should alt inop light be lit when field is on but engine isn't running?

[Salty]

I just installed a plane power alternator and regulator upgrade from a generator.

I can see it working either way, I have a feeling it's working correctly, but should the light go out when you apply the field voltage but the alternator isn't turning yet?

 

[GRG55]

If the Master is ON, my in-op lights stay on until I start the respective engine.

And it will sometimes flicker if the idle falls too low when the engine is running.

 

[BillTIZ]

We just installed the same system. Master on, light on, engine running, light off.
Yes it can come on or flicker at extremely low rpm.
Light still on with engine running, it’s not working.

 

[Raymo]

The light should be on if the alternator is not producing voltage. This is how you would know it has failed (field energized but no voltage output).

 

[bluerooster]

I just installed a plane power alternator and regulator upgrade from a generator.

I can see it working either way, I have a feeling it's working correctly, but should the light go out when you apply the field voltage but the alternator isn't turning yet?

Yes

 

[Salty]

The light should be on if the alternator is not producing voltage. This is how you would know it has failed (field energized but no voltage output).

Yes

These answers are contradictory. I think the first one makes the most sense though. Maybe my question was worded badly. What is happening now is that the inop lamp flickers a bit when I turn on the field, but stays lit. My engine isn't ready to run yet, so I don't know if it goes off when voltage is being created, I assume it will. I just wasn't sure if it should be lit when it had field voltage, but wasn't producing yet, but logic says if it's not producing, the inop lamp should be lit, so I think I'm fine.

 

[Raymo]

I have a PP 60A alternator with internal regulator. With the master switch on and engine stopped, the Alt Fail light is lit, which has power from the main bus and gets its ground from the alternator when not producing voltage. Once the engine is running, I flip the alt field switch to provide field power and the alt-fail light goes out. I could leave the alt field switch on all the time and it would do the same thing but I prefer to have all volts/amps committed to the starter vs the ~4 amps it requires to power the alt field.

 

[Salty]

I have a PP 60A alternator with internal regulator. With the master switch on and engine stopped, the Alt Fail light is lit, which has power from the main bus and gets its ground from the alternator when not producing voltage. Once the engine is running, I flip the alt field switch to provide field power and the alt-fail light goes out. I could leave the alt field switch on all the time and it would do the same thing but I prefer to have all volts/amps committed to the starter vs the ~4 amps it requires to power the alt field.

Thanks for the confirmation.

 

[BigBadLou]

The question should be rephrased to something like: did I spend enough money on a real VR that controls the light properly or did I waste money on a cheap Chinese POS that fakes the light?

If you open up the cheapo Chinese junk VRs (such as Lamar), you will notice that there's a relay that is energized from the ALT switch input (S) and it directly controls the charging indicator light (I).

The difference in function is obvious and scary.
The good VRs turn the light off only when the alternator is producing charge. If your alternator stops charging in flight, the light will come on and you will know immediately.
The bad VRs turn the light off whenever the ALT switch is on. If your alternator stops charging in flight, you won't know ... until your battery goes to sh*t and you can't do anything.

 

[Dan Thomas]

The question should be rephrased to something like: did I spend enough money on a real VR that controls the light properly or did I waste money on a cheap Chinese POS that fakes the light?

If you open up the cheapo Chinese junk VRs (such as Lamar), you will notice that there's a relay that is energized from the ALT switch input (S) and it directly controls the charging indicator light (I).

The difference in function is obvious and scary.
The good VRs turn the light off only when the alternator is producing charge. If your alternator stops charging in flight, the light will come on and you will know immediately.
The bad VRs turn the light off whenever the ALT switch is on. If your alternator stops charging in flight, you won't know ... until your battery goes to sh*t and you can't do anything.

The "bad" VRs are the old units that are just repurposed autombile regulators. They don't need to be Chinese. In the car, the S terminal was connected to the alternator's stator terminal, which produced a small voltage once the alternator was turning. That signal, fed to the regulator's S terminal, turned the regulator on and the light went out. It was automatic alternator control. In the airplane, we need some means of shutting down an alternator that is either overvolting due to a bad regulator, or is draining the battery via a shorted diode or energized field when the belt has broken, so that S terminal got connected to the alternator switch. That means that the light comes on if the master is on and the alternator switch is off, or if the overvolt sensor has interrupted the feed between the switch and regulator. It does not mean that the alternator has failed; it just means that the regulator is switched off. The alternator could be burned right out, or the belt broken, or the field wire broken, or the output cable broken, and the light would still be out with the regulator turned on. The light is almost useless.

The electronic ACUs measure output voltage and illuminate the light if the voltage is too low. Plane Power's regulator is an ACU.

 

[PaulMillner]

I just installed a plane power alternator and regulator upgrade from a generator.

I can see it working either way, I have a feeling it's working correctly, but should the light go out when you apply the field voltage but the alternator isn't turning yet?

It depends on how it's wired. The PlanePower regulator has the capability to tell you if the alternator is making juice or not... but you have to connect the stator terminal to the regulator for that to work (Beechcraft style). Otherwise, if you don't, it works like a Piper or Cessna... the light is on if the alternator field has no power, but the light is off if you power the field, whether the alternator makes juice or not.

So... how did you wire it?

Paul

 

[Salty]

It depends on how it's wired. The PlanePower regulator has the capability to tell you if the alternator is making juice or not... but you have to connect the stator terminal to the regulator for that to work (Beechcraft style). Otherwise, if you don't, it works like a Piper or Cessna... the light is on if the alternator field has no power, but the light is off if you power the field, whether the alternator makes juice or not.

So... how did you wire it?

Paul

Like this, except I also grounded the ground terminal that's to the left of the field terminal on the regulator.

 

[PaulMillner]

Like this, except I also grounded the ground terminal that's to the left of the field terminal on the regulator.

OK! The "AUX" terminal on the PlanePower alternator appears to be the same as the "STA" or stator terminal on the original Ford-style alternators. That provides the regulator with the information as to whether the alternator is really making power or not.

On a regulator-only retrofit, you'd connect a new wire between the Ford-style alternator and the PlanePower regulator, and add that functionality. That would change how the light works in a Cessna, to the better.

Paul

 

[PaulMillner]

The question should be rephrased to something like: did I spend enough money on a real VR that controls the light properly or did I waste money on a cheap Chinese POS that fakes the light?

If you open up the cheapo Chinese junk VRs (such as Lamar), you will notice that there's a relay that is energized from the ALT switch input (S) and it directly controls the charging indicator light (I).

The difference in function is obvious and scary.
The good VRs turn the light off only when the alternator is producing charge. If your alternator stops charging in flight, the light will come on and you will know immediately.
The bad VRs turn the light off whenever the ALT switch is on. If your alternator stops charging in flight, you won't know ... until your battery goes to sh*t and you can't do anything.

Big Bad Lou, spending regulator money is necessary, but not sufficient! One also has to run a NEW wire from the alternator's AUX or STA terminal to the AUX terminal on the regulator. I know Cessna didn't provide this wire. I don't think Piper did either. Beech put in the wire, but installed a separate relay to detect alternator operation (interestingly, a 6 volt AC relay, as that's closest to the character of the current from this terminal). Current design regulators, of course, can integrate this functionality.

Paul