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Wonky Ammeter Redux

 
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kmjone2(at)comcast.net
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PostPosted: Mon May 11, 2009 6:25 pm    Post subject: Wonky Ammeter Redux Reply with quote
Hello Folks,

I have a problem that is very similar to the Aeroelectric Connection issue of the same subject from 2001. I've got a Vans -40,0+40 ammeter (load meter) connected to a 40mV shunt wired exactly (minus the fuselinks) as Figure Z-13 in the Connection. I also have a 10mV shunt wired to read the aux SD-8 alternator loads. The signal wires from the two shunts are controlled by a switch on the panel. Main is wired to show negative, aux is positive ammeter deflection. The following is my scenario:

1. Ground operation with engine off; power supplied to main alternator feed through a radio shack 13.8V 3A supply.
2. Ammeter power is on the E-Bus, with alternate feed switch off.
3. Power supply is providing ~3A and I measure 3.8mV across the shunt. Shunt voltage to ground is 13.08V.
4. Instrument reads ~3.5mV at the sense wire connections
5. Instrument power voltage is ~12.2 volts
6. Ammeter shows full-scale discharge (negative). If I turn power supply off, this doesn't change???

If I switch on the E-Bus alternate feed, the ammeter returns to zero. Instrument voltage increases to 12.6V.

If I power the alternate alternator feed, ammeter shows slight positive deflection, but nothing near the 35% deflection expected.

How robust are the Vans ammeters and should I invest in a new one or re-wire the system? Why would opening the E-Bus alternate path cause a change in ammeter reading?

Many thanks.

KJ
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dennis.glaeser(at)eds.com
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PostPosted: Thu May 14, 2009 9:52 am    Post subject: Wonky Ammeter Redux Reply with quote
Kevin,

I'm confused about how you've got the ammeter wired to read both
alternators, especially your comment that one is wired to show pos, the
other neg. If you could provide a diagram of the shunts, switch, and
ammeter, it would help (me at least). My suspicion is that this is
where the problem may lie.

Dennis Glaeser
--------------------------------------------------
From: Kevin Jones
Hello Folks,

I have a problem that is very similar to the Aeroelectric Connection
issue of the same subject from 2001. I've got a Vans -40,0+40 ammeter
(load meter) connected to a 40mV shunt wired exactly (minus the
fuselinks) as Figure Z-13 in the Connection. I also have a 10mV shunt
wired to read the aux SD-8 alternator loads. The signal wires from the
two shunts are controlled by a switch on the panel. Main is wired to
show negative, aux is positive ammeter deflection. The following is my
scenario:

1. Ground operation with engine off; power supplied to main alternator
feed through a radio shack 13.8V 3A supply.
2. Ammeter power is on the E-Bus, with alternate feed switch off.
3. Power supply is providing ~3A and I measure 3.8mV across the shunt.
Shunt voltage to ground is 13.08V.
4. Instrument reads ~3.5mV at the sense wire connections
5. Instrument power voltage is ~12.2 volts
6. Ammeter shows full-scale discharge (negative). If I turn power
supply off, this doesn't change???

If I switch on the E-Bus alternate feed, the ammeter returns to zero.
Instrument voltage increases to 12.6V.

If I power the alternate alternator feed, ammeter shows slight positive
deflection, but nothing near the 35% deflection expected.

How robust are the Vans ammeters and should I invest in a new one or
re-wire the system? Why would opening the E-Bus alternate path cause a
change in ammeter reading?

Many thanks.

KJ

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kmjone2(at)comcast.net
Guest
PostPosted: Fri May 15, 2009 5:55 am    Post subject: Wonky Ammeter Redux Reply with quote
Hello Dennis,

Each shunt is connected to a double pole (2-5) switch (see attached). I
select the source for the display to read only one at a time. I swapped the
leads across one (main alternator) of the shunts to get it to read negative.
I'll stick '5' and '10' numbers on the face of the ammeter for the aux
alternator indicatioin.

I'll check that the output equals the voltage drop across each shunt, but it
should be pretty straight forward. Your thoughts?

KJ

---

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