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Alt inop light and G3X

jthocker

Well Known Member
I have been using the Plane Power alternator on all of my builds for the last 15 years or so. I have never bothered to hook up the wire for the "inop light". I have always relied on a voltage alarm instead. On my new aircraft I ran the wire from the alt plug to a discrete input for the G3X. I configured the discrete for "active low" and labeled it "Alt Inop". The plane power wiring diagram shows a light between the buss (12v+) and the white wire from the alt plug (assuming - or ground when alt is off or failed).
The problem is the alternator is charging 14.4v but the discrete remains active and the Alt inop annunciation is showing.

Anybody else see this?
 
Jon, I don't think it will work that way. Most of those discretes are for a contact position, open or closed, not a +12V signal. :)

Vic
 
Vic,
Discrete is configured as ?active low? , so it should complete the circuit for a light.
 
Vic,
Discrete is configured as ?active low? , so it should complete the circuit for a light.

The ?ALT LIGHT? connection provideds ground when the alternator is not running. It is at buss voltage when the alternator is running. The design allows for an old school light bulb to be connected to buss voltage and the ALT LIGHT connection. The light comes on when the alternator is not running.

But - this works only with a load, like an old school lamp. An led or a high impedance input like you want to use on your G3X will not provide enough load to pull down the ALT LIGHT voltage.

What you discribe however is opposite from expected - so perhaps you might want to verify you have the input properly configured.

Carl

Carl
 
Thanks Carl. I just assumed that when the alt failed or was not running the connection was grounded, thus a discrete that is configured ? active low? would be enabled when the alt is off or failed. It is enabled while the alt is off, but remains enabled after the alt is on line.
 
The ?ALT LIGHT? connection provideds ground when the alternator is not running. It is at buss voltage when the alternator is running. The design allows for an old school light bulb to be connected to buss voltage and the ALT LIGHT connection. The light comes on when the alternator is not running.

But - this works only with a load, like an old school lamp. An led or a high impedance input like you want to use on your G3X will not provide enough load to pull down the ALT LIGHT voltage.

What you discribe however is opposite from expected - so perhaps you might want to verify you have the input properly configured.

Carl

Carl

My PP and G3X are set up the way the OP describes, and works properly.
 
Thanks Carl. I just assumed that when the alt failed or was not running the connection was grounded, thus a discrete that is configured ? active low? would be enabled when the alt is off or failed. It is enabled while the alt is off, but remains enabled after the alt is on line.

Which would mean to me it needs to be "pulled" high with either a resistor or a lamp like the PP diagram shows. I would start with a 10K resistor and see if that works.
 
That was my point, Jon. It is not just a contact switch on the alternator. It needs a lamp or load (resistor) to pull it up.
 
I?m sitting on the sidelines here waiting for you all to figure out a working config before I do the same. :p I had a hunch someone might say a pull-up resistor. Now the question is how big.
 
a simple bosh relay may work? alt on the coil side, NO or NC contacts to your signal input.
 
A better use of the ALT LIGHT connection

a simple bosh relay may work? alt on the coil side, NO or NC contacts to your signal input.

While this may work, and considering the duplicity of an alternator idiot light when most have full EMS systems, I offer a more practical use of the ALT LIGHT connection.

If you use DPDT switches for you mags or electronic ignitions, use the second half of each switch to provide power to a simple piezo buzzer. The ground for the buzzer provided by the ALT LIGHT connection.

What happens is if you have either ignition switch on but the engine off, the buzzer sounds. If the engine is running the buzzer is off. I put the buzzer on the engine side of the firewall so it is obvious to anyone something is not right (as in a hot mag) if it sounds.

It has come in handy over the last 15 years or so.

Carl
 
Another question is, why NOT an old-fashioned 'idiot light' and/instead of a G3X connection? It's more obvious than an indication on the G3X, and it provides another indicator if you left the Master on (provided you have the field connected with a DPST switch such that field is on with Master).
 
Why not both?

Another question is, why NOT an old-fashioned 'idiot light' and/instead of a G3X connection? It's more obvious than an indication on the G3X, and it provides another indicator if you left the Master on (provided you have the field connected with a DPST switch such that field is on with Master).
Why not both? It would also solve the problem of needing a resister. BTW, when I tested my alternators I used a rat shack 12v LED and it worked fine - I assume it has a resister in there to allow the lower voltage LED to work at 12v.
 
JT decided not to use the PP alt fail connection. He has an EarthX battery in his new Redline RV8 and has configured his low voltage warning at 13.5 volts, which happens pretty quickly if your alternator fails - I did the same thing on mine. However, I did use the alt fail wire connected through double pole mag switches to the piezo buzzer on the fire wall to alert me of a hot mag. If I?m timing the mags I can just pull the fuse out to silence the buzzer.
 
I used a 10k Ohm 2W resistor for my G3X Alarm and it seems to work. But my Engine does not run yet.
 
It Worked...then It didn't

I wired the Alternator Lamp circuit (Plane Power AL-12 EI60, pin 3) to the Garmin GEA 24 - Discrete Input #4 (J244-Pin 43) and configured it as Active Lo.

Everything worked fine for the past 25 hours...The annunciation would "chime" and flash as configured when I switched off the Alt. Field...I was Fat-Dumb-And-Happy...

Then today, while on downwind, I pulled power back and "Alternator" began to flash along with the chime. The alternator was still producing power (14.2V at 15A load on the "B" lead) and every other indication of electrical system health was good...

So, I am going to try a 10Kohm pull-up on that input, tied to J244-Pin 50...barring any other feedback from Garmin or Hartzell.

We'll see...

B
 
That wasn't it...

Tried the pull up approach, using the resistance calculated from the recommended incandescent bulb ( 12VDC, 0.1A [100mA] => 120 Ohm ) -- to no effect.

The Alternator is pulling the Lamp signal hard to ground. The alternator still produces power ( 14.2VDC @ 15A ) even though it shows failure.

Bought a replacement alternator; sent emails to Hartzell -- will see what the overhaul/repair reveals.

In the mean time, I changed all my G3X indications to a much higher limit for Volts (13.4 VDC)...
 
Bad connection

Just to update this thread --

I removed the alternator put it with the "spare parts" and installed a brand new one, problem solved -- but not really.

A few weeks later, a buddy of mine was trouble-shooting his alternator and wanted to "borrow" the diode/regulator pack from my spare stock; I carefully removed the screws connecting and holding the diode/regulator pack in place and discovered that one of the 3 wires was broken and was just making a point-contact that was very susceptible to vibration...

So, key takeaways --
1. The ALT Light is probably a good thing to have wired into the G3X touch CAS.
2. It doesn't need a pull up resistor to make it work.
3. If it goes off (#assert) it means something is wrong - for real.
 
Success

I recently set this up as a discrete input on the GAD 27, no resistor or relay, and it works as hoped.

On the G3X, I configured GAD 27 discrete 1, active low, input state: active. This shows an alert when the G3X is first powered on, before engine start. The alert goes away after start, when the alternator is online.

Thanks
 
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