Ok, so I've looked on eBay, and all I see is high RPM voltage generators.

I also learned that (Vin / RPM) = V/RPM Ratio.

So 12V 1100 RPM motor. 12V / 1100 = 0.01090V / 1 revolution. 120 RPM x 0.01090 = 1.309VDC.

That's not going to work.


I also read on here AAC, that the current is "Motor current is inversely proportional to speed, due to the counter-EMF produced by the armature as it rotates."

So the faster it goes, the more current?

I also see load and no load current. Some pretty low numbers.

I would like to buy a DC motor on eBay, preferably a 12V gearhead motor, drop the voltage using either a buck, SEPIC, or Linier voltage regularor like a LM7805, and hook it up to female USB.

I need help with the motor part.

Here are some of the motors I've searched for on ebay.

Yes, some are very expensive, and some are within my budget.

This one.. says nothing other than it's a 2RPM 12V motor.

How will I know how much current I'll get when I turn these into hand crank generators?

I also just recently found this : DC Motor Calculations, part 1

 

You won't have much luck trying to back drive a worm and pinion gearbox, you cannot do it mechanically.
A straight gear or planetary you can.
You cannot run any higher than the continuous rated current of the motor.
Max.

 

You won't have much luck trying to back drive a worm and pinion gearbox, you cannot do it mechanically.
A straight gear or planetary you can.
You cannot run any higher than the continuous rated current of the motor.
Max.

Thanks. It seems hard to find the motor I'm looking for. Part of me wants to go with a Synchronous Motor (microwave turntable motor) 110-127VAC, another wants to get a straight or planetary gear 12 or 24VDC motor.

So if I dropped the voltage down, and converter the Synchronous Motor using a full wave bridge rectifier and voltage regulator to let's say 5VDC, then it's still outputs the 4W that every single one of these states, then according to ohm's law, that's 5V, 4W, 0.8A

That's not good enough.

Then I see planetary gearhead motors that costs as much as it would cost me to buy a handcrank generator of the same power.. sorta..

Like this one.. 12V 2.4A Ok.. why the hell is it $140?

That's expensive, and I could buy an already made 30W 120VAC generator for that price. Not to state the obvious, it's 120VAC.

I need a little help.. As far as finding that perfect motor. I see people on YouTube have made ones, but I want mine to be really good. I also don't want to crank the thing 120 times a minute.. like K-TOR, etc.

 

Thanks. It seems hard to find the motor I'm looking for. Part of me wants to go with a Synchronous Motor (microwave turntable motor) 110-127VAC, another wants to get a straight or planetary gear 12 or 24VDC motor.

So if I dropped the voltage down, and converter the Synchronous Motor using a full wave bridge rectifier and voltage regulator to let's say 5VDC, then it's still outputs the 4W that every single one of these states, then according to ohm's law, that's 5V, 4W, 0.8A

That's not good enough.

Then I see planetary gearhead motors that costs as much as it would cost me to buy a handcrank generator of the same power.. sorta..

Like this one.. 12V 2.4A Ok.. why the hell is it $140?

That's expensive, and I could buy an already made 30W 120VAC generator for that price. Not to state the obvious, it's 120VAC.

I need a little help.. As far as finding that perfect motor. I see people on YouTube have made ones, but I want mine to be really good. I also don't want to crank the thing 120 times a minute.. like K-TOR, etc.

The gears make them expensive.
I think if I were doing it I would decide how much current I wanted then look for one at that run current.
Then make your own gears with individual parts to match it.
Edit: The faster you spin it the higher the voltage.

 

Try and find a scrap cordless drill that has been scrapped due to having a faulty battery. Choose one that has the highest battery voltage that you can find and also a two speed gearbox. set the gearbox to the low setting. That will make the motor rotate faster when you turn the chuck.
Also avoid drills that have an automatic brake on the chuck.
Les.

 

Just use a simple stepper motor and an appropriate bridge rectifier to get your DC out. 5 volts at at few tens of RPM's with a properly sized one is easy.

 

Here are a bunch of DC gearhead motors with various reduction ratios:

http://www.kr4.us/Robotics-Motors-DC-Gearmotor

 

I also read on here AAC, that the current is "Motor current is inversely proportional to speed, due to the counter-EMF produced by the armature as it rotates."

So the faster it goes, the more current?

No, for a given load, the current decreases as rpm increases.
As you already stated, Motor current is inversely proportional to speed.
If a load is attached, the current is maximum at zero rpm due to zero generated counter EMF.
Max.

 

I'm gonna keep searching for that perfect planetary geared dc motor. I spent a lot of time yesterday looking online for my perfect motor. The voltage is there, but not the current.. According to the minimal specs I read on the product pages. I started searching for wattage dc motors today. So maybe I'll have some luck. Not too big, but also not too small of a DC electric motor is what I'm looking for. Sure I could just pick up a 300W scooter motor and be done. Thanks for all the help so far on this. I'll just have to keep searching.

 

For a larger motor there is bumper winch type that has a hi ratio GB.
Max.

 

Do a search for hand cranked dc generator or magneto. Surplus phone stuff on ebay.....etc.

 

I'm gonna keep searching for that perfect planetary geared dc motor. I spent a lot of time yesterday looking online for my perfect motor. The voltage is there, but not the current..

Are you aware of the torque that is going to be required to using step up gearing to back drive a motor?
Torque in a motor is related to current.
The generator will require the same torque to produce the same current, this will be Multiplied by the ratio of the gearing.
Max.

 

Do a search for hand cranked dc generator or magneto. Surplus phone stuff on ebay.....etc.

Found it yesterday. Not buying that.

http://www.banggood.com/30W-0-28V-H...ncy-Generator-with-DC-Converter-p-962684.html

 

You never really came out and said what power you wanted.
That one is 30w.
Max.

 

OK Guest3123.....glad you found what you wanted......or did you?....because I couldn't tell.

Let us know how that works out for you. I've never met a person who would use one more than a couple of times.

Or once in a necessary time.....such as a megger.

Have you considered solar?

 

Torque in a motor is related to current.
The generator will require the same torque to produce the same current, this will be Multiplied by the ratio of the gearing.

If I'm just turning it by hand.. I'm not really applying that much torque to it.. Am I..?

So let's say we have this motor. As an example.
DC12V 95RPM 22mm Diameter Planetary High Torque DC Gear Box Motor Speed Reducer

Voltage : 12VDC
Torque : 1.6Kg.cm(0.16N.m)
Gear RPM : 95

...

 

Let us know how that works out for you. I've never met a person who would use one more than a couple of times.

Or once in a necessary time.

They use it once only to find out how incredibly physically demanding and difficult plus just time consuming tedious trying to generate any useful amount of power actually is.

A typical person can only sustain cranking an optimally designed hand crank generator with a load of 10 - 15 watts for a few tens of minutes (most less) which in electrical power terms is barely enough power to put a decent charge in a cell phone.

Human power for anything outrightly sucks period.

 

If I'm just turning it by hand.. I'm not really applying that much torque to it.. Am I..?

So let's say we have this motor. As an example.
DC12V 95RPM 22mm Diameter Planetary High Torque DC Gear Box Motor Speed Reducer

Voltage : 12VDC
Torque : 1.6Kg.cm(0.16N.m)
Gear RPM : 95

...

Like I explained earlier, the torque required depends on the current demand on the generator.
If you crank that at 95rpm you will produce 12vdc, the torque required will depend on the degree of load (current) the motor is supplying.
Max.

 

If I'm just turning it by hand.. I'm not really applying that much torque to it.. Am I..?

So let's say we have this motor. As an example.
DC12V 95RPM 22mm Diameter Planetary High Torque DC Gear Box Motor Speed Reducer

Voltage : 12VDC
Torque : 1.6Kg.cm(0.16N.m)
Gear RPM : 95

...

Time to start studying and learning how to convert torque and RPM's into equivalent power.

My rough numbers say that motor will produce about 2 watts of power and there's not much you commonly use can operate or charge with 2 watts at 5 volts unless you want to be cranking for a very long time.

Unless you can find a motor that will give you at least a stable 2 - amps at a 5 volt load while spinning at 40 - 80 RPM you're not going to like your results.

Yo still have yet to define what you intend to do with the 5 volt USB power.

 

OK Guest3123.....glad you found what you wanted......or did you?....because I couldn't tell.

Let us know how that works out for you. I've never met a person who would use one more than a couple of times.

Or once in a necessary time.....such as a megger.

Have you considered solar?

Solar is too easy. The sun is also not always around. During this current winter, I've seen the sun disappear for roughly a week. Overcast for like 4 days.. Most of the winter season was overcast every single day.

At least I figured, with a hand crank generator I made..
1. I can be proud of what I made.
2. I learned something from this experience.
3. Hand crank generator can be used anywhere @ anytime.

I also wanted to mess with the puny 4W 127VAC microwave turntable motors too.
I also wanted to mess with stepper motors and survo motors too.
I'd use a bridge rectifier to convert the 2 or 4 polls to DC. Pretty easy.

Finding voltage seems stupid simple. Seeing how text books don't teach or give current output on the datasheets, finding the right motor seems difficult.

I also recently watched a video on no-load current, rated current, and stall current.

No load current is the current at which the motor doesn't have a load on it. Like a weighted flywheel, or wheel.
Stall current means grab the wheel while the motor is on, and the current skyrockets. In the video the motor was drawing only 25mA, but when he went to grab it, it shot up to 775mA.

Then he did a 12V motor.. the current was the same. I sat there, and was like.. wtf..?

It has to do with the windings, and all kinds of other stuff. I'm willing to learn, but it seems difficult to find a dedicated video that's geared in a way to teach me. I'm more of a visual and auditorial type learner. Getting hands on "which usually costs money", I learn and solve problems almost instantly.

Problem is.. Why do I need to buy these motors, for a simple hand crank generator, when I can learn math, or look at the datasheet and know exactly which motor to buy.

I've done that with Mosfets, resistors, capacitors, LEDs, batteries, equipment, tools, etc. No problems. But the second I want to make a beefy or acceptable generator, I find out it's not so easy.

Every little bit helps from AAC, YouTube, and Google search results. Little by little, even if it's not this year. I WILL MAKE A HAND CRANK GENERATOR.

Btw.. for everyone reading this. I did make the LM324 dark sensor circuit. It also has an SPX2940U to supply 5V from 9V (8.85V) battery.

Got pictures and a 15s FHD video of the circuit working.
Which can be found here..