Variable Speed Control Switch?

Discussion in 'General Electronics Chat' started by heatshrink, Oct 8, 2011.

  1. heatshrink

    Thread Starter New Member

    Oct 22, 2010
    12
    0
    Hey I want to replace a simple on off toggle switch on my Bobcat heater with one that is variable/3 speed. It is a 12 volt system with just 2 wires. Many I've looked at have 6 wire setups. Can I use the 2 wire hot and ground on a six wire switch and how do I wire it? Below is a link to one of the switches I'm looking at. Thanks.
    http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=ECHHC157_0006365944
     
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Please explain "Bobcat Heater." Do you have any specifications, make, model...etc?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    A "Bobcat" is a front end loader (think miniature bulldozer or bucket scooper). They come in many configurations. I'll have to guess that the on/off switch simply controls a fan; the heat comes from the liquid cooling system.

    I'm not certain if this will fall under the general category of "automotive modifications", as a Bobcat is certainly not designed to be operated on a roadway. However, we'll wait to see what the Moderators have to say.
     
  4. heatshrink

    Thread Starter New Member

    Oct 22, 2010
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    0
    It's a 743 Bobcat skid steer loader. It was made back in the early 1990's. It's not a road legal street machine. Call it a tractor but it is by no means automotive in nature. The heater is an aftermarket glycol circulated heater core with a 12 volt squirrel cage blower type fan. I need to raise the cab to see how many amps it draws in order to determine how many watts it uses. I just need to know how to wire it using any generic universal 3 speed switch that has more connectors than I have wires for. I could use a rheostat but I'd prefer to use a 3 speed or 2 speed type switch. Thanks.
     
  5. evanwidloski

    New Member

    Oct 8, 2011
    9
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    Is the old switch still functional, as in can you hook it up to a multimeter and find resistance? Thats the first thing I'd do
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Those switches are only part of the speed control. In older vehicles, they used power resistors to limit the current through the motor, which caused it to run more slowly. The resistors were usually located in the airflow of the heater box so that the air moved by the fan would keep the resistors from getting too hot.

    More modern blower controls use what's called 'pulse width modulation'; PWM for short, to control the speed of the fans. It's more complex than using resistors, but it is more fuel efficient when air conditioning is being used. Since you are just using it for a heater blower control, it doesn't make a difference as far as efficiency goes.

    It would help to have an idea on how much current the motor draws, but you probably will not be able to measure the current with a meter; you will more likely than not blow the fuse in the meter.
     
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