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Jabiru Alternator

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cluros(at)gmail.com
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Posted: Thu Sep 11, 2025 12:34 pm Post subject: Jabiru Alternator

Greetings all,



Is anyone familiar with the built in 20A alternator (generator?) on Jabiru engines? I just did a flight and during the runup the bus voltage only rose 0.5V which is apparently normal and they do not reach 14V until 2500 RPM. On takeoff roll the voltage started to rise then dropped to battery volts for the rest of the flight regardless of RPM. Charging system totally dead. A thorough examination of the wiring didn't find any obvious issues. At this point I think it has to be the alternator itself or the regulator. Does anyone here know a way to test the regulator?

Thank you,

Sebastien Seykora

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dj_theis

Joined: 28 Aug 2017
Posts: 68
Location: Minnesota

Posted: Fri Sep 12, 2025 6:10 am Post subject: Re: Jabiru Alternator

Hi Sebastien,



I’ve never worked on the Jabiru alternator but have spent countless hours on a similar “integrated” alternator on the Revmaster.  Both are 12 pole permanent magnet (PM) anlternators and suffer from similar design and manufacturing shortcomings.



Without going into any detail of the design or manufacturing flaws,  if you are lucky the problem is your regulator /rectifier.  If the problem extends to the stator, you might want to consider the available upgrade to an external field controlled alternator.



https://www.rotecaerosport.com/alternatorupgrade



I believe Jabiru stators are wound with 12 series wound (single phase) coils.



If this is what you have there will be 2 wires coming from the alternator, likely leading to a relay.  I don’t know if Jabiru used an isolating relay between the stator and the regulator, can you provide a wiring diagram?



There are a few things you can check.



1) Measure the resistance from wire to wire of the two output wires from the alternator stator, disconnected from the relay. These are the wires that should come directly from the stator and should be isolated from ground and have a measurable resistance (I don’t know the specification for stator resistance on the Jabiru but you will need a good DVOM that can measure single digit resistance). Knowing the expected resistance is important as one of the common failures is a breakdown of the insulation on the stator wires and the resistance will be (significantly) less than the spec.  Also check if there is an inline fuse in the stator wiring that could be blown.



2) Check that the alternator stator wires are isolated from ground.



3) Check that the relay (if it exists) is operational. (disconnected from the alternator and the regulator, energize the relay and verify that there is continuity between the contacts that were wired to one stator lead and one regulator lead.



4) Assuming the above tests don’t expose a problem… Testing the AC output of the alternator is a little more difficult but can be done. You will need to carefully wire and secure connections from the output of the alternator (the two stator wires) “without the regulator,” to an AC meter and run the engine from idle to the normal charge voltage. At idle (900 rpm) I would expect the voltage (AC rms) is well below the minimum charging voltage of 12.8 volts (note that it is the peak voltage, not the rms voltage that must rise above 12.8, and the rms underrepresents the peak by a multiple of about 1.4)

Increasing the rpm should show an increase the voltage linearly, (if the voltage shows 9 volts at 900 rpm you should see something close to 18 volts at 1800 rpm…double the rpm should double the open circuit voltage). You are measuring open circuit voltage (no load) and the connected voltage to a battery would be significantly less.  So restating, doubling the rpm should double the open circuit voltage AC rms voltage.  The open circuit voltage of a working PM alternator at moderate speeds will be astonishingly high! 20 volts (or more) is not uncommon when not connected to a battery at high rpm.



5) The rectifier/regulator is the last item to check and requires a capable bench AC source to do properly test but if all the above tests don’t expose an obvious problem, you should have a working charging system that pretty much identifies the regulator as the point of failure.



I hope this helps give you a little insight into what you might check.



Dan Theis.

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_________________
Dan Theis
Scratch building Sonex #1362
Revmaster Alternator problem solved.

user9253

Joined: 28 Mar 2008
Posts: 1942
Location: Riley TWP Michigan

Posted: Fri Sep 12, 2025 10:04 am Post subject: Re: Jabiru Alternator

One way to check a rectifier/voltage regulator is to substitute a new one.  if the new one works, then the old one must be bad.  Search eBay for AM101406 which is for John Deere tractors.  They sell for as little as $18, item number 176962600707.

AM101406 has 5 terminals.

B+  : Battery

AC: Generator

AC: Generator

L:  Lamp

IGW: Ignition switch

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Joe Gores

dj_theis

Joined: 28 Aug 2017
Posts: 68
Location: Minnesota

Posted: Fri Sep 12, 2025 11:04 am Post subject: Re: Jabiru Alternator

I second Joe’s suggestion.  



I’ve tested the JD rectifier/regulator and found them to be good substitutes for whatever OEM R/R are supplied (single phase PMs only, of course).



The only caution might be that these R/R devices have been on the market for a while and there might be less than ideal copies available.



Purchasing from John Deere (or a reliable substitute provider), as Joe implies with the JD part number, is generally a reliable source.

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_________________
Dan Theis
Scratch building Sonex #1362
Revmaster Alternator problem solved.

user9253

Joined: 28 Mar 2008
Posts: 1942
Location: Riley TWP Michigan

Posted: Fri Sep 12, 2025 11:45 am Post subject: Re: Jabiru Alternator

The eBay item I suggested is not a genuine John Deere part.  It is probably 

made in China.  I have been using a similar voltage regulator in my RV-12 for 

100s of hours without a problem.  It is very important to keep the voltage 

regulator cool.  Mount it using heat conductive paste and cool it with forced air.

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Joe Gores

dj_theis

Joined: 28 Aug 2017
Posts: 68
Location: Minnesota

Posted: Fri Sep 12, 2025 11:46 am Post subject: Re: Jabiru Alternator

I second Joe’s suggestion.  



I’ve tested the JD rectifier/regulator and found them to be good substitutes for whatever OEM R/R are supplied (single phase PMs only, of course).



The only caution might be that these R/R devices have been on the market for a while and there might be less than ideal copies available.



Purchasing from John Deere (or a reliable substitute provider), as Joe implies with the JD part number, is generally a reliable source.

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_________________
Dan Theis
Scratch building Sonex #1362
Revmaster Alternator problem solved.

matronics(at)rtist.nl
Guest

Posted: Fri Sep 12, 2025 1:26 pm Post subject: Jabiru Alternator

Jabiru uses Kubota regulators, type Kubota RP201-53710



On the Jabiru engines, a common issue is the connection from the coil to 

the regulator and from the regulator to the battery and ground. The 

spaces in the Kubota regulator are underrated for the application. 

Advice is usually to cut off the original and use good quality spade 

connectors.



Rob



On 9/12/25 21:04, dj_theis wrote:

 	  Quote: 	
		   



 I second Joeâ€™s suggestion.



 Iâ€™ve tested the JD rectifier/regulator and found them to be good substitutes for whatever OEM R/R are supplied (single phase PMs only, of course).



 The only caution might be that these R/R devices have been on the market for a while and there might be less than ideal copies available.



 Purchasing from John Deere (or a reliable substitute provider), as Joe implies with the JD part number, is generally a reliable source.



 --------

 Dan Theis

 Scratch building Sonex #1362

 Revmaster Alternator problem solved.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=515622#515622

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