Brushless motor to brushed motor generator - Project help.

After reading "The Martian" (saw the movie - it was crap compared to the book) It got me thinking about alternate power sources and charging for some of my projects...

Anyway, can anyone give me some insight on how to use a brushed motor as a power source in a charging circuit. I want to recharge a Lipo battery. I want to use a 2208 - 1050kv bushless motor (http://static.rcgroups.net/forums/attachments/4/4/4/4/7/4/t5371343-216-thumb-motor2.jpg?d=1355465189) with a pully attached to a 400 bushed motor (http://www.zagi.com/images/push_med.jpg)

I would like to continuously charge a 2200 mah lipo battery on my RC plane for a longer flight time. (http://www.relvad.ee/shop/images/Akud%20ja%20laadijad.jpg)

My thinking is that I would have the brushed motor mounted with a pully and prop and directly under it mount the brushed motor with a pully linking them with a heavy duty rubber band, so when the brushless motor spins to propel the airplane it will also spin the motor... I would then need to attach the leads of the brushed 400 motor to a regulating circuit of sorts and attach that to the balance plug of the 2200 lipo...

Will the power generated be enough to charge the battery (I know not enough to keep it charged) enough to slow the drain of the battery during flight for longer flight times? What would the charging circuit look like that I would need to regulate power spikes and whatnot? Am I on the right track or will this entire project burst into flames?

Thanks for your time!

Your request doesn't make any sense from an electronics standpoint. If you have the power to drive the BLDC motor why not use that power to charge the Lipo ?

You need to provide a reasonable explanation for wanting to do what you suggest.

If you have no such reason then just say so.

Thanks for your reply Raschemmel. I am using the power to drive the brushless motor, but I want to recover some of the power lost with the Brushed motor through the kinetic energy produce by the brushless..

A good analogy you be - on old bikes, there used to be a generator attached to the wheel to power a headlight. Think of the wheel as the brushless motor... the headlight as the charging circuit and the generator as the brushed motor.

To answer your question:

Your request doesn't make any sense from an electronics standpoint. If you have the power to drive the BLDC motor why not use that power to charge the Lipo ?

  • then I would be using the lipo to charge the same lipo, no?

My goal is to add a generator into an existing rc airplane circuit.

Thanks

lf this is some hairbrained attempt at a "Perpetual Motion" machine , forget it. The losses and added payload outweigh the gains and the discharge rate => 10 x the charge rate.

[quote author=Keith Brown link=msg=2630039 date=1456248162] I am using the power to drive the brushless motor, but I want to recover some of the power lost with the Brushed motor through the kinetic energy produce by the brushless. [/quote]

You can't. Here's one of the main reasons (if not the main reason) why:

Every time you change the "form" of the "energy", some amount of power is lost - almost always (in the end) as heat. This is known as the 2nd Law of Thermodynamics.

https://en.wikipedia.org/wiki/Laws_of_thermodynamics

So - in your scheme - you have a fixed amount of energy in the battery (electrical) - and you convert it to mechanical energy (brushless motor). Some of that energy is converted to heat along the way (wires, battery internal losses). After being turned into mechanical energy, more is lost (friction of the shaft and propeller, more heat from the windings). So you are already at a loss.

Now - you want to connect up a load - a brushed motor acting as a generator. Guess what happens - that's right, since you are converting mechanical back into electrical - you are going to lose more energy (friction of the belt, extra load on the brushless motor - increasing load on the electrical - more heat lost, heat loss in the windings of the brushed motor acting as a generator, friction in all of the bearings, etc, etc, etc).

...and you want to try to push that infinitesimal amount of electricity generated (compared to what was in the battery to begin with) - back where it started from - to increase a runtime.

Can you see here why doing this will actually make your runtime worse?

In the case of a bicycle generator, you are doing the same thing - but in that case, you can't even gain much from the extra energy expended to keep the generator running (other than having a light to help you see at night). By adding on the generator, you are expending more effort (energy) in pedaling the bike. There is extra heat losses and friction. You aren't gaining anything. You can't gain anything.

BTW - this is also why those "HHO"/"water-as-fuel"/"hydrogen boost" systems for cars can't and don't work, either (even if they had the efficiency to supply enough hydrogen for a car engine to run).

Remember:

  1. You can't win.
  2. You can't break even.
  3. You can't get out of the game.

https://en.wikipedia.org/wiki/Ginsberg%27s_theorem

Sorry guy - that's just the way it is.

:)

Don't forget the added payload (of the added brushed motor and charging circuit) for the airplane, requiring more thrust...

Thank you all for addressing my curiosity. I had a feeling it was a witch hunt, but thought I would pose the question. Thank you for saving me time and aggravation...

Keith

Besides all the other reasons, the biggest reason is the ratio of the discharge rate to the charging rate.
The battery would discharge long before you could charge it.

See Wikipedia.

And then there’s the forum post for a topic which makes no sense , prompting replies to that effect , which the poster doesn’t understand , which prompts more explanstions etc. etc. etc. (not referring to this thread per se but rather in general)
One post asking if a resistor is really necessary when uding an LED ran ovrr 120 replies. ( hsrd to believe I know).

raschemmel: One post asking if a resistor is really necessary when uding an LED ran ovrr 120 replies. ( hsrd to believe I know).

Hey, retire that iPad and get a computer! :grinning:

You got me ! (Android phone)
( I was probably in bed)