Why is this relay blowing fuses? ?

Discussion in 'The Garage' started by ihatefalling, Feb 6, 2012.

  1. ihatefalling

    ihatefalling Let it roll

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    Thanks for taking a look.
    I'm trying to wire in a relay to power some heated grips.
    I've got a DRZ400 - E Model.
    The key switch for the bike doesn't have an ACC position.....just off and on.
    When I turn the key to the on position, the headlight comes on.....that's where I'm getting the "switched" power into the relay.

    OK...here's the relay I'm using:

    [​IMG]


    From the picture below you'll see how I've got it wired up.
    1) a straight wire from the battery goes to 30
    2) 87 goes to the switch that turns the grips on/off
    3) 85 is grounded
    4) 86 is where I've run a wire and splice into the headlight (to activate the relay.)

    [​IMG]


    The theory is: When I turn the key on and the headlight comes on, power goes from the headlight into 86 - which in turn will allow power to run from 30 to 87 and then on to the grip heater switch.

    The bike has a factory 10amp fuse connected to the positive side of the battery.

    I keep popping that fuse. Here's as far as I've got............. When I have the headlight spliced wire hooked to 86 and 85 is grounded, then I turn the key switch to "on" thus powering the headlight and the relay....I pop the bike's fuse. The fuse will pop even if 30 and 87 aren't connected.

    Any ideas?
    #1
  2. bisbonian

    bisbonian Long timer

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    [​IMG]

    This is all I've got.
    #2
  3. lowflyer43

    lowflyer43 Adventurer

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    The diode to stop transient voltage spikes is polarized, look at the diagram, pin 85 is positive not ground. Just reverse 85 and 86. If you haven't fried the diode. Hope this helps:1drink
    #3
  4. GreaseMonkey

    GreaseMonkey Preshrunk & Cottony

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    If you look at that diagram there is an un-needed diode in the circuit. If the diode were to be shorted out it would act like what it is doing to you. Take a small flat screwdriver and pop the black cover off the relay and snip the diode out of the circuit (you don't need it in your application) and I suspect it will act normally.
    #4
  5. ihatefalling

    ihatefalling Let it roll

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    Thanks for the reply. Ill try and fix it tonight and will reply back
    #5
  6. wyowillys46

    wyowillys46 Hau Ruck!

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    The Flyback Diode is there on purpose. It's to prevent arcing across the headlight switch contacts or headlight relay contacts (that in turn power the grip heater relay coil) when the coil is de-energized. Cutting the diode out shortens the switch lifespan. Connecting the coil in reverse like OP as will cause a dead short and blow the fuse.

    http://en.wikipedia.org/wiki/Flyback_diode
    #6
  7. Luke

    Luke GPoET&P

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    Not an issue in this case. As long as the stock headlight is still installed it will absorb the energy from the coil when the switch is disconnected.
    #7
  8. GreaseMonkey

    GreaseMonkey Preshrunk & Cottony

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    Guys look at the schematic on the relay!
    [​IMG]

    Now look at his wiring diagram:
    [​IMG]

    Wyowillys, look at the picture in the wiki link you are posting, it is the same there. BTW IIRC this is usually referred to as a "tamping diode" and is there to prevent a secondary point bounce on the coil which energizes it momentarily. It has nothing to do with shortening any switch lifespan.

    I am on a netbook and it's late so I don't feel like typing, here is a cut and paste that says it well:

    http://www.the12volt.com/relays/relays.asp

    When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, you may attach positive voltage to either terminal of the coil and negative voltage to the other, otherwise you must connect positive to the side of the coil that the cathode side (side with stripe) of the diode is connected and negative to side of the coil that the anode side of the diode is connected.

    So how Bisbonian has it wired up is correct. So at this point there can only be two things- either the diode has shorted out and is passing current when it is not supposed to, or possibly Bisbonian has connected his terminals backwards from his diagram. Either way, clipping the diode will fix the problem and is fast and simple and if he did switch the connectors he doesn't need to be embarrassed on a forum.

    Now you two guys on the other hand need to start doing your fucking homework before you go off giving advice that is not only wrong but can also cost someone who thinks you know what you are talking about some serious aggravation.
    #8
  9. D.T.

    D.T. Difficult but useful

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    How about if he leaves the diode in and grounds #86 (cathode) instead (just like the printed schematic says)? The diode just makes it a polarized coil I assume.
    #9
  10. eepeqez

    eepeqez Long timer

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    While most relays (without a diode) will work with a signal of either polarity applied to 85 & 86, I always try to wire the relays correctly so that I don't introduce weird problems like this at some time in the future when I replace a relay and the only replacement available does have a diode. It's just good practice.
    #10