How many magnets & poles do i need to generate generate 5v dc?

oz93666

Joined Sep 7, 2010
739
If I’m not mistaken, there would be no way to avoid reverse polarity across the capacitor. Either it is reversed on normal operation, or when the inductor must dissipate the energy, the polarity is reversed. So don’t you also need a diode? Additionally, just a capacitor could lead to resonance.
That's not my understanding ... we just have half wave pulses , very spaced apart (only 4 magnets on a big rotor ) , just need a cap to average it all out.....I think...

@ Sensacel ...certainly a brushless motor would be sensible for high power extraction , but awkward to connect mechanically . I think OP want's an elegant compact design .... the question arises where is the other power going that the human generates in this exercise machine .Why not extract it all electrically ??? I think someone exercising could generate a few 100 watts of electrical power ,and it would be extremely easy to adjust the resistance the exerciser experiences with switches which changes the load on the generator.
 

shortbus

Joined Sep 30, 2009
10,045
I would remind again if all the same polls are facing outwards only DC is generated and even if direction of rotation is reversed the polarity of the current is NOT reversed
I doubt that statement, but could be proven wrong. It works with a brushed DC motor or generator because of the commutator on the armature. But when the motor/generator is spinning the armature coils are going past both poles of the magnet, one pole will generate nothing. The commutator is acting like a diode bridge only a mechanical one instead of a solid state one.

The alternator in your car puts out AC that is then sent through a diode bridge to make DC. It has to do this because the alternator lacks a commutator.
 

-live wire-

Joined Dec 22, 2017
959
That's not my understanding ... we just have half wave pulses , very spaced apart (only 4 magnets on a big rotor ) , just need a cap to average it all out.....I think...

@ Sensacel ...certainly a brushless motor would be sensible for high power extraction , but awkward to connect mechanically . I think OP want's an elegant compact design .... the question arises where is the other power going that the human generates in this exercise machine .Why not extract it all electrically ??? I think someone exercising could generate a few 100 watts of electrical power ,and it would be extremely easy to adjust the resistance the exerciser experiences with switches which changes the load on the generator.
Generating a few 100 watts is HARD. An Olympic burst cyclist had extreme difficulty bicycling at 700 watts for two minutes.
 

Reloadron

Joined Jan 15, 2015
7,501
Generating a few 100 watts is HARD. An Olympic burst cyclist had extreme difficulty bicycling at 700 watts for two minutes.
700 Watts is pushing 1.0 HP which is 746 watts in a perfect world. I have a generic generator out in the garage. Running an 8 HP gasoline engine it develops 4,000 watts continuous power and 5,000 watts surge. Yet, 8 HP = 8 * 746 = 5,968 watts. So yes, when we want to convert mechanical energy to electrical energy it comes at a cost.

Ron
 

oz93666

Joined Sep 7, 2010
739
Generating a few 100 watts is HARD. An Olympic burst cyclist had extreme difficulty bicycling at 700 watts for two minutes.
Well , your figure confirms mine .... for an hour a professional cyclist can output 400W of useable power , so it's reasonable to think you or I could produce 2 or 3 hundred watts during an exercise session .... but I am assuming this proposed exercise device is a bike.
 

Thread Starter

Chris Oremus

Joined Aug 16, 2018
10
I didn't know that I could buy "frameless" motor parts. That resource will be very useful in my other projects. But for this project such a large motor would be prohibitively expensive and I would like the experience of learning how to generate electricity with my hand made components.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Why not use a ex-Treadmill 1hp to 2hp DC motor?
You need a way to maintain the rpm for high current, but you wouldn't need many revs for a T.M. Motor.
Or better still, an auto-wrecker alternator.
Max.
 
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Thread Starter

Chris Oremus

Joined Aug 16, 2018
10
I am making a handheld torque converter that is powered by linear momentum which is converts to angular momentum stored in a rotating mass where it then provides resistance for exercise. The current rotor weighs about 700 grams with 90% of that at the outer most diameter. I haven't figured out how to calculate F=MA yet but I have done a Vo2 test and monitored my heart rate while using it. When going slow the exercise is easy enough for me to workout with a 5 year old child but when I push it harder to go faster it can take me to my max HR 185 BPM in 75 seconds. When I sprint I can burn up to 18 kcal per minute or cruise at a very comfortable pace sitting comfortably with my eyes closed listening to an audio book and still burn 600 calories an hour. It would be exciting to see how much power that I could actually generate and discharge it through a tesla coil!
For this first one my goal is to generate a useful amount of power and store it in the batteries thus successfully completing the conversion of stored fat calories into useful power. I need to keep this lightweight. My original prototype weighted 7 pounds which I've reduced to 3 pounds in the new model while creating more exercise power with less weight by using composite materials and a 2 speed transmission. I would like to accomplish my power generation goals with under 1 pound of added weight.
 

Thread Starter

Chris Oremus

Joined Aug 16, 2018
10
That's not my understanding ... we just have half wave pulses , very spaced apart (only 4 magnets on a big rotor ) , just need a cap to average it all out.....I think...

@ Sensacel ...certainly a brushless motor would be sensible for high power extraction , but awkward to connect mechanically . I think OP want's an elegant compact design .... the question arises where is the other power going that the human generates in this exercise machine .Why not extract it all electrically ??? I think someone exercising could generate a few 100 watts of electrical power ,and it would be extremely easy to adjust the resistance the exerciser experiences with switches which changes the load on the generator.
OZ93666
Yes I am looking for an elegant compact design. Making this invention has been my pride and joy. I have been trying to make it as compact and lightweight as possible to create a workout experience independent of gravity which is like a static interference to this exercise. When I make heavier models for bigger stronger bodybuilders to use it will be exciting to do a fitness contest to see how much power can be generated.

Would you please tell me more about how you would adjust the resistance by switching the load?
 

oz93666

Joined Sep 7, 2010
739
OZ93666Would you please tell me more about how you would adjust the resistance by switching the load?
Whether we are dealing with an off the shelf brushless motor , or what you are contemplating, having magnets on a rotor and coils outside ,it's all basically the same .... if no power is taken electrically from the coils there is no back force on the rotor , the person exercising feels no resistance .... when you start to take power to charge batteries the exerciser will feel resistance ... the more power taken electrically the more work he does ... if you short the coil wires , this creates the greatest resistance to movement , although in this case no useful electricity is taken it is all consumed within the coils and appears as heat ....

So by varying the loads you apply to the coils by switching in more batteries to recharge , or electrical resistors , you can infinitely vary the effort required from the exerciser .... If you want to go fully electric ( all the resistance to exercise produced by electrical work) , an off the shelf small brushless motor may be best , these are very well engineered to produce great power from a compact size, it would be a great challenge to design and make something similar yourself .

If you try shorting the wires on the brushless motor you have , you will see it's much harder to turn the rotor .
 
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ArakelTheDragon

Joined Nov 18, 2016
1,362
3-phase is used because its power output is constant whereas single-phase is pulsating.
You have to use a magnetic material to make an efficient generator.
Determining the design of such a generator is not a simple task and requires a high degree of magnetic circuit knowledge which few but experts in generator design have.
Also he probably wants a 5VDC output, meaning the AC has to be 9VAC.
 

Reloadron

Joined Jan 15, 2015
7,501
It must have changed :eek: I have always used AC x 1.414=DC (with capacitor added)?
Max.
Me too and I am getting pretty sick of it. They make changes and constantly fail to keep me in the loop. When things like this change I expect an ECN (Engineering Change Notification). Like you I looked at the RMS value and multiplied by 1.414 to get the peak value which is what a capacitor will charge to. Nobody tells me nuffin! Now I find that rather than multiply RMS to get Peak I need to divide. All those years of multiplication shot. :(

Ron
 

Thread Starter

Chris Oremus

Joined Aug 16, 2018
10
That's not my understanding ... we just have half wave pulses , very spaced apart (only 4 magnets on a big rotor ) , just need a cap to average it all out.....I think...

@ Sensacel ...certainly a brushless motor would be sensible for high power extraction , but awkward to connect mechanically . I think OP want's an elegant compact design .... the question arises where is the other power going that the human generates in this exercise machine .Why not extract it all electrically ??? I think someone exercising could generate a few 100 watts of electrical power ,and it would be extremely easy to adjust the resistance the exerciser experiences with switches which changes the load on the generator.
OZ39666 I just tried the braking effect of shorting the wires and I'm really impressed how well that worked! I am grateful and really excited to have learned such an effective way to create a brake. I have wanted a non-contact brake for years and this is the perfect solution. There are no moving parts and it will never wear out! It's the perfect brake and it harnesses energy. Thank you for enlightening me!
 
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