RV-8 Electrical Problem

I'm helping a friend track down an electrical charging issue and would like to see what others think. The airplane has a Denso alternator feeding a B&C LRD-14 voltage regulator. Switching and protection is via an EXPII. EMS is a Rocky Mountain unit. The current owner did not build the aircraft and there are no schematics available.This is a pristine, older model aircraft. It has flown perfectly for over 500 hours but recently developed a charging issue. Yesterday, myself and a friend (RV-8 builder) spent the day trying to help. The regulator is mounted on the cockpit side, aft side of front baggage compartment bulkhead. It is almost impossible to get to even if you take up the baggage compartment floor.

The indications:
Upon arrival, the battery (new in 2020) was down to 11.7 volts (as measured with a separate VOM). With master on, the Rocky Mount showed -1 amps and ERROR in the voltage window. We checked for voltage at the field connector with ALT switch on and it was zero. We put a charger on the battery and went to lunch. After about an hour on the charger, it was up to 12.6 and showed 50% charged.

Here's what we found:

The regulator has the #3 terminal jumpered to #6. At first, this surprised me but I expect they did this as the EXPII doesn't offer a traditional bus to monitor voltage.
The regulator had multiple other grounds attached to the mounting bolts.
The regulator was mounted onto a painted surface.
A check of continuity between the engine and airframe showed a good connection.
The alternator has been checked and tests good. The belt is tensioned correctly and is in great shape.

We couldn't see where the voltage regulator secondary ground was connected so unsure of the status of that ground.

We attached a separate temporary ground wire to the regulator and the field connection then showed over 10 volts when the alternator switch was turned on. We cranked the airplane and everything worked but it had an interesting result. After cranking, the amps were high and decreasing (normal) on the Rocky Mount. We were using a separate VOM to read the battery volts which started (after cranking) at 12.6 then slowly (over about a 20 second span) increased to 13.8. Perhaps this slow rise, rather than the normal immediate rise seen on a traditional amp meter is due to the measurement point (battery) rather than thru a shunt.

We then installed a more permanent/ temporary ground wire to allow it to be flown and tested before diving into a more difficult permanent fix, we then tried it one more time and we were right back to the original indications and zero volts at the field connector and -1 amp on the Rocky Mount. We timed out at this point as we had a two and a half hour drive back home.

Obviously, at a minimum, the regulator grounds all need to be cleaned up, the other grounds need to be moved to a grounding strip and the battery needs to be fully charged. In addition, we are thinking the regulator needs to be changed as it appears it is intermittant. I would love to do the full B&C check but at 6' 2" and 70 years old, I can't physically get to it to do the check. Swap out isn't going to be a walk in the park either.

I also realize that the EXPII could be a culprit here too.

Any other ideas?

B&C troubleshooting guide is a good place to start:
https://bandc.com/wp-content/uploads/2018/05/lr3c_technical_manual_revC.pdf#page=6

Walt, thanks but like I said in the post, I’d love to do the B&C checkout but the builder located the regulator in a nearly impossible place for a 70 year old fat guy to even see much less reach.

With a battery at only 50% charge, I am not surprised that there is a slow ramp up in voltage. That is to be expected, as the alternator is pouring a lot of amps into it and this keeps the voltage down. Volts won't go up above 14 until the battery gets to around 75% or greater charge and this takes time

If adding a new ground made it work properly the first time, this is where I would first spend my effort. It seems there is a grounding issue and the temp fix didn't stick. The fact that a new ground worked once points to a wiring issue much more than a defective regulator. I would also review the B&C docs to confirm the rest of the connections. ALso check the field switch and breaker for intermittent problems.

Larry

+1 on everything Larry said.

That's not a fun place to work. What I do is remove my panel to get access to that area - not sure if that's possible in this build.

What I see in the picture looks like they are using this VR as a common ground point - I see 6 separate ground wires going there. Might want to look on the other side of where it is mounted to see if the nut side is grounded well, and/or if the paint has been removed. Perhaps the "fat" wire which is 3rd from the left goes to another common ground point somewhere?

Looks like a bit more "sherlock holmes" activity is in your friend's future.