What's new
Van's Air Force

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

If you are building a 12iS, don't skip the lights

jrtens

Well Known Member
Friend
You will need them on hot days to keep the voltage regulator from overheating. (Yep - the exact opposite of the 12)

See the attached explanation from the 12iS FTS about one of the big electrical differences from the 12.

After the battery is topped off - and that happens rather quickly - I regularly see 7 amps without the lights.
 

Attachments

  • VR info .jpg
    VR info .jpg
    437.6 KB · Views: 559
Last edited:
That’s really weird. You would think the voltage regulator circuit would modulate the field windings to match output with load.

What if you had to drive your car around all the time with headlights, radio, and turn signals on?
 
The Rotax alternators are permanent magnet type. Thus they do not have field windings.
I can not believe that, "These regulators reject any unused electrical power
as heat
." Van's must have been misinformed about this. What Rotax
document is this statement based on? Suppose that 21 amps are available but
not used by the aircraft. If those 21 amps were turned into 300 watts of heat,
how is that heat dissipated? Where are the cooling fins?
 
It will be easy enough to test. Put a thermocouple on the voltage regulator and go fly.
Observe the thermocouple temperature first with a light electrical load, and then with
a heavy electrical load. Repeat a few times to be sure the numbers are consistent.
 
Permanent magnet alternators will either have a shunt type VR or PWM VR.

The shunt type WILL dump the excess amps as heat.
 
It is true that there are shunt type voltage regulators. But a shunt type can not
possibly be used with the Rotax iS. The Rotax iS generator output is rated at 420 watts.
A shunt type would need to be capable of dissipating 400 watts of heat. How is
that possible when the regulator is not much bigger than a pack of cigarettes?
The regulator is rated at 80 degrees C. If it had to dissipate 400 watts, it would
get as hot as a milk house heater. Why would Rotax design the voltage regulator
with old shunt technology instead of the new switching type? Well, they didn't.
The smaller the electrical load is, the cooler the regulator will be.
The voltage regulator does not care if the landing lights are on or not.
 
The fact that Vans guidance goes against conventional thinking, as you have pointed out, makes it hard to imagine that they put it in the FTS without some research and testing.

With a quick search, I found a 2016 Sling LSA safety advisory recommending the same - to turn on the lights to keep the B regulator from overheating.

Here is a note from that SA.
 

Attachments

  • sling.png
    sling.png
    23.1 KB · Views: 202
Greg and Scott at Van's Aircraft monitor these forums. Perhaps they will do some
flight tests with different electrical loads while recording the regulator temperature.
Then we will have the facts instead of rumors and old wives tales.
 
A regulator takes an incoming voltage and produces a stable output voltage, the difference between those two voltages is the heat produced.

The current produced by the alternator is based on load, it will only supply a load based on the demand. It doesn’t just produce 40 amps at all times.

The PCM controlled alternator on cars is so that when cruising in a high gear and low rpm the alternator is able to produce sufficient current to match the load and you don’t get a parasitic draw on the battery.
 
Today I was a passenger in my friend's Kitfox that has the same engine as a RV-12, a Rotax 912iS engine.
We had installed a thermocouple on voltage regulator B to monitor its temperature which is displayed on the Skyview HDX screen.
While cruising, I pulled the circuit breaker for Regulator B which disconnected it from the aircraft main power bus. The aircraft battery was now supplying aircraft electrical loads. We watched regulator B temperature which was 80 degrees F prior to pulling the breaker. Over a period of about 5 minutes, the temperature slowly dropped to 75 degrees F. The outside air temperature at our altitude was 54 degrees F. To prevent any voltage surges, my pilot friend reduced RPM to idle while I pushed the regulator B circuit breaker back in. We watched the Regulator B climb back up to 82 degrees, a little warmer because the battery was being recharged.
Conclusion from the experiment:
The temperature of regulator B goes down as aircraft electrical load is reduced.
Page 6-6 of the RV-12iS Flight Training Supplement is incorrect when it states, "These regulators reject any unused electrical power as heat. Allowing the power usage to fall below 7 amps for extended periods of time may damage the regulators."
 
Thanks for that information Jon.
Regardless of what aircraft manufacturers have written, the temperature of voltage regulator B is directly proportional to the aircraft electrical load. In other words, as the aircraft electrical load decreases, so does regulator B temperature. I have proven that with a flight test. The discolored wires mentioned in Sling's service bulletin are due to a high resistance connection. Keeping the regulator cool is a good idea. But doing that will not fix the poor electrical connection.
 
Thanks for your input Joe.

I still have a hard time believing that Vans would put that information in the FTS without doing a lot of testing - especially since they mention the very specific 7 amps and they went to a lot of trouble to add a cooling duct in the cowl.

I also posted this issue in the Rotax owner 912iS forum - no debate there. Because curious 12iS owners want to know, here is the response I got - from a wizard no less. :)

reg b.jpg

Since this is obviously fairly important to those of us with skin in the game, I would like to hear what other 12iS owners have to say?
 
Vans reply needed ?

I guess we need to hear from Vans, again. Until they contradict what they’ve gone to the trouble of carefully documenting, I’ll assume the manufacturers did their jobs correctly. Although this is an interesting discussion, I am not personally comfortable second guessing their codified recommendations. YMMV
 
The Rotax Wizard needs to go back to Oz and get his facts straight. :)
It is too bad that aircraft manufacturers are publishing rumors without verifying them. Give me the name of the Rotax manual and page number that says that Rotax 912iS voltage regulator B is a shunt type that dissipates unused energy as heat. If it made sense, I would not have gone to the trouble of installing a thermocouple to prove the rumor wrong. Saying that regulator B can dissipate 400 watts of heat defies the laws of physics. 400 watts is enough to heat a bathroom. That little regulator would be glowing red hot. Numbers don't lie. When I disconnected the load from the regulator, its temperature went down, NOT up.
 
Rotax regulators

Two models of regulator are used on Rotax 912xxx engines. The Ducati type used on the non fuel injected engines and a model manufactured by a Swiss company. I know something about the topology of the Ducati type having done a failure mode investigation on one that failed on a friends RV-12. The generator is a multi pole permanent magnet generator with a open circuit RMS voltage of between 17 and 30 volts (measured) over the typical engine RPM range. The topology of the regulator is a phase angle regulator running at variable frequency (related to the engine rpm). The rectification and conduction angle are controlled by bridge configured SCRs. The failure modes of the Ducati regulators are related to two major factors in my opinion.
1. Inadequate mechanical design and construction leading to poor mechanical connections and thermal issues.
2. Selection of SCR components that have a high saturation voltage leading to high dissipation and thermal runaway of the SCRs. All of the SCRs that I examined in the units that I dissassembled had failed short circuit indicating overtemperature, over current. Overvoltage failures generally present as open circuit.
The alternative regulator is used on the fuel injected engines which use the same or very similar permanent magnet generator (PMG). The regulators are interchangeable according to the bulletin from the UK light aircraft association. I have no knowledge of the topology used in the alternate regulator but I suspect it is similar with better engineering and component selection.
The key to keeping the Ducati regulator alive appears to be good thermal conduction to regulator mounting and adding a blast tube to provide cooling air. Providing good direct connection to the regulator reference terminal. The Vans wiring diagram provides connection through a myriad of connectors. My friend on his RV-12 bypassed all of the connectors and made a direct wired connection. To my knowledge the replacement regulator with mods of blast tube, wiring and thermal grease to the mounting plate has not failed ( he sold the airplane a year ago). The power dissipated in the regulator is a direct function of the current provided by the generator which is a function of load and battery condition. Demanding a high load at low engine RPM results in more dissipation in the SCRs than the same load at higher RPM (due to changes in conduction angle and time in saturation. So keeping the load low during ground operations helps.
Hope this sheds more light on explaining the regulator operation.

KT
 
I guess we need to hear from Vans, again. Until they contradict what they’ve gone to the trouble of carefully documenting, I’ll assume the manufacturers did their jobs correctly. Although this is an interesting discussion, I am not personally comfortable second guessing their codified recommendations. YMMV

I'd like to hear from Vans on this subject as well. At what OAT does this become an issue? Also, how do you keep the 'B' side from overheating if your aircraft doesn't have the optional lighting kit installed?
 
It is too bad that aircraft manufacturers are publishing rumors without verifying them.

No need to be condescending to the Vans team. Do you really think one little test makes you the authority now? It's nothing compared to the extensive testing required by the Vans engineering team to meet Rotax installation and ASTM standards. These are professionals and they take their job seriously. People who don't show respect don't deserve it themselves.

Just because it seems more logical to use switching regulators doesn't mean that Rotax did in fact use them. Perhaps a compatible switching regulator wasn't available for their 3 phase AC generators? Perhaps a switching regulator emitted too much noise? For some reason, they chose shunt type regulators.

Speaking of professionals, I put the question to Lockwood Aviation - widely recognized to be experts on Rotax engines.

shunt.jpg
 
Last edited:
Jon, I have the highest respect for Van's Aircraft. I believe they have not posted on this thread yet because they need time to conduct their own thorough tests. I would conduct more tests if I had a Rotax 912iS engine, but mine is a ULS. You have an iS engine. How about installing a type J thermocouple and conducting your own tests? Won't you enjoy proving me wrong? :) Type J thermocouples are available here: https://www.omega.com/en-us/temperature-measurement/temperature-surface-sensors/wt/p/WTJ-6-60
The thermocouple can be bolted to a spare ground stud on regulator B. Rotax recently increased the size of the stud from 4mm to 6mm. You need to measure yours prior to ordering the thermocouple. I prefer PFA insulation, but glass insulation is OK. Here is an example Omega part number: WTJ-14-36-TT. The thermocouple can be connected to display its temperature on your EFIS. You can monitor the regulator temperature to make sure that it is not overheating. I can offer advice on connecting to a Skyview system. One thing to keep in mind is that the red wire of a type J thermocouple is negative.
 
…Just because it seems more logical to use switching regulators doesn't mean that Rotax did in fact use them. Perhaps a compatible switching regulator wasn't available for their 3 phase AC generators? Perhaps a switching regulator emitted too much noise?

For some reason, they chose shunt type regulators.

Speaking of professionals, I put the question to Lockwood Aviation - widely recognized to be experts on Rotax engines.

View attachment 26377

We have our answer, well at least I do. I’ll go with the existing documentation.
 
Last edited:
It doesn't matter who is right or wrong. The important thing is to prevent your voltage regulator from over heating and failing. It must be an expensive part, not to mention the inconvenience and danger if it fails. So why not install a thermocouple to monitor the voltage regulator temperature? Then you can turn on or off electrical loads as required to keep the voltage regulator cool. A thermocouple only costs $20. Installation is relatively easy. Just bolt it to a ground stud on the regulator. If you have a Skyview EMS-221, the two thermocouple wires can be connected to an input on the 25 pin D-Sub. You might also need a 25pin male D-Sub connector. Below is a picture showing where to plug in the red and white thermocouple wires. Notice pin 2 is Red & pin 14 is White. After installation, you will need to go into the Skyview setup to display the "REG B" temperature. The temperature display takes up very little room on the bottom of the Skyview screen. The thermocouple can always be moved to monitor other temperatures like the cabin or avionics or fuel. If someone installs a thermocouple, please post your regulator temperatures at various electrical loads.
 

Attachments

  • EMS-221 D-Sub 25 pin.png
    EMS-221 D-Sub 25 pin.png
    23.8 KB · Views: 68
I apologize for saying "that aircraft manufacturers are publishing rumors". A Van's employee told me that information came directly from Rotax. The employee also said that Van's intends to monitor regulator B temperature while conducting flight tests. However, Van's is very busy right now getting ready for OSH. They will do testing when they are not so busy. In the meantime, It would be great if a RV-12iS builder conducts their own tests and reports the results here.
 
Below is a picture of my friend's Skyview display with REG B temperature displayed at the bottom and circled in black. It reads, "92, REG B, °F". I am posting this to show how much room it takes on the Skyview screen.
 

Attachments

  • REG B Temp.png
    REG B Temp.png
    404.4 KB · Views: 176
BATT AMPS annunciation on RV12is with Ducati VRs

Helping a friend isolate the following scenario:

After reaching 2500 RPM following engine start, the bus voltage is indicating 13.5 volts, but the alternator amps is only showing 4-5 amps with all the avionics turned on (another 12iS aircraft was tested, and shows 14 amps at this same stage). Intermittently during normal cruise flight (with flaps up, autopilot and landing light off), the BATT AMPS annunciation comes on the PFD and agrees with the battery discharge reaching the -3 amps warning level. At which time, the alternator amps seem to slowly creep up to around 7 amps, and eventually the BATT AMPS return to zero and the message goes out. However, when the landing lights are turned on, and the radio is keyed to load up the system, the charging amps never reach a level to adequately charge the battery, and the BATT AMPs condition remains until unloading the system.

Certainly the alternator should be able to keep up with entire system load. In reference to the OP regarding the FTS recommendations to keep the system loaded as to avoid overheating the VRs, it sounds like my above-described condition may be due to a damaged VR (the aircraft has only 35 hours on it, was built/first-operated in Tuscon, and has never utilized the procedure to load up the system after engine start). Have others experienced this issue describe in paragraph above? If so, what was your findings/corrections?
Also, how many other RV12iS operators are using the loading technique to keep the VRs cool?

Thank you in advance for any insight and/or feedback.
 
Robert, what is the electrical system voltage when the RPM is above 3000?
Does the voltage ever drop below 13.5 when RPM is above 3000?
The vast majority of electrical problems are due to bad connections.
Check every connection between the voltage regulator and the main power bus to be sure they are clean and tight.
 
Back
Top