Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Headlight mod on cbr, both lights on - electrical question

Discussion in 'Technical and Troubleshooting Torque' started by drewzor, Feb 4, 2009.

  1. Need some help calculating what resistance I need to add to the circuit.
    I'm dipping the high beam and running a bypass from the switch to keep the low beam on when switching to high beam (which will be dipped) to give me both lights on low beam.

    So here is the stats

    12v 55w 4.58amp per bulb

    battery 12v 6Ah

    So I would like to know what resistor I can use to limit the draw when both lights are on to make this suitable for the electrical system.
  2. Forget the battery capacity (for now) Alternator output is MUCH more relevant :roll:
  3. Generator is .290Kw

    can someone help and explain
  4. .29 kW = 290 watts = (average 12v) a bit over 24 amps. This will be at high rpm so if you take about 1/2 capacity your good for say 12 amps or about 150watts running all the time. 2 x headlights at 55w, plus battery charge 40w, plus tail light 15w, plus ignition 30w = 190w, you'll probably be OK provided your not stuck in traffic idling for long periods.

    And knowing Newie you won't :grin:
  5. Thank you, its appreciated!
  6. So to complicate things the bulbs I want are 100 watt

    So my calculations then

    100/12 = 8.3Amp

    But I will be connecting two bulbs so a draw will be 16.6Amp
    Problems is this circuit is on a 10Amp fuse.

    Can someone help with how to calculate resistance required?

    I'd like to run down to 50 or 55w per bulb or a resistor off the main power line after the fuse.
  7. Be aware your mod will probably render the bike unroadworthy (you've got to be caught but a lot of solo coppers do know their bikes).

    You also lose highbeam which isn't a good idea even from the point of view of being able to flash someone about to make you a bonnet emblem.
  8. As he said, it's not a great idea. Why not look into upgrading the wattage on your single low beam (ie, new wiring).
  9. This configuration will still allow me to flash one light, it will just be low beam. I only ride daylight hours too. please dont get distracted with the "why" of the request. My decisions rarely make sense lol

    How does it become illegal to have both lights on? or is it no high beam thats the problem?

    I would like to use tinted bulbs but they are only in 100w size.

    I would like to use a resister to throttle the current draw and effectively make the 100w bulb run at 50W.

    So My understanding so far is

    12v 10Amp Circuit with a max 110 Watt available

    100w bulb x2 = 200w

    200/12 = 16.6 Amp Draw

    1/2 of 16.6 is 8.3Amp

    So what Ohm resister do i need to drop 8.3Amp or 100Watt off the circuit?
  10. Designated Low Beam lights usually have a deflector fitted inside the light so that the light beam heads downwards out of the light and doesn't blind oncoming vehicles (applies during the day as well) hence H4 Hi/Lo globes have that little deflector in them.

    Just winding down the high beam light wont be legal, in fact you could get done for running high beam lights AND out of aligned headlights at the same time.

    Best way to do this legally is to work out a way to change both lights so they are High & Low beam (just like cars) but that would be beyond most weekend warriors capabilities (I certainly wouldn't want to do it).

    EDIT: On the subject of wanting to reduce the output power you will struggle to find a resistor capable of absorbing 50W worth of power remembering your average electronics resistor is 1/4, 1/2, 1 or 5W and the 5Watters are pretty big in size.
  11. Ok, thank you for the info.