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Diagnosing an electrical problem

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by huplescat, Mar 23, 2010.

  1. I did a bit of a search to see if something like this has been posted and didn't find anything, but it probably has so er...sorry.

    Last night I was riding home, pulled up at some lights and the bike stalled. Went to start again, the dash lights were dimmer than normal and there was no response when I hit the ignition.

    Luckily I was on a hill so I roll started her and things were fine until the revs dropped around a corner so again I had to roll start her, limped home by keeping the revs up and probably pissing off the neighbours, but the headlight was a lot dimmer than normal and she definitely ain't starting with the ignition.

    So I'm thinking alternator, I can run a multi metre over the battery but suspect it'll just say "Yep, it's 12v" and can't start the bike to see if it's charging.

    So is there anything else I can do to diagnose it? My mechanical skills aren't that hot but I have no idea how I'll get it to a mechanic as it is (can't roll start it from the bottom of a steep driveway). So either I figure it out myself or bight the bullet and have someone throw it on the back of a ute/trailer (not something I'm keen on).

    ANYWAY, any suggestions welcome, I want my baby back on the road :( She's a '94 VFR750. As far as I'm aware the R/R has been replaced already with an aftermarket one but if the symptoms sound the same I can do more digging.

    Thanks :)
  2. Buy yourself a charger, they are cheap and a worthwhile thing to have around.
    Charge the battery overnight.
    Try and start it again the next day, if it starts then get a multimeter and measure the voltage across the battery with the bike reving to a couple of grand, not idle. You should get 14.4 volts. If it is higher or lower there is a problem with the charge circuit or battery.

    Regulator is the first guess, a common Honda problem, much more common thann alternator failures. See THIS thread.
  3. Thanks Chris, will do :)
  4. ok so I bought a charger, I don't think it's going to do the trick though. Supercheap didn't have the one in the link and the other similar one was out of stock.

    So she sold me a different one with different specs for the same price that said it was ok for motorbikes, but looking at the instructions I think it's no good for mine.

    Instructions on the battery say "Charge at 12V at the amperage and hours stated below:

    STD: 1.2A x 5-10h
    QUICK: 5.0A x 10h"

    But the charger instructions say not to use the quick charge on bike batteries and the only trickle charge available for 12V is 2,400mA. 1,200mA (which I'm guessing is the same as 1.2A) is only possible on the 6V setting which the battery says not to use.

    Am I right in thinking that this ain't going to work with my battery?

    I can take it back if it's no good though so that's something at least.

    Bah, sorry for the nooby questions, I've never had to deal with this stuff before.
  5. I would think 2,400mA / 2.4A will be fine (unless someone more experienced says otherwise). I would only leave it on unsupervised if it has an automatic stop when the battery is charged.

    Otherwise, cjvfr has you covered. Before you do the multimeter test, check the wires to the alternator and the regulator/rectifier for dodgy looking insulation (burnt, melted or worn), and give the connections a spray of contact cleaner (available from jaycar and probably auto stores).