# hand-powered generator to charge phone

#### Rusty Rifle

Joined Dec 18, 2019
18
Hi all
I want to make a generator to charge up my phone ..may you help to find a good circuit to protect my phone from unstable speeds and improve the ripple factor?

I know i can buy one but i want to learn how to make my own

#### Papabravo

Joined Feb 24, 2006
19,558
How long do you think you can operate this hand charger? Would you be willing to hand crank it for 1 hour? How about 8 hours?
Have you ever seen the museum demonstration of trying to keep a 20 Watt bulb lit with a hand crank generator?

#### Rusty Rifle

Joined Dec 18, 2019
18
I know it is ridiculous idea to rotate it for a long time but I need to learn about it's circuit design
For example how to make use of not stable sin wave to charge a battery

#### Papabravo

Joined Feb 24, 2006
19,558
I know it is ridiculous idea to rotate it for a long time but I need to learn about it's circuit design
For example how to make use of not stable sin wave to charge a battery
That is a bit vague. Could you elaborate on "not stable sinewave". NOTE: there is a huge difference between time-varying and unstable (not stable). Unstable means "diverges to infinity". I've seen many AC sources that have variations in peak amplitude or frequency, but I have never seen one that diverges to infinity in amplitude or frequency. I suspect that you haven't either. So tell me what exactly you are talking about because your words and phrases, to be charitable, lack precision.

#### MrSalts

Joined Apr 2, 2020
2,596
Here's a good example of the human/mechanical equivalent of what it takes to toast a slice of bread.

#### Rusty Rifle

Joined Dec 18, 2019
18
Sorry for my English
I mean suppose we have a not perfect sin wave voltage come out of a hand generator which changes the amplitude and frequency over the time, how can we build a circuit can convert it to DC voltage?

#### MrSalts

Joined Apr 2, 2020
2,596
Sorry for my English
I mean suppose we have a not perfect sin wave voltage come out of a hand generator which changes the amplitude and frequency over the time, how can we build a circuit can convert it to DC voltage?
You can still rectify it, and stabilize it with a capacitor. The non-sine nature will cause some harmonics that might be a little more difficult to regulate but modern voltage regulators can handle most of what you would put it. What are the constraints of your project?

#### Papabravo

Joined Feb 24, 2006
19,558
Sorry for my English
I mean suppose we have a not perfect sin wave voltage come out of a hand generator which changes the amplitude and frequency over the time, how can we build a circuit can convert it to DC voltage?
So let us start with some estimates of how much power is required. How much power will it take to charge your phone from 50% up to a full charge?
Once we know that we can estimate the efficiency of the conversion scheme. This will let us know the input power. Once we know the input power we can propose a design for the hand cranked generator that will produce at least that much power. I suppose it would be handy to have access to a machine shop that can cut custom gears for you.

https://www.quora.com/Can-you-hand-crank-a-car-alternator-to-power-other-supplies

#### Audioguru again

Joined Oct 21, 2019
5,406
A phone is charged from 5VDC USB, not AC. A USB power unit might be powered from AC.
I charge my phone from a 5VDC USB power bank.

#### Alec_t

Joined Sep 17, 2013
13,223
A suitable hand-cranked generator driving a common USB wall-wart would probably work to give you 5VDC.