Easy Launch Control Question, I Think:)

Discussion in 'The Projects Forum' started by zillarob, Jun 24, 2012.

  1. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    NEWB altert!

    Hi guys, looks like a cool forum you have here. Nice to see people take the pride and initiative to do things for themselves, much more rewarding!

    Working on a form of traction/launch control.
    Basically, I have source that will pull to ground with a variable frequency and duty cycle. I would like to use this with some sort of relay to hold the ignition coil to ground to prevent the spark event from happening on certain cylinders.

    The problem I am running in to looks to be the response time of the relays, the reed type seems to be the best I can find. At 6000rpm, looks like the relay would need to be on for only 2.5ms to block a single cylinder from firing. The fastest I think it would ever need to switch is 200hz at a 50% duty cycle.

    I do have a general understanding of how the smoke travels through the wires. IIRC the smoke also travels at the speed of light, just trying to get a little closer to that speed-wise. Should I be looking at fet's? Having a hard time getting my head around how they work and if it would be applicable to this project.

    Any hints, links, or even a swift kick (preferably in the right direction), would be much appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    Swift kick number one: This site does not discuss automotive modifications.
    Swift kick number two: Explain what you're doing or you will get nowhere on this site.
    Swift kick number three: Relays don't stand a chance of operating at millisecond speeds.

    That being said, MOSFETs are generally fast enough and conductive enough to do this job.

    Swift kick number four: If you post a drawing of what you have, so far, we will get an idea about what level to speak to you. NEWB's aren't always beginners.
     
  3. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Lol , thanks.

    Been reading the stuff at the top of the page, excellent info in there. I kinda figured some kind of transistor was what I needed, just couldn't figure how to switch it with a ground signal. Have heard the terms pnp and npn before, but didn't realize what they did until now.

    On the input side, I have a single wire (A) that switches to ground. On the output side are two wires (B,C) that need to be shorted together if (A) == grounded, else (B,C) == open. Likely 12vdc but need to check (B,C), might be less.

    This is the info I have on (A):
    Output Type: Open Collector (Drives to ground) with weak pull-up (10 kΩ) to battery positive
    Current: 0.5 A max, current limited & thermal overload protected
    Output Clamp: 50 V Flyback Clamp (no clamp diode to supply)

    I will get something basic drawn up here in a few. Just starting to get my head around the basics of transistors and the resistor that lets them switch back, haven't made it to mosfets yet, lol. Any recommendations on a good schematic drawing program, or will paint suffice?

    Current guess is I need a npn and a resistor, just need to figure out which ones?

    Really do appeciate the help. Always fun learning something new, or more than likely, relearning something I have probably forgotten since high school!
     
  4. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    I use MSpaint but that's because I'm old and too lazy to learn new methods. I think you need a pnp transistor. The big question is: do B and C need to be conected together without touching any external ground?
     
  5. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    I agree on the pnp. Had a nice photochopped drawing of an npn before it clicked. Oh well, I think it is simple enough to visualize til I get some more time.

    Not sure on separate grounds. Think checking with an ohm meter is good enough?

    The two wires are specifically there as a kill switch, but I have no idea how they accomplish this. May kill power to the whole box or just stop triggering the spark, I am hoping the latter.

    I'll put the dvom on it tomorrow and see what we have.
     
  6. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Saved by photoshop! Flipped the little arrow around, hope this is right. This is what I was thinking.

    [​IMG]
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,716
    4,788
    It still isn't clear where this is going to sit in the overall system circuit. If I'm picturing it correctly, though, you might want to consider what voltage will be seen across the various terminals when you are NOT trying to ground the node.
     
  8. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    That's a P-channel MOSFET. Works a lot like a PNP transistor but both of them need the gate (base) controller to use a voltage that is related to the point you labeled as C. Only talking about that transistor drawing, from A to C is called Voltage gate to source (Vgs). It literally means that the controller must makke a voltage between the gate and the source, so the controller must be connected to wire "C" in some way that allows nearly zero volts from A to C as the condition required for turn off. That is why the rest of the circuit is important. If you could use a relay, this would not be true. A relay has isolated contacts. A relay doesn't care what B and C are doing. A transistor does.
     
  9. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Roadblock, those two wires shut the box down completely. Needs to reboot and resync before it fires back up.

    Plan B is hold the coil to ground, preventing it from firing. Primary voltage looks to be 550v. Not sure on amps, guessing quite a few. Also guessing this adds some complications with fields collapsing and other things I don't know about. Yet anyway, lol. Good news is they should be on a common ground I would think.
     
  10. WBahn

    Moderator

    Mar 31, 2012
    17,716
    4,788
    I doubt the amperage is very much at all, but you are going to have to work some to handle that kind of voltage with a FET. Perhaps there is something out there suitable for withstanding those kinds of voltages and, if so, you are lucky.
     
  11. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    You are right on the amperage, 600mA peak.

    Looks to be a capacitive discharge type so wonder how it would feel about me holding the primary low side to ground to keep it from jumping to the secondary?

    Time for some more reading!

    This is what I am working with if interested, Ign box HERE, Coil HERE

    Have a separate module that monitors the vehicle and outputs a ground signal based on what is going on.
     
  12. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    What kind of vehicle are we talking about here?
     
  13. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Uh oh, the no automotive stuff didn't click til I read the fingerprint thread a few min ago.

    This would be for, uh, backyard rollercoaster project that has traction issues. Specifically on take off and getting up the big hill ;)
     
  14. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Wonder if this would work? 2FFQP3P50

    [​IMG]

    Not sure about the diode but looks to be oriented in a way that wouldn't affect what I am doing.
     
  15. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    Hmmm...you didn't notice the first sentence in the first response.
    I think I'll recuse myself.
     
  16. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    No, I saw it lol. Figured that was geared more toward keeping "Y dont my blinkerz work?" type threads from cluttering the forum. This is more about the electronics in the middle than what is hooked on either end. This contraption will honestly never see the street.
     
  17. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    This is the the latest drawing. Not quite sure if/where the (flyback?) resistor goes yet.
    Probably should have used some different colors, hard to differentiate the module outline and the wires from the kill switch controller.

    [​IMG]
     
  18. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Honesty will get you a long way. Threads about powering go-carts and custom off-road rigs have seen the light in this forum, because the persons who started them documented them fully, with actual pictures that proved that was indeed the case.

    We don't have the automotive restrictions just for show. We actually care about our members and their well being. It's not just a legal thing.

    That said, I 'm closing this thread. Please don't try to open similar ones, it's pretty apparent.

    You may find what you are looking for in forums that provide this kind of information:
    http://forum.allaboutcircuits.com/showthread.php?t=54400

    Have a nice day.
     
  19. zillarob

    Thread Starter New Member

    Jun 24, 2012
    14
    0
    Thank you for reopening this thread Geo. I'm sure I speak for everyone here when I say I really do appreciate your time and effort in keeping the forum tidy and on topic according to the rules.

    Has been a lot of fun learning more about this stuff with everyone's help and I am looking forward to being allowed to continue with this project.

    This is where I am at now (and hopefully moving in the right direction:)).

    [​IMG]

    Added the resistor for the gate, hope it's on the right side. Looking into what value it needs to be and what I need to do about this collapsing field in the coil, if that needs to be addressed.
     
  20. WBahn

    Moderator

    Mar 31, 2012
    17,716
    4,788
    Could you perhaps explain what the title of this thread means? What is being launched?
     
Loading...