Today's Message Index:
----------------------
1. 05:51 AM - Dual alternators (dj_theis)
2. 09:29 AM - Is there a switch configuration that will do this? (David Carter)
3. 10:22 AM - Re: Dual alternators (Robert L. Nuckolls, III)
4. 02:36 PM - Re: Is there a switch configuration that will do this? (Robert L. Nuckolls, III)
5. 02:59 PM - Re: Is there a switch configuration that will do this? (David Carter)
6. 03:01 PM - Re: Dual alternators (Brian Phillips)
7. 06:34 PM - Re: Dual alternators (Robert L. Nuckolls, III)
8. 06:58 PM - Re: Dual alternators (gliderjohn@yahoo.com)
9. 07:33 PM - Re: Dual alternators (Brian Phillips)
Message 1
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| Subject: | Dual alternators |
I have a somewhat academic question regarding design and operation of a dual alternator
system. Ive imagined, but never tested, that running two alternators
that are feeding a single battery bus would be dominated by current from one
of the alternators.
My reasoning is that regardless of how closely the charge systems are matched,
small variations would result in a slightly higher output voltage on one of them.
This would then result in an even lower output from the lower voltage output
charge system, which would reduce its current contribution.
If the above assumptions are accurate, how would it change if the two alternators
shared a single regulator? (Im not advocating this arrangement)
Would the result change If the two alternators were PMA units, mechanically tied
together and producing a sin wave in phase.
WRT the dual PMA arrangement, Bob had advocated a center tap to ground with a tie
point between the two PMA stators. This arrangement (I believe) separates
the current load exactly in half between the two sides.
One final question Ive wondered about. How do twin engine planes with two alternators
manage (my assumed) tendency for two alternators in parallel quickly relying
on the larger voltage out unit for most of the current?
Dan Theis.
--------
Scratch building Sonex #1362
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=502409#502409
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| Subject: | Is there a switch configuration that will do this? |
I'd like to have a single switch control both my taxi lights & landing
lights. Sounds simple enough, right? Here's the catch. I want to control
the taxi lights directly from this switch by making a connection to +12v.
The landing lights, however, will be controlled through the Garmin GAD 27
electrical controller "magic box" so that it can provide airspeed-based
wig-wag. The GAD 27 light control switch input is active-low.
How I'd like it to work:
1. Switch down - both lights off
2. Middle position - +12v supplied to the taxi lights.
3. Top position - taxi lights no longer connected to +12v, GAD 27 light
switch input connected to ground.
I know I can do this with a relay, but I'd rather avoid adding an
additional failure point. It's not the end of the world if I use
separate switches for these functions, but I'd prefer they are combined on
one switch.
Thanks,
David
---
David Carter
david@carter.net
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| Subject: | Re: Dual alternators |
I've imagined, but never tested, that running two alternators that
are feeding a single battery bus would be dominated by current from
one of the alternators.
My reasoning is that regardless of how closely the charge systems
are matched, small variations would result in a slightly higher
output voltage on one of them. This would then result in an even
lower output from the lower voltage output charge system,
which would reduce its current contribution.
Yes, until system loads exceeded the capacity
of the alternator with the higher set-point. The
bus voltage sags allowing the lower set-point
alternator to wake up and begin to support the
load.
This is what happens with a B&C standby alternator
system. #2 alternator is set to some lower-than-nominal
regulation voltage. Should the #1 alternator quit,
voltage sags and #2 wakes up. Similarly, should the
#1 alternator suffer an open winding with subsequent
loss of capacity, the voltage might sag and again,
#2 steps in to take up the slack.
In both cases, #1 alternator is running maxed out
whether by reason of total system loads =or= loss
of capacity.
If the above assumptions are accurate, how would it change if
the two alternators shared a single regulator? (I=99m not advocating
this arrangement)
Cessna 336/337 Models do just that. Beech Barons too.
There is a switch for bringing a second regulator into
service should the first one fail. This philosophy
does produce a system whereby the two alternator
ammeters track each other fairly closely . . . in
my not so humble opinion, a totally misguided practice
to keep pilot's 'happy'.
There is no practical NEED for balancing the
loads on two alternators assuming (1) either
alternator can carry 100% of ships loads
with (2) demonstrated adequacy of cooling.
This shade-tree 'paralleling' scheme creates
single points of failure for both alternators.
How this got past in-house DERs is a mystery
to me . . . how the FAA bought it is a . . .
well . . . I won't go there.
Would the result change If the two alternators were PMA units,
mechanically tied together and producing a sin wave 'in-phase.'
The engines cannot be synchronized that tightly.
One final question I've wondered about. How do twin engine planes
with two alternators manage (my assumed) tendency for two alternators
in parallel quickly relying on the larger voltage out unit for most
of the current?
They parallel fields on a single regulator.
I designed a true paralleling regulator proposal for Cessna on
the 303 Crusader program thinking that there was a HUGH after market
opportunity to put the system on new and fielded Barons and Skymasters.
I don't know how the Cessna West was wiring their airplanes.
In any case, Cessna East didn't bite on the idea so I
was never funded to pursue the design. Twin Generators on
earlier Cessna and Beech models WERE fitted with paralleling
regulators which DID NOT compromise independence of the
two system. Turbine twins have always enjoyed that design
philosophy.
Here is a sketch on a generator paralleling system
on a Beech Model 18 I think . . . but typical of
all dual generator twins of the era.
http://aeroelectric.com/Pictures/Schematics/Parallel_Aircraft_Generators.jpg
This design uses voltage drop in the generator's
compensation windings as a current shunt. Any difference
in those two voltages biases the voltage sense windings
to depress excitation to the generator with the higher
load while elevating excitation on the lighter loaded
machine . . . pretty slick.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 4
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| Subject: | Re: Is there a switch configuration that will do |
this?
At 11:28 AM 6/17/2021, you wrote:
>I'd like to have a single switch control both my
>taxi lights & landing lights. Sounds simple
>enough, right? Here's the catch. I want to
>control the taxi lights directly from this
>switch by making a connection to=C2 +12v. The
>landing lights, however, will be controlled
>through the Garmin GAD 27 electrical=C2 controller
>"magic box" so that it can provide
>airspeed-based wig-wag. The GAD 27 light control switch input is
active-low.=C2
>
>How I'd like it to work:
>1. Switch down - both lights off
>2. Middle position -=C2 +12v supplied to the taxi lights.=C2
>3. Top position - taxi lights no longer
>connected to=C2 +12v, GAD 27 light switch input connected to ground.=C2
>
>I know=C2 I can do this with a relay, but I'd
>rather=C2 avoid adding=C2 an additional=C2 failure
>point. It's not the end of the world if I use
>separate=C2 switches for these functions, but I'd
>prefer they are combined on one switch.=C2
There MIGHT be a simple way to do this but it
depends on the 'pull down' current of the electrical
controller. Is there a spec for that device that speaks
to parameters of this input?
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 5
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| Subject: | Re: Is there a switch configuration that will do this? |
>> There MIGHT be a simple way to do this but it
>> depends on the 'pull down' current of the electrical
>> controller. Is there a spec for that device that speaks
>> to parameters of this input?
Here's what I was able to find in the installation manual: (top of page
26-8, or page 342 in Acrobat Reader)
https://static.garmin.com/pumac/190-01115-01_an.pdf
These active-low discrete inputs conform to the following specification:
Low: Vin < 3.5 VDC, or Rin < 375 =CE=A9 (input active)
High: Vin > 8 VDC, or Rin> 100k =CE=A9 (input inactive)
---
David Carter
david@carter.net
On Thu, Jun 17, 2021 at 5:37 PM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 11:28 AM 6/17/2021, you wrote:
>
> I'd like to have a single switch control both my taxi lights & landing
> lights. Sounds simple enough, right? Here's the catch. I want to control
> the taxi lights directly from this switch by making a connection to=C3=82
> The landing lights, however, will be controlled through the Garmin GAD 27
> electrical=C3=82 controller "magic box" so that it can provide airspeed-b
ased
> wig-wag. The GAD 27 light control switch input is active-low.=C3=82
>
> How I'd like it to work:
> 1. Switch down - both lights off
> 2. Middle position -=C3=82 +12v supplied to the taxi lights.=C3=82
> 3. Top position - taxi lights no longer connected to=C3=82 +12v, GAD 27 l
ight
> switch input connected to ground.=C3=82
>
> I know=C3=82 I can do this with a relay, but I'd rather=C3=82 avoid addin
g=C3=82 an
> additional=C3=82 failure point. It's not the end of the world if I use se
parate=C3=82
> switches for these functions, but I'd prefer they are combined on one
> switch.=C3=82
>
>
> There MIGHT be a simple way to do this but it
> depends on the 'pull down' current of the electrical
> controller. Is there a spec for that device that speaks
> to parameters of this input?
>
>
> Bob . . .
>
> Un impeachable logic: George Carlin asked, "If black boxes
> survive crashes, why don't they make the whole airplane
> out of that stuff?"
>
Message 6
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| Subject: | Re: Dual alternators |
Bob, in the Beech paralleling schematic below, what is the symbol in the
reg comprising the 6 parallel lines with the arrow through it, in series
with the shunt field?
Brian Phillips
On 18/06/2021 3:21 am, Robert L. Nuckolls, III wrote:
> I've imagined, but never tested, that running two alternators that
> are feeding a single battery bus would be dominated by current from
> one of the alternators.
>
> My reasoning is that regardless of how closely the charge systems
> are matched, small variations would result in a slightly higher
> output voltage on one of them. This would then result in an even
> lower output from the lower voltage output charge system,
> which would reduce its current contribution.
>
> Yes, until system loads exceeded the capacity
> of the alternator with the higher set-point. The
> bus voltage sags allowing the lower set-point
> alternator to wake up and begin to support the
> load.
>
> This is what happens with a B&C standby alternator
> system. #2 alternator is set to some lower-than-nominal
> regulation voltage. Should the #1 alternator quit,
> voltage sags and #2 wakes up. Similarly, should the
> #1 alternator suffer an open winding with subsequent
> loss of capacity, the voltage might sag and again,
> #2 steps in to take up the slack.
>
> In both cases, #1 alternator is running maxed out
> whether by reason of total system loads =or= loss
> of capacity.
>
> If the above assumptions are accurate, how would it change if
> the two alternators shared a single regulator? (Im not advocating
> this arrangement)
>
> Cessna 336/337 Models do just that. Beech Barons too.
> There is a switch for bringing a second regulator into
> service should the first one fail. This philosophy
> does produce a system whereby the two alternator
> ammeters track each other fairly closely . . . in
> my not so humble opinion, a totally misguided practice
> to keep pilot's 'happy'.
>
> There is no practical NEED for balancing the
> loads on two alternators assuming (1) either
> alternator can carry 100% of ships loads
> with (2) demonstrated adequacy of cooling.
>
> This shade-tree 'paralleling' scheme creates
> single points of failure for both alternators.
> How this got past in-house DERs is a mystery
> to me . . . how the FAA bought it is a . . .
> well . . . I won't go there.
>
> Would the result change If the two alternators were PMA units,
> mechanically tied together and producing a sin wave 'in-phase.'
>
> The engines cannot be synchronized that tightly.
>
> One final question I've wondered about. How do twin engine planes
> with two alternators manage (my assumed) tendency for two alternators
> in parallel quickly relying on the larger voltage out unit for most
> of the current?
>
> They parallel fields on a single regulator.
>
> I designed a true paralleling regulator proposal for Cessna on
> the 303 Crusader program thinking that there was a HUGH after market
> opportunity to put the system on new and fielded Barons and
> Skymasters.
> I don't know how the Cessna West was wiring their airplanes.
>
> In any case, Cessna East didn't bite on the idea so I
> was never funded to pursue the design. Twin Generators on
> earlier Cessna and Beech models WERE fitted with paralleling
> regulators which DID NOT compromise independence of the
> two system. Turbine twins have always enjoyed that design
> philosophy.
>
> Here is a sketch on a generator paralleling system
> on a Beech Model 18 I think . . . but typical of
> all dual generator twins of the era.
>
> http://aeroelectric.com/Pictures/Schematics/Parallel_Aircraft_Generators.jpg
> <http://aeroelectric.com/Pictures/Schematics/Parallel_Aircraft_Generators.jpg>
>
>
> This design uses voltage drop in the generator's
> compensation windings as a current shunt. Any difference
> in those two voltages biases the voltage sense windings
> to depress excitation to the generator with the higher
> load while elevating excitation on the lighter loaded
> machine . . . pretty slick.
>
> Bob . . .
>
> Un impeachable logic: George Carlin asked, "If black boxes
> survive crashes, why don't they make the whole airplane
> out of that stuff?"
>
Message 7
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| Subject: | Re: Dual alternators |
At 05:00 PM 6/17/2021, you wrote:
>Bob, in the Beech paralleling schematic below, what is the symbol in
>the reg comprising the 6 parallel lines with the arrow through it,
>in series with the shunt field?
>
>Brian Phillips
That is a carbon pile, variable resistor. Simply a stack
of carbon disks whose series resistance is a function
of compression force. A very common, high current analog
for a rheostat. Here's a carbon pile regulator in the
flesh . . .
http://aeroelectric.com/Pictures/Regulators/Carbon_Pile_1a.jpg
No transistors, no modern plastics, no software.
One of many fine examples of engineering dexterity
on the part of those who did not have our box
of tinker-toys to work with.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 8
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| Subject: | Re: Dual alternators |
Also helped a generation of pilots learn the habit of checking voltmeters i
n their pre-liftoff gauges check. You only need to smell batteries boiling
as you climb into a 200=99 overcast over one time to learn. On Th
ursday, June 17, 2021, 06:45:39 PM PDT, Robert L. Nuckolls, III <nuckolls.b
ob@aeroelectric.com> wrote:
At 05:00 PM 6/17/2021, you wrote:
Bob, in the Beech parallelingschematic below, what is the symbol in the reg
comprising the 6 parallellines with the arrow through it, in series with t
he shunt field?
Brian Phillips
=C2- That is a carbon pile, variable resistor. Simply a stack
=C2- of carbon disks whose series resistance is a function
=C2- of compression force. A very common, high current analog
=C2- for a rheostat. Here's a carbon pile regulator in the
=C2- flesh . . .
http://aeroelectric.com/Pictures/Regulators/Carbon_Pile_1a.jpg
=C2- No transistors, no modern plastics, no software.
=C2- One of many fine examples of engineering dexterity
=C2- on the part of those who did not have our box
=C2- of tinker-toys to work with.
=C2- Bob . . .
=C2- Un impeachable logic: George Carlin asked, "If blackboxes
=C2- survive crashes, why don't they make the whole airplane
=C2- out of that stuff?"
Message 9
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| Subject: | Re: Dual alternators |
On 18/06/2021 11:33 am, Robert L. Nuckolls, III wrote:
> At 05:00 PM 6/17/2021, you wrote:
>> Bob, in the Beech paralleling schematic below, what is the symbol in
>> the reg comprising the 6 parallel lines with the arrow through it, in
>> series with the shunt field?
>>
>> Brian Phillips
>
> That is a carbon pile, variable resistor. Simply a stack
> of carbon disks whose series resistance is a function
> of compression force. A very common, high current analog
> for a rheostat. Here's a carbon pile regulator in the
> flesh . . .
>
> http://aeroelectric.com/Pictures/Regulators/Carbon_Pile_1a.jpg
> <http://aeroelectric.com/Pictures/Regulators/Carbon_Pile_1a.jpg>
>
> No transistors, no modern plastics, no software.
> One of many fine examples of engineering dexterity
> on the part of those who did not have our box
> of tinker-toys to work with.
>
>
> Bob . . .
>
> Un impeachable logic: George Carlin asked, "If black boxes
> survive crashes, why don't they make the whole airplane
> out of that stuff?"
>
Thanks Bob, now that is amazing engineering, zero PN junctions, must be
near bulletproof.
Cheers,
Brian.
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