# Homework Help: Science fair DC motor help needed

1. Oct 23, 2014

### Brandon02

1. The problem statement, all variables and given/known data
Hello, I am a 6th grade student trying to build a DC motor for the science fair. My hypothesis is that the dc motor will run faster if I place batteries in parallel versus batteries in a series. Is there an equation i can look at to explain what is happening? the mootr will be like the one found on youtube built by howtolou. thank you.

2. Relevant equations

3. The attempt at a solution
voltage constant = (V-IR)/rpm???

2. Oct 23, 2014

### phinds

It will depend on the voltage required to drive the motor and the voltage of the batteries. For example, if it takes 20 volts to drive a particular motor, you can put a million 1.5 volt batteries in parallel and they will not run the motor. Sounds like you should study a bit of basic electricity before going any further.

It's a good project but without knowing a bit more of the basics you might find it overly frustrating.

3. Oct 23, 2014

### Brandon02

Thank you Phinds
I understand a parallel set up will not increase the volts but a series will. Maybe my project should be about increasing voltage only. But if I make a dc motor like the one on Internet, why can't I just add enough battery to make it run and then experiment with more batteries added in a series?
Brandon

4. Oct 23, 2014

### phinds

Too MUCH voltage is worse than too little. Too little just means it won't run. Too much means it will burn out (or the batteries will). The right voltage and not enough current won't work either. You need a happy balance of series AND parallel to get the right voltage with sufficient current capability. If the batteries are big enough (enough current capability) for the motor in the first place then series will do. You need to know what the motor specs are and what the battery specs are.