Converting an Alternator

If you have an internally regulated alternator and wish to convert to an externally regulated alternator then this will hopefully guide you through

(I must add here that if you don't have an alternator yet.. just get an externally regulated one and be done with it ! B&C sell some nice light weight alternators )

Firstly - Why would you want to?

Well the idea of an internally regulated alternator may sound like a great idea but there are some serious drawbacks to the alternators available on the market at present. Generally the available alternators are designed for cars. The problems include not actually being able to turn the alternator off. Sure, you have a wire that goes to the alternator that starts it up but that same wire won't turn it off. They are designed such that you would pull over to the side of the road and stop.... Not that easy in a plane.   Also.. they do not provide any overvoltage protection.. I can attest to that, having had the regulator start delivering 16.7 volts with no control.. not ideal!!

Also -

Maybe you want a lightweight alternator to replace an existing externally regulated alternator and you like the price of the one Vans Aircraft sell but it is internally regulated.

Before we start we need to know one piece of important information about your charging circuit.

There are two main types of alternators and we need to know which type you need. The types are known as Type A and Type B. The difference being where the regulator fits in relation to the alternator.

In type A circuits the layout is in the order of:   

TYPE A.jpg (12932 bytes)

BUS(+ve) - then - Alternator field - then - Regulator - then - Earth.

Therfore the regulator controls the earth feed to the Alternator field.

In type B circuits the layout is in the order of:  

TYPE B.jpg (12719 bytes)


       BUS(+ve) - then - Regulator - then - Alternator field - then - Earth.

Therfore the regulator controls the voltage feed to the Alternator field

Basically it is a matter of polarity. Simple but VITALLY important. So before reading the rest.. Find out what you need !!

Step 1

Step1.JPG (72513 bytes)

Remove the nuts indicated and remove the back cover.

Step 2

 Step 2

Remove the 5 screws as marked to remove the brushes and reglator unit

Step 3
Step 3AStep 3B
This is the regulator.  Turn it over and pry off the back cover with a screwdriver as shown and discard it.
Step 4

Step 4

The regulator Electronics are now revealed. They need to disconnected from the case (Which we need). You have two options. Cut the wires from the connecting pads (As noted in the picture) or de-solder them. If you cut them, you will need to desolder the remains when the regulator has been removed.

Step 5

Step 5AStep 5B

GENTLY pry the heatsink (With regulator attached) from the plastic housing.. prying under the screw lugs seems to work the best. When the heatsink/ regulator is removed, put the regulator in a vice at knock the regulator PCB off with a chisel and hammer.. it isn't to difficult.. it just requires a knock since it is glued on. Discard the regulator PCB.

This is the point we discuss the various alternator types.

TYPE A  - i.e. regulator controlling the alternator field EARTH
TYPE A - Step 6


Connect pins 1 thru 4 together by soldering a wire (at least 18g) to each if the four pads noted. It isn't a bad idea to bend the unused pins away a little. put solder over the entire wire in order to firm it up. Next replace the brushes and regulator housing and fasten the 3 screws noted.

TYPE A - Step 7

Step 7

Place the heatsink back in place ensuring it doesn't touch any of your new connecting wire. Fit the mounting screws.

TYPE A - Final assembly

Re-fit the cover and the job it complete. All pins on the connector are the regulator input. You can connect you external type-A regulator to either or all of the connector pins. The battery and bus are connected to the large B terminal.

TYPE B  - i.e. regulator controlling the alternator field VOLTAGE - This one is a touch more tricky.
TYPE B - Step 6

B type wiring

Connect the pins 1 thru 4 (Red) together and join pins 5 & 6 (Blue) with some pre-tinned 18g wire. (Tinned means soldered in case you are a newbie to soldering)

TYPE B - Step 7

Brush desolder

Now the brushes need a small modification. First de-solder the wire as noted in the photo. It would pay to use a solder sucker if you have one but the key here is to spend as little time as possible so the solder won't 'wick' up the brush braid. Remove the lower brush. (Don't lose the spring!!)
TYPE B - Step 8

drill here Clamped

Drill a hole approx 2.5mm in the back of the brush case and re-fit the brush with the braid through the center of the spring threading the braid through the hole. Clamp the case such that the brush is fully inserted into the case with the wire out through the hole. Now carefully solder some multi-strand copper wire to the brush braid. Once again, time is of the essence and keep the solder to a minimum while ensuring a good joint. It is important to not let the solder wick up the brush braid and make it too stiff.

TYPE B - Step 9


File a recess in the regulator housing so that the newly added wire can fit in the recess. Bacially keep filing until you hit metal then stop. Cut away at the terminal suround so that it can be bent up and won't touch its original mounting area.
TYPE B - Step 10

B completed

Re-fit the brushes and regulator housing with the newly added wire extending through the new recess. ensure that the original termal that connected to the brush mount is bent well clear of its original mount and trim below the top of the brush case. Solder the new wire to the terminal that is bent and trimmed.

TYPE A - Final assembly
It isn't a bad idea at this stage to have a double check that nothing touches where it shouldn't. Refit all screws and the cover ensuring that it also remains clear of the new terminal position.
Hope that is of some use. If you do this I would appreciate an email so I can gauge its usefullness. Happy Charging !!