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Thread: Connecting 2 circuits to one relay?

  1. #1
    Maximum Bitrate KyleYankan's Avatar
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    Connecting 2 circuits to one relay?

    Hi everyone - I have two quick questions.

    First off - I have my own version of a shutdown controlelr I'm making. I currently have it designed with 2 relays that keep power flowng to the system. They are in parallel - so if one is on, power is flowing.

    The two relays are powered by the ACC line, and the other by the 12v of my computer's PSU. IS there anyway to condense this to one relay? I imagined diodes, but I'd rather get what you guys say before I blow my psu. I included a quick picutre of the schmatic I want to use (ignore the transistor, I'm justgoing right to the PSU's 12v line to the relay on the left).



    Second question: My car's battery and my PSU's ground. Should they/can they be grounded together? Like a small grounding bar, or two grounds going to a blob of solder? And can I mount this to the PCs case? I'm not sure aobut mountin it to the PSU's case as this can create ground loops. Thanks for all the help.



  2. #2
    MySQL Error Scouse Monkey's Avatar
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    you can get dual relays that have to separate switch parts. have a look at your normal electrocis place for some.

  3. #3
    Maximum Bitrate KyleYankan's Avatar
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    Yeah - but the point was to use a locally available relay, and perhaps only need to buy one. I have plenty of Zener diodes laying around, so I figured it would be a nifty idea.

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    Stank Cheese n8scstm's Avatar
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    Radio Shack carries those relays so I consider that locally available.
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    Maximum Bitrate KyleYankan's Avatar
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    Not any of the radioshacks around me. In fact, only one of the radioshacks have a 30amp relay, and it's SPST, and I need SPDT at least. I asked the shop behind my house, and he said he can order them for me. I guess I'll just get two if there's no easy way.

  6. #6
    MySQL Error Scouse Monkey's Avatar
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    Quote Originally Posted by n8scstm
    Radio Shack carries those relays so I consider that locally available.
    exactly, thanks cheesy!

  7. #7
    Stank Cheese n8scstm's Avatar
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    Quote Originally Posted by KyleYankan
    Not any of the radioshacks around me. In fact, only one of the radioshacks have a 30amp relay, and it's SPST, and I need SPDT at least. I asked the shop behind my house, and he said he can order them for me. I guess I'll just get two if there's no easy way.
    Youre right. The auto parts stores near me sell the SPDT relays though. And if you need 30 amp then youre right again. But the radio shack by my house sells these. http://www.radioshack.com/product.as...t%5Fid=275-218 I dont know if they will work for you or not but if they will you might have another look. Maybe they were out of stock.
    2.4 celeron
    150 watt OPUS
    micro atx
    xp pro
    tv/radio tuner card
    audigy
    Dual monitor Radeon
    802.11G Mimo
    xm pcr
    dvd
    gps
    8" Lilliput touch screen
    IGuidance
    dual optimas
    battery isolator
    15" screen
    My Truck

  8. #8
    FLAC shakes's Avatar
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    sounds like you need a DPDT (which is what n8 linked) not an SPDT. Even if you do need a SPDT you can make a DPDT act like an SPDT.

    Of course you can tie the two grounds together. In fact, you should. All components in your system need to share the same logical ground (this being your battery's neg) to make sure they're using the same reference point. And really, it's better if it's the same physical ground as well.
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  9. #9
    FLAC shakes's Avatar
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    oh and the last DPDT i got was from a radio shack
    My JeepPC Install

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    "it's been agreed the whole world stinks so no one's taking showers anymore"

  10. #10
    Maximum Bitrate KyleYankan's Avatar
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    Quote Originally Posted by n8scstm
    Youre right. The auto parts stores near me sell the SPDT relays though. And if you need 30 amp then youre right again. But the radio shack by my house sells these. http://www.radioshack.com/product.as...t%5Fid=275-218 I dont know if they will work for you or not but if they will you might have another look. Maybe they were out of stock.

    Wow. I have about 4 of those. Too bad there 10 amp only, and I need 30 amp. 400 watt inverter :-/

    Sorry, don't mean to sound sarcastic - I just skinned my knuckles. I installed "most" of the carputer in the past 3-4 hours, and managed to get it working. :-D

    Also I talked to my mechanic friend. He said he'll call tommorow for me. He hopes they know whta tthe hell a spdt is.

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