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The bike is a 2000, 1500SE with the stock alternator.

Voltage at the battery terminals with a quality analog VOM measures just shy of 13 volts when sitting. Start the engine, (2000-3000RPM)and voltage stays the same.

There is also a Air Rider voltmeter/gear indicator mounted and at the highest the voltage measures is 13.4, usually around 13.1-2 range.

Does that indicate a bad alternator when measuring the voltage at the battery ? I think I know the answer. Just want some concurrence.

What should the voltage range be if operating correctly. For a standard alternator not the HO types.

TIA
 

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Voltage readings are a one time reading, at the time you read the meter and do not always indicate what exactly the problem is.

Bikes, cars and trucks have basically 2 types of alternators and Permanent magnets vs external excitation via a battery can cause a lot of things to go wrong while testing for volts.

No matter the type of system ALWAYS start with a KNOWN GOOD BATTERY, whether it is an existing or new battery it must be charged and tested for being charged otherwise your readings could be miss leading.

A good battery needs 12.7 volts after a sitting time. A good battery has all its electrolytes in place and that electrolyte MUST be examined if a wet cell battery by a hydrometer to test the specific gravity of the electrolyte. A density of 1.2xx to 1.3 would indicate a fully charged battery.

With that fully charged battery in place, connected with good cables and good connections the test can start.

Read the battery at rest all off voltage-------12.6-7 lowest
While starting the engine------------------------no lower than 10V
While cold idle--------------------------------------12.6-7
While above idle-----------------------------------higher than 12.7
while at 2000-3000 RPM-------------------------at max 15 v

Readings will vary from bike to bike because idle varies, electrical loading varies. The type of battery can change the reading and gel type or sealed will leave you with difficulty accessing the electrolyte but all batteries contain an electrolyte whether a flowing liquid, a gel, a glass mat or a sealed system. These batteries that use the gel or a seal are trying to stop the electrolyte from leaking out.

A digital volt meter can indicate the charge of these hard to reach electrolytes but the readings are accurate and you must use all the numbers to the right of the decimal. There is for example a big difference between a reading of 12.01 V and 12.10V. These little small differences will indicate how close you are to full charge. When working on your bike's charging system do not use the bike's system to charge and then rely on that charge as correct. Re-charge an existing and a new battery from an independent battery charger and then test that battery as fully charged.

Basic tools are needed, a volt tester a hydrometer, a file, a wire brush and protection.

Digital meters are easier to read, analogue meters must be mirrored to align the needle. Reading 12.45 on a digital is way easier than on an analogue but both meters can be accurate if of good quality.

Amprobe style clamp around ammeters are easy to use and convenient and make reading the amps moving through a wire much easier than any other reading. So get yourself an amprobe style if you do a lot of amp detail.

Back to alternators: A low amp or low voltage reading cannot always be blamed on the alternator. The reasons are many from a dity connection a broken connection to a rectifier covered in metal filings. The causes of bad watts is as varied as the many bikes out there.

To help repair and justify what you see you need to understand a few rules one is Ohm's Law, E = IR and its variations. To know this is very helpful, but to know this is an understanding of DC and not AC. These 2 currents act differently because they are different.

We use mostly DC on our bikes with some AC, like in the alternator. But that AC is used to create a form of DC that we bend and twist with diodes, rectifiers, SCRs to regulate voltage. A 12 V system is 12V nominally the real voltage bounces around 10-15 V range via a storage tank called a battery and an alternator using 20-70 VAC.

The complete bike and its 12V must be clean, secure, tight because 12 V is not much and almost everything can slow it down. Things like rust, dirt, water combine to mess with copper and other metals to bring 12 V to a halt. Bad connections are weak connections and if any connection is weaker than the copper wire the amperage and the voltage suffers. Old bikes age at a rate but the electrical system ages at a different rate but catches up as time passes.

Doing a proper PM helps with old age, mechanical, tune up, plugs, but doing an electrical PM also helps. There are many systems within a bike and all inter act to keep it working, the electrical system happens to inter act with all other systems and when the electrical system fails any or all others start to fail.

Many things can cause the voltage and current to drop, when attempting to repair the electrical system it will take close inspection of all components. A haphazard look and see will not be good enough. I know most of you say you are not good with electrics or I have gremlins. Electricity cannot be seen and that may be the reason gremlins are blamed. Electricity can be measured and to use the multimeter with expertise and understanding Ohm's Law can go a long way in understanding the simple and complex issues with the unseen part of our bike.
 

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I have a 97' SE and replaced the brushes this year because of a low charging rate. One of the brushes was worn more than the other and was "hung up". The new brushes need to be soldered in place, easy job.

With the new brushes, at anything over 2000 RPM, full electrical load I get readings between 13.7 and 14.1 on my digital voltmeter (Daves type).

Most times it sits right at 14.0.


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had same problem , checked will hen hemmings . He said anything over 13 volts at 1800 rpms or over is good with the stock alt. bike shows 13.4 at 2000 rpms. he done my alt in april.
 

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funone97 wrote:
had same problem , checked will hen hemmings . He said anything over 13 volts at 1800 rpms or over is good with the stock alt. bike shows 13.4 at 2000 rpms. he done my alt in april.
Good, may save myself some money till the fall.
My normal voltage is showing 13.2, sometimes 13.4. and no hard starting even after a lot of miles. Will drop into the 13 to 13.1 range some.
Thanks for the info everyone.
 

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funone97 wrote:
had same problem , checked will hen hemmings . He said anything over 13 volts at 1800 rpms or over is good with the stock alt. bike shows 13.4 at 2000 rpms. he done my alt in april.
what did he charge you to do your alternator?
 
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