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Ducati St2 Battery Light Stays On Permanent!

Discussion in 'Sport Touring' started by Dean Prior, Feb 2, 2020.

  1. I've recently brought an st2 and had to fit a new battery when I took delivery, but everytime I ride it the battery light stays on, does this mean that it's not charging, I've done about 5 miles on it in the 7 days, on the first day was when the battery was fitted, If it was draining the battery would it be flat by now?, it had a new regulator about 6 months ago, HELP!
     
  2. If someone has the circuit diagram.... I could give more definitive advice.
    98% Yes, something is wrong with the charging circuit or at least the wiring.

    WHat is the battery voltage when off?
    WHat is the battery voltage at tickover, 2000RPM and 4000RPM?
     
  3. I too have just bought an ST2, of 1998 vintage. My charge warning light comes on when starting and stays illuminated unless the revs are over 2k at least. It had me worried when I test drove the bike before buying, but just became a haggling point as everything is fixable.

    So, when I eventually got the bike I tested the battery with no draw 12.4v
    Turned on the ignition, drops to 12.25v
    Pressed they starter, no further voltage drop and engine starts
    Tested the voltage now going into the battery 14.25v at 3k rpm, between 12.5-13 on tickover at 1500ish rpm

    It all seems good to me and having just done 200Km on it today all is well except the charging light flickers when the bike is just ticking over at the lights.

    I'll investigate it further as I give the bike a thorough service and some TLC but at present I'm happy to live with it.
     
  4. @AirCon ST2 wiring diagram attached FYI
     

    Attached Files:

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  5. Pin 5 on the regulator (32) is your 'gen' light, so there's nothing else in circuit to control it. Try a substitute regulator if you can, but those voltages look fine. My guess is the driver circuit for the lamp is tired/failing with age (like us all!)...
     
  6. I'm glad someone can understand those things. Thanks for that info. I'll be doing some testing as I refurb it so will see where the issue lies, it could even be a loose or corroded connection I guess?
     
  7. A bit late to the party: I think that my ST2 is fine. It's been to France and Belgium with no problems. It is quite old (1999) and I bought it for not much money several years ago. The charging light has always come on at low revs. It goes out above about 2000 when I ride it.
     
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  8. @Dean Prior you still around or have you posted the question and then disappeared?

    FYI I did some more checks.
    Start her up, warm her up and tickover is set at c.1400rpm. No red low charge warning light.
    Turn on headlight (no daytime running lights on this model) and red warning light comes on.
    Increase revs to 2000rpm and the warning light goes out.
    Reduce revs to tickover and warning light comes back on.
    Turn off headlight and warning light flickers and goes out.

    I'm going to get a voltmeter display and put it into the circuit and place it where I can see it whilst riding, just to be sure to be sure. However, the 98MY has the 2 phase generator which a bit of research indicates has a weedy power output so what I believe is happening is that there is sufficient juice to charge the battery when the engine is running, even on tickover, however, as soon as a demand is made upon the power output of the generator i.e. the 55w headlight, the available juice to flow back to the battery is reduced to the degree it causes the warning light to come on unless the generator is spinning fast enough to pump out just that little more juice i.e. 2k rpm and above.

    In short, I'd say it's nothing to worry about in my case.

    In the case of the OP though, the questions @AirCon asked need to be answered. Is the light on all the time regardless of engine revs? and whats the voltage across the battery terminals?

    OP, we're here to help
     
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  9. your logic's sound on the 2-phase genny being a bit lame, and the battery having to take over at low revs when the headlight is demanding (they can be sooo demanding;)). I guess it'll just be good to remember that slow town riding with lights on could result in troublesome starting next day....
     
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  10. It would appear that the charge warning light comes on if the (+) voltage rail drops below that set by Zenar diode... circa 13Vdc.
    So long as it goes out when above 2000RPM happy days.
    A two phase generator set is never going to be as good as a three phase, IMHO.
    Given the inaccuracy of most multimeters under the £300 mark I think the voltages should be taken with pinch of salt.
    One decimal place is fine.

    Lithium anyone?
     
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  11. Sorry not disappeared, I'm a long distance lorry driver and have been very busy , I managed to get some time tonight to do a bit more investigation.

    My battery light never goes out even when I rev the bike and have the lights on or off it makes no difference it's always there.

    Apparently the rectifier/regulator wires can become burnt out, (yellow wires).

    I undid the plug earlier and found the inside of the plug was very very burnt out, apparently this is a common issue. So going to remove the plug, and solder the wires together and then re heat shrink them and see if that solves the issue.

    20200205_195518.jpg

    20200205_195533.jpg

    20200205_195525.jpg
     
  12. Thanks for the update Dean. Where’s that plug from? Where does it sit in the circuit? It’s had too much current draw going through it IMHO for it to melt like that.
     
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  13. I might be wrong but I think that when the terminals corrode (through ingress of moisture) the contact surface area between the two parts of the connectors effectively reduces, the current draw remains the same and the smaller contact patch heats up because of the higher resistance and melts the plastic. A bit like passing a 30 amp current through an 11 (or less) amp wire - it will get hot and the insulation will melt.
     
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  14. I can confirm that high resistance due to corrosion on these plugs is common. This increased resistance causes heating.
    I assume this plug is between the coils and the regulator.
     
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