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tinnemaha(at)hotmail.com
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 Posted: Thu May 10, 2007 6:09 am Post subject: Battery Capacity Check |
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Bob et al,
I have about 50 hours now on my Lyc O-235 powered ship with Z-11
Architecture (were it not for your help, the airplane would not be flying!)
As my electrical needs are very light, my only alternator is a vacuum pump
pad driven 20 amp.
Recently, while on an extended day VFR trip, I did a load shed/capacity
check as suggested below. Felt good to know real condition results.
However, when I turned the alternator back on for re-charge, the CHT went
way into the red and, after about 20 minutes of charging, the 30 amp fuse
protecting the AWG 10 'B' lead blew, incapacitating the alternator. The
rest of the flight was uneventful, and, after replacing the fuse, everything
functions normally.
One source suggested I replace the 30 amp fuse with a 40 amp one & only due
capacity checks on the ground. Do you have any suggestions, comments or
recommendations?
Grant
Bob,
| Quote: |
Where can I get info on how to do a Cap-Check? What equipment is
required?
I realize this is pretty basic stuff, but I am clueless.
Charlie Brame
RV-6A N11CB
San Antonio
|
The simplest way is to take the time on some long VFR
day flight to put your system into the endurance mode
(turn alternator off and load shed) and see how long
it takes for your battery to get down to 10.5 volts.
This measures the time your battery is capable of
supporting the ship's most useful endurance systems.
Turn the alternator back on and it should recharge the
battery to mostly full in the next 30 minutes or so.
The preferred way is to use test equipment like:
http://westmountainradio.com/CBA_ham.htm
or
http://www.aeroelectric.com/articles/battest.pdf
or install our soon to be released in-situ battery
cap checker.
The point is that while everyone would like to
BELIEVE that their battery is sitting there ready
willing and able to get them comfortably on the ground,
the vast majority of batteries flying as you read
these words would probably fall short of the pilot's
fondest wishes should the alternator crap.
Goto the archives search engine at:
http://www.matronics.com/archives/
Select AeroElectric and then search for
"duration of fuel"
There a rich history of discussion on the value in
KNOWING what your battery is capable of before
you launch.
Bob . . .
_________________________________________________________________
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nuckollsr(at)cox.net
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| Posted: Thu May 10, 2007 8:23 pm Post subject: Battery Capacity Check |
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At 07:07 AM 5/10/2007 -0700, you wrote:
| Quote: |
Bob et al,
I have about 50 hours now on my Lyc O-235 powered ship with Z-11
Architecture (were it not for your help, the airplane would not be flying!)
As my electrical needs are very light, my only alternator is a vacuum pump
pad driven 20 amp.
Recently, while on an extended day VFR trip, I did a load shed/capacity
check as suggested below. Felt good to know real condition results.
However, when I turned the alternator back on for re-charge, the CHT went
way into the red and, after about 20 minutes of charging, the 30 amp fuse
protecting the AWG 10 'B' lead blew, incapacitating the alternator. The
rest of the flight was uneventful, and, after replacing the fuse,
everything functions normally.
One source suggested I replace the 30 amp fuse with a 40 amp one & only
due capacity checks on the ground. Do you have any suggestions, comments
or recommendations?
|
Without a doubt, recharging the battery with a cruise
RPM alternator produces a max-effort recharge event . . .
which shouldn't be a big deal but the practice will
produce a short term (15 minutes or so) exercise of
the alternator. What size alternator do you have? Recall
that the b-lead fuse needs to be 20% or so LARGER than
the alternator's rated output to accommodate exactly
this same scenario . . . Had a Cherokee 140 nuisance
trip the 60A b-lead breaker at the outset of a trip
some years ago after we jump started the airplane
due to master switch being left on.
Obviously, the least stressful way to do it is
on the ground with test equipment. But at the same
time, the in-flight test is a proving ground for
whether or not all the design goals have been met.
You've discovered that your b-lead fuse is too small.
Bob . . .
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dave(at)abrahamson.net
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| Posted: Fri May 11, 2007 2:54 am Post subject: Battery Capacity Check |
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How about the CHT going in the red? Would the alternator in its "max
effort recharge event" make the engine work that much harder, or was
there some sort of momentary sensor problem? Grant, did
power/mixture settings, environmental conditions, flight attitude
change during the recharging cycle?
David
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tinnemaha(at)hotmail.com
Guest
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| Posted: Fri May 11, 2007 6:20 am Post subject: Battery Capacity Check |
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At 07:07 AM 5/10/2007 -0700, you wrote:
| Quote: |
Bob et al,
I have about 50 hours now on my Lyc O-235 powered ship with Z-11
Architecture (were it not for your help, the airplane would not be flying!)
As my electrical needs are very light, my only alternator is a vacuum pump
pad driven 20 amp.
Recently, while on an extended day VFR trip, I did a load shed/capacity
check as suggested below. Felt good to know real condition results.
However, when I turned the alternator back on for re-charge, the CHT went
way into the red and, after about 20 minutes of charging, the 30 amp fuse
protecting the AWG 10 'B' lead blew, incapacitating the alternator. The
rest of the flight was uneventful, and, after replacing the fuse,
everything functions normally.
One source suggested I replace the 30 amp fuse with a 40 amp one & only due
capacity checks on the ground. Do you have any suggestions, comments or
recommendations?
|
Without a doubt, recharging the battery with a cruise
RPM alternator produces a max-effort recharge event . . .
which shouldn't be a big deal but the practice will
produce a short term (15 minutes or so) exercise of
the alternator. What size alternator do you have? Recall
that the b-lead fuse needs to be 20% or so LARGER than
the alternator's rated output to accommodate exactly
this same scenario . . . Had a Cherokee 140 nuisance
trip the 60A b-lead breaker at the outset of a trip
some years ago after we jump started the airplane
due to master switch being left on.
Obviously, the least stressful way to do it is
on the ground with test equipment. But at the same
time, the in-flight test is a proving ground for
whether or not all the design goals have been met.
You've discovered that your b-lead fuse is too small.
Bob . . .
The alternator is an SD-20 (i.e. 20 amp), so I guess it is a little
under-rated if it blew a 30 amp fuse, eh(?)........I guess that's really a
good thing though.
I feel dumb asking, but when I upgrade the b-lead fuse (presumably to 40
amps) will I also need to install a larger b-lead (existing is AWG 10)?
Another way of phrasing this question, would be: 'Is it inadvisable to
exceed the rated current capacity of AWG 10 wire (30 amps) if that will only
be for a short time (i.e. 15 minutes or so)?'
Thanks again,
Grant
_________________________________________________________________
Now you can see trouble…before he arrives
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rjquillin(at)gmail.com
Guest
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| Posted: Sun May 13, 2007 6:38 pm Post subject: Battery Capacity Check |
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At 05:11 5/13/2007, you wrote:
| Quote: |
Your B&C alternator delivers 12V x 60A = 720W of electricity at
maximum rating. Assuming (big assumption) that the alternator is
about 75% efficient, that would be about 1KW or 1.3 HP of energy
taken from the engines output. You can apply the same formula to the
pump-pad driven version.
Rob
|
Good stuff Rob, you beat me to it.
For those not wanting to do the math, 746 watts equals 1 HP.
I might quibble that the B&C, or any other charging device, actually
delivers closer to 14 volts and for a 60A output is closer to 840W
output, but that's a minor nit.
What all this talk did was finally prod me into doing a load and
endurance test of a Concorde RG-35AXC, new in October 2006. From
calculations and actual measurements we've determined our "normal"
load is about 37 amps, and after load shedding to "essential"
equipment it drops to ~11 or 12 amps. All the essential equipment
installed is rated to 10.0 volts minimum.
The first test was per the ICAW, as nearly as I could replicate
without a constant current load.
The second test assumed an alternator failure at time zero with a
fully charged battery. We have a JPI EDM-800 installed with the bus
voltage alarm set point at 12.0 volts and tested it will annunciate
at that voltage. At 20 minutes (+/- one minute) into the test we
reached 12.0 volts and shed to essential at ~12.5 amps. Again, not
having a constant current load, adjustments were necessiated during
the test. However this time they were to maintain constant load
power, as newer avionics will increase their current draw with
decreasing supply voltage. Here I've tried to maintain ~140 to 150
watts. Note the adjustments at 1:00, 2:00, 2:30 and 2:45 into the test.
It was a pleasant surprise to find we have better than two hours endurance!
That battery delivered over 2.5kW/Hr of power.
Pics of the test setup and raw data upon request.
Ron Q.
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| Description: |
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Download |
| Filename: |
RG-35AXC_Load_Test.pdf |
| Filesize: |
13.52 KB |
| Downloaded: |
300 Time(s) |
| Description: |
|
Download |
| Filename: |
RG-35AXC_Endurance_Test.pdf |
| Filesize: |
17.3 KB |
| Downloaded: |
142 Time(s) |
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nuckollsr(at)cox.net
Guest
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| Posted: Mon May 14, 2007 8:06 pm Post subject: Battery Capacity Check |
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At 07:33 PM 5/13/2007 -0700, you wrote:
| Quote: | At 05:11 5/13/2007, you wrote:
>
>
>Your B&C alternator delivers 12V x 60A = 720W of electricity at maximum
>rating. Assuming (big assumption) that the alternator is about 75%
>efficient, that would be about 1KW or 1.3 HP of energy taken from the
>engines output. You can apply the same formula to the pump-pad driven version.
>
>Rob
Good stuff Rob, you beat me to it.
For those not wanting to do the math, 746 watts equals 1 HP.
I might quibble that the B&C, or any other charging device, actually
delivers closer to 14 volts and for a 60A output is closer to 840W output,
but that's a minor nit.
What all this talk did was finally prod me into doing a load and endurance
test of a Concorde RG-35AXC, new in October 2006. From calculations and
actual measurements we've determined our "normal" load is about 37 amps,
and after load shedding to "essential" equipment it drops to ~11 or 12
amps. All the essential equipment installed is rated to 10.0 volts minimum.
The first test was per the ICAW, as nearly as I could replicate without a
constant current load.
The second test assumed an alternator failure at time zero with a fully
charged battery. We have a JPI EDM-800 installed with the bus voltage
alarm set point at 12.0 volts and tested it will annunciate at that
voltage. At 20 minutes (+/- one minute) into the test we reached 12.0
volts and shed to essential at ~12.5 amps. Again, not having a constant
current load, adjustments were necessiated during the test. However this
time they were to maintain constant load power, as newer avionics will
increase their current draw with decreasing supply voltage. Here I've
tried to maintain ~140 to 150 watts. Note the adjustments at 1:00, 2:00,
2:30 and 2:45 into the test.
It was a pleasant surprise to find we have better than two hours endurance!
That battery delivered over 2.5kW/Hr of power.
Pics of the test setup and raw data upon request.
Ron Q.
|
GOOD WORK! A very learned gentleman once noted . . .
"When you can measure what you are speaking about
and express it in numbers, you know something
about it." Lord William Thomson Kelvin (1824-1907)
See:
http://sse.jpl.nasa.gov/scitech/display.cfm?ST_ID=330
You now have a benchmark by which you can craft
your Plan-B ritual for dealing with an alternator-out
situation . . . assuming of course that you've also
initated a plan for tracking the battery's abilty
to support Plan-B.
Thanks for sharing this with us . . .
Bob . . .
----------------------------------------
( "Physics is like sex: sure, it may )
( give some practical results, but )
( that's not why we do it." )
( )
( Richard P. Feynman )
----------------------------------------
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