A new regulator for the Rotax 912

Depending on whom you listen to, the Ducati regulator supplied with the Rotax 912 ULS in the RV-12 is either a good, solid piece of equipment or a failure just waiting to happen.  I have not had mine fail, but I have noticed that the charging voltage is a little low.  I don’t think I have ever seen it above 13.7 V while in flight, and it’s lower on the ground.  Given that Odyssey recommends 14.2 to 14.7 V charge voltage, I’d like to see it a little higher to get as much life out of the battery as possible.

I’ve read quite a bit on VAF about replacing the original regulator with one designed for John Deere garden tractors.  The compatible John Deere part number is AM101406, and aftermarket replacements are readily available.  They’re everywhere, as a matter of fact.  As it turns out, it seems to be a pretty popular regulator for other applications as well.  At $30 a pop or so, delivered, they’re pretty inexpensive as well.  The only challenge is mounting it, since the hole spacing on the Ducati is wider than the JD item.  The Ducati regulator is about 3-5/8″ between the hole, while the JD replacement item is more like 2-3/8″.

There are several ways to skin this cat.  Some guys have installed an additional nut plate.  My plane is built and I really don’t want that hassle.  I wanted to use the hardware I had on hand, and be able to switch back to the original regulator if needed.  Since mine has not failed, it will be fine to use as a spare.

Below are pictures of a mounting plate that I fabricated from some .125″ stock I had on hand.  Actually it was part of a piece of AL angle stock, with one side cut off with a band saw.  I marked and drilled holes to match the Ducati regulator, then counterbored 1/2″ holes on the bottom to clear a pair of AN3 bolts I had on hand that just happened to be exactly the length I needed.  This mounting plate allows me to use the original pair of bolts to mount the assembly in the plane, and if it ever becomes necessary I can drop in the original regulator with the same bolts.

A brief ground run confirmed that the charge voltage holds steady at 14.2 V down to about 1700 RPM or so, where it drops off slightly.  I noticed none of the voltage fluctuation I have seen with the Ducati regulator.  I’ll throw the original in the plane for a while just in case, but so far it’s looking good.

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