SPDT Relay Question

Discussion in 'General Electronics Chat' started by SQ123, Jul 8, 2008.

  1. SQ123

    Thread Starter New Member

    Jul 8, 2008
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    Hi guys,

    In my search for answers i came across this site, I was wondering if anyone can help me out,

    I'm intrested in Creating a Time delay relay for my Car audio system, I'm getting a turn on pop eminating from within the amp that can't be resolved,

    My solution is to Delay the Speaker outputs instead, So that even if the amplifer makes the pop, it wont be audiable through the speakers because they technically won't be connected because of the Delay,

    The relay woukd just be to delay the completion of one of the Speakers Leads,

    there are 6 speakers upfront, So i'm hoping to get 1 relay which can do this if its possible, if its necessary and i have to get 6 seperate ones, its not a problem.

    Any help in wiring this would be appreciated.

    Thanks.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Sounds like your amps are all single-ended, so the outputs go through capacitors that block the DC bias. The capacitors charging makes the pop. That presents a problem, as placing the speaker back in circuit with a relay may just delay the pop - the capacitor may not charge until the speaker is present.

    If you can get to one speaker, pull a wire off and then turn on the amp. If that speaker still goes pop when you hook it up after the amp is turned on, then using relays (or multi-pole switches) is not going to cure the problem.
     
  3. SQ123

    Thread Starter New Member

    Jul 8, 2008
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    i tried that,

    The pop isn't there when the speakers are re-connected.

    So i believe this may help.

    i was wondering if i can get some sort of diagram to do this
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    I hate to suggest a relay that might not have heavy enough contact buttons. Do you have any idea of the amplifier power, or current to the speakers?
     
  5. theamber

    Active Member

    Jun 13, 2008
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    I think you are getting high voltage transients from the inductive loads within the amplifier, I asume this problem happens when you switch off the power.
    Therefore you need to build a "snubber circuit".
     
  6. SQ123

    Thread Starter New Member

    Jul 8, 2008
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    Suprisingly i only get the pop when the amps powerup, Not when i switch off the amplifiers.

    The amps are bridged, they are all 4 channel amps,

    and each is running a respective set of speakers(i.e 1 for tweeters, 1 for Midbasses, 1for midrange)

    According to manufactuer's specs, i should be getting 140watts per speaker.

    I was thinking a relay system to delay the contact of he -ve lead for each speaker, till the amps fully powerup.

    any help would be appreciated.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    For the 140 watts power, I might suggest Tyco #1432782-1 relays. They are designed to mount with a bracket (built-in) and use .250 quick disconnects. Digi-Key has them as part #PB679 @ $2.30.

    Each relay is SPST and is good for 30 amps. The coil draws 133ma, so running 6 on a single switch is no problem. Have the switch off, turn on the amp, and turn the relay switch on.
     
  8. SQ123

    Thread Starter New Member

    Jul 8, 2008
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    I currently have a relay which is connected to the remote out wire from the head unit, because i have 4 amps installed,(to ensure each had adequate remote power)

    I'm thinking to have these switches hooked up to this remote wire out of the relay,

    so the switches would powerup whenever the system does,

    What wiring should i use to achieve this delayed turn on with the SPST switches?


    Also i see these Switches are brass, could i possible get these in a more conductive Metal? probaby silver:)
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Silver is a great conductor (better than copper) - unfortunately, it corrodes, and it's soft. Silver oxide doesn't conduct very well. Cadmium is often used alloyed with silver for relay contacts. There are other more exotic alloys used as well.

    If you do find higher power relays with pure silver contacts, they'll likely be rather expensive.

    Try to find relays that are rated for twice the current that your system requires. They'll have about 3x the life span as relays that are rated at your system requirements.
     
  10. SQ123

    Thread Starter New Member

    Jul 8, 2008
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    I thought i may not find A silver contacts.

    I just need this relay fix for this year,

    next yr i'm switching out amps,

    I would really appreciate it if someone could direct me to where i could find a diagram to achieve this delayed output by using the SPST relays. And if i can vary the delay time.

    Thanks alot,

    you guys have been a great help thus far.
     
  11. theamber

    Active Member

    Jun 13, 2008
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    Beenthere has give you a solution, however it bypasses the problem .Looks like you have power on transients. This is due to the DC to DC conveter inside the amps.
    The limitation of cars supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.
    For example the max audio power per speaker (with 4 ohm impedance) using 12V is (Vsupply+ - Vsupply-)^2/(8*impedance) 12^2/32 = 4.5 Watts per channel only.
    Some inductor in your amp is leaking inductance and this will throw spikes on.You can fix it or bypass it.
    If you want to suppress power up transients from reaching your outputs. Other way can be through isolation switches controlled by a window comparator that compares the supply voltage with a fixed comparison threshold.
    I think they sell line tamers or snubbers for this kinds of problems with amplifiers transients too however they may reduce your audio quality, but nowdays having those astronomical outputs and amplifiers being overdriven I think quality is not an issue but quantity looks more to be.
     
    Last edited: Jul 9, 2008
  12. theamber

    Active Member

    Jun 13, 2008
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