paul.r.kuntz(at)gmail.com
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 Posted: Sun Aug 18, 2013 7:58 am Post subject: AeroElectric-List: Re: Rotax 912 UL alternator drop-out |
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Several inputs suggested checking the connections on the leads coming from the alternator, and checking the system ground connections. I checked the faston-type alternator lead connections, which were clean and tight. I checked all of the ground connections, which were also tight. Yesterday I went up for a test flight and confirmed the symptoms under varying system loads. The normal system voltage with alternator on line is 13.8 volts, which is consistent with what others are reporting for the Rotax Ducati regulator. I see a max load of 10 amps with everything running, so I am satisfied that the total load is well within the standard Rotax system capacity. I also observed that the system voltage drops to 13.5 volts at the 10 amp max load, which seems abnormal. Under this max load, the alternator dropped out after a few minutes, indicated by system voltage dropping to around 12.5 volts -- consistent with fully charged lead-acid battery.
When I reduced the load to 3 amps, which is my practical minimum (one Dynon display, radio and transponder), the alternator came back and stayed there, with system voltage at the normal regulator set point of 13.8 volts.
I repeated this experiment a few times for various loads, finding that a total load above 5 or 6 amps will cause the alternator to drop out after a few minutes, and that it will come back when the load is reduced to 3 amps.
I am pretty well convinced that my voltage regulator is bad. I did learn from comments on this issue that Van's includes a voltage regulator cooling kit with its lighting kit for the RV-12, consisting of a length of plastic tubing that connects from the air intake duct to a shroud over the regulator, providing a direct blast of cooling air to counteract the increased electrical load of the lighting. So there is certainly indication that the Ducati regulator is susceptible to overheating under load. The RV-12 regulator is on the engine side of the firewall, however, and mine is on the cabin side. At 10 amps with the regulator mounted in the cockpit environment, I'm thinking the regulator should be able to handle the load without supplemental cooling. Others have noted the not-so-good reputation of the Ducati regulator, but there are thousands of them in service on Rotax engines worldwide, so rather than tackle a reconfiguration of my regulator and wiring installation at this point , I ordered a replacement Ducati from Lockwood Aviation and will see how it goes. I also ordered a overvoltage protection module from B&C, since the Pipistrel electrical system does not include one. I'll install it with the new voltage regulator.
I'll report my findings after installing the new regulator.
Paul Kuntz
On Sat, Aug 10, 2013 at 10:21 PM, Paul Kuntz <paul.r.kuntz(at)gmail.com (paul.r.kuntz(at)gmail.com)> wrote:
[quote]Thanks for the tips, everyone. I concur with Bob that my Ducati regulator is done for and should be replaced. I will take a look at the Schicke unit that Peter mentioned.
Cheers,
Paul Kuntz
On Friday, August 9, 2013, Robert L. Nuckolls, III wrote:
| Quote: | --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
At 12:55 PM 8/9/2013, you wrote:
| Quote: | Thanks for the tip. I'll check this cooling shroud idea. I'm also wondering if my regulator has already been compromised. Any opinions on what my repeated fail/recover situation indicates? I would guess that it cycled between failed and recovered 8 or 10 times before we established a state where it stayed on line, limited to a total current draw of 3 amps.
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If your regulator can't carry 10A without cooling, it's
probably broke. A functional part should be capable of
rated output for the alternator which is on the order
of 18A. I've not heard of any mass-movements to forced
air cool these regulators.
Bob . . .
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