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Electrical (Probably easy for a bright lad)

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Spiky, Jul 8, 2005.

  1. I'm attempting to fit small and sexy indicators to my highly-strung two stroke. The originals (which are the size of house bricks) work fine, but as soon as I fit one of the new indicators, the system refuses to flash. They light up OK, but will not wink.

    There's probably a really obvious answer to this, so be gentle with me, but WTF is the problem?

  2. likely it is a different load on the blinker system... caused by different (hot and loaded) resistence in the new compact blinkers compared to the original ones.

    there you go... simple wasn't it :)
  3. If you have the older "bi-metallic strip" type flasher-can thenew indicators may not have the required amperage draw (wattage rating of globe) to heat up the strip to turn the light off (strip cools down and lights go on.. and off and so on..)

    Some of the more modern flasher cans do the same thing if the globe wattage isn't high enough.

    Modern "el bling bling" flasher units may even be LED's, not normal filament globes, which could do the same thing.

  4. OK, this makes sense.

    What's the answer then? Different indicators or a minor rewiring job?
  5. you could try different flasher cans until you found one that worked... a better solution would be to put a new and an old blinker unit in line with a power supply, grab a multi metre and set it to amp scale and measure the current drawn on the meter.

    That will let you calculate how much difference there is between the new ones and the old ones.

    Of course if the wattage for both is listed that'd be quicker ;-)
  6. First check the wattage of the old globes, you can work out the current draw by dividing the watts by the voltage (double the watts first, as you have a front and rear indicator)

    eg, two x 15 watt globes / 12 volts (near enough, is really 13.8 v) is 30watts/12volts or 2.5 amps

    Your new indicators might only be two x 10 amp globes, so 20/12 or only 1.67 amps, possibly not enough to trigger the flasher can. (symptoms are exactly what you see, light stays on)

    You could buy a new electronic flasher can, most have standard socket fittings, or add an extra pair of indicators each side :shock:

    Hope that makes sense???


    (EDIT.. might just be adodgy earth on the new indicators as well, esp if the original had a metal body, and the new is plastic)

  7. the easy way is...fit a resistor in circuit :p
  8. In the flasher circuit will be a "flasher can" - and, inside it a bi-metal contact that opens and closes the circuit that turns the lights on and off. The strip is made of two metal strips bonded together, like a laminate.

    The strips are made of different metals, and they heat at different rates so they expand differently. This, in turn, makes the strip bend to one side when it gets hot, and straighten out when its cold. When the strip is cold, it touches a contact that allows current to flow to the lights. Before long, the current heats the metal, and it bends to break the circuit. No current, so it cools down again and straightens so the circuit closes.

    If there's not enough current, the strip never heats and the circuit stays closed, with the lights jammed on. If there's too much current, it heats too fast and the "flash" phase gets too short. So what changes the current? The wattage of the globes. If they draw too little current, then the circuit never heats. If you've gone to compact indicators (or LEDs), then the current may have dropped.

    Solution? Increase the current drawn by going to higher wattage globes (be careful not to cook the indicator lenses) or adding load resistors to the circuit. Or replace the flasher can with a "light duty" model.

    I suggest using resistors - you keep all your stock components, and you're not risking overheating the indicator lenses. What size resistors? If you've added LEDs, there should be something on the specs that tells you the current they draw (in Watts). If they're conventional globes, the current value is stamped on the metal shell.

    EDIT: for the purists - the calculation below uses power (in Watts) but refers to this as current. I know, it's wrong. But, as the voltage remains constant throughout the calculation (13.8V), and P=VI, then power is directly proportional to current so we can substitute P for I and treat the power value as through it was a current value.

    You need to match the drawn current to the same value as your old indicators.

    1. Check the old indicator globes, note the value in watts. Lets say they're 15W globes. So the old circuit required 30W (there are 2 indicators @ 15W each) to heat the strip.

    2. How much is the new setup drawing? Calculate the sum of the wattages on the new ones (lets say front and rear @ 10W each = 20W)

    And the difference is the shortfall in the current...

    3. Subtract the new value from the old 30W-20W=10W

    Remember that we need to divide this current between the front and rear indicators = 5W each.

    Now we know what current is required to heat the strip, what size resistor should go into the circuit?

    Introducing...Ohms law...

    power(W) = voltage(V)^2 / resistance (R)

    (Edit - formula corrected as suggested by the eagle-eyed Mr Iffracem)

    and we want to dissipate further 5 Watts, so:

    5=13.8^2 / resistance
    resistance = 190/5
    resistance = 38 Ohms.

    Well, 38 Ohms isn't a preferred value, so lets go with 39 Ohm. The flasher will go a little slower, but not significantly. But resistors come in different power ratings, so which one do we need? 5Watt, because thats the power it needs to dissipate. So we need 4 (one per indicator) 39 Ohm, 5Watt resistors...part No 37575826 at Radio Parts, 90 cents each each.

    EDIT - you need to replace my values (30W, 20W etc) with the ones for your bike!!!!!!

    The resistor goes in series with the globe - if you have a single wire running to the indicator, snip it and wire the resistor between the snipped ends. Insulate well, and cable tie it to the frame.

  9. thats, err, comprehensive to say the least Chairman. I've just been able to wire up my pushy with indicators thanks to your tutorial! Great post :)
  10. I stay away from wiring on bikes . The last one i attempted was when i was rebuilding the z650 and burnt out the whole wiring harness :shock: .
  11. Chairman - for me, that is the answer of the year so far.

    What's more, I understand what you're talking about and I reckon it's the solution.

    How sexy is this bike gonna look, eh? \:D/
  12. Well explained mr chairman :applause: :applause:
    (electric-chairman? :shock: )

    one small error in the ohms law explanation, I = current, not resistance, the formula is correct, just the symbol is wrong... yes I can be a pedantic old phart at times :roll:

    Oooo this is hurting brain cells that haven't been used since 1995 :?