Jump to content

electric resistance!!


fatoumata

Recommended Posts

Sounds like a homework question, so I can't just tell you the answer. Are you familiar with basic electrical circuits? With Ohm's law? If so, try drawing out the equivalent circuit, both with the starter motor on; and with it off. Don't forget the internal resistance of the battery. What, with respect to the headlights, is the difference between these two?

Link to comment
Share on other sites

To hopefully clarify, what I think npts2020 means is to look at this intuitively and consider that the battery has a limited amount of power it can produce. With and without the starter, how is this power distributed? If you think about it you should be able to come up with the answer easily.

 

If you still have trouble, or need to explain this in a report, you can solve for this mathematically using ohms law per my suggestion; P = VI and V = IR and come to the same conclusion. Let V = 12V for the car battery. There is a resistance in the light; in the battery; and two resistances for the starter (on and off). I'll let you decide appropriate values for these (a google search might be helpful). So calculate the current and voltage (and therefore power) in the light when the starter is on, and when it is off.

Link to comment
Share on other sites

  • 3 weeks later...

The power source (car battery) has internal impedance.

What this means to you is that when any load is placed on the battery its voltage drops.

The bigger the load the more it drops. A starter is a very significant load and thus the voltage drop is significant.

Anyway if you are running the starter the engine is not running and the alternator is not trying to hold the battery voltage up.

Even touching the brake lights will dim the headlights when the engine is not running just not as much as the starter.

Link to comment
Share on other sites

  • 2 weeks later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.