Overheating voltage regulator B

Joe, 
I’m glad you followed up with this information.  While we don’t have a schematic of the 912iS regulator, I believe you are essentially correct based on it’s probable design.  Some of the information out there leads folks to believe that the 912iS alternator is always running at full output, and the load is simply split between the shunt regulator and airframe loads.  That thinking then promotes the belief that fully loading the alternator with aircraft loads is better than shunting them.  It is true that adding load can reduce the workload on the shunt regulator and let it run cooler, but that’s not necessarily true of the the alternator.  When considering the alternator, more aircraft loads generally means higher load on the stator.   

Consider that with no loads connected, and the shunt regulator working at its max to keep the voltage in check, the total load on the alternator under this condition is only about 60 watts, or about 15% of rated output of the alternator.  So it can be said that shunting excess voltage rather than increasing the connected load reduces the workload on the alternator.  Yes, dissipating 60 watts can heat up the shunt regulator, and to some extent the stator windings, but the load imposed on the alternator by the shunt regulator is intentionally limited by the magnetic saturation of the stators iron core.  The bottom line is that if you intentionally load up your alternator to reduce the workload on the shunt regulator, you ARE imposing more load on the alternator.  I have replaced regulators and stators on the 912iS, and the latter is much more costly.  With this considered, it may be better to take steps to keep the shunt regulator cool than to intentionally place a high load on the alternator.   

Just answered one of my questions the si915i 006 is also 912i-024……

Paul,

I bought a Stator (latest upgrade) about 3 months back for a friend’s 912iS aircraft. It came with the new style connector on it along with the mating connector to be installed on the voltage regulator.  The new connector has a 45 amp rating, which is more than double the load that the 912iS alternator will put out.  I can’t tell what the amp rating is of the old connector, but I would guess 15-20 amps.  The 912iS alternator can provide about 17 amps on the 3-phase AC leads, so under full load that may be enough to eventually degrade the old style connector.  

Rotax used a Deutsch DTM connector for the stator-to-regulator harness until recently.  That connector is only rated for 7.5 amps per contact, so it's no surprise that it overheats in the Stator B harness (it's only slightly overloaded near maximum output in the Stator A harness).  Presumably this is the reason for SI-915i-006 and SI-912i-024.

Rotax parts suppliers sell the connector kit for this Service Instruction for $515 (search Lockwood or Motive Aero for part number 481510; LEAF doesn't list it).  If you assemble the same parts off-the-shelf from Mouser, it comes to about $58.  That's quite a racket: use an obviously inappropriate part, then profit handsomely by selling customers the replacement at a 9x markup!

If you have an Experimental aircraft and want to accomplish this upgrade, but you don't want to buy the connector set from Rotax (and the expensive tooling to install it; see below), you might consider using Amphenol ATP connectors instead.  ATP contacts are rated for 25 amps each -- more than enough for this application -- and the connectors are a sealed design intended for industrial and automotive under-hood applications (they're a bigger version of the Deutsch connector that Rotax used).  All of the parts needed for this upgrade can be purchased for under $20, delivered.

Here's a link for a Digi-Key Electronics shopping cart populated with all of the necessary connector parts for the Stator B harness.  If you're upgrading Stator A as well, just double the quantities for the wedgelocks, pins, sockets and sealing plugs, then add the black connector housings for Stator A: here and here.

If you don't have a crimping tool for the Size 12 contacts used in ATP connectors, Amazon carries a good quality tool for $31, the Iwiss IWD-12.

For the Rotax-specified connectors, the crimp tooling you'll need is this and this; or, the cheaper option, this and this.  Before you buy the first option (the DMC tool) read the last paragraph of the second post in this thread.

Eric,

The Amphenol (Rotax) connector kit that we received from Lockwood came with pins that were wire range 12-10, the same as in your Mouser shopping cart link. As a heads up, these connectors don’t fit into the orifice on the standard AF8 crimp tool that Rotax recommends in the service letter. I’m not sure why they have not corrected this. The connector pin has a stop collar that is just slightly bigger than the opening in the tool.  I think this is because the standard DMC AF8 tool maxes out at 12 AWG, and since the pin is for 12-10 AWG, the tool rejects it.  JRready makes an AF8 type crimp tool with a larger opening called the JRD-FT8 that works for this pin. You will also need the UH2-5 positioner. The DMC MH860 also works (next size up DMC tool), but is twice the cost.