Oldtime charging system testing

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Joined: Fri Sep 17, 2021 10:25 am

Oldtime charging system testing

Post by grimstone »

Hello there,
New oscilloscoipe user here so do not throw withe axes please.

i have a 62 old motorcycle with a electrical suystem of 6 volt.
The "alternator" is old type meaning it has carbn brushes, stator and rotor both have windings on them.
I cannot find a way to test this alternator like is it sdelivering the proper voltage, does it has any windings in short circuit, etc...
The charge controller is a new electonic one but has the same inputs/outputs as the old mechanical one.

Does anyoane hee has some advice on the test procedure and whatr to look for in the waves?

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Joined: Sun Sep 19, 2021 4:20 am

Re: Oldtime charging system testing

Post by jueja »

This, most probably, should be a generator and not an alternator....can you confirm this? If it is a generator it won't feature a rectifier because it'll output DC. A wiring diagram will be very helpful....

Generally on these kind of generators the voltage is induced into the rotor and the charging current flows through it. It would not self- excite at lower rpm and need higher kick-in rotational speed. To function properly there has to be one line from the generator going to the regulator telling it the system voltage and another one from the regulator to the field windings. This is where you can check its operation.

Steve Smith
Pico Staff Member
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Re: Oldtime charging system testing

Post by Steve Smith »

Hello and thank you for the post

I must admit my knowledge of these systems is limited too, however would you have a wiring diagram or "Description and Operation" information?

This will certainly provide measurements points about the charging system where we can capture AC/DC voltage and current

Do you have a charge warning light illuminated? (if applicable)

Would you have an increase in battery voltage and if so what is the current flow and at what engine speed?
I assume you have no increase in battery voltage?

Given you mentioned an "Alternator" we should have "Rectification" (internal or external) to the Alternator, and some form of voltage regulation

The voltage regulation will take control of the current flow through the rotor (field windings) and therefore a good starting point if you have no output from the alternator

Indeed a quick test is to measure the residual voltage generated by the alternator, disconnect all cables attached to the alternator and run the engine at sufficient speed to generate some form of output

What are your results from the above test.

Next we can look at the alternator field circuit, (this is where your wiring diagram is required)

With your field circuit permanently energized, you should achieve maximum output from your alternator, therefore confirming the integrity of the alternator, rotor, field circuit brushes and rectifier.

Regarding rectification, this is where the scope will provide you with additional information using our Guided Tests within PicoScope 7 here https://www.picoauto.com/downloads

Refer to Charging and Starting > Charging and choose from the Alternator Ripple tests

I hope this helps, take care......Steve

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