Need help for small circuit run timed reed relay

Discussion in 'The Projects Forum' started by caleb7777, May 11, 2009.

  1. caleb7777

    Thread Starter Member

    May 10, 2009
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    Hi there everyone.
    This is my first post here, I won't lie, and I am already looking for help.

    i came across this forum in searching for an answer to my problem.
    I am building an electric bike that will automatically shift up and down at a certain speed by changing the motor windings from star to delta on the fly using relays. This is not a problem. A speed sensor will put line 'a' to ground after the speed is reached and until the bike falls below that speed again. The ground line feeds the relays that switch the motor.

    The concern I and others have is that when the relay tries to switch over it will open the phases on the motor for about 30-40ms and if you are on the throttle it will put load on the motor and could damage the controller. It may last a long time but I would like to find a fix for this anyways.

    The simple fix is to disable the throttle for 50ms whenever the relay switches.

    If I place a normally closed reed relay in the throttle 5v+ and have it actuated it will disable the throttle.

    So here is what we need:
    When line 'a' goes to ground (motor upshifts) the reed relay is opened for 50 ms (5v relay) and when line 'a' ceases going to ground reed relay opens again for 50 ms. (Reed relay could be replaced for something that actuates faster).

    Essentially I need small circuit that will power the reed relay for 50 ms when line 'a' becomes grounded and again whenever it is no longer grounded.

    This in effect will turn throttle off directly when motor is shifting placing a lot less load on motor and controller I believe.

    i have found the 555 chip that may work but my problem is figuring out a circuit that will also trigger when line is no longer ground.


    Any help or suggestions would be appreciated!

    Caleb
     
  2. caleb7777

    Thread Starter Member

    May 10, 2009
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    Last edited: May 11, 2009
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Two suggestions, with and without reed relay. Assume there is a + V on "a" line, then adj Rx-1 for 5V for reed, or Rx-2 for 10 mA base max current.
     
  4. caleb7777

    Thread Starter Member

    May 10, 2009
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    will this operate for only 50 ms and engage at the time when switch is closed and again at the time when switch is opened?

    It seems too simple..... especially if Rx1 Rx2 are only resistors or are these something special?
     
  5. caleb7777

    Thread Starter Member

    May 10, 2009
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    perhaps this diagram will help, my apologies if it is not proper.
    I never draw these.
     
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  6. caleb7777

    Thread Starter Member

    May 10, 2009
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    I think I am getting closer here. Just lots and lots of reading on my part. But I am impressed i got this far without help. I really have no idea what this would do. i do not know what the values for C2 and R2 should be to generate a 1-5 ms pulse. Also i still have the problem that i think this will only work when the speed switch either opens or closes, not both.

    Oh by the way, this is the first circuit I have ever drawn.

    PLEASE HELP!!!
     
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  7. caleb7777

    Thread Starter Member

    May 10, 2009
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    This is where I am now. But I still don't know how to get a pulse from trigger line to feed pin 2 when speed switch opens AND when speed switch closes. 1-5 ms pulse I think would be needed.
     
  8. Cabwood

    Member

    Feb 8, 2009
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    Sounds like you want to generate a 5ms pulse each time the trigger line changes level. That would require an edge detector. I've drawn a circuit that uses a couple of XNOR gates, one to buffer the trigger signal, and the other to generate the pulses.

    The transistor is needed because the gate cannot drive the relay coil directly, and the diode is there to protect the transistor from the coil - something missing from your original circuit.

    You can adjust the output pulse duration by changing R1 or C1.

    Lastly, there are two unused gates on the 4077, whose inputs must be connected either to ground or the positive supply to prevent them from dancing. One of those could be used to invert the output pulse, if you wish the relay to be normally off.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Now that we know what line a looks like, we'll try again. Assumed two 555 pulses for one speed sw op. 555 timing approx. T=RC, R in meg,Ω, and C in μF. .47 X .1 =.047 sec. NO reed relays are more common ?? so you can use ALT with NO relay. Might eliminate or change RR2 if RR2's contacts were identified, clear as mud,; does either contact go to ground or +5V? or do they float inbetween. Any questions?
     
  10. caleb7777

    Thread Starter Member

    May 10, 2009
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    Thanks to both of YOU!
    @ bernard so that is 2 differentiator circuits and a transistor in between so that one pulses when switch is actuated and one pulses when switch de-actuated?

    I want to make that circuit and I have everything in the shopping cart ready to go but when I went to order the transistor there is too much specs that I don't know about

    Which should I get?
    https://www.alliedelec.com/Search/SearchResults.aspx?Ntt=npn&N=4294966088&Ntk=Primary


    Thank you!
     
  11. caleb7777

    Thread Starter Member

    May 10, 2009
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    As for the time values that the switch is closed they will vary. May be as short as 10s or as long as a few hours. It depends on the speed I am moving at and will always fluctuate so I need something that would pulse once when speed passed and once when speed fell below, (switch on/off)

    I am assuming bernards circuit will do this.
    I only chose it because I don't know the 4007 at all and after all my reading I get the 555 a little bit.

    Thanks to both of you!
     
  12. caleb7777

    Thread Starter Member

    May 10, 2009
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    So this would be the finished circuit?
    This would actuate RR2 for 50 ms if the switch is opened or if the switch is closed?

    Thank you!

    Would you suggest i use the reed relays or transistors or optoisolators for W1 and W2
    W1 must handle 48v @ 52-100 mA and W2 must handle up to 48v @<100mA
     
    Last edited: May 13, 2009
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Sorry, the 2N2222 got lost. Just about any small signal NPN silicon transistor should work.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just saw "revised circuit". 48V @ 100mA might be too much for some reed relays, best check specks if available. A mercury wetted contact reed relay might work, it [the one I have] is a little larger, and might be slower.' Need to think about W1; Replace W2 with a transistor, also need to think about it, bed time- long trip to Mexico today.
     
  15. caleb7777

    Thread Starter Member

    May 10, 2009
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    Thank you so much, I will order all this now and test it on a breadboard when it comes. i will use transistor for Relay 2 and reed for relay 1 for now then. I may try a transistor for 1 to see what happens.

    Thanks

    i will let you know how it works!
     
  16. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    ' not sure what ebrakeline looks like, but might be inductive, hence D2 ,if possible and would'nt hurt to add D1., shottky would be best but 1N4002 may be OK.
     
  17. caleb7777

    Thread Starter Member

    May 10, 2009
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    The reed relays operate at 10 mA each i believe, what is the approx max current this circuit could draw? I am limited to about 100mA total or I will overload the 5v bus I am stealing power from
     
  18. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Internet Express just swallowed my last post, 'try to remember , Ah! best guess at +5V current drain is 30 mA. My concern was for relay contacts not the coil. Wish you success.
     
  19. caleb7777

    Thread Starter Member

    May 10, 2009
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    Thanks AGAIN

    Will update when I have built it.
     
  20. caleb7777

    Thread Starter Member

    May 10, 2009
    26
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    Another question,

    The ground for this circuit is essentially fed from a Cycle Analyst (CA) It is its own small circuit/computer system that measures various power readings about your bike and battery and displays it. It also is the speed switch. I could fry the Cycle Analyst as it can only handle very little current on that line.

    What would be the simplest way to use the ground as only a trigger and have no load on that line. If the common ground for the circuit came from elsewhere and only the trigger came from CA then it would be easier on it because the current would not flow thru it yes? ie: if the ground on the 555 came direct from batt, less load to CA.

    I will draw it up different when I get home to show what I mean. But I don't know if I could use different ground source for reed relay 1 powering the delta switch.
    I am sure there is some simple way.

    Here are the two circuits I will try with different ground and hot source, not really different ground as whole bike shares common ground, the main difference would be the route taken. I want to keep current away from switch 1 as this is really the CA and can not handle much load.

    Would this work and help reduce current on the 'switch'?
     
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