I am having a project in my mind which is a closed system which needs to be powered by a small motor/generator.
I need some kind of a pretty mal dynamo which produces power by turning it - relatively slow with lets say 1 cycle per second (maybe a bit more).
It also needs to be small of course - my question is what exactly is the name of the device I am looking for and who can produce such device or who is maybe creating such devices?

The Device I want to build will be a low power device which maybe needs a few mW every houre or so in the size of an ESP32 NodeMcu for example but only powered by a battery which is inaccessible from the outside but can be charged by such a motor.
I am just not 100% sure how such a device is called. If I am looking for generator or dynamo I always endup finding huge devices - maybe there is no device in existence yet. I think it needs to be specially build but I Also don't know where to ask for it or who builds it.

Does anyone has an Idea? Please help. I need some directions.

 

AC or DC?
Any DC brushed or BLDC motor will generate when back fed.
You may have a real problem finding a motor/generator that outputs significant voltage at that low rpm, unless geared.
Max.

 

AC or DC?
Any DC brushed or BLDC motor will generate when back fed.
You may have a real problem finding a motor/generator that outputs significant voltage at that low rpm, unless geared.
Max.

To charge a battery it should be DC but I think you could just rectify it, right?
To be more clear: I want to use a cycle of the pedal of my bike. I don't know the exact words in englisch of that parts down there but if the motor fits into the pedal and the spinning part is where the pedal gets into the arm. Thats the place I want to place the device and charge it with the turns of each pedaling. It could be the whole pedal but the motor have to fit there and also charge a battery.

I think geared could be possible as well - I am basicaly have no Idea what to search for in the internet to find a suited company or anything who could produce such motor or maybe there is a charger already. Any Idea?

 

I am having a project in my mind which is a closed system which needs to be powered by a small motor/generator.
I need some kind of a pretty mal dynamo which produces power by turning it - relatively slow with lets say 1 cycle per second (maybe a bit more).
It also needs to be small of course - my question is what exactly is the name of the device I am looking for and who can produce such device or who is maybe creating such devices?

Informatic0re,

1 Cycle per second is slow.
Direct connection to a generator shaft usually does not work well, but speed-up gears will help.

I am not sure how fast this device needs to be cranked ...
https://www.ebay.com/itm/4W-Battery...r-Gear-Motor-Dynamo-Held-For-DIY/233214293581

2 Revolutions per second ?
https://www.ebay.com/itm/DC6V-12V-2...-Generator-Dynamotor-metal-Motor/264306650943

 

To charge a battery it should be DC but I think you could just rectify it, right?

Most BLDC with a permanent field will generate 3ph AC which can be rectified with a 3ph bridge.
To control the output usually requires a controllable field. (non PM).
Max.

 

Informatic0re,

1 Cycle per second is slow.
Direct connection to a generator shaft usually does not work well, but speed-up gears will help.

I am not sure how fast this device needs to be cranked ...
https://www.ebay.com/itm/4W-Battery...r-Gear-Motor-Dynamo-Held-For-DIY/233214293581

2 Revolutions per second ?
https://www.ebay.com/itm/DC6V-12V-2...-Generator-Dynamotor-metal-Motor/264306650943

Thanks - that looks like a start. I guess the big part of the second link is the gear part right?
300mA also sounds "okayish"

 

I just found this little guy:

https://www.amazon.com/Antrader-Electric-GA12-N20-Deceleration-Reduction/dp/B07FYBQ7Z4

>Any DC brushed or BLDC motor will generate when back fed.
So if I turn this guy - it will produce DC voltage.

 

Keep in mind that back-feeding a gearbox requires a great deal of effort, generally, dependent on the ratio.
The output from the motor is related to the rpm. IOW if the motor on its own turns at 1000 rpm at 12v, 12v will be generated at 1krpm when rotated.
Max.

 

Keep in mind that back-feeding a gearbox requires a great deal of effort, generally, dependent on the ratio.
Max.

I am aware of it - at least theoreticaly - how greate it will be, I have no idea. I guess I just have to try it out - I imagine if I am using my feet, it should be possible.

I found a 50rpm 6V motor with gear reduction - means if I turn it with the same amount, it produces 6V.
What would happen if I turn it faster? First thought: it produces more energy - but I guess also gets hot?
I guess I can just buy such a motor and try it out and do some experiments - at the end I can only learn something, right?

Thanks for your inputs!

 

About the only thing that will heat a motor/generator is load, typically no load-no heat.
Higher than its rated rpm, the voltage will increase up to a point.
Max.

 

Thanks - that looks like a start. I guess the big part of the second link is the gear part right?
300mA also sounds "okayish"

Yes, I assume, a planetary type gear inside.

 

I am aware of it - at least theoreticaly - how greate it will be, I have no idea. I guess I just have to try it out - I imagine if I am using my feet, it should be possible.

I found a 50rpm 6V motor with gear reduction - means if I turn it with the same amount, it produces 6V.
What would happen if I turn it faster? First thought: it produces more energy - but I guess also gets hot?
I guess I can just buy such a motor and try it out and do some experiments - at the end I can only learn something, right?

Thanks for your inputs!

Just remember:
Energy is transferred, not created so if you can easily turn the shaft without much effort (work) the amount of energy transferred is very low. Moving things is doing work, and power is the ability to move things continuously at a constant speed for a period of time.

 

Just remember:
Energy is transferred, not created so if you can easily turn the shaft without much effort (work) the amount of energy transferred is very low. Moving things is doing work, and power is the ability to move things continuously at a constant speed for a period of time.

Yes! Thank you! I know that of course- it must not turn without effort - I know that it can work the question is now, how efficient can it be and how balanced can I create it- ennough energy transfer to charge a battery somehow but also still be able to padle without issue.

If I can get the battery fully charged after maybe a 2h ride on my bike (I am talking about for example an 1200mAh battery, 3.7v) or at least charge it more as the device consumes over time - it is a win and I never have to touch that device ever again after installing it. Of course that is a dream - not a realistic assumption. Aim high - and if I have to bring my bike to a socket, well at least I tried

I know that I could use a dynamo or that thing in the middle of a wheel kind of dynamo but that is not what I am looking for.

 

Good luck. I was pretty sure you understand that but it never hurts to drive home the point that your body is the energy storage system for the transfer to the electrical generator.
https://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html

 

Good luck. I was pretty sure you understand that but it never hurts to drive home the point that your body is the energy storage system for the transfer to the electrical generator.
https://www.lowtechmagazine.com/2011/05/bike-powered-electricity-generators.html

Thanks for that article - very nice. They always talk about to get lots of watts out of that - I don't want to charge my phone or power my home with it. I have a scale at home which has no battery - to power it you have to press a button which transforms this press into electrical energy to power it long enought to measure my wheight. I love that device, I only use it because it works like that - I don't want to charge the battery 100% with driving around for 5 minutes.
There are also handcranked flashlight out there which existed already like 15 years ago or so - so it is not impossible

 

Miliwatts per hour?? Ouch! Then use any proper high wattage electric motor in autonomous async generation regime. Say You got a 0,1 kW 1500 rpm 220V motor with slip of 40 rpm at nominal power. It means, nominal power will get the 1460 rpms. Then turn it forcefully to 1540 and if will generate the full 0,1 kW. But You need not so much, then turn it to 154 rpm and You will get the 22V instead of 220 and 10W instead of 100. Or turn it to 15,4 rpm and get 2,2 Volts or turn to 1,5 rpm and get the 0,22V at full amperage but instead of 50 Hz You shall get only 0,5 Hz. The expression ``autonomous load`` means, it must be loaded with capacitor, with capacitance given by formula for three-phase motor into one-phase network. I mean C=4800*U/I (uF). However this formula is edited for 50 Hz grids, thus I suspect Your case must be used factor 4800000 instead, where U=0,22 and i=0,5 about

 

If dont like this idea, may use a better known method, proponated by Wind-scoraig-electric Scottish webpage (semi-genious owner Hugh Piggott). So, bring a bunch of HDD samarium magnets, fix it somehow in pancake form, for example at perimeter of 50 cm wheel. If perimeter them will be about 150 cm and magnet takes about 5, You will need about 30 pieces. Other identical pancake is made by just bunch of coils, where number of turns may be easily calculated by U=2pi()*B*v*A*z. Hugh is producing such generators for tens of kW working on so low wind as 10 -100 rpm, thus for Your needs this is effective enough. Ah, ya, just forgot to tell the magnet plate and coil plate each are flooded by epoxy and mounted on one axle, let may turn independently.
And the last idea- if the aim is so much shy as miliwatts, why not to use instead the simple solar cell for cost of few penses?