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Hot Rods Need help, 12v to 6v reducer not reducing

Discussion in 'The Hokey Ass Message Board' started by BillyBobsSpeedShop, Apr 11, 2020.

  1. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522

    BillyBobsSpeedShop
    Member

    Hope someone can help with some guidance, I purchased a 12v to 6v voltage reducer (the gold one with fin's) to reduce the voltage to my autopulse 6v fuel pump as I converted my T to 12v. Took the reducer out the box and wired it like it stated and I'm reading 12v thru the reducer at the pump wire? I swapped the wires and still 12v.

    When a reducer goes bad will it allow 12v thru and not reduce or would it just stop working? Also is there a ground needed, directions does state? Also will the voltage not drop till the fuel pump pulls amps? Below is the reducer I have.

    https://www.speedwaymotors.com/Elec...MIzOat8ebh6AIVRpyzCh2GnQIzEAUYASABEgIiffD_BwE


    Thank you
     
  2. razoo lew
    Joined: Apr 11, 2017
    Posts: 470

    razoo lew
    Member
    from Calgary

    That looks a lot like a power resistor to me. If so, you will need to connect a load to it to see the voltage reduction.
     
    tb33anda3rd likes this.
  3. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522

    BillyBobsSpeedShop
    Member

    Ok, so what's the best way to test it? Should I see the voltage drop while tht car is running?
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 49,870

    squirrel
    Member

    yes, when the pump is running is the only time you'll see the voltage drop.
     

  5. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522

    BillyBobsSpeedShop
    Member

    So I tested system today while the pump was running. I cut the fuel supply off and then slowly opened it while pump was running. When the shit off valve was opened up about a 1/4 way the volts where reading around 6.5 to 7.8, the more I opened it up the more volts the pump was using. With the shut-off valve all the way open the pump was pulling 10v but didn't go over 10v.

    I'm wondering if I need a different resistor or reducer?
     
  6. Budget36
    Joined: Nov 29, 2014
    Posts: 7,270

    Budget36
    Member

    Not sure the issue, but I think I'd just eliminate the reducer and run a 12volt pump.
     
    ffr1222k likes this.
  7. badshifter
    Joined: Apr 28, 2006
    Posts: 3,358

    badshifter
    Member

    That reducer specifically states it’s for a HEATER BLOWER motor. Your fuel pump isn’t pulling enough load on the reducer (not enough amp draw) to see the voltage drop you’d see with a higher amp draw of a heater blower motor. You’re time, money, and aggravation ahead to simply buy a 12 volt fuel pump.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 49,870

    squirrel
    Member

    As the fuel flow increases, the load on the pump motor decreases. This changes the current draw of the pump. Since you are using a voltage divider circuit to drop the voltage, this also changes the voltage balance, and the pump gets more voltage. That's just how the type of voltage reducer you have, works. It's resistance has to match the load exactly, if you want the voltage to drop exactly in half.

    If you want to keep it at 6 volts you'll need to use a solid state voltage regulator. Something like this might work.

    https://www.amazon.com/Aweking-Waterproof-Converter-Regulator-Transformer/dp/B06W9MZJ8X/

    Or get a 12v pump. Or just run it with that reducer, and see how long it lasts. Might last for a long time.
     
  9. BillyBobsSpeedShop
    Joined: Jan 6, 2008
    Posts: 522

    BillyBobsSpeedShop
    Member

    Squirrel thank for the information, makes sense why I'm seeing the voltage fluctuate. Ill look into the regulator
     

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