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Thread: 16 Position choke with only 4 Relays

  1. #1
    Join Date
    Mar 2006
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    49

    16 Position choke with only 4 Relays

    A few people have expressed an interest in how I make my 16 position choke box with so few parts so I thought I'd share.

    The basic principle involves using a 16 position rotary BCD encoded switch to control 4 relays which in turn control 4 pieces of choke wire, 1, 2, 4 and 8 ft.

    Each relay will switch part of the choke in or out according to the code from the switch giving 0 to 15ft in one foot increments. If you rotate the switch to position 5, relays 1 and 3 will be activated switching in the total choke of 5ft (1 + 4). Position 11 will switch in relays 1, 2 and 4 giving 11ft (1 + 2 + 8) and so on. Position 0 is no choke and if you don't need 15ft (who does) you can halve the cable at each relay to give you 0 to 7.5ft in 6 inch increments. Or you can use any initial length as long as you double it for each successive relay. Binary coded switch - binary math.

    For manufacturers this reduces components considerably and only 4 wires are required from the handle to the choke box (5 if you don't have power in the handle). The BCD switch is also very small and light weight.

    Other considerations - the BCD switch is rated at 250ma only so relay selection is critical. Personally I don't worry about it and I use large 60 amp automotive relays and a small driver board. 4 x BD135 transistors and 4 x 3k resistors is all you need, total cost - less than $2 plus a bit of proto board. Again if you're a manufacturer this is smaller, cheaper and easier than a box with 15 relays and all the related hookups and cable. If anyone would like a driver board I can make them (CNC routed board) for a reasonable price, just PM me.


    The only BCD switch I've found that's suitable and inexpensive is from Grayhill, Part Number 26ASD22-01-1-AJS. Best price I think is Digikey, about $15 in single units, cheaper for bulk.

    I've posted a pdf with a circuit diagram including the very simple transistor driver for large relays on the ASCRA site here - BCD_Choke_Switch.pdf

    I hope someone finds this useful

    Cheers,

    Garry J

  2. #2
    Join Date
    Jun 2002
    Location
    South of the City
    Posts
    1,054
    Quote Originally Posted by Garry J
    The only BCD switch I've found that's suitable and inexpensive is from Grayhill, Part Number 26ASD22-01-1-AJS. Best price I think is Digikey, about $15 in single units, cheaper for bulk.
    I've worked with these switches at work, very interesting idea. The switch is binary (actually hexadecimal) & combines the choke segments to give you the desired results. I'll have to give this a try.
    Russ Toy
    I am team burrito and I approve this message.

  3. #3
    Join Date
    Mar 2006
    Location
    Sydney, Australia
    Posts
    190

    work in progress.

    Started working on one, my choke from 1989 needs to be pensioned off, this design seems good.

    Needed to do some changes based on parts availability, I had my switch and stuff like that before Garry posted the design. I was originally going to use mini relays rather than transistors to fire the 40A relays. However I got inspired and decided to use transistors, went to frys and seems you can not buy 4 of anything there.

    So a trip to radio shack and I found a bag of 1A PNP transistors for $2.50, seemed like good value so design change 1, these need -ve to turn on rather than +ve, no big deal. These also need 470 Ohm resistors for the gate.

    Also I wanted to be able to see the status for the relays so they have leds (Radio Shack - $2.50 for about 20)to show which relays are on, these are visable externally so u can work out how much choke is on by adding (and subtracting) the numbers.

    I also wanted to be able to remove the choke form the controller, so I have a telephone cable with an RJ11 plug attached to the controller, this plugs into a jack on the choke box.

    Other thoughts, I would like to mount a digital voltage panel on the box, you can buy these for about $10 (Frys sell them). To provide stable power to the voltage meter I installed a 7812 volatge regulator (Radio shack), the regulator is good for upto 40V so dont think I will have any issues.

    Fun parts, the BCD switch needs a pin installed to limit travel, otherwise u can turn them indefinetly, first u have to work out where 0 is, (all BCD pins off) - mark it and then try the pin in a few spots till u get it right.
    Last edited by LindsayB; 09-02-2008 at 05:22 PM.

  4. #4
    Join Date
    Jun 2002
    Location
    Oslo - Norway
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    290
    Here is a picture of one of the two units Garry made to me.



    The size of the board is just 60 x 40 millimeters
    Last edited by Janders; 02-06-2009 at 07:23 PM.
    Best Regards
    Johnny Andersen
    Oslo - Norway
    http://www.amrc.no

  5. #5
    Join Date
    Jan 2005
    Location
    Used to be Keystone, PA
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    406
    Very interesting, I'll give it a try, Thanks much.
    Improving performance one hazardous material at a time.

  6. #6
    Join Date
    Jun 2002
    Location
    Auburn,Wa
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    1,640
    If 16 position is not availible a 10 position will work. Tens are easier to find. It gives a narrower range but in euros sometimes is a good thing. I tried one with a 10 position BCD using 2ft, 3ft, 6ft, 12ft.

    That gave the values of 0ft, 2ft, 3ft, 5ft, 6ft, 8ft, 9ft, 11ft 12ft, 14ft.

    Or using a 1,2,4,10 combo gives 0, 1, 2, 3, 4, 5, 6, 7, 10,11.
    The values of 1,2,3,6,10 gives 0,1,2,3,6,7,8,9.10.11.

    Raymond

  7. #7
    Join Date
    Jun 2002
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    NorthWesterner now in Philippines
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    9,516

    These go to eleven.

    Hmmmm... Slapshot's version of the choke reminds me a bit of something...

    oh yeah....


    Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and...
    Marty DiBergi: Oh, I see. And most amps go up to ten?
    Nigel Tufnel: Exactly.
    Marty DiBergi: Does that mean it's louder? Is it any louder?
    Nigel Tufnel: Well, it's one louder, isn't it? It's not ten. You see, most blokes, you know, will be playing at ten. You're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where?
    Marty DiBergi: I don't know.
    Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
    Marty DiBergi: Put it up to eleven.
    Nigel Tufnel: Eleven. Exactly. One louder.
    Marty DiBergi: Why don't you just make ten louder and make ten be the top number and make that a little louder?
    Nigel Tufnel: [pause] These go to eleven.

    PK @ OWH
    - - - - - - - - - - - - - - - - - - -
    Paul Kassens
    OWH Slot Car Talk "Mom"
    The Old Weird Herald
    email: paulk@oldweirdherald.com

    - - - - - - - - - - - - - - - - - - -

  8. #8
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    Jun 2002
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    Auburn,Wa
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    1,640
    Paul:

    Mine goes to 14.

    RB

  9. #9
    Join Date
    Jun 2002
    Location
    Oslo - Norway
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    I just need to say a big "Thank You" to BillyBob for helping me out with the relays for this project.
    Best Regards
    Johnny Andersen
    Oslo - Norway
    http://www.amrc.no

  10. #10
    Join Date
    Jan 2005
    Location
    Used to be Keystone, PA
    Posts
    406
    I have built this, and it works great. Thanks alot!!!!!
    Improving performance one hazardous material at a time.

  11. #11
    Join Date
    Nov 2002
    Location
    england
    Posts
    198
    will this work on a difalco?
    this is my Signature

  12. #12
    Join Date
    Jun 2002
    Location
    Auburn,Wa
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    1,640
    Bump
    Yes it will work on a Difalco
    Raymond

  13. #13
    Join Date
    Jun 2002
    Location
    Oslo - Norway
    Posts
    290

    Complete documentation

    Does anyone having the complete documentation for this choke?
    I've been in contact with Gary, but He does not have it anymore.
    Best Regards
    Johnny Andersen
    Oslo - Norway
    http://www.amrc.no

  14. #14
    Join Date
    Mar 2005
    Posts
    556
    Why do I do this to myself?

  15. #15
    Join Date
    Jul 2011
    Posts
    446
    Sorry guys I gotta bump this too.

    I'm building this for the USRA nats that will be held April 22 2015 at Speedzone raceway.

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