SPDT signal relay question

Discussion in 'General Electronics Chat' started by 1-3-2-4, Feb 22, 2013.

  1. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    I made a SLA battery charger from this design here

    http://shdesigns.org/gcellchg.html

    I spoke to the person that designed it asking about using a relay in it, since this is for lighting when the power goes out I was thinking since the battery would always be on charge why not have it switch over on it's own..

    Maybe I have been over thinking things but on a normal day the contact should be open which prevents the LED's from turning on.. when the power goes out the contact closes and the relay closes and the LED's come on.

    I put the charger in it's own project box but if I have it right I'd need to hook the relay to the battery directly in series with the LED's right? I was wondering if it's possible to slim everything down to the same box?

    You can kinda see what's going on here, the relay in the lower right is not set yet.

    Another thing I did not think about is battery voltage and when to turn the lights off before the voltage drops too low.
     
  2. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    I have a feeling I lost people here
     
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    It just a little strange, when you posted another thread - 15 Vdc power adapter.

    In the beginning that you seems just asked for help to buying the 15V/1A power, but the finally that you said that you already built a SLA charger, it may cause confusion here.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    If you power the coil of your relay from the incoming power and tie the lights to the battery through the NC contacts, that should give you what you are looking for.

    On second thought, put a diode between the 15V source and the charger and tie the relay in before the diode to prevent any possible back feed.
     
  5. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    That's the whole reason why I did not want to post this in that thread to limit confusion!

    Yep this is what I thought with the relay connections but I just wanted to be 100% sure, for the diode I have plenty of those.

    One extra thing I could do is use a comparator for a low voltage cut off so I wont deep cycle the battery providing I'm not out of power for 48+ hours..

    I assume it would be nothing but a voltage divider? I thought I had a smaller comparator but I have two quads sitting on the desk.
     
  6. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    You can adding a transistor(Q_ctrl) to drive Relay and to be a Switch to cut off when float charge.

    One way is adding the transistor(Q_ctrl) to detect c of Q1.

    Another way is using comparator to detect c of Q1, or the voltage where you like, and adding a resistor and a VR to be a Vref for the comparator, the output of comparator connecting a resistor to the b of transistor(Q_ctrl).

    You also need to adding a push switch crossed on the contacts of Relay, it will be a start switch, when you want to start a new charge.

    Something as above.
     
  7. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    Well in it's current state it's automatic so when it needs to go out of float charging it will do so.

    What I did think about last night was instead of using a panel meter to view voltage why not use some 5 mm leds, a person told me about the LM3914 however it would need to be calibrated first? anyways that along with a comparator with a voltage reference (which one?) to match the battery cut off voltage with a voltage divider to the reference voltage I can have the relay disconnect when the battery falls below 11.7 V
     
  8. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    I was wondering I have some parts from Mouser I ordered about 5-6 years ago still in the bag and the printed label badly faded but I ordered two 1N5550 diodes.. it was for another project I ended up doing that used less parts. I was wondering if I can use this for the diode (My 50 pack of 1n4001's are missing) I know this diode is way overkill but better then nothing I guess.

    I mean I'm pretty much 100 % sure it can be used just that it's overkill.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    Overkill is an understatement.
     
  10. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    Question at which voltage level of the battery will the charger charge at max current?
     
  11. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    When you say 15V source you mean the charger output?
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Yes...........
     
    1-3-2-4 likes this.
  13. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1
    Ok for some reason I was thinking the wallwart ha.
     
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