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Electronics for Dogs II · 10 October 05

In part II of Electronics for Dogs we consider resistance and how it really isn’t all that futile.

Electronics for Dogs part II

Sometimes resistance is very useful other times we’d prefer to minimize it. AGM batteries, for example, have very low internal resistance as compared to lead acid batteries. This allows high currents to go in and out of the battery without generating equally high levels of heat. Good for quick charging and quick get-aways.

On the other hand if you install an electric heater you are counting on resistance to do some selective heating and warm things up in the car come winter.

Whenever you attach a connector to a wire there is a small amount of resistance. Hopefully if you do it right this resistance is insignificant. A bad connector on a main battery line can quickly turn into a molten pile of metal when your EV tries to draw hundreds of amps of current through it.

Read more about voltage, current, and resistors.

By the way if you were going to make the example circuit with battery and LED you’d most likely also need to add a resistor, just like the cat suggests. LEDs can only handle a certain amount of current, so a resistor is put between it and the battery to limit how much current flows. For example a 5vdc circuit might use a 330 ohm resistor. Divide the battery voltage by the LED’s current rating to get resistance. Let’s say we wanted to hook up a super bright LED to our 12volt car battery. 12 / 0.03 = 400 ohms.

Nowadays you can buy LEDs or LED bulb packages that are designed for a certain voltage and already have the resistance built in. Check out these LEDS.

Now on to Electronics for Dogs Part III

Comments 7
  1. Karen    Oct 10, 2005 07:45 AM    #
    I think your critters remember more about this stuff than I do. It’s amazing how much you can forget once you put your mind to it…
  2. — Dan    Oct 10, 2005 17:59 PM    #
    “Ohm’s” isn’t just a good idea, it’s the Law. Watt smart animals you have. BTW, how do they prefer describing RLC networks: with phasers or differential equations? ;)
  3. Jerry Halstead    Oct 11, 2005 19:17 PM    #
    Round legged cat networks???

  4. — Randy Scott    Aug 01, 2007 21:58 PM    #

    Have you found LEDs bright enough to use as headlights?

  5. jerry Halstead    Aug 02, 2007 07:39 AM    #

    I haven’t really looked around for them. They do have LED replacements for all of the other lamps on a car.

  6. — James May    Aug 02, 2007 17:59 PM    #

    Hi Randy

    I really don’t think you can get LED headlights. None of the current (no pun) domestic LED lights have the kind of power handling / dissipation you would need for headlights. Semiconductors don’t like heat. It encourages dopant migration and early failure.

  7. — Jeremy W    Jun 22, 2008 18:53 PM    #

    i dont know about headlights but you can buy LED taillights from Amazon.com