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CB72/77 Battery
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Tim Allman
honda305.com Member


Joined: 02 Dec 2014
Posts: 296
Location: Guelph, Ontario, Canada

PostPosted: Fri Aug 09, 2019 10:05 am    Post subject: Re: Sealed batteries. Reply with quote

DJM wrote:

As far as measuring battery voltage while the engine is running and charging, I would be wary of drawing too many conclusions from the results.

What you are trying to measure is the DC voltage of the battery with a half wave rectified AC charging voltage superimposed over the top, this AC component varies from zero to perhaps 30 volts many times per second dependent on engine speed.

Few multimeters can measure this accurately, in fact do you set the meter on DC or AC voltage range?


Your rectifier is a full wave rectifier. If it weren't only half of the potential output of the generator would be available, something that would be noticed very soon.

Voltmeters (set to DC) measure average voltage which is what you would get if you sampled the instantaneous voltage rapidly for a time and averaged the values. This is equivalent to an unchanging DC voltage of the same value. So, you should trust the value that your meter on the DC setting gives you.

My feeling is that the electrical generation system on these bikes (and many others) is really rather quick and dirty. It is the battery that tames the voltage and current fluctuations and sacrifices itself in the process. It moderates the system voltage so that it will never go below the battery voltage and the peaks are limited because the battery absorbs them. The problem is that the battery is exposed to voltages above 14.2V at which point electrolysis of the water starts to occur and the water is lost as hydrogen and oxygen gases. A regulator will protect the battery from this because the regulator clips the peaks.

I don't know the answer to the question you ask. My best guess is that the voltage peaks were too high and causing premature battery failure.
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