MAF voltage Clamp

Discussion in 'Automotive Electronics' started by bearsbmw, Oct 17, 2016.

  1. bearsbmw

    Thread Starter New Member

    Oct 17, 2016
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    Looking to build a MAF voltage clamp circuit.

    Source voltage = 12v DC
    Signal range output = 0-5v

    I need to clamp the signal voltage output at about 1.5volts . What is the best method to this?

    Thanks in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Where is the load that you need to drive with this clamped voltage?
    How accurate does the clamp voltage need to be?
     
  3. bearsbmw

    Thread Starter New Member

    Oct 17, 2016
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    Not sure what you mean by the first question. The clamp needs to be fairly accurate with the ability to adjust .

    Cheers
     
  4. crutschow

    Expert

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    I mean what is the clamp signal going to drive, i.e. where is it going?
    What is the impedance of that load?
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    MAF = manifold/mass airflow? Trying to "fix" something on the antipollution devices for your car? Aren't they working?
     
  6. bearsbmw

    Thread Starter New Member

    Oct 17, 2016
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    It's going into the ECU but I'm going to run a three poll pressure switch that switches the signal from MAF to MAP at about 0.5psi . Sorry guys I'm a complete newb when it comes to electrical.

    Thanks
     
  7. crutschow

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    What vehicle is this for?
     
  8. bearsbmw

    Thread Starter New Member

    Oct 17, 2016
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    BMW
     
  9. #12

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    Here's an idea based on the TL431 chip.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Below is the LTspice simulation of a clipper using a TL431 programmable voltage reference to provide a sharp and stable clip point.

    It uses two opamps (all in one package) to buffer the input and output so there should be no concerns about loading the source or driving the load.

    The first op amp has a gain of +2 to amplify the signal sufficiently to allow clipping by the 2.5v minimum clip point for the TL431.
    The second op amp then has a 0.5 attenuator at its input to reduce the signal back to its original level.

    The clip level is adjustable from about 1.25V to 1.75V at the output as shown, as determined by pot U1's setting and the value of R1.

    The circuit requires just the 12V vehicle voltage for power.

    upload_2016-10-18_1-26-51.png
     
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  11. tcmtech

    Well-Known Member

    Nov 4, 2013
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    And what do you expect to gain from doing this? o_O
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Trying to trick the injectors to give more fuel? When changing the size(pounds per hour) of injectors is the correct way.
     
  13. #12

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    Crutschow covered the uncertainties by using (2) op-amps. My circuit assumes you can find out what the impedances are and adjust accordingly. (It's all in that 10K resistor on the top line, which might not even be necessary.) If this was a production line model, mine would win for cheapest use of parts. As a one-time circuit for a tinkerer that might not know how to match impedances? Crutschow wins.

    You and I approach this differently, but I can understand your point of view.

    I think changing the injectors won't fix anything in a modern car because the O2 sensor will just change the "fuel trim" (on time duration of the injectors). You have to fool the ECU.
     
  14. shortbus

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    I know that. but was looking at it from the OP's perspective. Many believe that "fooling" the MAP/MAF is the way to get more fuel, but duty cycle and pounds per hour and O2 sensor figure in. Running a low pounds per hour injector at almost 100% duty cycle will burn out many injectors. A higher pounds per hour injector at lower duty cycle is a better way to go.
     
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  15. #12

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    OK. You're in an area which I don't know very well.
    I was thinking 10% on time becomes 15% on time would make a huge difference.
    Running the injectors at 90% to 100%?
    Definitely going to have some heat problems.
     
  16. crutschow

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    How could you run an injector at 100% duty-cycle?
    Isn't it on only when the intake valve is open? :confused:
     
  17. tcmtech

    Well-Known Member

    Nov 4, 2013
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    To feed a modified engine or change A/F ratio?

    If its A/F ratio the easiest way is to tweak the O2 sensor signals which is easily done with Germanium signal diodes to make them read a richer 12.5 -13:1 A/F ratio as being the leaner ~14.4:1 stoichiometric one the computer want to see.

    To get more fuel through a smaller injector takes either more on time or higher fuel rail pressures which for the fuel rail pressure that can be cheated by modifying the fuel pressure regulator unit in one way or another which will be limited by whatever the fuel pumps own bypass valve limit is which could be as much as 150 - 200% of the nominal fuel rail set pressures you may have quite a bit of headroom to play with.
     
    Last edited: Oct 18, 2016
  18. tcmtech

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    I can't give directions until I know where the person wants to go. Can you? o_O:p
     
  19. #12

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    When the question is simple enough, I just go into stupid mode and design a circuit. Investigating whether the customer is asking for what he NEEDS is a whole 'nuther conversation...which I usually don't bother with. In this case, I wouldn't know whether he's right if he explained it to me.:D
     
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  20. bearsbmw

    Thread Starter New Member

    Oct 17, 2016
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    Guy's I'm simply running the MAF for off boost drive-ability and the map sensor for boost control. I have re-engineered the software calibration data in the stock ECU to accept these hardware changes.

    Thanks for the help everyone
     
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