Rectifier testing

Admin Posts : 390 Join date : 2017-10-17 Age : 61

A chance for wolfie to put his electronics expertese on display Very Happy

Mc C90 has blown a few bulbs all of a sudden....the battery is fooked and will need replacing but the bike still runs but the bulbs blew. I suspect the rectifier so i took it off to test it....im not sure if the results are ok.
The rectifier has four wires....green is the earth, red is the positive to the battery, yellow is from the alternator and the pink is also from the alternator. The diodes run from green to yellow, from green to pink and from the yellow to red and from pink to red in a diamond shape with green at the bottom, red at the top and the yellow and pink either side, the diodes point from green to red...(standard silicon rectifier)
so my understanding is the following; if i put the pos multimeter probe to the green and then the negative probe to each of the other three i should get a reading of about 0.5v for all three. In reality i get 0.7v on both the pink and yellow but 1.5v on the red which seems odd. If i then connect the pos probe to red and the neg probe to the other three i should get zero reading, which i do.
What do you think.? Is it fooked...

Posts : 81 Join date : 2017-10-19

I'm no auto electrics expert but all i'd do is test the charge rate. What is the DC charge to the battery when the engine is running at a decent speed. I reckon it should not be much more than 7.5v for a 6v system or 15v for a 12v system.

Admin Posts : 472 Join date : 2017-10-17 Age : 117

There's no mention of a regulator in there Rob? Since you have too much voltage by the sounds of it, my guess would be that the Rectifier is OK

And your measurements there all seem OK, You always get 0.7V across a working Diode (and in the case of Green-Red you are measuring two Diodes ie 1.5V).

Admin Posts : 390 Join date : 2017-10-17 Age : 61

Cheers Gra, I did wonder if the 1.5 voltage was merely doubling up across the two diodes, it does make logical sense...... but all of the clips I watched on youtube show the same voltage (approx. 0.5v to 0.8v) on all three positions..? Regarding the regulator, there is no mention of it in the C90 Haynes manual or on the wiring diagram so I assumed the unit was a regulator/rectifier although its only described as a rectifier..... I'll have to investigate further, a new rectifier is only £20 but no point replacing that if there is another problem somewhere else i.e. voltage regulator... Who said Honda 90's were simple...!!

Admin Posts : 390 Join date : 2017-10-17 Age : 61

andysej wrote:: I'm no auto electrics expert but all i'd do is test the charge rate. What is the DC charge to the battery when the engine is running at a decent speed. I reckon it should not be much more than 7.5v for a 6v system or 15v for a 12v system.

The battery is totally fooked so that will be the next thing to try once I get a new one fitted... but the bulbs definitely blew due to high voltage so I turned it off....

Admin Posts : 472 Join date : 2017-10-17 Age : 117

On this one there is (sorry it's not a clearer image).. For a Battery circuit there has to be some form of regulation.

Admin Posts : 390 Join date : 2017-10-17 Age : 61

That's a totally different circuit to the one for my bike... mine is a C90zz (79 to 81) last of the 6 volt models.... I'm at work at the mo but I will post the diagram when I get home...

Admin Posts : 390 Join date : 2017-10-17 Age : 61

Here is the circuit diagram.....no regulator!

Rectifier testing F7-A212-EF-2-BDA-4-F91-900-A-8329-B85-FA052

Admin Posts : 472 Join date : 2017-10-17 Age : 117

You actually said it above.. 'The Battery is fookt'.. that must be the load that limits the output Voltage then.
So without a Battery the Voltage can rise to far,

The Generator coil itself might be designed to Saturate at higher revs and add some regulation.

Admin Posts : 390 Join date : 2017-10-17 Age : 61

I think you are right Gra.... new battery on friday so i will soon know Very Happy

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