# How to create a mini generator that will charge my phone?

#### kitcat

I was studying generators. I learn most when it is hands on. I want to start a project that creates a mini generator which I can use to charge my Samsung phone. Just for fun. I want to use gas for fuel.

I don't have any idea on what books to study or what equations to look for. The books on my course are theoretical and don't tell about anything on how actually generators are made. How many rpm generates how much power.

I want to continue this project until it is finished. Whether it takes 4 years or 5 years. (I hope it doesn't take that much time!). Any help is appreciated. Thanks.

#### phinds

Gold Member
You can very likely find on-line instructions for building a small generator, but one that small is not very practical I would think so instructions are likely to be for something bigger than you need.

#### kitcat

You can very likely find on-line instructions for building a small generator, but one that small is not very practical I would think so instructions are likely to be for something bigger than you need.

I have already found instructions and videos on youtube showing how to build a small generator. I have a very specific set of requirements here. I want to generate only that much electricity to be able to charge my phone through usb cable like a cheap 5000mAh portable charger does. However I lack specific knowledge and information.

How much rpm and how much coil is needed to generate the amount of power required to charge a phone. I just want to see my phone charging.

so the questions in order are:

1. How much solenoid and rpm generates how much power? What kind of magnets I need. Which book and equations can help me understand this amount. RPM can be done by gas or even by using flowing water, but water is not going to generate enough power so if I know how much RPM I need, that sets the way.

2. How much power a phone charging usb cable needs? Where can I find information about the power requirements of a phone's charger. Any 10$portable charger stores some specific amount of charge, if I find how much power these chargers output, I find the power requirement for phone charger. Is this information available online anywhere? 3. Once I get the phone's charging power requirement, how do I convert the power generated by my generator into the power required by a phone. What books and what electronics I need to obtain to make this power conversion happen? #### davenn Science Advisor Gold Member 2. How much power a phone charging usb cable needs? Where can I find information about the power requirements of a phone's charger. Any 10$ portable charger stores some specific amount of charge, if I find how much power these chargers output, I find the power requirement for phone charger. Is this information available online anywhere?
HUH ?

Look at the label on your phone wall charger. it will likely be 5V at around 2 amps ( give or take a little)

3. Once I get the phone's charging power requirement,
So now you have that.

how do I convert the power generated by my generator into the power required by a phone.
You want your generator to be capable of generating a bit more current and voltage than what is needed
This gives some headroom ( that is, you don't want the generator to be working hard to supply needed
current.
Now, find info on the actual current requirement ... see the phone spec sheet that either came with the
phone or get it from the manufacturer.
Lets say it requires 1A, then I would be making sure the generator is capable of supplying 2 - 2.5 A
to give that headroom.

And since the output of the generator wont be smooth, you need it to be some ( say 3 - 5V more
than required) so that the output can be put through a voltage regulator chip and brought down to the
stable 5V needed by the phone

Dave

#### davenn

Gold Member
How much rpm and how much coil is needed to generate the amount of power required to charge a phone. I just want to see my phone charging.

so the questions in order are:

1. How much solenoid and rpm generates how much power? What kind of magnets I need. Which book and equations can help me understand this amount. RPM can be done by gas or even by using flowing water, but water is not going to generate enough power so if I know how much RPM I need, that sets the way.

for info specific to the actual generator, you would be unwise to build that part. Talk to some company that sells very small DC generators that will most likely have a ~ 12V DC output and capable of 2 - 5 Amps.
That bit isn't critical as the voltage regulator I mentioned in my last post will take care of that

ohhh and how portable do you want this thing to be ?

Dave

#### Rive

I want to use gas for fuel.
Then you can aim for some RC model motors: there are some which is using gas as fuel - if you can tolerate the noise and the low lifetime...

#### Spinnor

Gold Member
Buy some of the units in the link below and take apart and learn how others solved your rather complex problem? Discover the weaknesses of others designs and then design something better. Very hard without the proper skills, materials, and tools. Good luck.

#### jrmichler

And some generators from the bicycle world. The links are the first of each type that I found. There are other manufacturers and other suppliers for both styles.

The good old friction wheel against the tire: https://www.amazon.com/dp/B00H3RDVKO/?tag=pfamazon01-20

And the hub generator: https://www.nashbar.com/shimano-dh3d37nt-dynamo-front-disc-hub-36h-100mm-rotor-mount-edh3d37dsg/p875056?gclid=EAIaIQobChMI57-m54Wf4wIVQrjACh24WguwEAQYAyABEgIHifD_BwE

These generators are typically available in either 6 or 12 volts. The specification list the power, from that you calculate the current. They typically deliver full power at about 10 to 12 MPH, from that you calculate the RPM needed.

That said, you might be best off with something from @Spinnor's post #7 above.

#### sophiecentaur

Gold Member
Any DIY generator needs to be efficient enough to make it feasible to use. The crucial bit here is the Magnetic Circuit. You need to be able to make a rotor with a number of high strength magnets and a stator which allows very small gaps for the magnets to act - with as little flux leakage as possible. The ironwork would ideally be laminated too. To know the numbers of turns on the coils, you need to know the magnetic flux change - or you can experiment with different coils until you find the value you need.
If your generator is not efficient you will just wear yourself out trying to get enough out of it.

#### Fisherman199

The magnetic circuit is the main intrigue and should command most of your care and attention.
Good material will go a long way to ensuring the best results.
1.) High quality, un-laminated, purified copper.
2.) Cold-roled, grain-oriented, silicon steel (CRGOS) is the typical core material for modern electric machines.

#### sophiecentaur

Gold Member
The magnetic circuit is the main intrigue and should command most of your care and attention.
Good material will go a long way to ensuring the best results.
1.) High quality, un-laminated, purified copper.
2.) Cold-roled, grain-oriented, silicon steel (CRGOS) is the typical core material for modern electric machines.
Absolutely. In my opinion the OP will have great fun establishing the basic principle of Motion / Electricity but making something that's as good as the Alternator in the Wind Up Radio requires a lot of knowledge and skill.
Edit: The alternators, mentioned higher up, are driven by pedal power and the effort needed is buried somewhat by the cyclists other efforts. Up hill and down hill gives some variation too. When I was in my early teens, I fitted two dynamos on my bike and had two headlamps. Going up hill was noticeably harder work at night than in the day.

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