Results 1 to 10 of 10

Thread: 12V relay + diode question

  1. #1
    Low Bitrate
    Join Date
    Mar 2004
    Posts
    108

    12V relay + diode question

    i'm running a relay, triggered by 2 input voltages. for one input i'm using the 12v ACC line, the alternate input is 12v from the PSU.

    obviously, the std relay i'm using only has one trigger, so i'm using 2 3A/20V diodes to isolate the 2 lines. this setup was working until 2 things happened. 1) i permanently soldered the diodes on, and heated them up too long and burned them up (voltage passed both ways). 2) i wiggled the relay too much and broke it.


    so i've replaced the relay and diodes. the ACC line is hot and hooked up properly. the PSU 12v is hooked up properly and is hot. the diodes are preventing feedback correctly.

    the problem is, if i turn on the ACC, then the PSU, then the ACC off, the relay clicks off. it should stay on cause the PSU is on. basically (tested) the PSU is not switching the relay.

    so... not enough power? its hot at exactly 12v, i'm not sure what else would be the problem. help?!?

  2. #2
    Raw Wave rando's Avatar
    Join Date
    Mar 2004
    Location
    Redondo Beach, CA
    Posts
    1,973
    Double check the diode on the PSU 12v line. Is the voltage getting through? Also, what voltage does your relay switch at? Remember the diode drops the PSU 12v a little. Could this be the problem?

  3. #3
    Low Bitrate
    Join Date
    Mar 2004
    Posts
    108
    well, its an automotive 12V relay. the 12v ACC line switches it ok.

    PSU line before the diode is 12.02v, after is 11.90v. on my last relay/diode setup it worked fine. plain and simple, the PSU 12v won't switch it. really, what gives?

  4. #4
    Raw Wave
    Join Date
    Jun 2003
    Posts
    1,823
    the PSU 12v won't switch it. really, what gives?

    Connect the PSU directly to the relay (without diode) and see if the relay operates. Then atleast you know if your PSU is still working ok with the relay. If it still doesnt work then you know what to check next.

  5. #5
    Raw Wave rando's Avatar
    Join Date
    Mar 2004
    Location
    Redondo Beach, CA
    Posts
    1,973
    Your ACC line might be as high as 14V. The relay switch-on voltage might need the full 12V (or real close). It's possible the diode is dropping the voltate too low. Follow Ricky327's advice and see if the PSU 12v rail can power your relay, at all. It's also possible your 12v line has a problem and/or your relay coild draw a ***kload of current. That's pretty much the full range of possibilities.

  6. #6
    Low Bitrate
    Join Date
    Mar 2004
    Posts
    108
    well, it wont switch it at all. even the 12.02v straight from the PSU won't switch it.

    guess its time to try a different brand relay.

  7. #7
    Raw Wave
    Join Date
    Jun 2003
    Posts
    1,823
    well, it wont switch it at all. even the 12.02v straight from the PSU won't switch it.

    guess its time to try a different brand relay.


    The 12.02V is the voltage across the relay or with no relay connected? Because 12.02V should be fine for a 12V relay.

    Measure the voltage across the relay with your PSU supplying...it may be much lower than 12V. If this is so then your PSU is having problem supplying enough current to keep the 12V to the relay coil.

  8. #8
    Maximum Bitrate Altimat's Avatar
    Join Date
    Oct 2003
    Location
    WI
    Posts
    764
    Relays are fairly reliable. It should switch. Is the polarity correct on the diode?
    Fabricator

  9. #9
    Variable Bitrate Pokey's Avatar
    Join Date
    Apr 2004
    Location
    Tampa, Florida
    Posts
    284
    Check the resistance acoss the coil of the relay is zero ohms, those relays coil wires are extremely thin, and do break alot when moved around. if the relay is open, unwrap a couple of turns of the relay and resolder.

  10. #10
    Low Bitrate
    Join Date
    Mar 2004
    Posts
    108
    maybe i should restate that the 12v ACC line switches it fine. its just the 12v from PSU that won't trigger it.

Similar Threads

  1. Relay question
    By lopan in forum Power Supplies
    Replies: 2
    Last Post: 02-25-2004, 10:17 PM
  2. Automotive Relay Question
    By pbrinich in forum General Hardware Discussion
    Replies: 2
    Last Post: 01-29-2004, 05:27 PM
  3. Will someone help me program my relay control module
    By cproaudio in forum Software & Software Development
    Replies: 6
    Last Post: 09-04-2002, 05:50 AM
  4. RELAY QUESTION!!.
    By ifnh573 in forum Power Supplies
    Replies: 10
    Last Post: 09-24-2001, 10:29 AM
  5. A relay question
    By Dartman111 in forum General Hardware Discussion
    Replies: 1
    Last Post: 04-01-2001, 04:10 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •