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Low Voltage Warn on E-Bus instead of Main?

 
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nuckollsr(at)cox.net
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PostPosted: Wed Feb 15, 2006 5:24 am    Post subject: Low Voltage Warn on E-Bus instead of Main? Reply with quote

At 04:02 PM 2/14/2006 -0800, you wrote:

Quote:


The Z13-8 diagram shows the low voltage warning light connected to the main
bus. It seems to me like connecting it to the E-bus would be slightly more
useful. In that configuration, it should illuminate if the main alt drops
offline UNTIL the standby alt is engaged. At that point it stop indicating
unless/until the load exceeded the output capabiliy of the SD-8 standby
alternator. In that way it would essentially act as a "battery discharge"
warning (with the inference that if the voltage is below alternator
operating range, then the battery is discharging -- if only through the low
voltage warning circuit!) BTW, what is the current draw of the Low Voltage
Warning circuit? I presume it's very small and driven mostly by the
light/LED used.

Does anyone see a problem with this configuration? Does it miss a design
consideration that motivated it's original placement?

Yes. The normal e-bus voltage is .6 to .8 volts below the main
bus due to isolation diode drops in normal operation. The REAL
voltage of interest is at the main bus and it's purpose is to
annunciate alternator failure.

Further, when you react to the alternator failure by turning
the main bus OFF, you want the LV warning to go dark too. Without
an alternator, the LV light flashes all the time . . . you don't
want this thing flashing at you during battery-only, e-bus ops.

Bob . . .
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >


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nuckollsr(at)cox.net
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PostPosted: Wed Feb 15, 2006 6:01 pm    Post subject: Low Voltage Warn on E-Bus instead of Main? Reply with quote

At 01:40 PM 2/15/2006 -0500, you wrote:

Quote:


Scott wrote:

>
>
>The Z13-8 diagram shows the low voltage warning light connected to the main
>bus. It seems to me like connecting it to the E-bus would be slightly more
>useful. In that configuration, it should illuminate if the main alt drops
>offline UNTIL the standby alt is engaged. At that point it stop indicating
>unless/until the load exceeded the output capabiliy of the SD-8 standby
>alternator. In that way it would essentially act as a "battery discharge"
>warning (with the inference that if the voltage is below alternator
>operating range, then the battery is discharging -- if only through the low
>voltage warning circuit!) BTW, what is the current draw of the Low Voltage
>Warning circuit? I presume it's very small and driven mostly by the
>light/LED used.
>
>Does anyone see a problem with this configuration? Does it miss a design
>consideration that motivated it's original placement?
>
>
>

How would you know if the main buss went offline?
If you happened to be looking out the window in the brief
time that it might light until the standby alt kicked in
automatically, you might never see the warning.

How would you not know the main bus was off? That
takes the whole panel down. What failure would you
anticipate would produce this effect?
Quote:
I suppose you could hook the low voltage warning "sensor" to a switch,
initially monitoring the main buss, and then you manually
switch it to the E-buss and thus "acknowledge" the warning.

The low voltage warning is not intended to monitor
a bus, it's intended to provide active and almost immediate
notification of alternator failure. Total loss of the main
bus takes a combination of failures and is difficult not
to notice.

Bob . . .


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deej(at)deej.net
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PostPosted: Wed Feb 15, 2006 7:12 pm    Post subject: Low Voltage Warn on E-Bus instead of Main? Reply with quote

Robert L. Nuckolls, III Main? wrote:
Quote:


Quote:
How would you not know the main bus was off? That
takes the whole panel down. What failure would you
anticipate would produce this effect?


Well, I never claimed I was omnipotent... *grin*

I was thinking something along the lines of the main
alternator going offline, the main panel running on battery,
and then the aux alternator kicks in on the aux buss.
Depending on how things are wired, it may be possible for
the main buss to be running off the main battery with no
main alternator, and the E-buss to be running off another
battery and be on the aux alternator. If this was the case
and the low voltage were wired to the aux buss, you may
not immediately realize that you lost your alternator
on the main buss.

At least that's what occurred to me from his initial
query. I never claimed it had to make sense... heh heh Smile

do not archive

-Dj

--
Dj Merrill
Sportsman 2+2 Builder #7118
http://econ.duke.edu/~deej/sportsman/

"TSA: Totally Screwing Aviation"


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