Advice needed: adding continuity to simple launcher.

Discussion in 'Ground Support' started by BryRocket, Apr 10, 2019.

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  1. Apr 10, 2019 #1

    BryRocket

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    Hello,

    I’m trying to make a simple wireless igniter using the below wireless relay. I would like to add that this is solely for personal use to ignite nichrome wrapped igniters for testing motors. I intend to use a 1000mAh 20C-30C 3s Lipo. I also plan to open up the transmitter and put it in its own box with a power switch for a little added security. At the “pad” (there will never be a pad, just test stand), I’d like the receiving unit to have a voltage meter, power switch and continuity indicator if possible for everything from ematches (low current) to larger wrapped igniters. There are two main questions I’d like to get advice on:

    1. Should I add an inline resistor between the battery and the relay? It says it’s rated to 40A and I believe the battery could throw 20-30A. Is it necessary?

    2. Is there a safe and easy way to add a continuity check at the receiver? Could I put a multi position switch that can be switched to send current through an indicator LED and resistor with inline momentary switch for continuity and then toggle that switch to an ARM setting to put power to the relay? I’d also like to put another switch downstream from the relay with an LED between the relay and switch to indicate if power is flowing from relay before closing the downstream circuit to the igniter.

    Open to any and all suggestion from you more talented EEs.

    Beware, I may come at you with MS Paint drawings.

    Parts:

    12v 40A wireless relay.

    https://www.amazon.com/dp/B075QJ8QWM/ref=cm_sw_r_cp_api_i_qJKRCbGQX26AS

    IMG_1872.jpg

    Thank you much.
     
    Last edited: Apr 10, 2019
  2. Apr 11, 2019 #2

    DaveW6DPS

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    You relay is marked as being rated for 30A DC, the 40A is for AC.

    I don't like to have batteries with no short circuit protection. At minimum a resistor sized to limit to just over the maximum current you need.


    You can put in a pushbutton for a local continuity check. Just wire the ignitor lead to the common terminal, the firing circuit to the normally closed, and the continuity tester to the normally open.


    I don't know what you mean by this.
     
    Last edited: Apr 11, 2019
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  3. Apr 11, 2019 #3

    BryRocket

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    So I could perhaps use a 1ohm resistor there or a simple auto 10-15A fuse?


    I apologize but I’m not following that all that great.


    I was trying to protect against if the relay was closed and power was flowing when I turned the unit on with some kind of indicator if that was the case. Probably poorly thought out and articulated worse.

    And I’m sans MS Paint at the moment. But something like that is what I was talking about.

    IMG_1873.jpg
     
  4. Apr 11, 2019 #4

    jsdemar

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    A 10-15A autoreset thermal breaker is the best choice. I've been using them in launch controllers for 25 years. Saves the wiring, relay, and battery from a dead short. It will let full current flow through the igniter momentarily. But kicks out in a few seconds for a dead short. It resets as it cools a few seconds after.
     
  5. Apr 11, 2019 #5

    BryRocket

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    Something like this:

    Fastronix 15A 12V Type 1 Automatic Reset Circuit Breaker with Cover https://www.amazon.com/dp/B07NSFHT2V/ref=cm_sw_r_cp_api_i_GJPRCbZR6J692

    Or this:

    Flameer 15Amp Circuit Breaker Thermal Breaker Thermal Protector Switch for Generator https://www.amazon.com/dp/B07HF6Q73W/ref=cm_sw_r_cp_api_i_cKPRCb1GWC94Y

    Thanks John.
     
  6. Apr 11, 2019 #6

    jsdemar

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    First one is ok. Second one is not autoreset.

    This is the one I used in my wireless controller.
    Bussmann UCB-10 Circuit Breaker (, Type I, ATC Footprint Automotive 'Snap-Off' - 10 A), 1 Pack
    https://www.amazon.com/dp/B000Q0AVHQ/ref=cm_sw_r_cp_api_i_QRPRCbHQPSXKX
     
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  7. Apr 11, 2019 #7

    BryRocket

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    Perfect. Thank you. That’s one hurdle crossed.
     
  8. Apr 11, 2019 #8

    DaveW6DPS

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    In the alternative, use the second relay out on the board to energize the continuity check using a high brightness LED, or you could use a piezo buzzer if the current would not be too high for your e-matches. The LED across the ignitor leads would indicate a hung relay, etc., which I think is what you are after.
    rough sketch 2.jpg
     
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  9. Apr 11, 2019 #9

    Rex R

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    I would be not be surprised if that battery could throw 60 amps in a dead short (once) since a 30c 1 amp hour pack is rated at 30 amps (for 2 minutes if I did the math right)
     
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  10. Apr 11, 2019 #10

    BryRocket

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    Hello and thanks for your input. It appears you have a 2 channel relay in this diagram but my relay has a single channel.

    IMG_1875.jpg
     
  11. Apr 11, 2019 #11

    jsdemar

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    I prefer using a tone for continuity and not an LED. The LED is too difficult to see in the sun.

    At the pad box, put a momentary-on pushbutton from the armed 12V through the buzzer, through a 100 ohm resistor, to the igniter terminal. Series circuit.

    Use something like this:
    https://www.amazon.com/DIKAVS-3-24V-Enclosed-Electronic-Buzzer/dp/B072HRZXLG/

    It has to be a continuous tone active beeper with the oscillator built in. The ~10mA test current is safe for everything except old flashbulb igniters (which nobody uses anymore?). The 100 ohm resistor is optional and limits the current to the igniter if the buzzer fails to a short circuit.

    You can also put a buzzer across your igniter terminals. If you hear that tone before hooking up the igniter, the relay is welded ON. There are intermittent tone buzzers that might be better for that feature.
     
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  12. Apr 11, 2019 #12

    BryRocket

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    Would something like this work? Did I mention I struggle with electronics?

    IMG_1876.jpg
     
  13. Apr 11, 2019 #13

    jsdemar

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    r1.png
    The "LED and Resistor" can also be the "BUZZER and resistor".
     
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  14. Apr 11, 2019 #14

    BryRocket

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    Thanks John. I like the idea of the buzzer. I responded with that last post prior to reading yours so I’ll add that. Both of them.

    Doesn’t the COM output the (+) and the NO output connect the (-) on my relay? Is the COM channel an “always on” output? Looking at your edited diagram makes me think I’ll be hooking up 2 positive leads to the igniter.
     
  15. Apr 11, 2019 #15

    jsdemar

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    Can you send me a link to the wireless relay product you are using? The relay output are usually not connected to anything unless you connect them.
     
  16. Apr 11, 2019 #16

    BryRocket

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    https://www.amazon.com/dp/B075QJ8QWM/ref=cm_sw_r_cp_api_i_e-YRCbWJJXZJB

    I’m not confident in how I think it works at all. I won’t have the unit for a few more days so I can’t test it just yet.
     
  17. Apr 11, 2019 #17

    jsdemar

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  18. Apr 11, 2019 #18

    BryRocket

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    Cool. Thanks John. I'll wait till this one arrives and see if I can figure it out to make it work. If not I'll look elsewhere for a different relay.
     
  19. Apr 11, 2019 #19

    DaveW6DPS

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    I was mislead by the A and B buttons and the OUT1/OUT2 marking on the terminals.

    This would work fine, as long as the continuity test current is below the safe test current for any ignitor you may use. I would not want above 10mA or so.
     
  20. Apr 11, 2019 #20

    jsdemar

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    See my post #11 above.
     
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  21. Apr 12, 2019 #21

    UhClem

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    Hmmm. The relayer (MOSFETer?) I built in 1995 used high brightness LEDs and they are easily visible at 50 feet. Even brighter LEDs are available now.

    I found a 20,000mcd rated LED at All Electronics for $0.50. That should be bright enough even at 1mA.
     
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  22. Apr 12, 2019 #22

    jsdemar

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    The high-intensity LED's take more current.
    And you don't get an audible warning. A unique tone warns the user that the relay is stuck (arming will fire the igniter).
    Even for continuity, no need to look at a bright LED. Just push the button, hear tone, good to go.

    In 1995, I built a 32-pad launch system. The main control box had 32 green LEDs to show the selected pad, and 32 red LEDs for armed/cont status. The whole range could be visualized in one glance. The continuity button on the main controller gave the tone for the selected pad. The pitch of the tone was proportional to the resistance of the igniter (the same tone produced at each pad box).
     
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  23. Apr 12, 2019 #23

    UhClem

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  24. Apr 14, 2019 #24

    kc9qzf

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    Continuity Circuit 2K.jpg
     
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  25. Apr 15, 2019 #25

    sghioto

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    Your best color choice for the LED indicator is white.
    We use standard 5mm super bright white LEDs at 20ma.
    Easily visible at 300ft.
    SG
     
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  26. Apr 15, 2019 #26

    beeblebrox

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    All you need is a piezo buzzer in series with the igniter...short the buzzer to launch. very low current, flashbulb and ematch safe... <50 micro amps
     
  27. Apr 16, 2019 #27

    jsdemar

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    No, buzzers typically take more current than that. And if the buzzer fails to a short, it is a bad day.
     
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  28. Apr 16, 2019 #28

    beeblebrox

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    Not true, I have been using them for decades, they don't fail to a short. I built launch controllers in the early '80s using them and a couple are still in use today. They were built for U.S. Rockets. The launch controllers made by and sold by AeroTech use them as well. They are extremely reliable. I have never in more than 40 years ever seen one set off an e-match, flashbulb or any other sensitive igniter you can dream of. They MUST be piezo-electric buzzers...
     
    Last edited: Apr 16, 2019
  29. Apr 16, 2019 #29

    jsdemar

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    Please point to a specific device. I have always used piezo buzzers (active devices, not just the element which requires an oscillating current), and they require several milliamps.
     

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