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12V and relays

Discussion in 'Technical and Troubleshooting Torque' started by Pompy, Sep 20, 2015.

  1. I have a little question\confusion.
    I made a wiring harness to connect some accessory chargers too, basically it is connected to the battery and through a relay switched of the numberplate light, giving me switched power to charge iPhones etc. I would also like to be able to charge batteries, camera and heated vest. When I connect the battery to the charger, it trips the relay, have I done something wrong? The battery is 7.2V and the charger seems smart enough that although the relay turns the power on, the battery won't charge until the bike battery is being charged, no problem there, but my other "switched" stuff is running........

  2. The motorbikes battery is at 7.2v ?
    Something sounds wrong with the circuit.

    Can you give us some more details.
    With the bike off the relay is not activated and the output is nil ?
    But when you connect the charger the relay operates ?

    Can you try to draw the circuit out for us so we know what connections you have made, and what relay you are using.
  3. The battery for the heated vest is 7.2V when i connect that to the charger, that trips the relay. i have a + and a - from the battery to the relay, also a + from the number plate to switch the relay, then from the relay a + goes to a distribution block which has a - from the battery, does this make sense?
  4. Ahh, I think I get it, you can't connect the 12 volt of the bike system directly to the 7.2volt of the heated vest. You need a 12volt to 7.2 volt regulator/charger.
  5. cjvfrcjvfr no, when I connect the spare 7.2v battery to the charger it trips the regulator, switching the power on even tho the ignition is off, I am guessing the 7.2v vest battery is triggering the relay?
  6. triggering the relay, as in, the battery voltage of the vest is turning on your other accessories?

    for the relay, which pins connect to what? should be numbers on the relay like 30, 86, 87 etc

    looking at this diagram, the tail light wire should connect to 86, and you should have a ground wire from 85. that will turn on the relay.

    power from battery comes in on 30 (hopefully fues), and goes out on 87, so 87 goes to your accessory plugs etc

  7. So there is a charger in between the 12 volt bike circuit and the 7.2 volt heated vest batter?

    It sounds like you are powering up the bike electrical system from the 7.2 volt vest battery. The normal way to prevent backflow like that is a blocking diode.
    • Like Like x 1
    • Agree Agree x 1
  8. Yep, I'll put my specs on, get a torch and check the pins
  9. Yep, but speak of diodes goes above my skill set
  10. You can think of it like a water flap valve that allows electricity one way but not back the other way,

    Can you draw up your circuit and post a scan of it up here?
  11. you'd hope the charger would prevent that!!
    but if not, a couple of chunky diodes (one or two of these, which can do 3A each)
    • Agree Agree x 1
  12. diodes are easy to use, and if connected the right way (ie normally) there is no penalty to having them there.
    they just help when stuff gets connected backward, or when power wants to go the wrong way
  13. so that would go in line with the + from the relay to the terminal block I have?
  14. Or better still, in the + for the vest battery charger?
  15. yup, power out from the relay, to your distribution block.

    how many you connect (in parallel) depends on the current draw. those ones will pass 3amps through them
    you could put 1 on each wire out from the terminal block to each device that needed it, but I guess you only need diode for things that have power themselves.. ie the battery.
    stuff that doesn't have own internal power probably don't need a diode.

    "Or better still, in the + for the vest battery charger?"

    yup, that would be enough. what is the current rating of the charger?

    first, need to check wiring and make sure relay is in correctly :)

    tbh, I forget which way around they go :D that's what google is for :p
  16. I may even be able to get a charger that already has a diode, it is lighter socket type, fairly generic (reach cheap Chinese) type
  17. if output is 4V 0.7A, then the 12V input should be less than 0.3A, so a normal 1N4004 diode (1A) would be fine, but the 1N5404 3A diode at 35c is cheap, and will handle more current and not get warm etc.
  18. Thanks everyone for your help, nitrider is truly a community!!!!!