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sjhdcl(at)kingston.net
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 Posted: Thu Mar 23, 2006 8:46 am Post subject: Endurance Bus Voltage Measurement |
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Bob and others,
My electrical system is pretty much finished. I have started with Z-12 and
used SB-8 instead of 20A alternator.
On the endurance bus I have wired:
GNC300XL GPS/COM 0.221 A measured when not transmitting
Attitude Indicator 0.16 A
Autopilot (2 axis independent controlled) 1.6 A each
Volts/Amp E.I. gauge 0.089 A
If both axis of the autopilot are engaged, the total load is 3.67A.
My problem lies with the installed volt/amp gauge. The reason I installed
it on the endurance bus is to monitor the
decreasing voltage while running battery only. While this of course of a
highly unlikely situation with 2 alternators
I decided to install it there anyways. The better use of the gauge on to
monitor to current draw current SD8 operation
to ensure it is below the max output of the alt.
Enough rambling. Here is my problem:
I currently have no fuses installed in the MAIN Bus. I turn the Endurance
X-Feed on and measure 12.81V at
the endurance bus fuse block attachment. However I also measure 6.77V at the
MAIN fuse block terminal. The diode is
allowing current to leak backwards. With no fuses in the MAIN fuse block
the volts/amps gauge reads the correct
12.8V. It does not indicate current at this point since the shunts are in
the alternator leads, not battery leads.
Now the confusing part starts. If I install ALL the fuses in the Main fuse
block, the volt/amp gauge indicates 0V.
I still measure 12.74V at the endurance bus fuse block and the volt/amp
gauge turns on so the voltage sensed by
the gauge does not match the voltage at the terminal. Now if I turn the
MASTER ON, the voltage is then correct
back to 12.8V. With all the fuses on (Endurance switch ON, MASTER OFF) the
voltage at EBus is 12.74.
Voltage at MAIN bus is 0.45V.
Is it normal for the diode to leak voltage back to the MAIN bus when the
Endurance switch is ON?
Here is a couple of other weird anomalies with the volt/amp gauge. If I only
install the fuse for the dimmer control
module (on MAIN bus), the indicated voltage jumps to 36.6V. The HI VOLTS
light does not come on, and the
measured voltage at the EBus is still only 12.8V.
Remove the Dimmer fuse, install the Encoder fuse (again on MAIN Bus) and
indicated voltage is 2.3V. Measured
at Ebus is still 12.8V.
Remove encoder fuse, install Low voltage Warn fuse, volt/amp gauge indicates
0V. Measure 12.8V still.
So:
Is the diode working correctly by allowing voltage to leak to MAIN bus
when on EBus Feed switch is on?
Any ideas on why this volt/amps gauge reads odd in some cases?
I have contacted E.I. and they state to check the wiring. Done. Obviously
the first step. They also said that "if there
is not bus voltage on the shunt you may not get a correct rading on either
volts or amps position."
Besides this all instruments/indictors/lights work correctly. When the
MASTER is On the volt/amp also works
correctly.
Thanks
Steve Hurlbut
RV7A
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jebrick(at)comcast.net
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| Posted: Thu Mar 23, 2006 11:43 am Post subject: Endurance Bus Voltage Measurement |
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Pay close attention to what EI said... "if there
is not bus voltage on the shunt you may not get a correct reading on either
volts or amps position."
I have the Z11 architecture and had to install a second shunt in the wire
from the ebus switch to the ebus. And then a relay to switch between shunts
when ebus switch is turned on.
Jb
RV-4 N474JB.
--
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Sun Mar 26, 2006 6:49 am Post subject: Re: Endurance Bus Voltage Measurement |
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I ditto what JB says.
I also want to add that poking around with a mulimeter and trying to figure out why there is voltage where you think there should not be, can be frustrating, unnecessary and lead to Analysis-Paralysis.
All electronic circuits and their parts can be considered to have tiny add-on phantoms. Every straight wire is a resistor, inductor, and capacitor plate, too. Every diode has some leakage. All insulators have some conductivity. Young electronic engineers have posters on their walls that remind them that "Ohm's Law is Only a Crude Approximation".
So asking the question is the right thing to do; but even simple things can get REAL complicated when one examines them too closely.
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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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