Alternator does not kick in until high RPM's

Here's a new one I just started seeing in the last few flights. My alternator used to come up to voltage soon after startup, at less than 2500 RPM. Now it does not kick in until after the run up at 4000 RPM or more. Once it kicks in, it behaves as it used to, showing a charge at even a fast idle. After that, normal operation for the entire flight.

Anyone else seen this? I'm wondering if this portends an impending regulator failure. Maybe I should order one to have on hand? Thoughts?

The rectifier / regulator could be going bad. Before you replace it, check all of the connections and make sure that the case is well grounded. Some people have replaced it with a John Deere unit. See this thread.
Joe Gores

BigJohn said:

Here's a new one I just started seeing in the last few flights. My alternator used to come up to voltage soon after startup, at less than 2500 RPM. Now it does not kick in until after the run up at 4000 RPM or more. Once it kicks in, it behaves as it used to, showing a charge at even a fast idle. After that, normal operation for the entire flight.

Anyone else seen this? I'm wondering if this portends an impending regulator failure. Maybe I should order one to have on hand? Thoughts?

Click to expand...

An alternator should be constant voltage from idle. I would say something has already failed. Hard to say what. If it is a claw pole alternator, then likely the regulator, but diagnostics should tell for sure.

On second thought, if a wire were loose it might act this way too. Anyway, diagnostics seems to be in order.

I saw similar issues with my -8 and Dynon D180. Some times amps were zero until I increased RPM. Went away after jiggling the wires to the ammeter shunt.

Later I saw "HIGH AMPS". Over 70 from a 60 alternator.

I since soldered wires where I had butt splices. A very small resistance change in a connector can show huge swings in the readings.

Check your connections carefully. This may or may not be your issue. By the way, during zero amp readings and hig amp readings the voltage was rock steady. That is the clue.

Don

The rotax uses a dynamo doesn't it?

Dave12 said:

The rotax uses a dynamo.

Click to expand...

No it has an internal permanent magnet alternator that has an external rectifier/regulator unit.

Check your battery and it's connections. Long shot, but I've seen failing batteries and bad terminal connections do some weird stuff. Once on the submarine I was on we couldn't get the battery to take the load when we backed off on the motor generator DC voltage. We let the voltage drop as much as we felt comfortable with and it suddenly took the load. We finally tracked it down to a corroded cell-to-cell connection.

Here's a follow-up

I sprayed Deoxit (sp?) on the connector to the regulator and reseated the connector. Problem solved. My theory is there was just enough oxidation on the connector to prevent current flow until the voltage ramped up enough to break through. Now to see if it stays fixed.

Started up today to go to a PCB and no alternator output at any RPM. So no pancakes. Will order new regulator tomorrow. Looking for instructions for new mounting location. Any body know where to find them?

John, After your post I began to experience a similar thing - no initial alternator output and basically running off the battery until the oil warmed up and I could pulse it up to 3500 rpm or so -then it would kick in and remain on (during flight). This was an intermittent phenomenon on the ground I downloaded flight logs, graphed them, and had a great discussion with Dean at Lockwood.

One thing he had me try was to ensure that the stator was making voltage. The highlights:

"Dean: One more test to try. Pull the connector from the regulator/rectifier. Put some alligator clips on the 2 yellow leads coming from the stator. Set your multimeter on AC volts, and run the engine at about 2000 rpm. You should see something like 15 to 18 volts. After doing the test, check all the spade connectors carefully and make sure they’re all engaged again. Some contact cleaner might be a good idea – certainly wouldn’t hurt."
++++++++++++
I tried this and got the following.
Before master on: Battery at 13.2 V
Turn on master. (That basically runs the Skyview and fuel pump. No lights or avionics.) Drops to ~12.3 on the multimeter.

Started engine with regulator socket disconnected and the yellow wires from the stator on AC voltage test.
2000 RPM: 15.3V
2200 RPM: 16.6 V
2300 RPM: 17.2 V
2400 RPM: 18.1 V

Since that seemed all well, I did not continue the test by warming up the oil and going to higher RPMS. The battery showed 12.4 volts during the test and -5 A powering the stuff, as expected, obviously not getting charged.
I again checked the connections and cleaned with contact cleaner before reattaching the plug.
+++++++++
The next day I continued to get some intermittent voltage drops and amp indications during ground ops. So I ordered a new regulator.

I don't intend to relocate the regulator until the next annual in April.

Negative amps

Mine runs well during warm up and in flight but after landing I see -2 amp while taxing. If I raise the RPMs I will get 1 amp and if I shut down auto pilot and lights this helps with amps.

The RPMs needed to get in the positive while taxing is too much to continue normally so I slow it down and go negative back to the hangar.

Regulator in the engine compartment with the air hose off the plentium trying to add cooler air.

Patrick - as long as you are seeing 13+ Volts you know the regulator is working. Without it even a freshly topped off battery would be reading about 12.3 V or so if the master switch is on and you'd be seeing -5 amps or so powering the Skyview and the fuel pump.

With the Dynon the amps can jump around because Dynon says the Rotax engine is a noisy engine electrically. Normal amp readings may jump around from -4 to +8 on a regular basis, but should never stay there in one spot.

Combining topics..........

For anyone who got to this thread by searching, there is more information here.

roger lee said:

With the Dynon the amps can jump around because Dynon says the Rotax engine is a noisy engine electrically. Normal amp readings may jump around from -4 to +8 on a regular basis, but should never stay there in one spot.

Click to expand...

Kinda seems like a strategically placed capacitor inside the "box" could quiet this down and make for a smoothed out reading. Not something a builder should attempt, but maybe an idea for the avionics folks at Stein's place.

Interesting

I have the AFS 4500 in my Kitfox with the 912S and my amp reading never jumps around. It is very solid, usually 10-12 amps after startup and then runs a constant 7 amps or so during flight, depending upon what equipment I have turned on. All lights are LED's and I can see a 1 amp change when I cycle them or the fuel pump. When taxing back to the hangar with low (1400) rpms, the amps and volts will drop off a little, but I run it up for a minute or so prior to shutdown. The amps will initially increase and then drop down.

Vic

Roger does not say which Dynon model. I have the D-180. The ammeter display is useless. With the engine OFF, the data log shows the amps varying from negative -245 to positive +9 amps. Both of those numbers are unrealistic. A capacitor will not help smooth the output from an alternator that is NOT running. Does anyone have a D-180 with a steady ammeter reading?
I want to determine if the problem is with the RV-12 aircraft circuitry or within the D-180.
Joe Gores

I replaced my voltage regulator at 120 hours. I eventially plan to relocate it under the panel, like the new plans show. Now, the voltage regulator is not grounded by any of the wires on the connector. It is grounded through the bolts on the case (there is a symbol.) While that may be perfectly adequate, it is also a good idea to put some heat transfer paste under the regulator base. (I only put mine on the black plastic section, not the case body.)

Still, case contact did not seem to me to be a very good ground. I added the wire shown, using the same method as for an additional engine ground wire on the other side. The Phillips head screw on the left is a short metric M6 that goes into an existing tapped hole on the aft cylinder.