Stolen from the Vulcan Verses.
Using a Test Lamp to Test Your Rectifier/Regulator
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Fig. 1 We will use a test lamp and the bike's battery to test diodes D1 thru D6.
First disconnect both the positive and negative leads of the battery posts. Also disconnect the connector from the Rectifier/Regulator. At this point, I assume you have checked to see if the alternator stator is not shorted to ground and that the windings have continuity. Testing the stator for shorts to ground is a good test..but the test of resistance of the windings is nearly useless. Most...even the best of DVMs will yield around 0.4 ohms for this test. Doesn't tell you much.
A better test is one where you test the inductance of the winding. This can be done with a DVM that has L-C-R capability. From any two of the wires emanating from the stator, I get 1.16 mH. That's 0.0016 Henrys of inductance..which indicates the winding is present and not shorted. There are three to check...they should be close in inductance since the number of turns of wire are close to the same. There's some mutual coupling going on in there...but I won't get in to that here.
Now, lets test those diodes. Diodes D1 thru D3 deliver the positive peaks of energy coming from the stator. The anode of D1 is connected to the A3 terminal on the regulator. This is where you want to touch the spike of your test lamp. The pig tail of the test lamp will be connected to the POSITIVE post of your battery. You will need a jumper about 24" long (alligator clips on both ends) connected to the negative post of the battery and B in Fig. 1. Your test lamp should light up indicating that D1 is "on" or conducting. To test the diode for reverse..switch the connections at the battery (test lamp on the negative...jumper on positive) and the test lamp should be off. To make things go quicker..you could test all three (D1 thru D3 ) for conduction..then switch the battery connections and check them in reverse. Your spike will be moving from A1 thru A3 as you make these tests.
Follow the same procedure for D4 thru D6 except this time your jumper will be connected to G in Fig. 1. These diodes provide the ground reference for the stator. This procedure works really well..in fact better than that confusing idiot chart in the service manual (Fig. 2). I have been trying to figure out what was in the mind of the person that created the stupid thing in the first place! It's my belief, you can test just about anything if you have some idea how it works. The SCRs (thyristors) in there that do the regulating, create a momentary short circuit to ground if the battery voltage exceeds a pre-determined value. This is supposed to prevent over-charging the battery. If all the electrolyte is boiled out of a battery, the stator starts spending all its life shunted to ground by these thyristors..thus..the stator gets real hot & gives up the ghost.
I will do some more research and get back with you on this one. You would be surprised how many really great electrical tests can be performed with a simple test lamp. If you're going to trip around the country like JR Allas and some of the rest of you guys & gals, you should put a test lamp in your tool pack. You should have a good DVM also...but that's for home..not out on the road. Allan(Flash) Gordon
1986 Black Kawasaki Vulcan VN750 "Black KAWK"
VN750 #9300 & VROC #33453
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