in close coupling between the rotor and stator.

spec

spec said:

POST Issue 2 of 2016_11_26

View attachment 102549​

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Spec:

Love your HAND-DRAWN schematics. They are so clear and legible.
Reminds me of one of Electronic heroes, Forrest Mims III.

schmitt trigger said:

Spec:

Love your HAND-DRAWN schematics. They are so clear and legible.
Reminds me of one of Electronic heroes, Forrest Mims III.

Click to expand...

Thanks ST,

The circuits are just sketched out on the settee while watching TV/listening to my missus. That is why the lines are such a mess. I use sketches for skeleton/outline circuits when I am too lazy/tired to do them in EAGLE.

I try to keep the layout simple because I am not clever enough to follow more complex circuit layouts.

spec