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Thread: Stepping down voltage

  1. #1
    turbo addict
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    Stepping down voltage

    I know we got some smart electrical guys on here. What's the best way to step battery voltage down to a constant 8 volts?

  2. #2
    Supporting Member Turbo Mopar Contributor
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    Re: Stepping down voltage

    Quote Originally Posted by thedon809 View Post
    I know we got some smart electrical guys on here. What's the best way to step battery voltage down to a constant 8 volts?
    First we need to know
    1)how much current you need?
    2)How clean does the power need to be? Ripple?
    3)Voltage accuracy?

    For example, if the current requirement is low you could use a series resistor and zener diode.
    Higher requirement could utilize a voltage regulator either linear or DC-DC.

    If you could say 8V +/- 0.1V at 100mA.
    If you are not 100% sure of the requirements, let us know what you are going to do with the 8V.

    Here are a few modules that I have used in the past. Adjustable voltage with 50mV ripple
    https://www.ebay.ca/sch/i.html?_from...r&_sacat=92074
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  3. #3
    turbo addict
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    Re: Stepping down voltage

    Quote Originally Posted by chromguy View Post
    First we need to know
    1)how much current you need?
    2)How clean does the power need to be? Ripple?
    3)Voltage accuracy?

    For example, if the current requirement is low you could use a series resistor and zener diode.
    Higher requirement could utilize a voltage regulator either linear or DC-DC.

    If you could say 8V +/- 0.1V at 100mA.
    If you are not 100% sure of the requirements, let us know what you are going to do with the 8V.

    Here are a few modules that I have used in the past. Adjustable voltage with 50mV ripple
    https://www.ebay.ca/sch/i.html?_from...r&_sacat=92074
    I need to step down voltage for a speed sensor. Here is basically what I'm trying to do. Early ZJ grand cherokees with the 4.0l came with the 42re but they had a standalone TCM whereas all other RE equipped vehicles had the tranny controlled from the PCM. I'm trying to see if the 42re TCM will control a 46re that's used behind a gen3 hemi. The only inputs the 42re TCM seemingly need are TPS and 2 speed sensors. The Jeep used an 8v reference for the 3 wire speed sensor. If this proves successful, it will be a gamechanger for making hemi swaps more affordable as 46re's are dime a dozen.

  4. #4
    turbo addict
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    Re: Stepping down voltage

    Another diagram

  5. #5
    Supporting Member Turbo Mopar Contributor
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    Re: Stepping down voltage

    This is a low current application and thus I would get a good quality name brand linear regulator.
    7808 style is old school and only needs 2 external cap as per the datasheet to work well.
    https://www.digikey.com/product-deta...1-5-ND/4280196
    or even the TO-92 package should work well for the small current you need
    There are tons of options here,
    Last edited by chromguy; 02-27-2020 at 11:25 PM.
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  6. #6
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    Re: Stepping down voltage

    Thank you sir. I will order one of those up and build a harness. I have a 96 ram 1500 so it will be the test mule. If it works, a hemi swap will be likely in it's future.

  7. #7
    Supporting Member Turbo Mopar Contributor
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    Re: Stepping down voltage

    Quote Originally Posted by thedon809 View Post
    Thank you sir. I will order one of those up and build a harness. I have a 96 ram 1500 so it will be the test mule. If it works, a hemi swap will be likely in it's future.
    you are welcome, remember to also order a 0.33uF and 1uF cap as per datasheet
    Regards,
    Miles

    DD '87 Sundance T1, SLH with rear disks
    '87 CSX #432 2.5 CB TII, SLH

  8. #8

    Re: Stepping down voltage

    When I have done this for my cars (swapping to a newer style hall effect speed/distance sensor) I just used a 220 ohm resistor. I think that is the value. My understanding is that the 8v requirement is not very strict...

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