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Newbie - Need some help w/ switching relays

Discussion in 'General Electronics Discussion' started by Albe, Mar 11, 2016.

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  1. Albe

    Albe

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    Mar 11, 2016
    Hi Folks,
    I'm Albe, a noob to the forum and sort of new to the world of electronics. I'm familiar with the basics of the basic components, wiring, schematics and soldering. I've done work in the electrical field and overall a jack of all trades; master of some.

    I'm having some trouble figuring out a design to control a power window conversion I want to do to my car. For what it's worth, I've done power window conversions before on older American style vehicles that use the switch to change high current and polarity, no relays what-so-ever.

    That being said, the car I'm converting is a '98 Volkswagen Jetta. Sure, the "easy" solution would be to find a junk vehicle and just swap the parts over but aside from finding a parts car with all the parts in working order, I've been told the VW power windows are a nightmare and have a tendency to be troublesome. This conversion utilizes a universal motor that adapts to the spline of my manual window regulators. These kits do come with their own switches but I have and want to utilize factory VW switches.

    The problem is this; the switches control low current, possibly digitally, that in turn signals a central control unit that then determines which way to power the window motor. The switches have two common inputs and one output. What it looks like to me is that there would be a positive common, a negative common and when the switch was depressed in one direction the central unit would receive either a negative or positive power flow.

    Going off this same theory, I drew up a schematic using standard bosch style 30 amp relays to control high current and polarity reversal needed to make the window motor go up or down, the only problem I have is getting one relay to fire in
    one direction and the other to fire in the other direction. By using two relays with one trigger wire is posing to be troublesome. The power keeps looping back through the relay coil and energizing the other relay.

    Can anyone help? I was thinking this could somehow be done with transistors? or with the relays and added diodes but from what my novice brain came up with I'm certain it's not going to work.

    Thanks so Much!
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hi Albe. Show us your schematic if you have one. Welcome to EP.
    Adam
     
  3. Minder

    Minder

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    Apr 24, 2015
    You may be able to do it with steering diodes, but it depends on the nature of the switch etc.
    M.
     
  4. Kiwi

    Kiwi

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    Jan 28, 2013
    "The switches have two common inputs and one output."

    Would this work?
    Use the single output as a positive input and the original inputs as the outputs.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Automotive power windows can become a complex arrangement especially if one requires master control.
    As Arouse says, a circuit diagram of what you have or at least a flow chart or block diagram of what you hope to get.
     
  6. Albe

    Albe

    7
    0
    Mar 11, 2016
    Hi Everyone. It's nice to be here.

    I'm attaching a quickie schematic I had drawn up. The switch schematic you will see is the internals of the VW switch. Unfortunately the center contacts (shown in green and cyan/blue) of the switch are what I am referring to the inputs and are common across the left and the right side.

    I realize driving the relays in the exact way isn't going to work because of the relay coil. I actually had this hooked up on the bench and found out the hard way. Sometimes the best learning comes from hands on

    I also tried to lay it out with a transistor to drive the relays but I'm at a loss when sending the negative/ground signal to the output. I can't drive a transistor with a ground can I ?

    Take a look-see and I greatly appreciate your input! :) oh and p.s. disregard the high current side. I have that drawn out and 99% sure it'll work. That's just switch the high current polarity. I just to need to figure out how to drive one relay in the up direction and the other relay in the down direction.

    -Albe

    jetta-power-window-relays_smaller.jpg
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    If you need to simply operate the relays, remove the 100R resistors, feed power into the right hand side of the switches, remove the diodes(second one won't allow relay to work anyhow), and run each relay independantly from each switch.
    Output from the relays is voltage free and isolated from any other connections so can be configured any way you need within reason. (SinglePoleDoubleThrow)

    Don't know what the rest of your circuit or "controller" you refer to looks like BUT in many cases the motor is reversed by changing the connection to the motor via relays to get up and down.
    If you were to connect output as shown in attachment, it will give you reversing but you will need some form of travel limit. Note that with your relays there can be no provision for isolating the circuit from energising both relays simultaneously other than via a properly configured switch mechanism.
     

    Attached Files:

  8. Albe

    Albe

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    Mar 11, 2016
    I had thought about removing the resistors and doing it that way however the resistor is an internal pathway inside the actual switch. I will have no way to tap a wire into there and through the harness. There just isn't room in the switch body to get a wire through without ruining the integrity of the switch.

    When I had this hooked up with only the one relay I could get it to work. As soon as I hooked up the second relay triggering the switch in one direction or another made the relay(s) latch until I disconnected the power source.

    Thoughts on maybe using a comparitor/timer circuit? (I'm saying that knowing very little about it. LOL)

    Thanks so much!
     
  9. Bluejets

    Bluejets

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    Oct 5, 2014
    Is there more to the circuit than you have shown because what is drawn and what you say is happening does not match.
     
  10. Kiwi

    Kiwi

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    Jan 28, 2013
    upload_2016-3-13_17-52-56.png
    Would this work?
    The output voltage will be +2.5v at rest.
    Closing the UP switch would take the voltage to +5v.
    Closing the DOWN switch would take the voltage to 0v.
    The outputs could then be connected to the inputs of an Arduino, or similar, that can be programmed to operate relays depending on this voltage.
    The relay contacts and motors can be wired as shown in Bluejets diagram.
     
  11. Albe

    Albe

    7
    0
    Mar 11, 2016
    Well there's an entire control system Volkswagen uses to control the windows which is why my use of the factory switch is going to require unconventional wiring. I was hoping to utilize the factory switch not just for the aesthetics and ease of replacement as well if it breaks down the road. The window conversion kit I was going to use attaches onto the splined shaft of the manual window crank so I don't have to try and find a donor car or 800 different pieces to make factory power windows work.


    I like where you're going with this however I'm not sure what to attach it to next. I mean I know what an arduino is (well generally speaking), it's just a matter now of making an arduino to work with it.

    Just out of curiosity (and pardon what I think is another dumb question), how do you figure on what voltages are what? I mean how do you calculate a voltage across a series of resistors without a known load on the circuit? I was always under the impression you had to know the current draw to calculate the voltage drop from the resistor.

    Thanks so much folks!
     
  12. Bluejets

    Bluejets

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    Oct 5, 2014
    Resistors are arranged as a voltage divider.
    I think an Arduino would be an overkill.
     
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