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
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