Hello friends,
I am a STEM coach with a national competition in two weeks. My students (all under 15), have been working on a three-way system for using a hand cranked generator to assist our battery in powering an RC motor.
I don't know that much about circuits and electricity, but in my mind, the picture should have worked. Can someone assist with the basics of electricity or how I need to change this to get both the battery and generator to send power to the motor? No matter what I put where, the battery attempts to power both the battery and the generator (making it spin). All help is appreciated.
How do you become a STEM coach without knowing that a generator is just a motor?
Oh boy, starting from scratch here. The hand crank (your "generator") is synchronized to the rest of the system. When current flows from the battery to spin the motor, it's also pushing back and causing the generator to act as a motor itself, because at the end of the day the only difference between motor and generator is the intended purpose, the construction is really the same. Assuming the hand crank is commutated (DC and not AC) You should be able to add some diodes to the circuit to keep current from flowing back to the hand crank when it's not being used. Without a ton more detail about the components you have, I cant tell you if that will work or if another solution would fix it.
>>989642
Hope this helps
>>989641
Um they needed a volunteer? I teach Biology dawg. I know a generator is a motor, the point is they want the motor for the car to get all the power from both.
>>989642
This picture is the splitter(?) we ordered. Its a small motor in the car, a 5000 MaH battery, and a small hand crank generator.
>>989643
How easy is it to install a diode? I can't even solder anything, meaning the kids definitely can't do it.
>>989644
http://www.mouser.com/Search/m_ProductDetail.aspx?Fairchild-Semiconductor%2fS1MFL%2f&qs=sGAEpiMZZMvdy8WAlGWLcBokLwvq76c1lPtjllRUbEw%3d
Get yourself two of these. Unfortunately, you'll have to cut the cables of the splitter and solder them on. That's the only way I can think to do it.
>>989642
>>989643
All the diodes will do is make the 'generator' always spin in one direction because motors can run with the polarity switched.
>>989644
Your hand powered generator can never keep up with the current output of a battery; the only situation in which it might be useful is if it always puts out more voltage than the battery which will stop a reverse current flow to the generator.
In pure physics the energy from the generator and the energy from the battery should combine to produce more power, in reality the power supplied by the generator (watts) is too low to make it anything but a load on the battery.
>>989649
Tons of YouTube videos out there. Tens of thousands. If an illiterate Chinese 8 year old can make hundreds of PCBs in a factory every day your spoiled 15 year olds can figure it out for a single project. A cheap soldering iron is <$10 and a small roll of solder is $3
>>989649
Highschool kids that have never played with a soldering iron but are involved in a national competition?
Jesus christ what is wrong with this world.
Watch a youtube video or something. It's literally wrap bare wires together, apply some paste flux for super easy soldering, hold the hot metal stick against the wires and then touch the solder wire to the hot area.
>>989651
So this will never work in any capacity? We really just need to generate data and try it, whether it actually will revolutionize energy generation is irrelevant. We made 3rd last year with a perpetual motion machine because we had data on how it worked (or didn't work, as it is).
>>989651
If the hand crank is commutated it will only spin one direction. If it's a synchronous gen it will go both directions. Given that this stuff sounds like it comes out of a plug-and-play kit and not some BSEE lab parts bin, I would assume it's commutated. And there's no way to know the output voltage of the gen, so it might work to charge the bat/run the motor or not. Hell if anyone knows until you try, since we don't have nameplate info.
>>989657
that's the hand crank we're using at the moment
goo gl/vEiU4z
>>989656
Then you need to hook up a load to the generator and measure the voltage across it when you spin it as fast as you can. First connect your generator to the motor directly and see if you can even make it spin from hand cranking.
>>989657
Brushed DC motors spin in both directions when you reverse polarity.
>>989656
>Perpetual motion machine
>Not DQ'd
What a shitty competition
>>989659
The car will start when cranking the hand crank and even move some, until you stop cranking.
>>989658
Case in point, that is a brushed dc motor and you can clearly see you can reverse the polarity by spinning in the opposite direction.
A diode will stop the motor from spinning, but power still wont get to the motor unless the generator puts out a voltage that is higher than the battery.
>>989665
Logic with your statement dictates if I powered the car with more voltage from the crank, then the battery wouldn't get its power to the battery then?
>>989662
Then collect your data. Put a volt meter in parallel with the motor and an ammeter in series with it and record the values as some one cranks and the car moves. Power = voltage x current. That is the potential help that your generator can give.
>>989668
Sorry that last battery should say motor
>>989668
No it's not so simple since your generator is just another motor in this case, it can be a load or a power source.
What I am thinking of is the initial biasing of the diode, to get the diode to open up you have to have a voltage difference of about 0.7volts in right direction of current flow. So I'm thinking the generator needs to put out battery voltage plus 0.7.
But I could be wrong, stick it into a spice simulator and see what it predicts.
Consider the situation where you have two batteries with roughly identical output voltages. Each battery has the same internal resistance.
If the internal (off-load) voltages are equal, each battery will contribute exactly half of the current drawn by the load.
As the internal voltage of one of the batteries rises, it will contribute an increasing proportion of the current. The output voltage will also rise slightly.
When this reaches the internal voltage of the second battery, the first battery will contribute all of the current, the second none of it.
If it rises above the internal voltage of the second battery, not only will the first battery provide all of the load current, it will also force current into the second battery, charging it (assuming that it's a rechargeable type).
Conversely, if the internal voltage of the first battery drops far enough, the second will provide all of the load current as well as charging the first.
The range of voltages over which this occurs is determined by the voltage drop across the batteries' internal resistance, i.e. the difference between the off-load voltage and the voltage when loaded.
Cont'd from:
>>989676
Adding diodes to the battery and the generator will prevent reverse current, i.e. the battery won't drive the generator as a motor if the generator's voltage is too low, and the generator won't charge the battery if the generator's voltage is too high.
But unless the two power sources are providing almost identical sources, only one of the two (the one producing the higher voltage) will actually be used. In particular, if the generator voltage never exceeds the battery voltage, it will never provide any power and you can save the cost of a diode by just removing the generator altogether.
Practical power-balancing systems typically use switching regulators to control the current supplied to the load according to a given policy.
E.g. in this case, the policy would probably be to
1. Get as much power as the load needs from the generator and supply it at the desired voltage.
2. If that is insufficient, get as much power as possible from the generator.
3. Take as much power as necessary from the battery to maintain the desired load voltage.
Needless to say, if you can't solder a diode, all of this is way beyond anything you should consider. The point is that you can't just connect a generator, a battery, and a load with a Y splitter and expect it to work.
>>989649
Does your VCR also flash 12:00 as well?
