Ongoing Arrow alternator/charging problem

[Chuck]

Hi everyone,

This group seems especially knowledgable, I hope you don't mind a
question about a friend's plane.

Its a 78 Arrow and is being used by a FBO for training. For the last
month or so, they can't seem to keep the battery charged. Started a
month ago and the alternator was found not putting out anything.

Swapped it for a rebuilt alternator and two weeks later -- dead
battery again. Same thing -- no output.

Took the alternator back to the seller who tested it and confirmed
that it wan't putting out. Bought a brand new one and installed it.
Seemed to be putting out, but pretty low amperage except at high RPMs
(Arrow has a load meter, not charge/discharge meter) .

Exactly two flight hours later -- dead battery. Apparently, the
alternator isn't putting out again. And the A&P is at a loss. I
suspected the voltage regulator, but he says he's had it tested.

Has anyone else run into a problem like this before? Or can anyone
offer a suggestion on where to look for the root of this problem? I'd
like to help him get this fixed -- we're both working on Instrument
time and we're splitting the time between his Arrow and my Cherokee.

Thanks guys...



Chuck

[nuke]

> Swapped it for a rebuilt alternator and two weeks later -- dead battery
again. Same thing -- no output.

Just curious if anyone tried to figure out what failed in the original
alternator?

You might also have the battery checked too.


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.

[[email protected]]

There's another box in the charge circuit, the overvoltage relay. It
could be tripping at too low a level. And if the battery is old or has
been overcharged, it won't charge regardless.

Put a voltmeter on the battery terminals, check the voltage. Then
start the engine, turn on the alternator switch and check it again.
With the engine at taxi speed, you should get over 13 volts if the
regulator circuit and alternator are working. If you're getting 13
volts and the battery still dies, replace the battery.

[Chuck]

A couple of people on here hit on what we think was the solution --
the battery.

Apparently, although not old, it had been discharged too many times
recently. We swapped the battery out today and then took it on a 2.7
hour ride. Everything worked perfectly.

So, although we don't know why the rebuilt alternator gave out so soon
after installation -- the ongoing problem after replacing it the
second time was the battery.

Thanks for all the suggestions guys...


Chuck

[John_F]

An intermittent open circuit on the alternator output terminal can
kill the diodes in an alternator. You can play hope and poke for a
long time and some day you may replace the correct item. or you can
run a simple test.

This is easy to test. For a 12 volt system apply a 12 ohm resistor
between ground and the alternator output terminal to get about a 1 amp
load. Turn on the master and measure with a DVM the voltage drop
between the battery + and the alternator terminal. Shake, thump and
move wires, amp meter circuit breakers, master relay etc and watch
for any voltage change. If the voltage changes more that a millivolt
or so find out what is loose and fix it. This method allows you to
measure EACH crimp connection, each wire section and each item in the
path that the 1 amp current is flowing in. V=IR If i= 1 amp then
V=R One millivolt is one milliohm. The method is called a Kelvin 4
wire ohm meter measurement. The DVM must be able to read millivolts.
Remember if the alternator outputs 60 amps then the voltage drop is 60
times what you measure with the one amp load. The voltage drop should
be less than 1 volt at full output.

John

On Wed, 15 Dec 2004 01:28:50 GMT, Chuck > wrote:

>Hi everyone,
>
>This group seems especially knowledgable, I hope you don't mind a
>question about a friend's plane.
>
>Its a 78 Arrow and is being used by a FBO for training. For the last
>month or so, they can't seem to keep the battery charged. Started a
>month ago and the alternator was found not putting out anything.
>
>Swapped it for a rebuilt alternator and two weeks later -- dead
>battery again. Same thing -- no output.
>
>Took the alternator back to the seller who tested it and confirmed
>that it wan't putting out. Bought a brand new one and installed it.
>Seemed to be putting out, but pretty low amperage except at high RPMs
>(Arrow has a load meter, not charge/discharge meter) .
>
>Exactly two flight hours later -- dead battery. Apparently, the
>alternator isn't putting out again. And the A&P is at a loss. I
>suspected the voltage regulator, but he says he's had it tested.
>
>Has anyone else run into a problem like this before? Or can anyone
>offer a suggestion on where to look for the root of this problem? I'd
>like to help him get this fixed -- we're both working on Instrument
>time and we're splitting the time between his Arrow and my Cherokee.
>
>Thanks guys...
>
>
>
>Chuck

[nrp]

Another test trick with Lycoming belt driven charging systems is to
drive the alternator only with a 1/2 hp or more hand held electric
motor instead of using the engine. The direction of rotation isn't
critical. If you want to have "variable" speeds, put a cone pulley on
the motor.

This makes it a lot easier and safer to work around. Disadvantages are
getting access if your cowl doesn't split, but of course that is always
a problem.

Recognize though that in service the alternator spins probably close to
10,000 RPM.

[Chuck]

Following up on the follow up. Two days after replacing the battery,
it died again. Man, was my friend ****ed. This plane is used as a
trainer and flown a LOT.

The A&P pulled the cowl and when he looked at the alternator -- he
found the spring that holds the brushes against the stator sticking
out of the top and the hold-down screw gone.

They took the alternator out and back the the place that just rebuilt
it. I understand there were more than a few harsh words about shoddy
repairs, multiple tries, and loss of revenue. They (of course)
rebuilt it again and didn't charge for it.

It came back and was put in yesterday. This morning, he and I flew it
for 3.5 hours. No problems. HOPEFULLY this is the end of the power
problems.


Chuck



On Thu, 16 Dec 2004 05:44:30 GMT, Chuck > wrote:

>A couple of people on here hit on what we think was the solution --
>the battery.
>
>Apparently, although not old, it had been discharged too many times
>recently. We swapped the battery out today and then took it on a 2.7
>hour ride. Everything worked perfectly.
>
>So, although we don't know why the rebuilt alternator gave out so soon
>after installation -- the ongoing problem after replacing it the
>second time was the battery.
>
>Thanks for all the suggestions guys...
>
>
>Chuck
>