> After reading Bud's post a few moments ago, I have a
> couple of general questions about ammeters and
> voltmeters which perhaps an expert can answer for me.
> Up til now, I've planned to measure the voltage at the
> plus side of the battery...Is that the best place to
> measure?...or are there multiple places where voltage
> should be measured?...and how is that
> accomplished?...with a rotary switch?
> Similarly, I've planned to place my ammeter in series
> on the output side of the alternator...will that
> do?...or again, are there multiple places where
> amperage should be measured?...and if so, where?...and
> how is that generally accomplished?...with a rotary
> switch?
> (I have the EXP 2 Bus by Control Vision along w/ their
> indicator module; however, the word I'm getting from
> others is that the warning lights on the module are not
> to be trusted, and that led to my purchasing a
> delightful little pair of Mitchell instruments.)
In certified planes the amps are sometimes measured out of
the alternator regulator (plus scale only) or in/out of
the battery (plus and minus scale)
The latter is more useful but often is not the case
Voltmeters are damped so they don't move violently.
Ammeters aren't (mine anyway - analogue not digital) and
can change rapidly. Tha is why i knew that all four Ducati
replacments I tried after my first one died at 175 hours
were not working the way I would want - a 5 cycle per sec
oscillation between 2 and 10 amps - which would have also
been the volts oscillating between probabaly 13.5 and 15
volts.
With only a voltmeter I would have been unaware of this
(maybe that would have been better).
I found the Schicke recifier/regulator and it has been
perfectly normal ever since with no oscillations.
And that word "oscillations" is a hint why you should NOT
put an ammeter in the line between the stator and the RR.
The stator produces AC voltage and therefore current so
the ammeter would read zero unless you had an AC ammeter !
I measured up to 30 v AC coming out of the stator at full
welly.
This all means that I would always have an ammeter AND a
voltmeter. On;y with both can you be sure of what is
happening. The voltmeter can be digital, but an analogue
ammeter is the best way.
In terms of this resistor, you can either put the whole
current through an ammeter (made to suit) in which case
the current is measured across a small value resistor
inside; or the small resistor (known as a "shunt") can be
fixed in the cable and the ammeter measures across it.
This "shunt" way avoids long runs of cable into the panel
taking the whole current (with Rotax is it not much - max
19 A)
HIR (Hope I'm Right !)
Richard Holder
G-OWWW
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