The "idiot" light tells you (when it is on) that the alternator output
voltage is lower than the bus/battery voltage. And nothing else.
When the light is out, the battery is not necessarily charging ( as output
voltage may be below the c.13.4 volts required for charging).
My preference is for a voltmeter; which will tell the state of charge of
the battery before start-up and whether charging is taking place during
engine run. The amount by which charging is taking place (as indicated by
an ammeter), I find a little academic.
Duncan McFadyean
On Friday, March 22, 2002 4:42 AM, Fred Fillinger
[SMTP:fillinger@ameritech.net] wrote:
> McFadyean wrote:
> >
> > For the Rotax alternator with permanent magnet field, none of this is
> > needed. So a LED will do without any paralleling resistor. Series
resistor
> > may be needed however, typically 600 ohms or thereabouts depending on
> > voltage.
>
> Inoperative, there's infinite resistance to ground; operative it has
> to go high to bus voltage so the lamp won't light. But it does
> measure one semiconductor junction's worth to ground on a diode check,
> so I think I know what's in there. A dummy resistor load will surely
> work, but wastes current. I think just an LED to the "L" terminal
> will work, but having not gambled in many years, I've lost the ability
> to spot a good 1 to 5 shot.
>
> Another thought is that they call these idiot lights on cars. Best I
> think is volt and amp meters, as the alt lamp may not identify all
> faults. Circuitry to add aural/visual alerts on overs and unders
> isn't too complicated, even w/o meters, if so capable or desirous to
> learn another hobby.
>
> Best,
> Fred F.
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