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Need help with a 12v solenoid

  1. Apr 2, 2015 #1
    I'm not so smart when it comes to electrical things, so please forgive my ignorance.

    Here's what I am trying to do. I have a quad axle dump truck, I'm trying to have the drop axles automatically come up when put into reverse. The drops are raised and lowered via 2, 12 volt solenoid valves. I currently have the solenoids 'powered' to lift them and when they are lowered, the current is removed via 2 toggle switches in the cab of the truck. I ran a wire from the back up beeper to one of the solenoids and it now activates the solenoid and lifts the axle when the truck is shifted into reverse, but when I power the solenoid in the cab to raise the drop axles when empty, the back up beeper is being powered and always is beeping.

    I am thinking I need some sort of diode with one lead in and two out, so no power goes to the back up beeper, so I can run one to each solenoid lift valve, but not sure. What do i need to fix this problem? Thanks in advance.
     
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  3. Apr 2, 2015 #2

    sophiecentaur

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    The two solenoids will keep needing current whilst they are activated (obviously) so is it a good idea to use them for a long time? Isn't the purpose of the beeper to tell you that they are lifted (and using current)? I don't understand why you would want to turn the beeper off unless the solenoids are de-activated.
    If I am talking rubbish then I haven't understood the question (haha - nothing unusual there , then). If the problem is just about the beeper going when the lift is down then show us a diagram of the circuit you're using and we may be able to spot something; there's no reason why a beeper should keep going if a solenoid (in parallel with it) is not activated.
     
  4. Apr 2, 2015 #3
    Lol, your good. Perhaps I didn't explain it well. The beeper is just a safety device, to let anyone on the ground know that the truck is backing up and it can only beep when backing up. The beeper is activated via the reverse safety switch located on the transmission, when the truck is shifted into reverse. This same type of switch turns on the back up lights on cars and pickups.

    What i need is to stop the 'backup beeper' from beeping when the 2, 12 volt solenoids are activated.

    Yes the 2, 12 volt solenoids are always activated when the axles are up, which is the majority of the time.
     
    Last edited: Apr 2, 2015
  5. Apr 2, 2015 #4

    sophiecentaur

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    OK. Why don't you just use another beeper (with a different sound) that's just there to tell you when the solenoids are activated? If you don't want it going for ages, you could have a short timer on the bleeper and have an indicator lamp that's on all the time the solenoids are powered. :smile:
    It may be an idea to put an extra (low current) fuse in series with the lamp / beeper to protect the thin wires to them - assuming the solenoid is fused for lots of Amps - which could melt any thin wire.
     
  6. Apr 2, 2015 #5
    I don't need to know when they are activated. I already know this when we lift them or they wouldn't lift. What i am needing is the backup safety beeper to not be powered when I power the 2, 12 volt solenoids to lift them.
     
  7. Apr 2, 2015 #6

    Svein

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    Yes - you connected it that way. Sit down and create a truth table with inputs "backup beeper power" and "solenoid power"; outputs "backup beeper sound" and "raise drop axles". That will give you the start of a solution.
     
  8. Apr 2, 2015 #7
    It has to be connected that way, but what I need is a way to stop the back bleed of power from the 2, 12 volt solenoid to the back up beeper.
     
  9. Apr 2, 2015 #8
    circuit.PNG
    This should do it. Just make sure you install the diode the correct way around.


    Oh and please disregard the battery symbol at the top. That should just be two +12V fuse taps and not a battery with + and - I didn’t see that when I grabbed the symbol and dragged it into the schematic. I guess I need glasses.
     
    Last edited: Apr 2, 2015
  10. Apr 2, 2015 #9

    sophiecentaur

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    Right. So your solenoids can be operated either directly by a switch or as a consequence of selecting reverse - i.e by two independent switches.
    All you need is for a diode in the connection between the vehicle electrics and the solenoids, letting current flow through the solenoid when the reversing beeper etc are activated but blocking current from the 'extra' switch to the beeper circuit so that only the solenoid is activated by your switch. You need the 'arrow' on the diode to point towards the solenoid in the circuit. If that verbal description is not enough then I'll need to draw a diagram but it's pretty simple.

    I see that the last post contains what I meant to get across!!
     
  11. Apr 2, 2015 #10
    Yes Tom, that is how it needs/is connected, thank you for the diagram! Now, what isolation diode would you recommend?
     
  12. Apr 2, 2015 #11
    Yap, I just need to know what type of diode to get. Thank you!
     
  13. Apr 2, 2015 #12

    sophiecentaur

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    Reverse breakdown is no problem for any rectifier diode you can find. (>12V) Forward current to drive a beeper and lamp(?) need only be a few Amps or so. Very easy requirements that many diodes will satisfy. No need to go chasing a specific device number. Anything in an eBay supplier's catalogue to suit.
     
  14. Apr 2, 2015 #13
    I looked, most seem to be something for a circuit board. I need something with coated wire leads, as this goes under the truck cab and will be exposed to the elements to a certain degree. I'll use heat shrink butt connectors to connect. Thank you.
     
  15. Apr 3, 2015 #14
    The diode will also need to handle the solenoid current. Nothing special a run-of-the-mill generic blocking diode with enough current rating to handle the solenoid current. This ebay page has a big selection of them. You just need to know what current the solenoids draw. Check the size of the fuse in the solenoid circuit and get a diode with the same rating or a bit higher so the fuse will blow before the diode pops.
     
  16. Apr 3, 2015 #15
    I just looked again and to me they looked like they are all soldering types for a circuit board. Of the few that might work, are 3 phase. Thank you.
     
  17. Apr 3, 2015 #16
    You can solder leads on to it and heat shrink the whole thing can't you? I've done it before.
     
  18. Apr 3, 2015 #17
    I suppose so, but then I would need to make some sort of enclosure to keep it isolated. I was hoping to be able to use one that was enclosed already that had plugs on it or wire leads.
     
  19. Apr 3, 2015 #18
    Put some long leads on it, heat shrink over it and ty-rap it up inside the engine compartment where it will be safe and dry. You ought to see what my old car looks like!
     
  20. Apr 3, 2015 #19

    jim hardy

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    Do you know the resistance of that solenoid? How much current it draws ? Same for the beeper?

    When you turn off the solenoid its inductive "kick" will try to pull current through the diode and beeper.
    If solenoid's current is much more than beeper expects, it may wreck Mr Beeper.
    A diode across Mr Solenoid would be a good idea.


    If solenoid current is an amp or less, ie Rsolenoid >12 ohms, the 1N4000 series 1 amp diodes are cheap and available most everywhere.

    I can't imagine solenoid requiring more than 5 amps, at that current it'd get really hot. Look for 6 amp rectifiers in a blister pack at electronics shop. Or pillage from a dead PC power supply.
     
  21. Apr 3, 2015 #20

    jim hardy

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    @sedgehammer get one of these, 10A 50V are real cheap.
    70548.jpg
    In TomK's post #8, use it in place of the diode...
    tie the two AC terminals together and run to beeper
    run the + terminal to junction of solenoid-toggle swtch
    tie - terminal to vehicle's ground.
    That'll do both jobs, steering current and suppressing inductive kick.
    And it's easy to mount where you can see it.
     
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