Converting to a B&C Alternator

May 2021
Updated August 2022

I bought my Fly Baby in 1996, after flying original Fly Baby (N500F) for seven years.  Unlike the primitive prototype, N45484 (aka "Moonraker") came with a complete electrical system.

I've owned the plane for about 25 years now...but in all the time I'm had it, my PRIMARY maintenance issues involved the electrical system.
In addition, when the previous owner bought the plane in 1993, the generator failed on HIM on the flight home to Seattle, and he had to get it rebuilt in San Francisco.

So...when I started noticing the charging system was developing an intermittent failure in early 2020, I wasn't too pleased.  But it always seemed to come back; I'd take off without the generator producing, but a few minutes after takeoff, the bus voltage would shoot up to 14.4 volts.


As ever, when problems turned up, the question arises:  Is it the generator, or the regulator?

Zeftronics had provided a set of measurements to take to ensure the generator was up to snuff.  I ran those measurements when the issue first arose, and the Armature-to-Ground resistance was above the range Zeftronics specified.  They wanted it less than 0.1 ohm, and I was seeing about 1.9 ohm.

I continued to fly the airplane, monitoring the generator output.  It usually kicked in after the engine had run at full power for a couple of minutes (e.g. takeoff).

Then in March 2021, the charge departed and didn't come back.  I ran the Zefttonic measurements again, and both the Field- and Armature-to-ground readings were outside the specified range.

Decision Time

So:  Time to make a decision.  I figured I had four options:

1. Remove generator, take it to a rebuilt shop

This is what I had done in 1997.  Why not do it again?

I didn't know if the company I'd used was still there...and whether they'd work on an aircraft generator.  They didn't want to, last time.

I estimated the cost as $150.

2.  Remove generator, rebuild it myself

It isn't rocket science.  The rebuilding parts were available through Fresno Airparts... a new set of brushes and some bearings cost just $40.

The problem was the uncertainty.  I didn't know that I could rebuild the generator, and removal and replacement of it is a royal pain.  I'd hate to pull it off, fix it, and find out I was still having problems.

3.  Buy a rebuilt generator

To my surprise, they were available online.  Cost about $350.

The final option:  Remove the generator, and replace with a B&C alternator.  B&C makes an alternator that's a direct replacment for the Delco generator/regulator systems used with small Continentals.

The drawbacks here?  I'd have to rewire the airplane to accommodate the regulator compatible with the B&C alternator.  That was going to cost about $300.

That didn't include the cost of the alternator itself.  But when I had my problems in 2015, a friend offered me a used B&C alternator.  Even better, this alternator already had the Continental drive gear installed!  Normally, you have to buy the alternator, remove your drive gear, and ship it to B&C for them to install.  Already having the gear on the alternator give me a real leg up.

Going with the B&C

Seemed pretty logical, by this point.  But there was one other factor:  I was sick to death with dealing with the Delco generator/regulator system.  I had so many problems over the years, and I just didn't want to keep dealing with it.

So the decision was made:  Go with the B&C

The regulator Question

Aircraft Spruce listed the B&C regulator for my alternator, and also carried a recommended "Overvoltage Protection Kit."  Clicked onto the ACS web page...and both were back-ordered.

Gulp.  Had I left the window behind?

Set a query by email, and got a response the next day.  The company WERE discontinuing the regulator and overvoltage kit.

But...they had something better. Their Automatic Voltage Controller (AVC1) was a single unit design to replace the two previous kits.  Their tech convinced me this would be a good choice.

(BTW, I got excellent service from B&C tech support both then and on other issues later.)

But First....

Before ordering the Controller, I decided to remove the generator and look at it.  I already had the rebuild kit for the generator.  If the problem was something obvious, I could just fix it and re-install the generator.  In any case, I'd already bought the gaskets, and if I decided to continue with the B&C, I could install the alternator while waiting for the AVC to arrive.

Removing the generator

As Hamlet says, "Aye, that's the rub...."  I'd pulled the generator back in 1997, and I still remembered what a bear of a job that was.  Three studs stick out from the accessory case for bolting the generator or alternator in place, and the top one is very, very difficult to get to.  There's the left mag immediately above and to the left, along with the sort of "tower" for the tachometer drive above and to the right.

Between the two, it's almost impossible to get a wrench on that top nut, and when one does, there isn't enough room to move it.

Back when I removed the generator in 1997, I ended up removing the magneto.  I didn't want to do that again.  Back then, I carved up a variety of wrenches to try get to that nut.  I tried to re-use them to no avail.  I carved up other wrenches.  No luck  I bought several ratcheting wrenches and tried to modify them.  Still no go.

Eventually, I found the key:  I had to remove the Tachometer drive "tower."  With that gone, there was just enough room to get a wrench on that top nut and turn it a few degrees.

Since the tower and the generator share the same gasket, it had to come out anyway.

Finally... finally... I had the generator out.  In the picture below, you can see it resting temporarily on the engine mount, after I backed it out and turned it for removal.

Generator Checks

With the generator out of the airplane, I put it on the workbench and re-ran the Zeftronics measurements.

Passed.  Every one of them.

I went over to an old pickup truck in my hangar and hooked up the generator to the battery.  It spun, just like it was supposed to.

So.  NOW what?  Obviously, the handling of the generator had caused whatever was messed up to correct itself.  I examined the unit, and didn't see anything obvious messed up with it.  Even the brushes looked pretty good. (And yes, I had tried banging it with a hammer while it was still installed to see if it would start working again).

Just reinstall it?

Not on your life.  It took a heck of a lot of work to get that out of the airplane, and I was NOT looking forward to trying to stick it back into place.

A side-by-side comparison of the Delco generator and the B&C alternator is kind of illuminating:

It bolts into the same place as the Delco, but it's obviously much smaller, much easier to handle.  The weight is about ten pounds itself, a good indicator of the ease of installation.

So... order the regulator from B&C, and start the installation of the alternator.

Alternator Installation

Being ten pounds lighter, inserting it into the engine was a breeze.  The alternator itself fits nicely on the palm, and the unit was quickly in place.

One little problem, though:  The studs sticking out of the engine accessory case were long enough that there wasn't enough room to slip the washer and nut into place.

So pull out the alternator a bit, get the lock washer and nut started on each of the three studs, then tighten them evenly to get the alternator tight into position.  Re-install the tachometer "tower," and it's ready for the voltage controller.

By the way, this is what the installation finally looked like:
The arrow points to that stubborn top nut.  It's dim up there, but you can see the limited space between the end of the stud and the opening in the alternator.

Also, you can see the silver tach "tower," and the very bottom of the left magneto (straight up from the tip of the arrow).  Not a lot of room to swing a wrench.


In an ideal, perfect world, the B&C Voltage Controller (regulator) would have had the same foot print (attachment points) as the Delco regulator.

No such luck, of course.  B&C's regulator is designed to work with their full range of products, and most users want it as small as possible.  The Delco unit is much larger, and uses a three-bolt pattern for attachment.

The regulator mounting on my airplane consists of three studs sticking out of the firewall.  The back of those studs is right against the fuel tank, so removing those studs...much less adding studs to match the new voltage controller... is impossible without draining the fuel and pulling the tank out.

I elected to mount the B&C Controller on a piece of 1/8" aluminum plate, and drill holes in the plate to match the stud pattern on my airplane.

Sounds simple...but of course, I have homebuilt airplane, not something built in a factory.  The holes in the Delco regulator are large to accommodate rubber shock mountings.  The stud pattern on my airplane didn't match the "theoretical" mounting pattern for the Delco.

So it took me several tries, and I did eventually have to enlarge one hole a bit.  Also the plate isn't vertically aligned in the's cranked a few degrees to the right.

That bothers me, but not enough to take it off and re-do it again.


The stock Delco regulator has the following connections:
1.  regulator directly to the Armature on the generator
2.  regulator to a cockpit switch, and from there to the Field on the generator
3.  Connection to the 12V bus

The B&C Controller has six connections... but, in reality, its actually simpler in the wiring.  One connection is for a cockpit warning light, which I chose not to install.  Two connections go to the 12V bus.  Two more connect to the alternator itself, and the sixth connects to the 12V bus via a cockpit switch.

The biggest change was the cockpit switch.  Previously, one wire went through the firewall from the regulator to the switch, and the other half of the switch was connected to a SECOND wire through the firewall.

Since the switch would not connect the regulator control to the 12V bus, I didn't need to use that second wire.  The other terminal on the switch would be just going to the 12V bus, and there was a bus point just a few inches from the switch itself.  In this picture, you can see the back of the split master switch, with the pale yellow and red connectors.  The 12V bus in located at the bottom of the picture, under the red boot.

I debated leaving the second wire in place, but ended up pulling BOTH wires and running a single new wire.  Since it was connected to 12V, I wanted a red wire, and both the previous wires were white.  They were also shielded, which my implementation didn't need.  I did need to put a fuseholder in this connection to the 12V bus...I used a stand-alone ATO-type fuseholder, like the other fuses on the airplane.

Here's the updated schematic:

The check marks show where changes were made.

The wiring was all using aircraft-grade wire.  My airplane was originally wired with ordinary hardware-store stuff, and after twenty years, the insulation was starting to crack.  I replaced it all in 2010.


One thing B&C wanted was a 10,000 microfarad capacitor on the output of the Voltage Controller.  This would help reduce noise introduced into the electrical system.  I bought B&C's capacitor and matching Adel clamp, and drilled a hole in the mounting plate to hold it.'s how it looks.


I took things fairly slowly; basically completing it in daily stages and re-checking the previous work the next day. The mechanical installation happened on a Saturday, the re-wiring work on Sunday, and the final connection and securing the wire harness on Monday. I could have test-run it in Monday afternoon, but I always prefer to hit major milestones with a fresh eye.

So Tuesday , it was ready to go when I arrived at the airport. I checked the wiring one last time, and used a DVM to verify the input voltage were where they were supposed to be. With that, reinstall the forward turtledeck (with just two bolts holding it) and the lower forward belly panel.

Roll it out in front orf the hangar, chock it, climb in and start.

Voltage was flat (12.1V) after the start. Ran it up to ~2,000 RPM. Still flat. Damn!

Then I noticed the system voltage had popped up to 13.6V. Either it took a few seconds to start working, or the RPM had to be held for a bit. In any case, it was working.

Flight test verified a good, solid 14.4 volts (the B&C spec).
One thing I did notice is a LOT of radio noise. My Icom has a squelch adjustment from 1 (squelch off) to 32 (max squelch). I had been running at a setting of 7. Had to increase it to 20 before it stopped continually breaking squelch.
On the ground, stuff on the radios is a bit choppy, like it's still affected by the alternator noise. In flight, with the engine at cruise, it was a lot less noticeable. On the ground, afterwards, the effect at idle seemed to be less as well. I'm thinking the battery had gotten charged and the alternator wasn't working as hard.

One thing interesting is that the charging system doesn't always start working on its own.  Most of the time, it charges normally, but occasionally it just doesn't start.  All I've had to do is cycle the power to the controller, and it starts going.

I'm suspecting this is ground issue.  The Controller is grounded through its case, to the attachment plate, then through the studs to the firewall.  I wonder if there might be a bit of variability in the quality of that ground.

My condition inspection is due, and I'll probably install a dedicated ground wire.


The B&C system was providing a solid 14.4 volts...but my Odyssey Dry Cell battery wants a 14.7 volt charge.  One thing nice about the B&C voltage controller is that it is removes a screw, and there's an adjustment potentiometer in there.  Each turn raises the output by 0.1 volt, so I needed to turn it three times.

So I removed the screw...but couldn't see the potentiometer. I didn't know what screwdriver it would take.  All I saw in the hole was a silver dot like a solder point.

Called B&C Technical Support, who had already given me good help in planning my installation.  The Tech was stumped as well.  He told me it needed a small, standard-blade jeweler's screwdriver., but I still couldn't see the recepticle for it. As we talked on the phone, I grabbed my biggest flashlight and stood on the left tire to get a better view.  I then saw the slot for the screwdriver.

What happened?  It was bright in the hangar, and there wasn't much light making it into the hole to illuminate the adjustment screw.  Seeing it was so bright, my eyes hadn't adjusted down to being able to make out details in the hole,

One of the weird things:  The adjustment screw seems to be off-center.

I closed the hangar door to get things dark, and took my big flashlight again.  Was able to crank the screw around three times.

When I took off, it was still reading 14.4 volts.  But as we continued, the voltage started sliding up.  After five minutes, it was averaging 14.7 volts...just about what I was looking for.  I think the multiple starts on the ground testing had dragged down the battery, and the voltage was sucked down as the battery recharged.  As it reached full charge, the regulator established the targeted value.

Anyway, that's about it.  The system has been reliable (so far...) and I'm pretty happy with it.  It's a ten-pound reduction of weight forward of the firewall, but I haven't noticed it, flying.  MAYBE it's a bit more tail-heavy, but not enough to notice.

Anyway, thanks to TJ at B&C Tech Support, my airplane is fully powered again.

Update August 2022

Full year into the operation of the B&C alternator, and it's still working great.

Mentioned above some difficulty getting it to start working after engine start.  This appears to be a technique issue.  Start the engine with the "BATTERY" half of the master switch on and the "Alternator" part of the switch off.  Once the engine is running, turn on the Alternator switch.  Works every time.

Ron Wanttaja