Today's Message Index:
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0. 09:54 AM - Coming Soon - The List of Contributors - Please Make A Contribution Today! (Matt Dralle)
1. 09:37 AM - Re: Re: voltage fluctuations (Robert L. Nuckolls, III)
2. 12:50 PM - Re: Re: voltage fluctuations (Robert L. Nuckolls, III)
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Subject: | Coming Soon - The List of Contributors - Please Make |
A Contribution Today!
Each year at the end of the List Fund Raiser, I post a message acknowledging everyone
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Subject: | Re: voltage fluctuations |
I was able to work on this last weekend and found that there was
indeed some voltage loss between main bus and master switch. Got
that taken care of, got rid of the jumper between pins 3 and 6 on
voltage regulator and added a dedicated bus voltage sense wire, and
then monitored voltage at a number of locations with the engine
running using my trusty Radio Shack multimeter: 14.08 V at battery;
14.06 at battery bus, 14.05 at main bus, and 13.31 at e-bus that is
fed through a diode. With the e-bus alternate feed switch turned on,
e-bus voltage jumps to 13.96. Voltage readings are now steady at the
battery and bus locations.
Very good. This validates our hope that there
are no problems with the hardware.
EIS and two EFIS screen voltage values are only indicated in tenths
of volts on the screens, and these values seem to fluctuate by 0.1 or
0.2 V; not sure why that is, but perhaps that isnt really a concern.
ALL digital dispalys are subject to some
degree of 'bobble' in the least significant
digit. Which has to do with the manner in which
DC votlages are filtered, sampled and converted
to binary values for furhter processing. Then
there are the effects of naturally occuring
variations in the bus votlage itself.
Unless the designer has gone to the trouble to
oversample, do running averaging or perhaps
convert to more digits and toss out the last
one . . . you're going to see this bobble.
As much as plus or minus two counts in the
least significant digit is of no concern.
Back in the days when the best voltmeters
installed might look like this:
[]
You couldn't see the fluctuations . . . but they
were still there.
EIS (fed from e-bus) = 13.5 V
pilot EFIS, primary power source (fed from e-bus) 13.4 V
pilot EFIS, secondary power source (fed from main bus & TCW power
stabilizer =13.8 V. So looks like my intended secondary power
source for covering engine-start brown-outs is actually serving as my
primary power source due to its higher voltage.
Copilot EFIS, primary power source (fed from e-bus) = 13.2 V (a bit low)
There is no secondary power source connected for the copilot EFIS.
So, all good overall, although thinking I should adjust the voltage
regulator until I get 14.2 V at the battery so that it recharges a bit faster.
14.4 volts is not out of line. Reading from the
Hawkjer-Enersys manual on Odyssey batteries:
Emacs!
It sounds like the power management philosophy for
the 'secondary power sources' could use some
refinement. Without detailed schematics describing
just how electrons are being herded through the
system, it's not possible to offer a detailed
assessment.
The take-away from this exercise was predicted
by one of my heros:
"When you can measure what you are speaking about, and
express it in numbers, you know something about it; but
when you cannot measure it, when you cannot express it in
numbers, your knowledge is of a meagre and unsatisfactory
kind; it may be the beginning of knowledge, but you have
scarcely in your thoughts advanced to the stage of science,
whatever the matter may be." -Lord Kelvin- 1864
Bob . . .
Message 2
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Subject: | Re: voltage fluctuations |
I almost forgot . . .
>So, all good overall, although thinking I should adjust the voltage
>regulator until I get 14.2 V at the battery so that it recharges a bit faster.
>
> 14.4 volts is not out of line . . .
When setting your voltage regulator, adjust
for the desired magnitude AT THE REGULATOR'S
SENSE POINT.
In this case, at the main bus. Adjusting
for voltage at the battery does not account
for inevitable VARIATIONS in voltage drop
between the sense point and the battery. If
the battery is taking a charge, current through
the charge path DEPRESSES voltage at the
battery . . . which approaches zero as the battery
charges.
A fully charged battery's terminal voltage and
the sense point at the bus will be essentially
equal. So while cranking on the little screw, measure
from the bus.
Bob . . .
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