ST1300: What are the signs of a failing alternator?

AV8R

AV8R

Joined
May 19, 2018
Messages
1,120
Location
Southern California
Bike
2005 ST1300 PA
Apart from outright catastrophic failure, ie dead - no current or volts; what symptoms are characteristics of an alternator on its way out? And how is that different from just brushes or regulator (is it separate from the alternator) needing replacement?

My bike is approaching 80k and the volt meter seems to indicate an output that increases with engine RPM. In a range between 12.4 to 13.4v with a new battery. Resting volts is between 12.9 and 13.1. Starts and runs OK, but this behavior seems off to me.
 
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Sounds about bang on what it should be to me.

I'm sure Larry will be along shortly to correct me. Until then, ride it like you stole it. :biggrin:
 
Ya, but my buddy’s 2009 STP volts seem to be always around 13-14

Ride like I stole it.... just got back from a short holiday stay at the local mountains called Big Bear California. Being a popo bike, im sure some thought i did steal it (not being in uniform and all)
 
The only alternator failure I have had was catastrophic. I was merrily riding down the freeway when my tach and speedo both quit. So I headed to the first offramp. By the time I got to the side of the offramp, the bike died. It had drained the battery! You might want to check your connections too, just to make sure you have good solid connections going to the battery!
 
I had a failure on mine as well but it just went no indication until the battery went dead I did not have a volt meter at that time .The voltage does not seem that bad to me.
 
170 K miles on my '07 ST13.
NO trouble with the Alternator or ANY Electricals.

At 80K Miles U should have a strong
system that puts out the rated Watts & Amps.
Good Luck.
 
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AV8R said:
...not being in uniform...
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In your position, I'd probably take the P out for a giggle once a week.

Seriously though, those voltages are the exact same we'd look for to see a healthy system on the old SV650. Smaller capacity motor, still a 12v electrical system.

My bike doesn't have a volt meter (one more thing to make me think "something ain't right here"). But then I haven't nearly as many farkles as you!

I do need to attack mine with a multimeter some day before next winter, due to random electrical gremlins, but my money is already on the 24pin connector behind the lights being corroded.
 
AV8R said:
Apart from outright catastrophic failure, ie dead - no current or volts; what symptoms are characteristics of an alternator on its way out? And how is that different from just brushes or regulator (is it separate from the alternator) needing replacement?

My bike is approaching 80k and the volt meter seems to indicate an output that increases with engine RPM. In a range between 12.4 to 13.4v with a new battery. Resting volts is between 12.9 and 13.1. Starts and runs OK, but this behavior seems off to me.
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Are you checking V with an onboard VMeter, if so how is it hooked up and what make is it? If you’re using a handheld high end or a HF model? I have three cheepo multimeters and only one is close to accurate when checked against my HP or Fluke meters. Also, resting V should be checked after the battery has rested for a couple of hours after riding or on a charger for accuracy.
It’s best to check at the battery but hard to do so on a P model. On my P I usually check off my heated gear dongle with a coax to sae adaptor. The dongle is mounted directly to the batt.
Even 13.4V at speed is low unless you’re running high Amp accessories but could be due to a faulty meter, what it’s tied into, etc. As long as you’re running above a break even V of 12.6 you’re still good though.
 
Im measuring with an SAE dongle hangining off the battery terminals that I use for charging. The only real indication that something is amiss is my siren emits a sickly tone when the el cheapo battery voltage indicator reads <12.9v.

Also, I can see the voltage go up when rpm does. Is this normal, i mean isnt the whole purpose of a voltage regular is to keep it relatively constant?
 
I'd put a volt meter on mine so I could monitor engine running health. One day at a stop light I looked down and at idle it read 12.6 volts. Hmm, I wondered. Since I used a toggle to turn off my HID headlights for colder weather starts so the balast could be turned on after the engine started and have a better chance of firing both HID's, I toggled the power off and it went up to 13.1. With a voltage rise to closer to where the the voltage was recently with my headlights on, the investigations began, battery..alternator...what? I finally worked out one of the legs in my 28A stator on my '91 was not producing power.
 
The alternator has the regulator and brushes integral to the unit. Any degradation of the output can't be adjusted without replacement or rebuilding of wear items which requires removal of the alternator. System voltage should not vary much with RPMs once over 1200-1500 rpms. Honda says to measure output at 5000 rpm but there should be insignificant change from 1500 to 5000.

Without some sort of output monitoring, there is no warning of reduced output until the output is less than the system voltage required to run all electrical loads and the equation draws the system voltage below the amount necessary to run the engine. I had an alternator failure at 116,000 miles and the only warning was a brief period of the instruments and GPS flashing on & off, then the engine's fuel injection quit and I rolled to a stop. After I replaced the alternator I installed a Clearwater voltage monitor to give me at least some warning of an electrical system problem.

Trapperdog is on point, any monitoring device must be installed in a manner that eliminates excessive voltage drop from measured right at the alternator output. Your numbers seem a little low to me, I'd rather see 13.6 to 14.4 volts with the engine running, but you may be measuring V in a way or with an instrument allowing a large voltage drop.
 
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AV8R said:
Also, I can see the voltage go up when rpm does. Is this normal, i mean isnt the whole purpose of a voltage regular is to keep it relatively constant?
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I'd say the main purpose of a voltage regulator is to prevent overcharging of the battery. There will always be a ramping up of voltage from idle to a certain RPM (1500?) where the output jumps. You'll see this on most any bike and some cars just by turning on the headlights and increasing throttle.

This may not be as apparent on newer cars since (in CA at least) they now idle a little higher than older models to improve control of emissions.

But you have a point - assuming all your connections are good between your alternator and battery and between your yelper and connection point (including a relay in good shape) it should sound proper at idle let alone at anything above idle.
 
Try and borrow a high end multi meter just to eliminate the possibility that yours is faulty. I have onboard digital VMeters on all my bikes. One has a Datel which is fairly accurate, but the other three have cheapo flat ones. Even with the cheapos being somewhat inaccurate, either due to design or installation, noting any anomaly’s is very helpful.

My knowledge base lies in stators with external R &R’s, both Shunt and Series types so I know little of the ST’s alternators. So this thread has me wondering how our ST regulator dumps excess current. Is the internal regulator a Shunt, Series, or other type? Is it referred to as a regulator or a regulator rectifier?

Perhaps not pertinent to the ST, but some faulty regulators can show normal readings when cool, and irregularities when hot.
 
Im betting that alternators dont die catastrophically most of the time, but that by the time most realize that its sick as as it gives up the ghost. Electrical systems are black magic to most, but im pretty comfortable around them. Problem here is lack of access to the alternator so a static test can be done on the stator windings and regulator bridge - AFAIK anywho. Which is why im asking those who been there, done that and own the T-shirt. :)
 
Voltage only tells part of the story. I use a DC Amp Clamp meter that can be put around the battery cable. This will tell you more about what is going on.
you have to pull off the seat and side cover to get to the battery cable. This is the one I use.

https://www.amazon.com/Signstek-UT2...ocphy=1013638&hvtargid=pla-568862818733&psc=1

or you can get it at home depot or Fry's, Make sure it says that it will measure DC current..
Got to push the blue button to get it in the right mode....

the alternator is three phase, So it has three windings each with its own set of diodes. So you could loose one winding and be running at 66% and not know it.
 
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spiderman302 said:
the alternator is three phase, So it has three windings each with its own set of diodes. So you could loose one winding and be running at 66% and not know it.
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That's exactly what happened to me on an old '72 Chevy. Weak charging was the symptom so I pulled the alternator off and checked the diodes on a Fluke. (LOL) One was bad and Chevy sold replacements. I think I replaced brushes while I was in there. It's too bad it couldn't be that simple on our STs.
 
Another failure mode is the rotor winding goes open circuit and Poof zero output. The bike rolls to a stop in 5 or 10 minutes.
 
AV8R said:
Im measuring with an SAE dongle hangining off the battery terminals that I use for charging. The only real indication that something is amiss is my siren emits a sickly tone when the el cheapo battery voltage indicator reads <12.9v.

Also, I can see the voltage go up when rpm does. Is this normal, i mean isnt the whole purpose of a voltage regular is to keep it relatively constant?
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No, the alternator puts out AC volts which is converted to DC by the Regulator/Rectifier. At idle the alternator will put out less voltage than a higher RPM, so what you are seeing is normal.
 
dduelin said:
System voltage should not vary much with RPMs once over 1200-1500 rpms.
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I was wondering about this myself, On the way home from the UP of Michigan on I-75. I was traveling at a constant speed and my volt meter was dancing between 13.7 and 14.1 up and down while maintaining a constant speed of around 70 mph. (I put a new OEM alternator in this past January 2019). I never noticed this "dancing" of the voltmeter under a constant speed before. At first I thought my new alternator was failing, but then it went to 14.1 volts and stayed there for most of the rest of the ride. Then I was recalling that when the cooling fans kick on the voltage would drop like that- I just never noticed it under constant speed before?
Would the cooling fans kick on while under way traveling around 70 mph?
Something (phantom) was putting a draw on my electrical system while at a constant speed that I have never seen before. My bike is basically stock electrical - except for GPS, battery tender,voltmeter, and a charging port in my top case. I have nothing else wired to it. I did have my phone plugged into the top case charging port but I don't think it would have made the voltmeter dance like that.
 
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AV8R said:
Im betting that alternators dont die catastrophically most of the time, but that by the time most realize that its sick as as it gives up the ghost.
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This is one of the reasons I replaced mine ( no apparent issues) at 137,xxx miles. https://www.st-owners.com/forums/threads/alternator-core-failure.166684/page-4 post #80.
I felt it was better to replace than push it to the edge of the envelope and have problems 3000 miles from home. However I see alot of riders are getting over 170,xxx plus out of there original alt.
My new alternator runs the following numbers:
Idle : 13.7 to 14.3 volts
Under way: 13.9-14.1 volts. The voltmeter varies output in some situations, on others it never moves from 14.1 for long periods of time. I don't fully understand all the workings of the system but there is reasons the system has various demands put on it and causes the voltmeter to dance.
 
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