PA28 Low Voltage Light

[Dave]

Hi people,

Our PA28 has developed a problem. The Low Voltage indicator keeps
coming on. The engineer has replaced the Voltage Regulator which didn't
solve the problem at all. Then he changed the Overvolt relay. I flew it
for 50 minutes with no problems and then the next time I took it up
(some days later) the light came on within 10 minutes of takeoff, then
7 more times in the 1 hour flight.

It comes on at seemingly random times and can be reset by recycling the
alternator switch. Sometimes it stays off for 10 minutes, sometimes
half an hour (which makes tracking down the problem even harder!)

Any ideas?

Dave

[Stucky]

> Our PA28 has developed a problem. The Low Voltage indicator keeps
> coming on. The engineer has replaced the Voltage Regulator which didn't
> solve the problem at all. Then he changed the Overvolt relay. I flew it
> for 50 minutes with no problems and then the next time I took it up
> (some days later) the light came on within 10 minutes of takeoff, then
> 7 more times in the 1 hour flight.
>
> It comes on at seemingly random times and can be reset by recycling the
> alternator switch. Sometimes it stays off for 10 minutes, sometimes
> half an hour (which makes tracking down the problem even harder!)
>
> Any ideas?

Your alternator is going offline, the battery is powering the main bus, and
thus the low voltage light is on. Focus on why the alternator would go
offline. Verify a good connection on the alternator field.

[Michelle P]

I have said it before and I will say it again. Check the ground
connections. Check Alt to engine engine to Air frame and airframe to
battery. Use the voltage drop method, not resistance.
Michelle

Dave wrote:

>Hi people,
>
>Our PA28 has developed a problem. The Low Voltage indicator keeps
>coming on. The engineer has replaced the Voltage Regulator which didn't
>solve the problem at all. Then he changed the Overvolt relay. I flew it
>for 50 minutes with no problems and then the next time I took it up
>(some days later) the light came on within 10 minutes of takeoff, then
>7 more times in the 1 hour flight.
>
>It comes on at seemingly random times and can be reset by recycling the
>alternator switch. Sometimes it stays off for 10 minutes, sometimes
>half an hour (which makes tracking down the problem even harder!)
>
>Any ideas?
>
>Dave
>
>
>

[nrp]

Maybe bad/worn alternator slip ring brushes? I can't explain why it
would sometimes come back on though in the air.

Our C-172 had essentially similar symptoms but it was the Cessna
overvoltage sensor that was tripping it off. We traced it to a bad
ground on a filter capacitor near the regulator, and the OV sensor was
tripping at an unusually low voltage. We finally drove the alternator
on the ground with a juryrigged electric motor (so we could work around
it) & used an oscilloscope to monitor the alternator output.

I'm not familiar though with Piper charging circuits.

[john smith]

> I have said it before and I will say it again. Check the ground
> connections. Check Alt to engine engine to Air frame and airframe to
> battery. Use the voltage drop method, not resistance.

You said it better than I would have.

[Mike Noel]

My Archer has experienced alternator output problems for two reasons:

1. Too much mechanical resistance in the elevator trim system and the
electric trim would trip the over-voltage relay.

2. The ground cable between the alternator and the engine block was loose.

The first condition tripped the over-voltage relay after operating the trim
a few times.
The second condition showed up on the alternator output gauge as erratic
current output but did not trip the over-voltage relay.

"Dave" > wrote in message
oups.com...
> Hi people,
>
> Our PA28 has developed a problem. The Low Voltage indicator keeps
> coming on. The engineer has replaced the Voltage Regulator which didn't
> solve the problem at all. Then he changed the Overvolt relay. I flew it
> for 50 minutes with no problems and then the next time I took it up
> (some days later) the light came on within 10 minutes of takeoff, then
> 7 more times in the 1 hour flight.
>
> It comes on at seemingly random times and can be reset by recycling the
> alternator switch. Sometimes it stays off for 10 minutes, sometimes
> half an hour (which makes tracking down the problem even harder!)
>
> Any ideas?
>
> Dave
>

[Dave]

Hi Michelle,

Thanks for your tip.

Please can you explain in more detail the voltage drop method? I am new
to aricraft maintenance. Where am I measuring the voltage drop? Between
the terminals of the battery?

I take it I need to have the alternator being driven...probably by an
electric motor or something? And then check that each connection is
secure while monitoring the voltage across the battery?

Dave


Michelle P wrote:
> I have said it before and I will say it again. Check the ground
> connections. Check Alt to engine engine to Air frame and airframe to
> battery. Use the voltage drop method, not resistance.
> Michelle
>
> Dave wrote:
>
> >Hi people,
> >
> >Our PA28 has developed a problem. The Low Voltage indicator keeps
> >coming on. The engineer has replaced the Voltage Regulator which didn't
> >solve the problem at all. Then he changed the Overvolt relay. I flew it
> >for 50 minutes with no problems and then the next time I took it up
> >(some days later) the light came on within 10 minutes of takeoff, then
> >7 more times in the 1 hour flight.
> >
> >It comes on at seemingly random times and can be reset by recycling the
> >alternator switch. Sometimes it stays off for 10 minutes, sometimes
> >half an hour (which makes tracking down the problem even harder!)
> >
> >Any ideas?
> >
> >Dave
> >
> >
> >

[Denny]

Dave, get a mechanic, or a fellow plane owner, to help you this time...
Next time you will be an expert helping others... It will take,
literally, a text book to diagram and explain what the others are
referring to for troubleshooting.. SImple once you have seen it done...
Difficult to explain in this forum...

denny

[Michelle P]

V=IR fundamental of electricity.
Voltage=Currnet*resitance or Rearranged Voltage/Current=resitance
Having said that it las little to do with the actual test.
Take a good Volt meter (I prefer the the Fluke products). Hook one of
the leads to the Alternator case.
Start the aircraft and measure the voltage at the engine case. then at
firewall, then again at the battery.
Ignore the polarity of the voltage reading. You can take measurements
across each point but write it down and add it up.

If the total drop is 0.5 volts then you are probably ok. If it is close
to 1 volt it is too high.
Ideally there will be no voltage drop. The larger the drop the bigger
the problem when you try to start the engine since you are running
hundreds of amps through these connections.
Michelle

Dave wrote:

>Hi Michelle,
>
>Thanks for your tip.
>
>Please can you explain in more detail the voltage drop method? I am new
>to aricraft maintenance. Where am I measuring the voltage drop? Between
>the terminals of the battery?
>
>I take it I need to have the alternator being driven...probably by an
>electric motor or something? And then check that each connection is
>secure while monitoring the voltage across the battery?
>
>Dave
>
>
>Michelle P wrote:
>
>
>>I have said it before and I will say it again. Check the ground
>>connections. Check Alt to engine engine to Air frame and airframe to
>>battery. Use the voltage drop method, not resistance.
>>Michelle
>>
>>Dave wrote:
>>
>>
>>
>>>Hi people,
>>>
>>>Our PA28 has developed a problem. The Low Voltage indicator keeps
>>>coming on. The engineer has replaced the Voltage Regulator which didn't
>>>solve the problem at all. Then he changed the Overvolt relay. I flew it
>>>for 50 minutes with no problems and then the next time I took it up
>>>(some days later) the light came on within 10 minutes of takeoff, then
>>>7 more times in the 1 hour flight.
>>>
>>>It comes on at seemingly random times and can be reset by recycling the
>>>alternator switch. Sometimes it stays off for 10 minutes, sometimes
>>>half an hour (which makes tracking down the problem even harder!)
>>>
>>>Any ideas?
>>>
>>>Dave
>>>
>>>
>>>
>>>
>>>
>
>
>

[David Lesher]

john smith > writes:

>> I have said it before and I will say it again. Check the ground
>> connections. Check Alt to engine engine to Air frame and airframe to
>> battery. Use the voltage drop method, not resistance.

>You said it better than I would have.

I go one step farther. Don't "check" as much as remove, clean,
reinstall, tighten every ground.


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A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Nathan Young]

On 22 Sep 2005 13:02:19 -0700, "Dave" >
wrote:

>Hi people,
>
>Our PA28 has developed a problem. The Low Voltage indicator keeps
>coming on. The engineer has replaced the Voltage Regulator which didn't
>solve the problem at all. Then he changed the Overvolt relay. I flew it
>for 50 minutes with no problems and then the next time I took it up
>(some days later) the light came on within 10 minutes of takeoff, then
>7 more times in the 1 hour flight.
>
>It comes on at seemingly random times and can be reset by recycling the
>alternator switch. Sometimes it stays off for 10 minutes, sometimes
>half an hour (which makes tracking down the problem even harder!)

Get a voltmeter on the aircraft bus, have someone go flying with you
and have that person monitor and notate the voltages over time.

There are a lot of failure modes and failure points in a Cherokee
electrical system. Getting a handle on the bus voltages throughout
the course of a flight is a great start to finding the problem.

Grab the data, post it here, and we'll be able to generate solid
answers vs. a shotgun replacement mentality.

[[email protected]]

: Grab the data, post it here, and we'll be able to generate solid
: answers vs. a shotgun replacement mentality.

... which is unfortunately the typical "repair" procedure for electrical
gremlins. Gets expensive quickly and is almost always completely unnecessary.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************