Battery Replacement and Cold Cranking Amps

Great. I am certain that this level of capacity testing was not done. I
will have it done soon and let you know. Thanks.

-sami

MikeM wrote:

"Testing" the battery means making sure it is fully charged, then
discharging it using a known load current, timing how long it takes
the voltage to reach 11.5V, and then computing the capacity by
multiplying the time to reach 11.5V by the load current.

According to Gill & the FAA, your battery should be up to delivering
a load current representing all the stuff it takes to get safely on the
ground for 30 min: this should include engine instruments, fuel gauges,
electric gyros, radios, transponder and some lighting.

A guess for the essential electrical load on your aircraft would
be about 25A. To test the battery, connect a 12V/25A=0.48 Ohm,
12V*25A=300W resistor to the battery, and time how long it takes
the battery to reach 11.5V. If your battery wont hold up this
load for 30 min, then it should be replaced...

Cranking is a separate test. An automotive service-station type of
carbon-pile battery tester can be used to put a load of ~225A on
the battery for 3 or so minutes. If the battery peters out short of
3 min, then replace it.

MikeM

O. Sami Saydjari wrote:

I have a Gill G25 battery in my Piper Arrow III (PA28R-201T). I
recently had a situation where I ran out of juice after 4 attempted
starts. While I am sure that I can improve my starting technique (I
am a newbie for this particular plane), I would like to have a bit
more power in my battery, especially in very cold conditions such as
we have up here in central Wisconsin.

An A&P told me recently that I am "stuck" with my G25 battery. He
said that he tested it and that it was "fine."

Based on a recent article in "Aviation Consumer", I learned that the
G25 has only about 225 cold cranking amps. I noted that the G35S has
250 cold cranking amps.

(1) Is it true that I am stuck with a G25 battery and that NO OTHER
battery in the world can go in my plane? I find that a little hard to
believe.

(2) If there are other possibilities, can someone recommend one that
has better cold cranking amps that the G25?

Thanks in advance.

-Sami (N2057M, Piper Turbo Arrow III owner)

Often overlooked are the master and starter solenoids. These things
get burned contacts and they begin to present a resistance that shows
up as reluctant cranking. A voltmeter placed across the solenoids' big
terminals should show 13 volts when the system is off, and NO voltage
when it's on (or cranking). Any voltage while the solenoid is closed
indicates resistance across the contacts. Even a small amount of
resistance at high current flows will cause significant voltage drop
(E=I*R; A .02 ohm resistance at 200 amps gives a 4-volt drop). Check
the cable connections the same way. Check both the master and starter
solenoids with the engine cranking.
An ohmmeter isn't really good enough to detect bad solenoid
contacts. The resistances are small, and increase with heat caused by
electical flow. An ohmmeter won't detect the heated resistance.


Dan

Dan,
No voltage across the contact is unrealistic. O.5 volt is considered to
be the acceptable limit.
If you replace the master and starter solenoids. Have your A&P install
diodes reverse to the flow across the contractor terminals. The will
prevent the contact from arcing when they disengage. It is the contact
arcing that increases the resistance and causes the voltage drop. 0.5
volts across the contacts is 0.0013 ohms.
Michelle

Dan Thomas wrote:

Often overlooked are the master and starter solenoids. These things
get burned contacts and they begin to present a resistance that shows
up as reluctant cranking. A voltmeter placed across the solenoids' big
terminals should show 13 volts when the system is off, and NO voltage
when it's on (or cranking). Any voltage while the solenoid is closed
indicates resistance across the contacts. Even a small amount of
resistance at high current flows will cause significant voltage drop
(E=I*R; A .02 ohm resistance at 200 amps gives a 4-volt drop). Check
the cable connections the same way. Check both the master and starter
solenoids with the engine cranking.
An ohmmeter isn't really good enough to detect bad solenoid
contacts. The resistances are small, and increase with heat caused by
electical flow. An ohmmeter won't detect the heated resistance.


Dan



--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

Thanks for the informed input. The resistance across the contacts
would get larger as the solenoid ages, and there are a lot of old
solenoids out there. We had a starter solenoid weld itself closed and
burn out the starter. New starter $1200, new solenoid $28. They're
worth replacing.
Two other items that can cause hard starting in the cold: (1)The
impulse couplings on the mags can get sludged up somewhat, and when
cold they won't give the sharp snap needed to make a spark. (2)If the
engine isn't preheated and the weather is cold enough, the first
combustion cycles will create enough water vapour in the cylinders to
frost the sparkplug electrodes and short them. My old A-65 is famous
for this. You get a very brief run and then it dies, and no amount of
fooling with it will make it go.

Dan

Michelle P wrote in message k.net...
Dan,
No voltage across the contact is unrealistic. O.5 volt is considered to
be the acceptable limit.
If you replace the master and starter solenoids. Have your A&P install
diodes reverse to the flow across the contractor terminals. The will
prevent the contact from arcing when they disengage. It is the contact
arcing that increases the resistance and causes the voltage drop. 0.5
volts across the contacts is 0.0013 ohms.
Michelle

Dan Thomas wrote:

Often overlooked are the master and starter solenoids. These things
get burned contacts and they begin to present a resistance that shows
up as reluctant cranking. A voltmeter placed across the solenoids' big
terminals should show 13 volts when the system is off, and NO voltage
when it's on (or cranking). Any voltage while the solenoid is closed
indicates resistance across the contacts. Even a small amount of
resistance at high current flows will cause significant voltage drop
(E=I*R; A .02 ohm resistance at 200 amps gives a 4-volt drop). Check
the cable connections the same way. Check both the master and starter
solenoids with the engine cranking.
An ohmmeter isn't really good enough to detect bad solenoid
contacts. The resistances are small, and increase with heat caused by
electical flow. An ohmmeter won't detect the heated resistance.


Dan



--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

(2)If the
engine isn't preheated and the weather is cold enough, the first
combustion cycles will create enough water vapour in the cylinders to
frost the sparkplug electrodes and short them. My old A-65 is famous
for this. You get a very brief run and then it dies, and no amount of
fooling with it will make it go.


Very interesting. I never heard of that. Is it common? I did note
that the engine did sputter briefly on my first try. I wonder if it was
not adequately preheated (used forced air for only about 2 hours).
Well, I have an A&P looking at it over the next couple of days. I will
report his findings. Thanks for all the sage advice.

-Sami

Wow, you'd think if the starter stuck on, the first thing you'd
do is reach for the master! Quickly! Seen that happen on one
plane actually, when someone turned on the master, the prop
started spinning.

Paul

"Dan Thomas" wrote in message
om...
We had a starter solenoid weld itself closed and
burn out the starter.

Student and instructor didn't realize the solenoid had stuck after
starting the engine. There was a bit of "funny noise" in the headsets,
but they didn't get alarmed until they saw the ammeter indicating a
massive charge rate. Engine noise will drown out most starter noise,
especially if the starter drive disengages with engine speedup as an
O-200 does.
One bush operator I know of installs a red indicator light on the
panel, wired across the starter feed, to alert the pilot to a stuck
starter. It isn't rare.
We always make sure the prop path is clear when turning on the
master. It's not wise, either, to hangar airplanes with wings
overlapping props.

Dan

"Paul Sengupta" wrote in message . ..
Wow, you'd think if the starter stuck on, the first thing you'd
do is reach for the master! Quickly! Seen that happen on one
plane actually, when someone turned on the master, the prop
started spinning.

Paul

"Dan Thomas" wrote in message
om...
We had a starter solenoid weld itself closed and
burn out the starter.

My plane has a red light which comes on when the starter
solenoid is engaged. One of the after startup checks is
"Starter warning light out". This is in a Scottish Aviation
Bulldog, but I use a PA-38 checklist and I belive that's
in the checklist. Mine has stuck once. Another press on
the starter button freed it. Never had any problems since.

Paul

"Dan Thomas" wrote in message
om...
One bush operator I know of installs a red indicator light on the
panel, wired across the starter feed, to alert the pilot to a stuck
starter. It isn't rare.

(Dan Thomas) writes:

Often overlooked are the master and starter solenoids. These things
get burned contacts and they begin to present a resistance that shows
up as reluctant cranking. A voltmeter placed across the solenoids' big
terminals should show 13 volts when the system is off, and NO voltage
when it's on (or cranking).

Actually, get the meter probes on the WIRES, as the path
look like this:


wire-lug-nut-bolt-solenoid-bolt-nut-lug-wire

By measuring from the wire to the wire, you confirm that the lug's
well-connected to the wire, the nut is cleanly contacting the lug,
etc....

You likely want an analog meter (remember those) as it will be hard to
read bouncing digits on a DVM.
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