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CTLS Generator failure in flight

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Hi all

Cruising the other day at 8500 the generator light came on full brightness and the amp meter showed -10 amp discharge and battery voltage started to go below 12 Volts.

By all indications the generator had failed.Turning everything non essential off allowed me to get to destination and maintain comms in the circuit. The battery was recharged and contacts cleaned on the Ducati regulatorand everything worked normally after that. Several hours have been flown since without problem. Yesterday during flight the generator light came on again in flight , again indicating generator failure.The question is this: Are there any known problems with the CTLS that fit those symptoms? Is there anything that needs to be checked besides the known earth problems?Any assistance would be appreciated.

Niels

 

CTLS VH-NKO

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Hi Niels,

 

 

This sounds like a bad connection.

It may be a bad connection in the large flat plug that goes into the side of the reg/rec. Pull this out and make sure all wires into it are in solid and look at the pins on the reg/rec side to look for arching. Then tighten the 5 grounds in the engine compartment and the one inside the instrument panel. There is a very likely chance one of these two checks and fixes will correct the problem. The grounds may be hand tight, but wrench loose. Put a wrench on all of them and make them tight.

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But you are drinking an awful lot of electrical power and the Ducati regulator can easily overheat in those conditions since it is lossy and somewhat under-spec'd. 10Amps is 130W or so and at that rate, you will see 40W dissipated just in the regulator, which will kick its temperature up by 80C if airflow is poor and more like 100C at the semiconductor die inside. If it overheats, it might fail until it can cool down (that's a common mode for SCRs when current limited). Might want to try running a thermocouple taped to it to see how hot the case really gets. Anything over 130C at their junctions is dicey for the SCRs.

http://contrails.free.fr/elec_ducati_en.php

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Thank you Kurt for you for sharing your valuable knowledge Of the Ducati Regulator/Rectifier.

I have learnt a lot about the inner workings of the device.

 

Niels

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The intermittent part doesn't lead me to believe the reg/rec is bad or going bad, but anything is possible.

 

Wires and connections first.

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It is usually wiring with all CT electrical issues, however, the Ducati's do tend to fail when heavily loaded and can latch in thermal runaway which would also give him his abrupt dropout. Intermittent problems like loose connections usually come and go and are less binary. His problem seems to show up after the system has had some time to heat up and does not come back once tripped.

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We recently replaced our rectifier regulator in CTsw (650 hr) and solved repeated low voltage alarms. We did extensive diagnostics (see below) and found a definite temperature dependence, which pointed directly at the rect-reg as the failing component. Here were our diagnostic steps:

  • Check all ground wires, clean if corroded, and tighten.
  • Clean all male (easy) and female (difficult) contacts on the rect-reg plug.
  • Operate an accessory-plug voltmeter (inexpensive at auto part stores) and watch the D120 indications and independent voltmeter indications in parallel. Take an observer; this is too absorbing for the pilot to do it. The D120 should consistently track about 0.5 volt lower than the accessory plug voltage (we assume that a protective diode at the + power input of the D120 causes the D120 to report its internal supply voltage 0.5 volt lower than the supply voltage--not verified with Dynon). This step verifies that the problem is not internal in the D120.
  • Make multiple flights from a cold start. What we observed was initial supply voltage of about 12.5 (lower than it should be), gradually dropping as the under-the-cowl temperature increased. In our particular test conditions, 10 minutes into the flight we would get the first alarm.
  • Sometimes an increased load (landing light) would temporarily restore a higher voltage.
  • Our voltage bounced around quite a bit, and the largest excursions in the low-voltage direction triggered the alarm.

After replacing the rect-reg, our supply voltage, except at idle RPM, was steady at 13 V (12.5 indicated by D120).

Do all the checks, but the rect-reg units are running in a hotter environment than they were designed for, so don't chase your tail forever before replacing them. Ours cost $170; they are available in the U.S. from Lockwood and California Power Systems.

 

AFTER ANOTHER TEN HOURS OF FLYING...

 

Well, some of the voltage variation problems returned. Going through the wiring diagram for our plane (unfortunately, wiring seems to have changed constantly at the CT factory, so this may not apply to you) and following suspect wires, we found another problem. There are two wires that go into a single pressure terminal on the back of our ignition switch. Both wires have been "tinned" (multi-strand wires that have had solder applied to the end) and are, therefore, slightly different diameters. One of the wires could be pulled out by hand! We tightened the single screw on this connector, really putting the pressure on the two wires. Since making this adjustment, and with the new regulator mentioned above, we have had no voltage issues with about 100 hr of additional flight time. I guess the lesson here is that wires other than ground wires may be the culprit with CT voltage problems.

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I can confirm the Dynon is 1/2V low on my D120. The voltmeter in the 496 GPS is accurate though. 13V is too low to charge well, BTW. You really could use a 1n4007 diode to the control pin to get you up to 13.8V which is ideal.

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Hello all

Thank you everybody who took the trouble to read my post and specially all of you who replied.It is certainly encouraging me to continue on.All contacts on reg/rec have been cleaned on both sides of the plug and socket with pure alcohol and then treated with Stabilant 22All wires and associated connectors are tight and there was no evidence of pitting or arcing or any other stress.All earth wiring points in the engine compartment have had the spanner applied, none were loose.However the the problem seems to be more permanent now. There is now no charge after the Rotax is started and the Gen button is pushed.It seems more likely now the reg/rec has failed? I checked the two yellow wires and the resistance shows about 0.5 Ohms.I have now retrieved the ROAN Internal generator checklist from this site they would be happy with that value.Hobbs meter is not turning while the GEN light is on, it must be connected to the Ducati output presumably. No output no Hobbs turning.I have still to check the earth connection of the Ducati to the earth rail, it seems to separate to the plug wiring.Question: can you run the Rotax with the top cowling removed to check the AC output? Has anyone done this check?Or is there a simpler way to prove the DUCATI is u/s?Is there anything else I should do?

Thank you all for trying to help.

Niels

CTLS

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There is no real way to test the reg/rec other than replacing it and yours sounds like it is going out. If it has 18-22 ACV going in with the yellow wires and 12DCV coming out then I would normally think it's okay, but it's beginning to looks like a new reg/rec is in your future.

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Niels, you mentioned that you downloaded the trouble shooting list. Not sure if it was this one but if so, others may want to download this: ROAN_Generator troubleshooting.pdf

 

I know you've gone thru the wire connections but might want to really make sure that the connections in the mulit-pin regulator plug are fully connected and making good connections to the regulator. I have added a tie wrap to each end of the connector to "cinch" this to the regulator and insure that it remains fully engaged and doesn't "walk" out of the regulator.

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Looking more like thermal runaway on the SCRs and a dead ducati. They can't take it for long. BTW, why are you drawing so much power? I run ~60W load with lights off. You are more than double that.

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In the 18 months I've had my CTLS in Santa Rosa, have had to replace the voltage regulator twice. Both times it solved the electrical system issues which would appear intermittant but get worse over time.

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Just a wild-assed guess, could a failing or open capacitor cause the problem?

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not likely. The cap is there to filter noise and protect everything else if the battery drops out. Doesn't change the power through the R/R. You would hear it in the intercom if the cap open circuited.

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There is no real way to test the reg/rec other than replacing it and yours sounds like it is going out. If it has 18-22 ACV going in with the yellow wires and 12DCV coming out then I would normally think it's okay, but it's beginning to looks like a new reg/rec is in your future.

You can sort of with a DMM that has diode test. Disconnect the Reg/Rect On diode mode, measure from either of the G connections (the lighting coil inputs) with the red probe to B+ with the black lead on the RR tabs. Should be ~0.8V for both. Reverse the leads and should be open circuit for both. Now put the red lead to the ground tab and measure with the black lead to each of the G connections. Should be open circuit. Should also be open circuit with leads in the other direction. That won't tell you if the SCRs are completely burnt up but usually they short

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I had the alternator light come on for the first time, cold, when flying up for my annual. I shut down, pressed on the orange connector, and everything worked.

 

I've noticed that while cold, I can get 13+ volts at 2400 RPM. AFter a warm restart, I can't get more than 12 volts unless I run the engine over 3000 RPM. Maybe this thermal cut-out is real.

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Aside from the failure mode, the RR is designed to compensate the charging voltage downward as it heats up. This would be appropriate if the battery were similarly getting hot, but mostly it is just the RR that overheats

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Low voltage at low rpms can be normal especially with lights and everything on, but it should increase with throttle. If you have low voltage at low rpms you shouldn't be in that state very long anyway and that means your just using a little more battery.

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I've noticed an extra volt after a cold start, 13.2 V with transponder and position lights on. After landing, the same 2200 RPM idle gives me about 12.2 on the Dynon unless I turn off the transponder.

 

Would a bad connection to the VR give me the alternator light?

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I noticed similar issues in my Sky Arrow.

 

Periodically, after a flight, taxiing in my "GEN" light would flicker on at about 2,200 rpm. Normally its off even at idle.

 

By the subsequent flight, it would be fine if cooled down.

 

That problem seems to have resolved itself - I had forgotten about it and it has not been an issue for a year or so.

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A poor connection in the system would indeed give you a lower than normal voltage and or a poor ground. After installing my upgraded ground wires to CT engines all grounding based problems have gone away. Some problems can not be fixed by just adding a better ground. It is possible that your reg/rec is causing your issue. The only real way to check this is to replace this reg/rec with a known good one.

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Chanic

 

Drinking a lot of power ? The CT is fully glass, Transponfer, GPS, flashing red beacon headlight and all those little gadgets that one uses in flight today.

So when you add up the amps, 10 A sound about right. Your diode test is excellent for proving a dead Ducati on board and "thermal runaway" should be be considered when it happens after the Ducati gets hot. The Ducati lives a tough live!

Thank you for all your thoughts.

 

Niels

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Ray Watts

 

Thank you for your detailed reply. All steps were considered and very helpful. See my reply below to "Run to eat" for the solution to the problem.

 

Niels

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