What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Alternator help

flyinga

Well Known Member
Helping a friend with an alternator problem with his RV7A, IO360 parallel valve with Nippon-Denso 14684N self regulated alternator. He has a Rocky Mountain Instruments engine monitor with a Hall Effect sensor on the alternator supply wire (measuring alternator output current).

A few months ago, he noticed a negative amperage reading (-1 or 2 amps) and decreasing voltage. Once voltage got down to 12.3 +/- volts the alternator would "kick in" and voltage would again start to rise to 13.7 +/- volts with amperage +10 to 20amps (or so). A few minutes later, the cycle would repeat.

These are the things we did with no changes in what was previously observed:

Swapped alternator with his spare which NAPA said was good.
Installed new (not rebuilt) alternator.
Replaced field 5 amp CB/switch with new.
Replaced wire from switch to alternator field.
Replaced plug on alternator.
Replaced Odyssey PC680 battery.
Verified voltage reading on RMI with digital volt meter.

So basically we have changed everything in the charging system with no changes.

Is this normal for this alternator? If not, any suggestions about what's going on?

Thanks
 
Helping a friend with an alternator problem with his RV7A, IO360 parallel valve with Nippon-Denso 14684N self regulated alternator. He has a Rocky Mountain Instruments engine monitor with a Hall Effect sensor on the alternator supply wire (measuring alternator output current).

A few months ago, he noticed a negative amperage reading (-1 or 2 amps) and decreasing voltage. Once voltage got down to 12.3 +/- volts the alternator would "kick in" and voltage would again start to rise to 13.7 +/- volts with amperage +10 to 20amps (or so). A few minutes later, the cycle would repeat.

These are the things we did with no changes in what was previously observed:

Swapped alternator with his spare which NAPA said was good.
Installed new (not rebuilt) alternator.
Replaced field 5 amp CB/switch with new.
Replaced wire from switch to alternator field.
Replaced plug on alternator.
Replaced Odyssey PC680 battery.
Verified voltage reading on RMI with digital volt meter.

So basically we have changed everything in the charging system with no changes.

Is this normal for this alternator? If not, any suggestions about what's going on?

Thanks

For what it's worth, I had this exact problem.. and a new alternator DID fix it. :confused:
 
Jim, I had an electrical problem somewhat like yours and did much of what you did. Finally changed the $4.95 Master switch and that corrected the problem.
 
Check the ground connection as well. With the internally regulated alternations, once they start, they are self-energizing, so there really is no field connection. That "I' terminal is just a come-alive control for the ECU. If it is disconnected once the alternator is running, it has no impact.

I would also check the B-Lead wire from the alternator and the connection to the buss, maybe loose, corroded, bad crimp.
 
I had an old electrician tell me once, "When the problem doesn't make any sense and defies the laws of physics... look for a bad ground." I have found this to be true in 30 years of troubleshooting control systems.
 
From the archives

(The following is an excerpt from an article I wrote 14 years ago):

Terror at 3100 feet

An exaggeration by Vern Little.

January 24th, 2006—a beautiful, sunny day after a month of steady rain. Freshly armed with the Flight Authority for my freshly minted RV-9A, I arrived at Boundary Bay airport for my first flight.

I had previously decided that a safety pilot would be beneficial, and Mike Langford had volunteered. So we strapped in, fired up the engine, waved to the adoring throng of two persons, and taxied for take-off.

We taxied to position, advanced the throttle slowly and launched ourselves into the calm skies. Cleared to enter Vancouver Terminal airspace by the Nav Canada upper class, we proceeded to level off around 3000 feet and perform some basic flight exercises.

Having spent more than three kilo hours building my airplane, I knew it inside and out. Mike was along in case a ‘situation’ arose that needed my attention.

This was the right thing to do.

Within a few minutes, I noticed a few things on my instruments that concerned me. I had low oil temperature (68 degrees F), no indication of cylinder head temperature on #1, and low CHT on #4 cylinders. Most seriously, was a spurious over-voltage alarm.

Mike took control (he was very happy about this for some reason), while I attempted to make sense of the instruments. After some futzing about, I decided that we were in no danger, but it would make sense to land soon and fix the problems.

After a perfect landing (really, it was), I taxied back in and tore off the cowlings (briefly interrupted by a photo-op).

Here’s what I learned:

• CHT probes work better if you plug them in the socket! Easy fix to #1 cylinder (blush).
• CHT probes will indicate about ½ their normal temperature if one lead is shorted to ground (double blush).
• Sometimes electronic devices fail without warning, as did my Oil Temperature probe. This is exacerbated if you pot them in corrosive silicone sealant. (if it smells like vinegar, don’t get it near electronic devices).

As for the over-voltage alarms, there is a lesson to be learned. Those who have survived my lectures on Aviation Electrics may recall my discussion on alternators, regulators and batteries.

Figure 1 shows how these three major components are related. In normal operation, the alternator is attached to the engine with an accessory belt, which spins the armature.

The armature is wound with a coil of wire that is connected through brushes to a source of power derived from the voltage regulator. The voltage regulator drives a current through this ‘field coil’, thus making a spinning electromagnet.

A moving magnet will induce a current in a nearby loop or coil of wire, such as the stator (non-moving) coils in the alternator. Since the magnet (energized field coil) is moving, it produces a corresponding moving current (alternating current) in the stator coils, which is converted to direct current by semiconductor devices called diodes.

This direct current is used to charge the battery and power the electrical system of the aircraft… if everything works right. The regulator keeps everything working smoothly and sets the charging voltage of the battery.

My over-voltage alarms were caused by a malfunctioning alternator-battery-regulator system. The key data here is that it was ‘too much’ voltage as compared to ‘not enough’ voltage. This meant that the alternator was producing too much juice.

Another piece of data was that it was not a continuous over voltage that would have cooked my battery, but rather it was spurious or intermittent.

Fixing the problems

I found two problems. The first one was that the alternator belt was loose. By itself, this could cause both over and under voltage conditions. A slipping belt would cause the alternator output to drop. This would be sensed by the regulator, and it would send more field current to the alternator. When the belt grabs again, the alternator puts out a large pulse of current before the regulator can catch up and turn it down again.

This cycle can repeat, providing a pulsing voltage, indicated by flashing instrument lights.

After I torqued the alternator spec to 12 ft-lbs at the alternator nut, I decided to keep looking for potential problems.

I turned the master switch to ‘ALT’ (which is the normal position for flight) and proceeded to measure voltages, starting with the main battery, and tracing through the master contactor, main bus, ALT circuit breaker, master switch and regulator input and output.

I found a 1 volt drop between the main battery and the regulator input! This was clearly too much, and my math indicated that it should only be 0.2 to 0.3 volts. So, I had another problem. My voltage regulator was not getting the right voltage input, and so was getting confused.

Further probing found a corroded electrical connection at the master breaker. Simply pulling it off and reseating it fixed this problem.

After flight testing, everything worked fine.

What can be learned from my experiences?

• On the first flight of a new aircraft, it makes a lot of sense to have a safety pilot along to steady the nerves and take over when necessary.
• Things work better if you plug them in.
• Sometimes things fail, and you should know enough to determine (in flight) if it’s serious or just an inconvenience.
• Electrical systems need to be exercised routinely to minimize the effects of corrosion.
• Alternator belts need to be more than ‘finger tight’.
• A basic understanding of how things work allows you to find and correct problems quickly.
• 14.2 volts good. 12.5 volts bad. 15.5 volts very bad.
 
I would check the continuity of the fat wire going from the B lead to the bus, inlcludng anything it it's path (breaker, fuse, shunt, etc.). Be sure to giggle all wires/connectors while testing, as often it is vibration that is causing the intermittent change. Many internally regulated alternators get there sense voltage from the B lead, even if they have a separate ignition lead. BTW, internally regulated alternators do not have a Field terminal, excluding uniquely designed one like the plane power. The field is directly wired to the internal regulator with no access, even if there is an F terminal on the alt. ND cases are sometimes shared between Int and Ext regulated versions. If there is an active F terminal, it is for testing and nothing should be connected to it. Many of these alt's do have an Ign (I) terminal and require 12 volts on it for the Alt to operate, but this is not a field input, just an on/off input.

A B lead wire with a a poor connection (intermittent low to high resistance or intermittent open) can cause the symptoms you describe in some/many alternators.

larry
 
Last edited:
Alternator

It did turn out to be a corrosion on the B wire and it was loose. Cleaned, tightened and it works great.
 
It did turn out to be a corrosion on the B wire and it was loose. Cleaned, tightened and it works great.

generally it is considerate to state that, so we don't waste time trying to help when it is not necessary.

Larry
 
Back
Top