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diode for super low voltage?

Discussion in 'General Electronics Discussion' started by Arky, Jan 15, 2016.

  1. Arky

    Arky

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    Jan 15, 2016
    I am wiring a 2 step launch control box to a car ECU. I need a wire from the "2 step box" to ground out the signals (from ECU to ignitor) above a set RPM. The single wire from the "2 step box" needs to intercept three separate ignitor signal wires. When I hook them up all up together, the "2 step box" functions properly, but the ignitor signals are feeding back into each other and causing coils to fire at the wrong time and the truck runs poorly. SO, I'm trying to using a diode on each 3 ignitor wires, but the voltage is too low for the diode to "turn on". The box doesn't function at all. I only have a digital meter so I'm not able to get an actual reading on what voltage the ignitor wires are sending since they are quick pulses. Searching online seems to agree the voltage sent is less than .5v. I've used the smallest silicone diode radio shack had in stock (1n914).

    Is there a diode that will turn on with that insignificant amount of voltage? What are my other options?
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What is the voltage level please, oh and welcome to EP :)
    Adam
     
  3. Arky

    Arky

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    Jan 15, 2016
    I'm not sure. It's a pulse and my DVMM won't read it. I need to get my hands on an analog ASAP.
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What is a two step launch control pleaee?
     
  5. Arky

    Arky

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    Jan 15, 2016
    http://www.enginebasics.com/EFI Tuning/2step rev limiter.html

    The next link is the device I have "BEE-R power builder" and this is the method I am trying to use to hook it up: http://forums.nasioc.com/forums/showpost.php?p=22303812&postcount=21

    More reading here: http://forums.nasioc.com/forums/showpost.php?p=34229089&postcount=72

    I'm using this to cut ignition cycles, yet still deliver fuel, which causes high manifold pressure that will spool a turbocharger in a drag racing launch application.

    Clear enough?
     
  6. duke37

    duke37

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    Jan 9, 2011
    A schotky diode will have a lower voltage drop than a silicon diode such as a 1N914 or 1N4148.
    If a small schotky diode does not work, you may have to amplify the pulse.
     
  7. Arky

    Arky

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    Jan 15, 2016
    Here's the voltage on 1 of 3 IGT wires. There are 3 of these wires I need to tie into the 2 step box. I honestly don't know how to interpret these readings accurately. Any help reading the voltages?

     
  8. Gryd3

    Gryd3

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    Jun 25, 2014
    Look at the scale you are using, and try to find something on the display with a similar scale.

    You have it set to 2.5V... but there is no 2.5V scale for the needle... well, not exactly.
    Use the 250V scale and adjust the decimal point! The 2.5V setting is the highest you can read on that setting. (Needle all the way to the right)
     
  9. Arky

    Arky

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    Jan 15, 2016
    Ok so after seeing the analog meter in action does appear to be a pulse or waveform? It appears to me that the bee-r 2 step box grounds the ignition signal to make the ignition cut. If the wire I'm trying split is actually a grounding wire will diodes even work like I'm trying to do?

    If so, based on those reading I'm getting about 1 volt at 3,500 rpm. If I use a schottky diode with smaller voltage drop will it completely ground the ignition signal? I'm sorry I'm a total noob on this stuff. I'm trying to learn.
     
    Last edited: Jan 16, 2016
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    Do you have a wiring diagram of the vehicle? It should/may give you a basic electrical diagram or at least a method to test the signal is proper. This may give us/you the missing puzzle piece on the best way to join the signals.
    You can use diodes for V+ signals, or grounded signals, just reverse the direction of the diode. All you are trying to do is prevent one of the igniter wires from feeding back into the other two.
    If the diodes don't work, you may need a buffer (amplifier) mentioned above... You hook up a basic amplifier to each igniter wire, then tie the outputs together for your new component. (The higher levels will also give you more wiggle room with diode selection)
     
  11. Arky

    Arky

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    Jan 15, 2016
    Thanks for your reply! I have the EWD for this vehicle and over the weekend I have found that each igniter wire is within spec as far as voltage. Mine is .5v at idle and 1.5v at redline. I have Schottky diodes come in from Amazon tomorrow (tuesday). I will update this thread after their installation.

    The buffer (amplifier) scenario you mentioned is great information I know nothing about. It will be my new topic to google for the day.
     
  12. Gryd3

    Gryd3

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    Jun 25, 2014
    Sounds good, keep us posted!

    *Some benefits and drawbacks to the amplifier approach.
    The input of an amplifier/buffer is usually a high impedance, which means that it won't divert very much current or alter the original signal. The output of the amplifier/buffer is much stronger allowing you to connect the output to things that would normally interfere or things that would be too big to drive.
    The amplifier/buffer's output can either amplify, reduce or mimic what is presented on the input. It can be as simple as a diode, or as complex as a number of op-amps and a dual power supply.
    Of course, it's an 'active' component, so it will need to be powered as well, and is a little trickier to build than finding in ideal operating diode ;)
     
  13. Arky

    Arky

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    Jan 15, 2016
    The Schottky diodes worked a little, I guess. When it hit the desired RPM it would slightly misfire, but I could easily rev past the set RPM limit. They actually interrupted the signal a bit, but it felt like it wasn't fully grounding the ignition coil signal wires.
     
  14. Gryd3

    Gryd3

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    Jun 25, 2014
    I guess it's time to try to buffer the signal...
     
  15. duke37

    duke37

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    Jan 9, 2011
    A FET can produce a very low resistance with no offset voltage, you would need one for each wire and a driving transistor to get the phase right. Presumably 12V is available.
     
    Gryd3 likes this.
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