Battery Charging using DC Motor

Question

I have been trying to wrap this idea around my head that I can successfully charge a battery by using a DC motor. Here is the example: You have let's say a 16,000mAh 6S Lipo Battery. This battery is your primary energy source. This battery will power a brush-less DC motor. When the DC motor is creating high RPM's, this energy would be used to recharge the primary battery, while also powering other components within the device. In this example, the device housing these components would be a cooling fan for a motor design I am working on.

Is this possible?

If it is, one thing I concern myself with, is that the battery designs of today, mostly only have one connection, which is used to plug into the charger or to plug into the device you wish to operate. If this is in fact possible, I would like to speak further with you on perhaps helping me develop a solution. Thanks!

jw0752 · Accepted Answer

Hi Dan,

Example one: We have a battery that is supplying energy to a motor. The motor spins as a result of the conversion of electrical energy into mechanical energy. Heat is also produced in the process and this energy is lost to the environment and is not practically recoverable. Suppose for this example 80 joules of energy is going into spinning the motor and 20 joules of energy is being wasted as heat. This motor is said to be 80% efficient. Now let's assume that we have a crank on the motor and we can turn that crank very fast. We begin turning the crank with all our might and the chemical energy of our muscles is converted to the mechanical spin of the motor. At some point we will be spinning the motor fast enough so that it is no longer using energy from the battery. The crank is keeping the motor spinning and the electricity that is being made by the motor by our efforts on the crank exactly equals the energy supplied from the battery. At this point the system is in electrical equilibrium. If we want to charge the battery however we have to increase the energy and speed of the turning of the crank. Now the voltage that we are producing by turning the crank is greater than the voltage of the battery and energy starts to flow back into the battery and the battery recharges. In this direction we will not be as efficient and perhaps 50% of our effort will be lost to heat and will not be practically recoverable. Since electrical energy can only move one direction at a time we can not use the battery to spin the motor and use the spin of the motor to recharge the battery simultaneously at the same time. We also loose energy to heat in both directions.

Example two: We have a battery spinning a motor and at the same time we have a battery of a lower voltage connected across the circuit. In this case energy from the higher voltage battery spins the motor as before. Energy from the higher voltage battery will also flow to the lower voltage battery and recharge it. However the energy we loose from the big battery will be much greater than what is gained in the smaller battery. All the while we are doing this the motor will run use the same energy as before and contribute nothing.

There are no circuits no matter how sophisticated that can get around the fact that we can not create energy. We can convert energy from one form to another but always with a cost of loss of some of the energy that is converted. It is like pouring water from one container to another using leaky pipes. We will always have less after the process than we began with. Check out the Second Law of Thermodynamics.

I hope this clarifies a bit.

John

jw0752 · Answer

Hi Dan, shabaz is correct. If you make a motor spin with a battery the energy comes from the battery and is converted to mechanical energy and heat in the motor. In order to charge a battery with a motor it is necessary to use mechanical energy to spin the motor and the energy then comes from the source of how you are spinning the motor and goes to the battery where it is converted to chemical potential energy and heat. There is no way to use a battery to spin a motor and use the same motor to charge a battery at the same time. This would be like reaching down and grabbing your own ankles and lifting yourself into the air. There are a lot of snake oil sales people trying to sell these ideas but there is no free lunch when it comes to energy. John

jw0752 · Answer

Hi Douglas, Thinking outside the box is good. shabaz did a good job of summarizing and expanding my post. Certainly some energy can be recovered if there is a need for the energy and if it is economically justifiable. In most cases the cost of the harvesting or recovery technology is more than the value of the return. By the way I think most of the heat loss in a motor comes from resistive and inductive losses rather than friction. 2AM here and time for me to shut down for the night. John

michaelkellett · Answer

I am quite sure that you have NOT seen any such thing but it may be that some freak circumstances or clever tricks have deceived you. If you could describe what you have seen and better still offer pictures or links I'm sure that plenty of E14 people will be very happy to explain what you might have seen - and why it doesn't do what it seems. MK

shabaz · Answer

Hi Douglas, Recovering energy from heat generated by the motor in its normal activity is not the same as using a motor to drive a generator, which was the question the original poster asked. The original poster had a battery supplying power to a motor which was performing some useful purpose (not mentioned - lets say perhaps driving a fan). In addition the original poster wanted to use the motor to also drive a generator to charge the battery back up. This actually would have resulted in less operational time before the battery needed a recharge,because of additional inefficiencies - therefore would have actually been worse than just using the battery to drive the motor to drive the fan in the first place. Regarding your point, yes if there are inefficiencies resulting in heat then that could be collected to allow the battery to run longer. Another option is to make the motor more efficient, e.g. with better bearings and better commutation. In some cases DC motors can be very efficient (more than 90%) so the motor would at best run for under 10% longer. For large scale generators I think they may already perform heat recovery. Businesses can also do things to recover this energy. There is a useful website here . 
 I too had the dream of making a perpetual motion device too. But since then, and with the advancements in the field of electronics its getting closer to that dream of coming true. 
 It isn't. There are no advancements in the field of electronics that could achieve this.

Former Member · Answer

Lord knows I can't lift myself into the air John 
 Absolute classic! i just burst out laughing for no apparent reason as far as the people round me are concerned hah! On a serious note... like others have already said, the energy that turns the charging motor must come from somewhere, heres another example; Your car battery keeps its charge because of the alternator motor that spins from the cars engine. Its easy to believe that this energy is free because the engine is already running but in reality causes a small amount of drag, and wastes some energy through heat, light and sound. This results in the engine consuming more fuel, but its considered a worthwhile system cost to keep the battery topped up.

Robert Peter Oakes · Answer

Wow, it is very simple and a few good engineers have already tried to explain There is no free lunch, there is no system that is 100% efficient, never mind over 100%, there are some very lab science research specific examples that are close to 100% but still less than 100% Due to friction, Heat, Resistance, etc you will NEVER get out what you put in. Conservation of energy is real and a fact. Do you really believe that if I connect a motor to a battery, the motor will get to the point where it is not drawing power from the battery and in fact can reverse the flow and start charging the battery instead, this would mean that the motor (Lets say it takes 100W to turn it) it is generating over 100W internally + any heat loss, friction loss and resistance loss, then in addition, it is generating enough to also re-charge the battery, this would mean it is generating in excess of perhaps 120W on its own. therefore if you could simply start the motor spinning without a battery (Perhaps a lawn mower starter cord) you could have it power a 20W light bulb and itself forever, now that would sell right. but it is impossible. This goes right along with Water Seer W ind-powered Water Seer pulls 11 gallons of clean drinking water from thin air | Inhabitat - Green Design, Innovation, A… Solar Roadways Home - SolarRoadways and the like. Actually both the roadways and the water seer will actually partially work at least, given just the right circumstances, just won't be returning any investment in the next 10,000 years or so... and are so far from meeting even part of their claims it's not funny When you get a bunch of really good engineers telling you the same thing, perhaps they have a point?

Robert Peter Oakes · Answer

Water Generator... Claims to generate water 7*24*365. No Wind, No Water No Moisture in the air, no water (Desert Regions) you need to dump heat to get the water to condense, this heat goes into the surrounding soil and heats it up, we're talking kilowatts of power based on the claimed water output !!!!!, warm soil = no condensation Day and Night... nigh it gets colder, usually colder than the soil, so no condensation if there is wind and low humidity, all the wind over the water in the container will evaporate it anyway, its a complete scam, the physics does not add up, same for solar roadways, same for using the motor to charge the battery is is running from. There similar because there all examples of where people try to demonstrate breaking the laws of thermoDynamics, Conservation of energy and other fundamentally sound engineering facts by quoting all sorts of fancy terms that have no foundation in true research and appear to just be scamming money from gullible folks who dont know better. In this case the poster is convinced by the apparent output (Greater than unity gain of input to output ) but does not have the background to know it is not possible Even your example of the geothermal, if you just stick to energy in vs out rather than money in vs product out, it is still not 100% efficient and certainly not greater than 100%. yes you're providing less PAID for energy that you get out, but that other energy is coming from the surrounding ground anyway, I digress.

jw0752 · Answer

Hi Enrico, I have found that people who use their imaginations to try to come up with new ideas, even when they do not have an in depth background in the science, are often the source of new and innovative things. This is because they have not yet been taught what is impossible and they are free to go beyond the bounds of this restriction. I hope that Dan doesn't get discouraged as he asked his question in a very well written way and he did a good job instigating this discussion. If you proceed to use the Arduino to demonstrate the Carnot cycle it will be a very interesting project but you will have to give Dan some of the credit for the inspiration. John

shabaz · Answer

Sounds like those mythical 'free energy' ideas. If the battery is powering the motor, then a certain amount of energy is needed to do this. That energy came from the battery (due to a chemical reaction).

If you wish to use the motor to charge the battery then that energy comes from.. that's right, the battery itself.

So the answer is yes, it is possible (with a complex circuit since you're using a brushless motor) to charge a battery but won't result in anything useful since work is being done to put energy back into the battery (and that energy originally was supplied from the battery) and you have conversion losses at all stages. There are probably hundreds of such discussions on the Internet - for some reason it seems a popular thought. See here for some more discussion on it: https://www.physicsforums.com/threads/how-to-use-an-electric-motor-to-recharge-a-battery.535694/

ntewinkel · Answer

Due to friction, Heat, Resistance, etc you will NEVER get out what you put in. Conservation of energy is real and a fact. Agreed - the only way to get more energy than you put in is to steal it from somewhere else. For example, heat pumps are considered more than 100% efficient (compared to direct use of electrical energy through a resistor for heat) because they move warmth from outside of the house to inside. But the "free" energy is obtained from the heat in the outside air. I don't see how the Wind-powered water generator and solar roadways pertain to this free energy question. I might be reading it wrong, but that wind-powered water maker seems to use wind power to push moist warm air down into an underground reservoir which I presume is cooler and causes the water to condense out. Seems legit. I'd never use it here in my temperate rainforest, but I suspect certain desert areas could benefit. Although like you said, might not be worth the investment, especially if drilling a well (where possible) takes less energy to begin with. The solar roadways use solar panels to generate electricity. Solar panels are already proven legit. Not sure if it's financially worth it, but I guess part of the claim is that those roadways will last longer than regular tar-based pavement. Might work well in places like California where there's plenty of sun and it's never covered by snow. Maybe using those panels just for cross-walk and other special danger areas could be worth it for the safety factor.

Capper · Answer

Of course you can charge a battery from a dc motor, that's how generators work. You just can't do it at the same time you're powering the motor. Look up regenerative brake " https://en.wikipedia.org/wiki/Regenerative_brake " Keep thinking, Scott

pettitda · Answer

I suppose if you had two sets of armature coils you could technically "charge" the battery from one set of coils and discharge the battery from the other set of coils. Although arguably you couldn't say you were charging the battery because the net flow of current would be out of the battery not into it. It would be more of a Rube Goldberg experiment than anything else.

Battery Charging using DC Motor

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