B and C auxiliary alternator not showing voltage

[Ron B.]

I’m not able to get the auxiliary alternator running on a friend’s RV-14A. His engine was removed for repairs and the aux alternator isn’t showing voltage on the G3X. The main alternator is.
I have tested all wires for connectivity and I checked the sense wire for 12 volts. The B and C aux alternator has an external regulator and it goes through a VPX PRO. Don’t know anything about the VPX PRO , might be something in that ? It worked fine before tear down. I even spun the prop and looked inside the alternator to see if it turned.
With the engine running above 1800, and the main alternator field turned off (the auxiliary field on) , we have zero volts displayed on the G3X. I know the voltage has to drop below a threshold voltage for the auxiliary to kick in, but I don’t remember seeing zero voltage in red , while testing the auxiliary alternator . Any ideas where to look or what I’m doing wrong? Thanks Ron

 

[Walt]

Are you sure the setting for Volts 2 is not the backup battery?
Single bus or dual bus setup?

 

[Ron B.]

Are you sure the setting for Volts 2 is not the backup battery?
Single bus or dual bus setup?

Thanks for your attention Walt
I didn’t change anything with regards to volts 2 and as you can see from the attached photo the voltage is higher on the left side. The only thing I did since it has last flown is swapped out the PlanePower main alternator for a B and C alternator ( probably why the voltage on the left is lower in the second picture).
Single buss as far a I can tell.( not very smart)

 

[dmattmul]

I’m not able to get the auxiliary alternator running on a friend’s RV-14A. His engine was removed for repairs and the aux alternator isn’t showing voltage on the G3X. The main alternator is.
I have tested all wires for connectivity and I checked the sense wire for 12 volts. The B and C aux alternator has an external regulator and it goes through a VPX PRO. Don’t know anything about the VPX PRO , might be something in that ? It worked fine before tear down. I even spun the prop and looked inside the alternator to see if it turned.
With the engine running above 1800, and the main alternator field turned off (the auxiliary field on) , we have zero volts displayed on the G3X. I know the voltage has to drop below a threshold voltage for the auxiliary to kick in, but I don’t remember seeing zero voltage in red , while testing the auxiliary alternator . Any ideas where to look or what I’m doing wrong? Thanks Ron

Yet it's reading 5 amps at 1120 RPM ? (Is this increasing as RPM is increased?) As Walt mentions go into config and try the 5 or 6 places on the input. (It will show up immediately in the config pre-view window). In config mode go to the VPX tab on the engine interface and see how that is named.

 

[Hangar 1271]

Another post here on VAF said the voltage threshold for the backup to start is 13V. Did your voltage get that low? My PlanePower is 13.3V (13.6 +/- 3V).

 

[MED]

I’m not able to get the auxiliary alternator running on a friend’s RV-14A. His engine was removed for repairs and the aux alternator isn’t showing voltage on the G3X. The main alternator is.
I have tested all wires for connectivity and I checked the sense wire for 12 volts. The B and C aux alternator has an external regulator and it goes through a VPX PRO. Don’t know anything about the VPX PRO , might be something in that ? It worked fine before tear down. I even spun the prop and looked inside the alternator to see if it turned.
With the engine running above 1800, and the main alternator field turned off (the auxiliary field on) , we have zero volts displayed on the G3X. I know the voltage has to drop below a threshold voltage for the auxiliary to kick in, but I don’t remember seeing zero voltage in red , while testing the auxiliary alternator . Any ideas where to look or what I’m doing wrong? Thanks Ron

Have you checked the ANL fuse?

 

[Ron B.]

Yet it's reading 5 amps at 1120 RPM ? (Is this increasing as RPM is increased?) As Walt mentions go into config and try the 5 or 6 places on the input. (It will show up immediately in the config pre-view window). In config mode go to the VPX tab on the engine interface and see how that is named.

I never noticed the 5 amps. Too much to watch for in such a short time. I should have studied the picture more.
Thanks

 

[dmattmul]

I never noticed the 5 amps. Too much to watch for in such a short time. I should have studied the picture more.
Thanks

Also if the main alternator field is off why is it still producing 54 amps? I assume the amp readings are on the b leads ?

 

[Ron B.]

Also if the main alternator field is off why is it still producing 54 amps? I assume the amp readings are on the b leads ?

It’s very likely that it’s on when the photo was taken.

 

[dmattmul]

I've looked over my EFIS data and my pad mount B&C alternator (BC410-H) puts out about the same amps at ~ 1,140 RPM so it appears the unit is working just not talking to the G3X. The VPX input tab on the EIS has only 2 options Bus 2 Volts and Aux Battery Volts. If Aux Battery Volts is picked the display will read 0 volts. If it's wired to the GEA24 there are over 10 different input configurations to pick from. My first panel builder (very well known) was hesitant to wire direct to the VPX and used the GEA24. Mt second panel builder for the 10 wired direct to the VPX. The good thing is you can go through the list and try each input, and you will see a preview of the output while remaining in config so it's easy and fast. (Ask me how I know) Please let the group know what you find, helps everyone and good luck.

 

[Ron B.]

Problem solved. You need to turn on the essential buss switch for the unit to read voltage. Again , what a dummy. Not the first and certainly not going to be the last.