Solid State Voltage Regulators For 3 Brush Motorcycle Generators


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How to change rotation on a Splitdorf "DU" model generator


There are 4 steps required to change rotation on a splitdorf generator:

1. Change the position of the commutator head
2. Change the field coil wiring
3. Change the adjustable brush holder
4. Re-polarize the generator

 1. Generator rotation is always determined looking at the pulley end of the generator.
 2. All discussions of “top”, “bottom”, “above” and “below” are referenced with the generator’s     terminal post in the 12 O’clock position.

DU-1  - The DU-1 requires a different armature, there is no getting around this.  Each rotation uses a different armature.  The difference is in the windings.  Left hand rotation is p/n 14012, right hand rotation is p/n 14094.  If you have a DU-1 and need to change the rotation, your best bet is to find the correct generator.  Without seeing the armatures side by side it is very difficult to tell the difference

Changing Rotation

Step 1. Commutator head position – DU-5 and DU-7
The procedure is different for each model generator.

DU-5 – The DU-5 commutator head has 2 sets of  ¼ - 20 mounting holes for the through bolts.  The commutator head must be rotated so that it is advanced as far as possible in the desired direction of rotation.  For example, on a clockwise generator the head must be rotated counter-clockwise (looking at the commutator end) and the “other” set of holes is used to retain the head.  If your generator has been previously worked on there is a good chance that it was re-assembled with the head carelessly installed in eiterh set of holes.  If the wrong holes were used, reduced current output would result.  See the figure below.

DU-7 – The DU-7 commutator head is the same for either rotation.  The difference is in the 8x32 holes in the edge of the body that retains the commutator head.  The holes are positioned differently for each rotation.  You will either have to obtain the correct body for the desired rotation or re-drill and tap the holes.  To re-drill your holes take a flexible tape measure (your wife’s cloth one will work good).  Wrap it around the outside of the generator body near the commutator end.  To change from CW to CCW rotation measure 1.5 inches clockwise (looking at the commutator end) from any one of the holes.  Mark the spot.  This is where you will drill your first hole.  Now do the same for the other two holes.  In other words you are shifting all 3 holes 1.5 inches clockwise.  For CCW to CW rotation, do the same thing but shifting the holes counter-clockwise 1.5 inches.   Now tap the holes 8x32.  Take your time and be very careful to locate your holes correctly.  The commutator head can be used for a template for the 3 holes.

Step 2. Field coil wiring – This change is the same for all models.  Looking at the commutator end, For CCW rotation the left field coil lead goes to the top (positive) brush holder.  This is the fixed holder nearest the terminal post.  For CW rotation the left field coil lead goes to the bottom (negative) brush holder.  That’s all there is to it.  The right field coil lead always goes to the adjustable brush holder.  See the drawing below.


 Step 3. Change adjustable brush holder –  To understand this you must understand the purpose of the adjustable brush holder.  To increase current output from the generator you must move the adjustable brush holder in the direction of generator rotation.  To decrease output, move the adjustable brush holder opposite generator rotation.
   You will need to find a donor brush holder to change rotation.  The changes are the same for all models, but DU-5 brush holders are different than DU-7 holders.  For DU-7 brush holders that have 2 screws, the instructions below are referenced to the longer of the 2 brush holder screws.  This is difficult to explain but look at the diagram above.  For CW rotation, the carbon brush in the adjustable holder must be able to get as close as possible to the top (positive) brush when adjusted for maximum output.  To do this the adjustable holder must position the brush above the screw that holds the adjustable holder in place.  For CCW rotation, the opposite holder is required.  This one will position the brush below the screw that retains the adjustable brush holder and as near as possible to the bottom (negative) brush when adjusted for maximum output.
  The generator will work without making this change but you will only get 1-2 amps out of it instead of 4-5 amps.

Commutator heads, L to R; DU-1, DU-5, DU-7.  The appropriate mounting holes on the DU-5 are shown for each rotation.

Step 4 - Re-polarize the generator –  You must do this or it will never work.  This procedure is the same for all models.  Assemble the generator except for the end cap.  Make sure the brushes are seated properly and that the armature turns smoothly.  Get a well charged 6 volt battery (from your bike is fine).  You also need 2 test leads with an alligator clip on each end.  Attach one lead to the battery’s negative terminal and the other end to the generator’s negative brush holder.  Take the other lead and attach one end to the battery’s positive terminal.  Take the other end and being very careful, touch it to the top (positive) generator brush holder.  Don’t hold it on for more than 2 seconds at a time.  If everything is hooked up properly 2 things will happen.  1. The generator will re-polarize. 2. The armature will begin to revolve in the new direction of generator rotation.  It only takes a second or two to polarize.  If the armature revolves in the correct direction, you’ve been successful in changing your generator’s rotation!

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