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Harold Lanfear
Joined: 02 Dec 2006
Posts: 6
Location: West Grove, PA
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 Posted: Mon Mar 31, 2008 2:16 pm Post subject: E-Buss diode vs. Switch |
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I am planning to follow Aeroelectric's Z13 / 8 diagram; but as I've started wiring, I was looking at the diode that separates the e-buss from the main buss. In use, the diode allows power to flow from the main to the e-buss in normal use. However, should the main buss fail, the pilot 'flips' a switch to allow power to flow from the Battery buss to the e-buss and power cannot feed the main buss because of the diode.
My question is this; why not eliminate the diode and replace the on-off switch with an on-on switch so power is fed either from the Battery Buss or the Main Buss but never both? Either way the pilot manually changes the switch and the diode is not needed (and you eliminate any voltage reduction due to the diode). Apparently I'm missing something, can somewhat explain what that is? Thanks much, Harold
[quote][b]
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nuckolls.bob(at)cox.net
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| Posted: Mon Mar 31, 2008 5:48 pm Post subject: E-Buss diode vs. Switch |
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At 06:07 PM 3/31/2008 -0400, you wrote:
| Quote: | I am planning to follow Aeroelectric's Z13 / 8 diagram; but as I've
started wiring, I was looking at the diode that separates the e-buss from
the main buss. In use, the diode allows power to flow from the main to
the e-buss in normal use. However, should the main buss fail, the pilot
'flips' a switch to allow power to flow from the Battery buss to the
e-buss and power cannot feed the main buss because of the diode.
My question is this; why not eliminate the diode and replace the on-off
switch with an on-on switch so power is fed either from the Battery Buss
or the Main Buss but never both? Either way the pilot manually changes
the switch and the diode is not needed (and you eliminate any voltage
reduction due to the diode). Apparently I'm missing something, can
somewhat explain what that is? Thanks
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Voltage drop in diode is not significant. Use of
single switch offers a single point of failure for
BOTH power paths to the e-bus. Recommend you wire
as depicted.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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nuckolls.bob(at)cox.net
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| Posted: Mon Mar 31, 2008 5:48 pm Post subject: E-Buss diode vs. Switch |
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At 03:52 PM 3/31/2008 -0700, you wrote:
| Quote: | The purpose of the E-bus is to be able to achieve a rapid load reduction
in case of either alternator failure, main battery contactor failure, or a
stuck starter. To understand the need for the diode approach, you need to
examine your switching alternatives and the effect on running equipment
under each scenario if you use a switch instead of a diode.
For example, if the alternator has failed, which will normally be deduced
from falling voltage, you will need to switch THREE switches (alternate
feed ON, contactor OFF, inter-bus OFF) to get to the load reduction --
otherwise the alternate feed will back feed the main bus. If you switch in
the wrong sequence (harder to avoid with three) you may also shut down
and/or reboot gear you'd, uh, rather keep running.  Either way, that's
"suboptimal".
If the main battery contactor fails, you still have three switches to
throw to be sure you're settling things down, and if you don't flip three
or are unsure of the problem, you are still feeding current to the
downstream side of a battery contactor that is at best in an uncertain
condition. If you have a stuck starter (whether contactor or motor)
you''re back to having to flip three switches.
The voltage drop associated with the diode is a minimal price to pay for
the simplicity and reliability of the diode approach. Note that when you
have feed through the main bus and diode, you're going to be running with
the alternator/regulator in play anyway, and by definition should have
more than adequate of voltage even through the diode. Further, that
voltage drop can be greatly minimized to the point of being
inconsequential by using a Schottky diode, such as those available from
Perihelion.
Bottom line, the voltage drop issue only exists when you have an
alternator anyway, it can be minimized by using a Schottky, and you will
have fewer switches to maintain, and flip.
Ron
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Excellent treatise on the subject sir . . .
Bob . . .
| Quote: | On Mon, Mar 31, 2008 at 3:07 PM, Harold Lanfear
<<mailto:hlanfear(at)verizon.net>hlanfear(at)verizon.net> wrote:
>I am planning to follow Aeroelectric's Z13 / 8 diagram; but as I've
>started wiring, I was looking at the diode that separates the e-buss from
>the main buss. In use, the diode allows power to flow from the main to
>the e-buss in normal use. However, should the main buss fail, the pilot
>'flips' a switch to allow power to flow from the Battery buss to the
>e-buss and power cannot feed the main buss because of the diode.
>
>My question is this; why not eliminate the diode and replace the on-off
>switch with an on-on switch so power is fed either from the Battery Buss
>or the Main Buss but never both? Either way the pilot manually changes
>the switch and the diode is not needed (and you eliminate any voltage
>reduction due to the diode). Apparently I'm missing something, can
>somewhat explain what that is? Thanks much, Harold
|
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