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Voltage indicator blinking before engine start


OR75

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The voltage starts blinking pretty much right after I turn the master switch on. Is it an indication that the battery is getting weak ? 
Concord 35XC sealed 12V battery on a battery minder. About 4-5 years old . 
the starter showed a couple of hesitations in the past few starts. 

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What voltage is able to blink?

 

If we are discussing the voltage light in the annunciator panel...

Go directly to Clarence’s post below...  :)

 

It’s an important sign that your alternator isn’t turning enough rpm to keep up...
 

Usual cause... the engine hasn’t started yet...

When does it stop flashing?
 

Often when a certain rpm is achieved... which is faster than usual taxi speed...

For more info regarding the instruments in your plane... there will be a paragraph covering each instrument with their specific details...

That paragraph can be found in the POH for your plane...

Some parts of the annunciator panel can be adjusted...

Use caution, the annunciator may have two skills...

  • High voltage steady light?
  • Low voltage flashing light?

You may want to check your voltage with a meter... there are many portable digital devices discussed around here somewhere...

Some expensive devices don’t handle high voltage very well...

PP thoughts only, not a mechanic...

Best regards,

-a-

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it flashes when i turn the master and before the engine starts 

Once the engine starts, even at low rpm, no flashing and the voltage on the bus is 14.0V

My question is: is it normal for the Low voltage annunciator to blink as soon as the master is turned on ? or does it indicate my battery is weakening ?

 

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Note that the test procedure that Clarence cited says to check after engine start.   Before engine start it is not unusual to have a voltage warning, since it's primary purpose is to indicate alternator failure.

Note that the light is supposed to come on at voltages below 12.4 to 12.6 volts.   The battery will often not be able to supply that much to the bus unless the alternator is turning.

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Just now, OR75 said:

it flashes when i turn the master and before the engine starts 

Once the engine starts, even at low rpm, no flashing and the voltage on the bus is 14.0V

My question is: is it normal for the Low voltage annunciator to blink as soon as the master is turned on ? or does it indicate my battery is weakening ?

 

It is not unusual for the annunciator to come on before the engine starts.   It's mostly indicating whether there is enough voltage to charge the battery.

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OK, we had this issue on 201JX. With the master switch and the radio master on, but no avionics on and no avionics fan (pull the circuit breaker for the fan), measure the voltage at the battery terminals, and then from the radio bus to a ground in the front of the airplane. The only loads should be the battery master relay and the radio master relay. The front voltage will be lower, but it should be only about .3 or .4 volts lower, due to unavoidable losses through the positive cable that comes forward from the battery to the starter solenoid and thence to the rest of the busses. If it is a lot lower, like more than a volt lower, check where the grounding cable from the negative post of the battery is bolted to the airframe. On ours, the loss was 1.25 volts. Upon removing the ground cable from the airframe (it attaches to the forward avionics shelf in our airplane) I found corrosion and primer between the cable and the structure. The hole on the right is where the battery ground attached. This view is looking downward on the aft left surface of the avionics shelf, and the tail of the airplane is towards the top of the photo.

963F5374-8B33-43B3-A78F-279E6F433D8C_1_201_a.jpeg

And here is the shelf after clean up. The grounding area was cleaned with a stainless steel bonding brush,  then treated with Alodine 1132 from an Alodine pen. This was on both lower and upper surfaces. Also provisions for assured electrical bonding were made where the shelf attaches to the fuselage stringers, one on each side. This is visible under the cleco on the right side of this picture:

7CD1BBE1-18AB-49E9-805E-6A3B5BA9EA02_1_201_a.jpeg

The voltage drop going forward went from 1.25 volts to .3 volts with this change alone. No wonder 1JX was never a very energetic starter, even with a fully topped off battery. And of course everything was fine with the alternator on, just like the OP experienced.

 

Edited by testwest
Adding pictures and information
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