Today's Message Index:
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1. 05:25 AM - Re: Saggy bus voltage on Cessna 182 (Robert L. Nuckolls, III)
2. 05:44 AM - Re: Saggy bus voltage on Cessna 182 (Robert L. Nuckolls, III)
3. 07:01 AM - Re: Saggy bus voltage on Cessna 182 (Alec Myers)
4. 12:05 PM - off-line for a couple days (Robert L. Nuckolls, III)
5. 11:17 PM - ANL fuses (JOHN TIPTON)
Message 1
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Subject: | Re: Saggy bus voltage on Cessna 182 |
At 02:29 PM 6/3/2016, you wrote:
>I'm going to look for a high impedance connection between the A
>terminal of the alternator and the bus: the regulator is seeing
>13.8V at A, but with the load current flowing from A to the bus the
>bus voltage is 0.6v lower, at the other end of a thick cable and 60A breaker.
Yea, that seems excessive. An easy experiment
to run is install a simple, 4AWG welding cable
jumper from alternator b-lead to the hot side
of the starter or battery contactors (I believe
your battery is up front in that a/c?). Bypass
the normal ships wiring and see what the effects
are.
Bob . . .
Message 2
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Subject: | Re: Saggy bus voltage on Cessna 182 |
At 09:30 PM 6/3/2016, you wrote:
>
>I worked through the wiring from the B lead post on the alternator.
>The wiring goes from the alternator post, to some kind of filter
>bolted to the engine side of the firewall (which doesn't appear in
>the Cessna service manual wiring diagrams) then to the 60 amp
>alternator CB, then to the bus.
b-lead filters were marginally effective
in suppressing some noises in the ADF.
The capacitors on most wiring diagrams
of that era were flagged as part of the
ADF installation kit and often did not
show on the production line as-manufactured
documents.
>The voltage on the alternator B lead post is the same 13.9V (13.8V
>with heavier load) that I see on the A terminal of the regulator.
>
>I looked at the voltage drop along the B current path: it's about
>100mV per terminal - there doesn't appear to be one connection
>that's any worse than the others.
>
>There's also about 150-200mV drop across the 60 amp CB, when the bus
>is loaded up. The terminal screw also gets hot - nearly too hot to
>touch. Is this expected? It's a thermal-type breaker but I don't
>know how warm they are intended to get, outside an overload condition.
At the current levels you're running during
ground tests, that breaker shouldn't warm up
to the touch. Those were the least expensive
breaker Cessna could put their hands on and
with all due respect, the one in your airplane
has probably delivered fair value.
If this were my airpalne, I'd do a 337 mod
to take the b-lead to the starter contactor
through an ANL60 current limiter per common,
modern practice. Dump the filter . . . even
if there IS some observable noise in your ADF,
it's unlikely to be a performance issue for
its utility.
That would reduce the number of joints and
greatly reduce the voltage drop from b-lead
to bus.
>I'm stumped on two questions:
>
>Why, although the regulator field terminal voltage is well within
>normal operating range (4-7v), the regulated voltage is low at 13.8
>to 13.9V. This is the case with two different regulators.
I'm with you. Are these 'original' electro-mechanical
regulators or an aftermarket, electronic replacement?
>Secondly why I'm losing 0.6V, distributed equally across four crimp
>terminals and a CB. I'm going to estimate the current at 20 amps,
>including LED landing and taxi lights, halogen position and beacon
>lights, strobes, pitot heat and full avionics bus, and recharging
>the battery soon after cranking. Is this to be expected?
No . . . that's a lot more than factory new.
Recall that the 'galloping ammeter' phenomenon
common to those aircraft has root cause in
the build up of resistance in the bus to regulator
"A" terminal that eventually forces a negative
resistance in the dynamics of the voltage regulator
loop. This is common on older airplanes where
voltage sense -AND- field supply current share
the same feed wire.
Many mechanics replace something . . . often
the split rocker switch . . . and the problem
goes away. The customer is momentarily satisfied
that the ammeter stops hopping around. But the
fix is temporary in that the fix reduces the loop
resistance just below the point of instability.
The problem will return. The elegant fix is to
renew every metallic joint in that loop from
bus bar to "A" terminal. THEN the problem is
held off for another 30-40 years.
I suspect your 60A breaker is demonstrating
effects of age with increased resistance that
promotes the heating you've observed.
The REAL fix is to install an after market
regulator with separate Field Supply and
Bus Sense leads.
If your old and new regulators are electro-mechanical,
there may be a case for long term storage
drift of set point in a downward direction.
I've never had occasion to study the effects
of long term storage on new old-stock components.
The real acid test would be to run the regulator
on a test stand independent of all effects
of aged wiring in the a/c. But it IS a
vexing puzzle.
Bob . . .
Message 3
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Subject: | Re: Saggy bus voltage on Cessna 182 |
Alas, Canadian airplane so no 337 type process available...
Both old and new regulators are Lamarr, solid state.
With "lights on", I used the service manual electrical loads table to calcul
ate the current draw on the alternator at close to 50amps (vice my previous e
stimate at 20): pitot heat, strobes, position lights, beacon and avionics al
l use more current than I thought.
Paul Milner kindly pointed me to the Cessna service kit to replace the 60 am
p CB, which involves shortening the bus bar so the replacement breaker will f
it. I think the approved breaker is $400 or thereabouts, so if it does need r
eplacing, does anyone know a PMA alternative?
On Jun 4, 2016, at 08:42, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric
.com> wrote:
At 09:30 PM 6/3/2016, you wrote:
>
> I worked through the wiring from the B lead post on the alternator. The wi
ring goes from the alternator post, to some kind of filter bolted to the eng
ine side of the firewall (which doesn't appear in the Cessna service manual w
iring diagrams) then to the 60 amp alternator CB, then to the bus.
b-lead filters were marginally effective
in suppressing some noises in the ADF.
The capacitors on most wiring diagrams
of that era were flagged as part of the
ADF installation kit and often did not
show on the production line as-manufactured
documents.
> The voltage on the alternator B lead post is the same 13.9V (13.8V with he
avier load) that I see on the A terminal of the regulator.
>
> I looked at the voltage drop along the B current path: it's about 100mV pe
r terminal - there doesn't appear to be one connection that's any worse than
the others.
>
> There's also about 150-200mV drop across the 60 amp CB, when the bus is lo
aded up. The terminal screw also gets hot - nearly too hot to touch. Is this
expected? It's a thermal-type breaker but I don't know how warm they are in
tended to get, outside an overload condition.
At the current levels you're running during
ground tests, that breaker shouldn't warm up
to the touch. Those were the least expensive
breaker Cessna could put their hands on and
with all due respect, the one in your airplane
has probably delivered fair value.
If this were my airpalne, I'd do a 337 mod
to take the b-lead to the starter contactor
through an ANL60 current limiter per common,
modern practice. Dump the filter . . . even
if there IS some observable noise in your ADF,
it's unlikely to be a performance issue for
its utility.
That would reduce the number of joints and
greatly reduce the voltage drop from b-lead
to bus.
> I'm stumped on two questions:
>
> Why, although the regulator field terminal voltage is well within normal o
perating range (4-7v), the regulated voltage is low at 13.8 to 13.9V. This i
s the case with two different regulators.
I'm with you. Are these 'original' electro-mechanical
regulators or an aftermarket, electronic replacement?
> Secondly why I'm losing 0.6V, distributed equally across four crimp termin
als and a CB. I'm going to estimate the current at 20 amps, including LED la
nding and taxi lights, halogen position and beacon lights, strobes, pitot he
at and full avionics bus, and recharging the battery soon after cranking. Is
this to be expected?
No . . . that's a lot more than factory new.
Recall that the 'galloping ammeter' phenomenon
common to those aircraft has root cause in
the build up of resistance in the bus to regulator
"A" terminal that eventually forces a negative
resistance in the dynamics of the voltage regulator
loop. This is common on older airplanes where
voltage sense -AND- field supply current share
the same feed wire.
Many mechanics replace something . . . often
the split rocker switch . . . and the problem
goes away. The customer is momentarily satisfied
that the ammeter stops hopping around. But the
fix is temporary in that the fix reduces the loop
resistance just below the point of instability.
The problem will return. The elegant fix is to
renew every metallic joint in that loop from
bus bar to "A" terminal. THEN the problem is
held off for another 30-40 years.
I suspect your 60A breaker is demonstrating
effects of age with increased resistance that
promotes the heating you've observed.
The REAL fix is to install an after market
regulator with separate Field Supply and
Bus Sense leads.
If your old and new regulators are electro-mechanical,
there may be a case for long term storage
drift of set point in a downward direction.
I've never had occasion to study the effects
of long term storage on new old-stock components.
The real acid test would be to run the regulator
on a test stand independent of all effects
of aged wiring in the a/c. But it IS a
vexing puzzle.
Bob . . .
Message 4
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Subject: | off-line for a couple days |
Dr. Dee and I are off to Ft. Hays, KS to do
our practicals exams. We'll be super-saturating
on EMT-stuff for the next 20 hours. Be back
on line tomorrow night.
Bob . . .
Message 5
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Are these car 'Audio' ANL fuses
https://www.amazon.co.uk/Auto-Audio-Subwoofer-Amplifier-Fuse/dp/B00CQLJEE4
suitable for our use (eg: RV9 battery feed)
John
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=456858#456858
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