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John Vance

What triggers a "Generator" warning light

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My CTLS has two warning lights on the panel, one marked "Engine", and the other "Generator". From the wiring schematic, the "Engine" light appears to be triggered by whatever events the Dynon 120 EMS deems worthy of frightening the pilot's wife. But the "Generator" light is just wired to the "L" and "C" pins of the Ducati regulator. Does anyone know what event(s) trigger that light? I assume it's a minimum voltage output or perhaps a voltage range. My FD manual is oddly silent on this.

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Low or no generator output.

 

Long version: It compares the generator voltage to the battery voltage. If the generator is outputting normally, battery bus voltage will nearly match (the bus is connected internally to the case) and there will be an almost equal potential on both sides of the lamp (there's always a little electrical flow, but not much). But, when the genny isn't outputting enough, the battery will discharge through the light bulb, and back to the battery positive terminal.

 

G = yellow - from generator
R = red - to battery, positive terminal
B = battery positive terminal
L = warning lamp circuit
C = control or field circuit
 
Here's an image of a test circuit. The aircraft systems normally replace item 6 and a couple other changes, but it largely conveys the point.
 
post-1078-0-73873200-1488584097_thumb.png
 
Flight design does do a weird thing on some aircraft where the hobbs goes through the generator test circuit. It's really goofy. But it works.

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Flight design does do a weird thing on some aircraft where the hobbs goes through the generator test circuit. It's really goofy. But it works.

 

 

Unless the warning light bulb burns out, then the Hobbs doesn't work.

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Thanks, Corey. Your explanation clears some things up for me. It looks as though momentarily switching the generator breaker on prior to the engine start sequence would allow the rectifier to "see" battery voltage and could serve as a test of the warning light. Does that sound right? If so, I should add that to my checklist.

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Unless the warning light bulb burns out, then the Hobbs doesn't work.

Yup, replaced a perfectly good Hobbs because of that one - loose bulb.

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You can actually write those off in the logbook if that happens. Just simply put in the logs that the meter rolled, put in the new hobbs time, and the calculated total times prior to the rolling. All you are doing is reestablishing time.

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And if you leave the master on, the Hobbs still runs.  Easy way to rack up plenty of engine and airframe hours.

 

Mine doesn't run with just the battery master on, in fact it won't run if you forget to turn on the generator switch. I'm not sure what it would do with both switches on and not running. I use the time off the EMS for maintenance anyway.

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The Hobbs runs only when the oil pressure is 15 psi or greater. You can sit on the ground all you want and play with the panel without racking up time.

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The Hobbs runs only when the oil pressure is 15 psi or greater. You can sit on the ground all you want and play with the panel without racking up time.

 

I believe you are speaking of the hour meter built into the Dynon EMS. I have yet to see a Rotax powered airplane with a stand alone hour meter tied to oil pressure.

 

It is however common practice for older GA aircraft powered by Lycoming and Continental to have the hour meter tied directly to the battery, and operated through a oil pressure switch. Other methods are a pressure switch in the pitot line, or landing gear squat switches.

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Back to the original topic for just a moment...if you turn on the generator breaker with the master off and engine not running, should that light up the generator warning lamp? I'd like an easy way to verify that it works during preflight, plus I'm not sure mine is working.

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Back to the original topic for just a moment...if you turn on the generator breaker with the master off and engine not running, should that light up the generator warning lamp? I'd like an easy way to verify that it works during preflight, plus I'm not sure mine is working.

 

On my airplane with engine stopped and everything else off, if you turn the generator switch on the light is illuminated.

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On my airplane with engine stopped and everything else off, if you turn the generator switch on the light is illuminated.

 

Thanks, Tom. That helps.

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Mine doesn't run with just the battery master on, in fact it won't run if you forget to turn on the generator switch. I'm not sure what it would do with both switches on and not running. I use the time off the EMS for maintenance anyway.

 

I have seen at least one that runs with the master on and engine off.  But that airplane has an avionics update, so it may just me a wiring anomaly in that airplane.

 

And yes, you can remove the hours by log entry.  But if you are buying an airplane that shows 2000hrs on the Hobbs and there is a log entry that says "correction, the hours are really 500," are you going to buy that airplane or pass on it?  I would at least need some proof on that other than the log entry.

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John, my generator light goes to "on" when I push in my generator breaker.  Same as Tom.  Question - Why do we have a on/off switch (actually a breaker/switch) for the generator?  Is this so that the charging circuit can be shut down, should there be an electrical fire or if the volt meter indicates that the regulator is allowing an over charging condition?

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John, my generator light goes to "on" when I push in my breaker.  Same as Tom.  Question - Why do we have a on/off switch (actually a breaker/switch) for the generator?  Is this so that the charging circuit can be shut down, should there be an electrical fire or if the volt meter indicates that the regulator is allowing an over charging condition?

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Question relating to this thread: Often after I start..and especially after not flying for more than a week... the light stays on for a while but eventually goes out sometime before takeoff (at irregular intervals).  It's been staying on a bit longer for the last year or so; is that telling me something I need to pay attention to?  The voltage regulator hasn't been replaced since we've owned the airplane (almost 7 years and 500 hrs), so I'm wondering if swapping it out at during the conditional this year would be something I need to consider.  The battery's pretty new; been in for less than a year.  The voltage meter gives me a consistent 13.7 and hasn't wavered.

 

Thanks.

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Andy, although your volt meter indicates a good charge during flight, do you still use a battery maintainer when you put the CT away?  If you do use the maintainer, does this show the battery is fully charged or does it go into the charging mode?

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I h

 

Question relating to this thread: Often after I start..and especially after not flying for more than a week... the light stays on for a while but eventually goes out sometime before takeoff (at irregular intervals).  It's been staying on a bit longer for the last year or so; is that telling me something I need to pay attention to?  The voltage regulator hasn't been replaced since we've owned the airplane (almost 7 years and 500 hrs), so I'm wondering if swapping it out at during the conditional this year would be something I need to consider.  The battery's pretty new; been in for less than a year.  The voltage meter gives me a consistent 13.7 and hasn't wavered.

 

Thanks.

 

I had exactly the same fault. The time for the light to go out would depend on the state of battery charge. The cause was the yellow leads into the regulator from the generator had bad connection. I tightened the crimp connectors and that fixed it. You can take the spade connectors out of the black plastic block by using a small screwdriver to push the tang down then it will slide out.

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I have seen at least one that runs with the master on and engine off. But that airplane has an avionics update, so it may just me a wiring anomaly in that airplane.

 

And yes, you can remove the hours by log entry. But if you are buying an airplane that shows 2000hrs on the Hobbs and there is a log entry that says "correction, the hours are really 500," are you going to buy that airplane or pass on it? I would at least need some proof on that other than the log entry.

Such an extreme would raise eyebrows. However, if the last annual was 4 months ago and shows 480 hours, wouldn't you go "yeah thats probably right"? Plus, a 2000 hour airplane looks a lot worse for wear usually. On top of that, they are more likely to spend a few nickels on replacing the meter to cover up something this crazy.

 

As usual, context is everything. Usually you only see a few hours max.

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As usual, context is everything. Usually you only see a few hours max.

 

Sure, but if you put the airplane away a week and everything was off but the Hobbes and master, how long would that take to run down the battery to the point the Hobbes no longer worked?  Ten hours?  Fifty?  A hundred?   

 

I just don't like it.   :)

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Sure, but if you put the airplane away a week and everything was off but the Hobbes and master, how long would that take to run down the battery to the point the Hobbes no longer worked?  Ten hours?  Fifty?  A hundred?   

 

I just don't like it.   :)

 

If it were just running on the hobbs meter, the battery's own self-discharge uses more energy. It would go for a couple months.

 

In a CT with the way they are wired, a day at most (since the alternator lamp is running), unless its on a charger.

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I know it is an old thread---does the FD have an alternator or a generator?  I thought it was an alternator, or is there a reason why it's called a generator on the warning bulb??

/iaw

 

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