Generator Not Charging

Ground aborted today because the generator would not charge.

After start I noted that the amps were negative (-5) and battery voltage was below 12 volts. I have experienced the problem before but always during run-up the amps would go positive and battery would indicate 12 1/2 volts or so and generator would work properly during remainder of flight. Not so today. Ran power up to max and generator would still not charge. Returned to ramp, decowled, and checked all connections to the regulator and battery. Nothing found loose. Any other ideas?

Sounds like a voltage regulator-rectifier to me:

Denny,
Got an extra $170.55 plus shipping to allow you to see positive charging numbers on your Dynon EMS? If you have checked all your connections and they are secure you are likely to find that the Ducati 'voltage regulator/rectifier' has crapped out. Actually it is better that the voltage regulator/rectifier is bad than a bad stator (located well under the carbs and ignition), but it is still painful to the wallet. California Power Systems and Lockwood are your best source for the part. There is talk out there of people using a John Deere garden tractor (rated up to 30 amps) regulator/rectifier for about $100. less; but I'm sure a Rotax tech would frown.

The diodes fry inside the Ducati regulator and they are sealed (potted) units so they go in the trash can. The Ducati units will go anywhere from 0 to infinite hours before you fry one; but many people have a problem in the first 500 hours of engine time.(Yup...me too) Send me a private message for more information. Jay

Typically an alternator will output around 14 volts. I would not consider 12.5 an indication of a good system. Perhaps yours is different than what I have in a RV-6A.

Turn on the master switch and measure the voltage from ground to terminal C of the voltage regulator (where the small yellow wire connects). That voltage should be the same as the battery voltage. If not, there is a wiring problem.
If the voltage on terminal C is equal to the battery voltage, then I suspect the voltage regulator is bad. If you have not done so already, consider adding cooling to the new regulator. Van's sells a cooling kit as part of the lighting kit. Heat is the regulator's enemy.
System voltage with the engine running at cruise RPM should be close to 14 volts.
Joe Gores

Thanks for Prompt Replies

Thanks to everyone who weighed in with possible fixes to my generator-not-charging problem. I will troubleshoot tomorrow and let you know what I find.

Denny,

As usual there is a lot of good advice above.

To test the regulator;

1) Check the Stator coils. With power off, remove the regulator plug and measure the resistance between the two heavy yellow wires in the braided jacket, (?G? terminal on the regulator) with an Ohm meter. This should be about ? an ohm and NO reference to ground.
2) Check the regulator enable input. Turn the Master ON ( Mag A & B OFF) and measure the voltage from ground to the thin Yellow wire (?C? terminal). This should read battery voltage (DC volts)
3) Check battery wire continuity. With the Master still ON, one at a time, measure from ground to each white wire (?B? and ?R? terminals). Both should read battery voltage. Turn the Master OFF and Reconnect the regulator.
4) Check the regulator ground. This step requires EXTREME CAUTION, if you are not up to the task don't attempt it. The negative output from the regulator is connected to the airframe through the regulator mounting bolts and nutplates on the firewall shelf. This connection must be able to carry the full 20 amp output of the regulator. Because resistance of this connection may vary with load an ohm meter should not be used. The best way to test the ground connection is with a volt meter while the regulator is under load. Start the engine and turn all electrical devices on. Using extreme caution, set your meter on DC millivolts and measure from ground to the aluminum case of the regulator. This voltage should be under 100mv.

Measure all voltages using a known good ground. If you pass these four tests you likely have a faulty regulator.

If you have an outside tie down, water can pool on the firewall shelf. Over time, the regulator ground connection may degrade. Installing a wire (#12) from one of the regulator mounting bolts to the existing ground lug connection on the oil tank holder/battery box may help.

Installing a higher output (non Rotax) regulator may shift the next failure to another component, maybe the alternator $tator coil$.

Mike Miller 120290

Mike Miller,
That is excellent trouble shooting advice.
A regulator that is securely bolted to the firewall shelf will also conduct heat to the firewall shelf. A small amount of heat conducting grease, available at computer stores, will also help to conduct heat away from the regulator. If heat conducting grease is used, make sure that there is still a good ground connection.
Joe Gores

AC output

Has anyone checked what the AC output voltage is from the alternator? I'm just curious.

According to page 12 of this document, the AC voltage can be as high as 240 VAC depending on RPM.
http://www.rotax-owner.com/pdf/UNDERSTANDING%20THE%20914%20ROTAX.pdf
On page 13, it says that the regulator voltage output is 13.5vdc.
Joe Gores

Be careful with that meter:

The troubleshooting tips with a meter are correct; be cautious though...most people do a horrible job with a meter and often make things worse...lol. I think you'll find the AC output of the stator is 45VAC...but don't quote me on that number. Heat is the culprit on the regulator design; it would be a relatively cheap fix to use heavier duty components to fix the design...I guess Rotax just recognizes that we love to use lots of watts in our recreation...so the design sticks and an alternate power source is available as an option. There isn't enough space under the cowling to install the optional alternator on the RV-12 without some relatively complicated fiberglass work...and we already know how much we like working with cloth and resin!


Jay Sluiter
Albany, OR

It Was The Voltage Regulator That Failed

Received a new voltage regulator from CPS in CA today. $170 plus UPS charges.
Installed it and battery is now being charged at 13.5 volts. Thanks to all for your helpful suggestions. Working through the suggestions convinced me that the voltage regulator was faulty. By the way, I only had 130 hours on my original voltage regulator when it failed.

Hi Denny,
Glad you figured it out - That regulator sure is $$. Let me know when you want to meet for lunch one of these days. Sedona?

new regulator

I had to buy a new regulator before my first flight ... and your right about the price ... $$$.