My kid's Science Project

[Russell Ensslin]

His Project was to make a homo-polar motor out of a battery, a magnate, and a coil. His hypothesis was that a bigger battery would make the coil spin faster.
He used a 1.5 volt size C battery and a 1.5 volt size AA battery. Alas, they produced the same speed and the AA battery died sooner.

Was the speed the same because the voltage was the same?

 

[JFletcher]

His Project was to make a homo-polar motor out of a battery, a magnate, and a coil. His hypothesis was that a bigger battery would make the coil spin faster.
He used a 1.5 volt size C battery and a 1.5 volt size AA battery. Alas, they produced the same speed and the AA battery died sooner.

Was the speed the same because the voltage was the same?

Yes. Everything else being equal, the larger battery (higher capacity in mAh) will just run longer than the smaller one.

 

[Russell Ensslin]

what is mAh?

 

[JFletcher]

what is mAh?

Milliamp-hours. Smaller batteries typically list capacity this way.

eta: here is a fairly comprehensive list of smaller batteries and their ratings:

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

 

[GoldDigger]

His Project was to make a homo-polar motor out of a battery, a magnate, and a coil. His hypothesis was that a bigger battery would make the coil spin faster.
He used a 1.5 volt size C battery and a 1.5 volt size AA battery. Alas, they produced the same speed and the AA battery died sooner.

Was the speed the same because the voltage was the same?

And given that the voltage is the same, the current at that voltage and speed will be the same. But the larger battery can deliver that amount of current for a longer time.
If he takes two AA or two C batteries and puts them in series the result will be a higher speed (2X?) and probably a higher current. Could be an interesting experiment.

 

[junkhound]

homo-polar motor out of a battery, a magnate, and a coil

You do not need a coil for a homo-polar motor. Or is the science project some other type of motor?

BTW, the pair of magnets from an old microwave oven magnetron field work great for a homo-polar motor.

It would blow the judges away using the magnetron as the rotor ! But you would probably need to attach and axle to the magnetron.

 

[Russell Ensslin]

We called it a homo-polar motor but one of the "coils" wasn't even a coil; just a wire with a curve to complete the circuit.

 

[Russell Ensslin]

And given that the voltage is the same, the current at that voltage and speed will be the same. But the larger battery can deliver that amount of current for a longer time.
If he takes two AA or two C batteries and puts them in series the result will be a higher speed (2X?) and probably a higher current. Could be an interesting experiment.

But if the batteries are in series, how does that increase the voltage? How will that increase the amps?

 

[ggunn]

But if the batteries are in series, how does that increase the voltage? How will that increase the amps?

Putting batteries in series adds their voltage, and applying more voltage to a load increases the current through the load.

 

[GoldDigger]

Putting batteries in series adds their voltage, and applying more voltage to a load increases the current through the load.

Since batteries are close to voltage sources, you add the voltages when putting them in series.
Now the behavior of the current through the motor will depend on whether the motor in question is loaded (including frictional resistance) or free spinning. Odds are very good that the current will increase given a free spinning motor, but it is not guaranteed. Homopolar motors are odd ducks and I do not have any hands on experience with them.