Mini hand held generator creation help needed

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Joined Aug 17, 2019
15
Hi all

I am looking into making a mini hand held generator to charge small appliances like phones and so on.

I am totally new to all of this, but what i want to know is what i will need... as advice on a few things

So to start things off the way the gear system works is a little diffenent then a crack handle, the way the handle works is it has a in stroke and a out stroke...i will add a image on the way the strokes work... sorry in advance as it will be a ruff sketch.
Just a few details on the way it will work... on the in stroke the bottem teeth will move the gear abd the top gear will jump/ skip over the gear then on the out stroke the top teeth will bite and the bottom teeth will skip over... this will ne connected to other gears which will then connect to a customer generator but this way i think there will be a tiny pause in between strokes which may cause the power to stop, what i want to know is is there a way to help to keep power in the line without it stopping in between strokes ??

The voltage i am looking to have it 5v

Can any 1 shead some light please
 

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Thread Starter

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Joined Aug 17, 2019
15
Hand operated :)

There will be about 2.5 - 3 cm movement per stroke... so in total 5 - 6 cm per circle... 6 been the max and that is if when using it you let it out all the way
 

LesJones

Joined Jan 8, 2017
2,414
Can you clarify something about your picture. On the picture of the gear the teeth on the left hand side look triangular but on the right hand side they looked ratchet shaped. What shape do you intend them to be ?
One way to avoid a pause would be to have the generator coupled to a crankshaft and flywheel and the part you push and pull attached to the connecting rod in the same way as the piston in a piston engine.

Les.
 

Thread Starter

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Joined Aug 17, 2019
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I did think this as well... i was thinking just to have the 1 and use this so that when u press it will spin up and then jump over the gears on the way back ... but the reason i thought to have to rows was to try and get motion on both strokes

And sorry its my bad drawing they are both meant to have a curve on the teeth

And just to you know the size of the device will only be like 6 cm width by like 11 cm long and about 1cm depth
 

Thread Starter

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Joined Aug 17, 2019
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They will not be fixed

But springs will be on the ends to help create tension

The bars with the teeth will be what move back and forth, the wheel in the middle will be fixed in place. Grant but will spin, i was thinking of making the bars out of plastic so its a little bendy to be able to jump over the gear teeth

Not sure if it be better to just have 1 bar so it revs up everytime u press down... and then it will jump over the gear

What u think?
 

BobTPH

Joined Jun 5, 2013
2,102
So, are you planning on stroking this thing for hours? You are not going to get much power out of a 3cm stroke.

What are your expectations for of its charging power?

Bob
 

LesJones

Joined Jan 8, 2017
2,414
By adding a bridge rectifier to the output of the generator (Assuming a permanent magnet motor is being used as a generator.) you could dispense with the ratchet system and just use a rack and pinion. Although the polarity from the generator will reverse the output of the bridge rectifier will remain the same.. Also if it is being used to charge batteries the interruptions in the output will not matter. I agree with Bob that you will have to operate this device for a VERY long time to charge the battery.

Les.
 

Thread Starter

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Joined Aug 17, 2019
15
So, are you planning on stroking this thing for hours? You are not going to get much power out of a 3cm stroke.

What are your expectations for of its charging power?

Bob
Nah its for a top up design... so its not designed to give you full charge... more of a if your out and about and have no means of charging that you can use it to top up your battery on the go

This is y i wanted it to have a stroke both in and out and it would give power on the in and out stroke
 

djsfantasi

Joined Apr 11, 2010
5,829
whats a rectifier ?? Im a total noob when it comes to this... sorry
A bridge rectifier converts alternating polarity voltages to straight DC. That is, as the generator spins backwards and forwards, the polarities of its output alternate between +- and -+. A bridge rectifier takes this, and turns it into +- all the time. What your mechanical solution tries to do, only much simpler.
 

Thread Starter

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Joined Aug 17, 2019
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Thanks man... but the way trying to design it is so say on the in stroke it turns clock wise... the out stroke would then pull back and kick in keeping it turning clock wise... so it should be spinning in the shame direction... but per in and out stroke you are getting movement on the gears.


So it will not be going back and forth
 

djsfantasi

Joined Apr 11, 2010
5,829
Thanks man... but the way trying to design it is so say on the in stroke it turns clock wise... the out stroke would then pull back and kick in keeping it turning clock wise... so it should be spinning in the shame direction... but per in and out stroke you are getting movement on the gears.

So it will not be going back and forth
Whatever you want. Personally, I think the wasted mechanical energy in keeping rotation in the same direction is going to cost you power.

And is it going to work? The gear teeth cannot be triangular. Plus you’re going to need two opposing springs to keep the pinions in line. And what is the friction of slipping pinions going to do?

Plus, the additional complexity in designing the mechanics is going to cost more than adding a bridge rectifier. But you know your requirements better than I do.
 

WBahn

Joined Mar 31, 2012
24,967
The bars with the teeth will be what move back and forth, the wheel in the middle will be fixed in place. Grant but will spin, i was thinking of making the bars out of plastic so its a little bendy to be able to jump over the gear teeth
And just how long do you think these plastic bars are going to last before they get worn to point of being worthless?

Why do you want the person using this to exert effort to move it both ways? Have you taken into account the movements that the operator will need to make and ensured that most people can comfortably exert the needed force in both direction for an extended period of time?

Why do you need the motor to turn the same direction all the time when a simple bridge rectifier would greatly simplify the design? Do you have an actual reason, or is it simply a case of being the first thing you thought of and now you are wedded to the idea and unwilling to consider alternatives?

Have you actually run any numbers? A limited bit of searching seems to indicate that human hand-cranked generators typically deliver 5 W to 10 W with the upper end being at a level of effort that most people tire from rather quickly. I don't know if these figures are accurate or not. Smartphone batteries seem to be typically in the 3000 to 5000 mAh range at 3.8 V, so let's call it 4000 mAh making the energy about 15 Wh. If topping up means 10% of the capacity, then at 100% efficiency you'd be looking at about 10 minutes of hard effort. So with a realistic efficiency you'd be looking at somewhere between 20 minutes and 40 minutes of effort for most people to top of their phone. Not out of the realm of reasonableness. By I suspect that the efficiency of your approach is going to be much lower than for a rotary crank, not only in terms of the generator itself but in terms of the motion of the person operating it.

Given that there are already many hand-cranked devices out there on the market, not to mention small solar cells and the like. What does your device bring to the table that they don't?
 

Thread Starter

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Joined Aug 17, 2019
15
I know their is hand cranked devices out there i have also designed something with a crank handle but you need both hands or for the device to be fixed in place, the way I am looking at you will be able to do this 1 handed. yes I know ppl will get tired but that is when u can swap hands.

i am totally new to all of this, so not 100% on how things work this is y im trying to get answers to help me as i am still in the design stage and trying to find the best way to get it as efficient as possible.

the reason i was thinking it should go in 1 direction is so there isn't a stop / pause on the generator. plus i wasn't sure if it would still work as good if the motor was going back and forth, this is partly the reason i asked / posted this. it might be the way iim explaining thing as its harder to type it then say it =/

and as for it been made out of plastic the bars i know they will not last for ever the design isn't meant to last for ever as what its build for most ppl change every 2 years and would replace what it will be attached to plus its will vary on person to person as its more for a back up / when needed then 24/7
 

LesJones

Joined Jan 8, 2017
2,414
You would need two hands for your push and pull device unless you include a return spring. I don't think your plastic bars would last two years as each time you charged a device would require a few hours use. The squeeze operated torches such as this would be easier to operate with one hand.

Les.
 

WBahn

Joined Mar 31, 2012
24,967
I know their is hand cranked devices out there i have also designed something with a crank handle but you need both hands or for the device to be fixed in place, the way I am looking at you will be able to do this 1 handed. yes I know ppl will get tired but that is when u can swap hands.
If you are doing something that a typical person can operate single handed, then both your efficiency and your peak output are going to go in the tank. I'd be surprised if you ended up being able to get even 1 W out of it. Do some measurements using yourself as a test subject and see how much force you can apply on something that is being operated one handed and then run the numbers.
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