Today's Message Index:
----------------------
1. 08:01 AM - Maintenace Charger (Mark Richards)
2. 08:37 AM - Re: RV-6A load analysis/architecture (Robert L. Nuckolls, III)
3. 08:46 AM - Re: RV-6A load analysis/architecture (Robert L. Nuckolls, III)
4. 08:53 AM - Re: It's the little things (Robert L. Nuckolls, III)
5. 10:20 AM - Re: Maintenace Charger (Robert L. Nuckolls, III)
6. 01:22 PM - Alternator Wye - what voltage? (Paul Millner)
7. 01:59 PM - Re: Power Supply Connections (William Curtis)
8. 03:20 PM - Re: Re: Power Supply Connections (ROGER & JEAN CURTIS)
9. 04:48 PM - Re: Alternator Wye - what voltage? (Robert L. Nuckolls, III)
10. 09:13 PM - Re: Maintenace Charger (Mark Richards)
Message 1
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| Subject: | Maintenace Charger |
Hi Bob;
Little off topic but I was wondering if you could give me a specific
recommendation for a maintenance charger for my RV batteries. I have 6
U2400's also called US145xc's. These are 6volt deep cycle wet cells
rated at 251 amps. At 12 volts this gives about 750amps for the system.
Anything out there that you think would work well.
Thanks
Mark
Message 2
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| Subject: | Re: RV-6A load analysis/architecture |
At 12:03 AM 8/28/2011, you wrote:
Vern & Ken, thanks for the input. I figured 10A or so ought to cover
charging, but after a cold day start that battery might be pretty
taxed. I did forget to consider the lower RPM during taxi and such.
Most belt driven alternators on a Lyc are running
pretty fast . . . even at idle/taxi speeds. They'll
produce a considerable percentage of rated output.
Legacy alternator/generator sizing in TC aircraft
calls for retaining 25% of rated output for battery
charging. There's no particular driver for having
recharge take place before takeoff . . . only that
the battery be topped off in the first hour to 90
minutes of operation.
Alternator: here's where I don't understand the present installation.
The present installation has an "Overhauled lightweight 35 Amp
alternator" from Mark Landoll's Electrical Service. It includes a
Transpo F7078 external regulator. The sales documentation (attached)
shows the regulator installed as attached to the alternator. But,
the as-built has the regulator installed behind the instrument panel,
separated from the alternator. The field line appears to be directly
switched. The regulation signal, as stated by the Landoll data sheet
as "the wye junction of the Ford stator is the source of the signal
for the F7078 regulator. At 1200 RPM, the stator magnitude is only 35
mV." I'm not up to snuff on my motor/generator theory, so I can't
visualize what is happening with this setup. This setup doesn't seem
to match what I see in the Aeroelectric Connection. Is this an
optimal way of doing things, or are there advantages to the ways that
Bob describes vs. this Transpo setup? Will the split between
alternator and regulator create unforeseen issues?
This is a pretty 'old' example of alternator design
and implementation. The first alternators we installed
on Cessna aircraft had an "S" or stator terminal which
was a tap on the center of a 'wye wound' stator. This
was used to sense whether or not the engine was running
and operate a field disconnect relay.
http://aeroelectric.com/Pictures/Regulators/Legacy_EM_Regulator_(Ford).pdf
In automobiles, this feature disconnected the alternator
field supply when the engine wasn't running thus preventing
battery depletion in a parked car. Since airplanes had alternator
and battery switches, this feature was not needed. The field
relay was controlled directly through the battery/master switch.
Later, the solid state ov module was added in series
with the relay coil lead
http://aeroelectric.com/Pictures/Schematics/Cessna_OVModule.jpg
Even if we kept the alternator, I would change the panel mounted
B-lead breaker protection to ANL style near the battery.
That works.
We might up the size of the alternator a bit and go with simple
external regulation (generic Ford regulator or such). So, my
questions about operation and potential for problems is mostly to
satisfy my desire to learn.
That would be okay too. The Transpo regulator
is probably adequate to the task too but without
knowing more details on how it uses/needs the
'stator' connection, I can advise that going to
a generic 'Ford' regulator is a sure bed.
Second question: We will have a crowbar circuit for OVP, but does
anyone see a problem with relying on the GRT EIS4000 to supply the
"low voltage" warning? The EIS has a low-RPM maskable low voltage alert.
Yes, you want ov protection to be automatic and
FAST . . . MILLISECOND fast.
Bob . . .
Message 3
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| Subject: | Re: RV-6A load analysis/architecture |
At 12:38 PM 8/28/2011, you wrote:
There is nothing fundamentally wrong with any of
this. The recommendation to switch the output of
the voltage regulator eliminates a lot of
problems with switching the input/sense side of
some regulators (Bob has a lot of documentation on this problem).
The Wye center point is just like the neutral in
your house wiring... it should always be close to
ground potential except when something bad
happens. My guess is the regulator can sense
this (similar to a ground fault detector). Not
sure what it does when something goes wrong.
Not exactly. The 'wye-center-tap' on an alternator
will output considerable current . . . at about
1/2 system voltage. It's used for (1) controlling
field supply disconnect relays in some designs
and/or (2) producing a residual output for getting
an alternator to self-excite. This terminal was often
labeled "N" on some alternators which led individuals to
believe that it was some sort of ground or low-side
supply.
As for the crowbar... yes! Its very simple
and cheap insurance. Dont depend on an
audible warning. The OVP protection is much faster.
The only issue is keeping the alternator cool
when loaded to full capacity at low airspeeds and
taxiing. You should be fine if you pay attention
to cooling, but theres not a lot of
margin. If you can, my suggestion of attaching a
temperature probe to the alternator may
helpprogram thhe GRT EIS to provide a warning
when exceeding about 150C on the diodes so you
can do some load shedding. This applies to any rating of alternator.
The only alternators that get into cooling trouble
in flight are those not properly integrated into
the system on day-one. New installations on TC
aircraft are tested at max running load during
best angle of climb with data corrected for hot-
day conditions. This is how some alternators get
blast tubes and others do not. Alternator failure
due to overheating on an alternator bolted to the
front of a Lycoming is very rare and is traceable
to some poor choices.
If in doubt, do put a thermocouple on the diode
heat sink and slip another into the stator winding
for exploring the operation during the 40 hr flyoff.
But that's a lot of effort that's more likely to
be intellectually satisfying than practical.
Bob . . .
Message 4
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| Subject: | Re: It's the little things |
My unspoken assumption had been that if the unit received comm, it
must have comm power, right? Well, when nothing else pans out,
you'll try anything. I whipped out my little voltmeter and tested
the comm power pins. 3 volts?? Is that possible? No idea, but when
I touched the Main power pins, I got the full 12 volts. I checked
out the fuses and voila! My comm power fuse had blown. As I was
saying about dopes and electronics...
I'm not sure how to explain the 3 volts I did get -- I thought fuses
were all-or-nothing affairs, but perhaps not. Anyway, I popped in a
new fuse and presto, I get "loud and clear" reports from everybody I
talk to. SO.. Maybe the "Comm" power pins need to be relabeled
"Transmit" power. And there you have it -- The $100 fuse.
The 3-volts you were seeing was probably coming OUT
of the radio as opposed to 'sneaking' across an
open fuse. Garmin has long been fond of the separate
input power for the transmitter of some models. On
some models, this input would like to have 28 volts
supplied even if the rest of the radio is running
on 14 volts.
Be sure and check for details on your particular
radio. You may want to add a 14/28v up-converter to
accommodate the transmitter. It will give you a lot
stronger output.
http://www.kenneke.com/avionics.html
Emacs!
Bob . . .
Message 5
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| Subject: | Re: Maintenace Charger |
At 09:57 AM 8/29/2011, you wrote:
>Hi Bob;
>
>Little off topic but I was wondering if you could give me a specific
>recommendation for a maintenance charger for my RV batteries. I
>have 6 U2400's also called US145xc's. These are 6volt deep cycle
>wet cells rated at 251 amps. At 12 volts this gives about 750amps
>for the system. Anything out there that you think would work well.
If you're simply wanting to maintain batteries
that are topped off at the time the RV is parked,
just about anything would work. But if you want
to top-off less-than-full batteries, then something
a bit more robust would be called for.
Anything with Schumacher's name on it would be a
good bet. Here's a 12A, processor controlled charger/
maintainer you can probably pick up at Walmart
for $50 or so.
Emacs!
Bob . . .
Message 6
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| Subject: | Alternator Wye - what voltage? |
>> The Wye center point is just like the neutral in your house
wiring... it should always be close to ground potential except when
something bad happens.
The wye is close to neutral in a three-phase AC generation or motor
situation. That's NOT true in our airplanes, where the phases are
rectified to DC, since each phase-to-phase pair alternates between being
ground on one end and bus voltage on the other end. In that case, the
wye floats at about half of bus voltage, but of course is alternating
current, not direct.
In fact, Bob N's former employer, Beechcraft, took advantage of that on
the 12 volt Bonanzas... they attached a six volt *AC* relay between the
wye and aircraft ground. When the alternator was putting out power,
that relay would close, turning off the "ALTERNATOR FAIL" light. If for
whatever reason the alternator quit (open field circuit, broken belt,
whatever) then the wye would float near ground, the AC relay would open,
and the FAIL light would light. Very clever!
I've been tempted to add just such cleverness to my Cessna Cardinal
someday...
Paul
Message 7
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| Subject: | Re: Power Supply Connections |
Below is a link to my home 12 volt electrical system. Hyperlinks are
included to all the components. All my various electronics components
(cable modem, LAN switch, router, telephones, NAS, 12 volt CFL lights, etc)
attach to this system. Additional, I tap into it to charge/run the
electrical system on my "still at the house" RV-10.
http://wcurtis.nerv10.com/house/dc/12volt.pdf
It served me well this past weekend as Irene came through and power was out
for about 12 hours. Before shedding load, not including lights, my devices
consume about 6 amps. The single Sears U1 battery lasted about 4 hours
before I turned on the generator.
I put this system in due to frequent power failures (brown-outs and
black-outs) in my area. It is cool watching all the WiFi SSIDs in your area
go away and yours is the only remaining. I did find out that the power
backup on the Internet service provide is only about 6-8 hours however.
--
William
N40237 - http://wcurtis.nerv10.com/
Message 8
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| Subject: | Re: Power Supply Connections |
I tap into it to charge/run the electrical system on my
"still at the house"
William
Do the Feds know you have a still at your
house?? You may get a knock at the door as soon as they find out where
you
live. =98=BA
Do not archive
Message 9
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| Subject: | Re: Alternator Wye - what voltage? |
At 03:15 PM 8/29/2011, you wrote:
>> The Wye center point is just like the neutral in your house
wiring... it should always be close to ground potential except when
something bad happens.
The wye is close to neutral in a three-phase AC generation or motor
situation. That's NOT true in our airplanes, where the phases are
rectified to DC, since each phase-to-phase pair alternates between
being ground on one end and bus voltage on the other end. In that
case, the wye floats at about half of bus voltage, but of course is
alternating current, not direct.
Actually, it is DC albeit half-wave, 3-phase
rectified which is pretty 'bumpy'.
In fact, Bob N's former employer, Beechcraft, took advantage of that
on the 12 volt Bonanzas... they attached a six volt *AC* relay
between the wye and aircraft ground. When the alternator was putting
out power, that relay would close, turning off the "ALTERNATOR FAIL"
light. If for whatever reason the alternator quit (open field
circuit, broken belt, whatever) then the wye would float near ground,
the AC relay would open, and the FAIL light would light. Very clever!
That 'relay' was in fact a little two-transistor,
plus jelly-beans dc voltage level sensor. I remember
it well. We supplied about 4 versions to Beech and
Cessna. During my early years at Electro-Mech, I was
cleaning up some drawings and got two capacitors transposed
in the bill of materials for the Cessna Wallace Plant
version. The thing still passed functional test but
behaved badly on the airplanes. Worse yet, the puppies
were potted.
Needless to say this young fellow was embarrassed to
report to the boss that we needed to do a recall on
about $30,000 worth of production and launch a
quick-turn replacement program. That was more money
than I made in a year at that time!
Fred would have been fully within 'normal' supervisory
parameters to have chewed my you-know-what down
to bed-rock. He didn't miss a beat. "Talk to production
and get a reading on the replacements . . . I'll have
sales notify Cessna and start he recall. Get back to
me with a schedule." That's about the only words we
had on the matter. I didn't need him to tell me to
revise the functional test fixture to offer a more
realistic functionality.
I always appreciated this man's focus . . . and his
class. I've had about five supervisors that I truly
revered in my life and Fred Coslett was one of them.
I've been tempted to add just such cleverness to my Cessna Cardinal someday...
I can probably dig up the schematic of the original but
an active LV warning like the AEC9005 is probably
closer to the best-we-know-how-to-do today. Better
yet, the 9024 program has stumbled back to life. The
first 5 or so devices will be offered to individuals
who can put them into flying airplanes right now. We'll
want to get some field testing of the product and the
installation instructions before listing the thing in
the catalog.
Haven't got a schedule but the software IS moving
forward again.
Bob . . .
Message 10
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| Subject: | Re: Maintenace Charger |
Bob:
Thanks for the reommendation.
Mark
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