Fluctuating idle/voltage

TerryS · Oct 29, 2016

My 1990 ST still has the original RR and alternator, and usually shows a steady 14.1v. Lately I have noticed the voltage fluctuating 13.9 - 14.1 at idle, in time with the idle itself fluctuating up and down a little. Once moving, the voltage is rock steady at 14.1v. I have just fitted LED headlights and the change sort of coincided. Is this normal behaviour or should I be suspicious eg of the RR?

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kiltman · Oct 29, 2016

Where are you taking the reading from? When I had my 1990 with the OEM alternator the reading at the battery was 14.9 - 15.1. It was lower in the high 13's when taken around the fuse block

CYYJ · Oct 29, 2016

Terry:

Don't rule out the possibility that what you have is an indication problem, rather than a problem with the alternator. You stated that you just installed additional electrical equipment (the LED lights) - it is quite possible that you may have nudged or loosened the wires that lead to your voltage indicator during the process of installing the lights.

I'm not saying that this is the most probable cause, I'm just saying 'keep an open mind' and don't jump to conclusions about the alternator. One way of checking the accuracy of your voltage indicator is to put a separate, known-good voltmeter across the battery terminals when the engine is running, and see if you see the same voltage reading on it as you see on the permanently installed voltage indicator.

Michael

vinny · Oct 29, 2016

I would think it's normal with the idle fluctuating up and down that the voltage will follow it. Your real problem is to steady the idle as that would likely indicate fuel issues. Maybe try a carburetor sync. Probably just a coincident you noticed it after installing the LED lights.
Sorry, I have to tell you this... I have dyslexia and I read the original post as "flatulenting" voltage... LOL

Blrfl · Oct 29, 2016

TerryS said:
Lately I have noticed the voltage fluctuating 13.9 - 14.1 at idle, in time with the idle itself fluctuating up and down a little. ... Is this normal behaviour or should I be suspicious eg of the RR?

You've just replaced one of the heavier loads on the system with a much lighter one, which changes the electrical landscape quite a bit. What you're seeing is well within the range of what you should be seeing on that bike (12.6 to 15) and only about 8%, so it's not even worth worrying about.

--Mark

ST1100Y · Oct 29, 2016

TerryS said:
...I have noticed the voltage fluctuating 13.9 - 14.1 at idle...

I'm with Mark here...
You possible observe an interaction between the LED power-supplies varying their current/draw, and the VRR coping with that.

TerryS · Oct 29, 2016

Blrfl said:
You've just replaced one of the heavier loads on the system with a much lighter one, which changes the electrical landscape quite a bit. What you're seeing is well within the range of what you should be seeing on that bike (12.6 to 15) and only about 8%, so it's not even worth worrying about.

--Mark

Thanks Mark. That's kind of what I thought; without knowing how the RR and alternator interact at low rpm, it seems like the RR is cycling "on", which loads the alternator and drops the idle, which causes the RR to cycle "off". I might just be at a delicate combo of revs and electrical load.

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moddy · Oct 29, 2016

Another theory is, at idle, is the lowest cycles of AC your regulator is getting. A fluctuation in 50 rpm will be the highest percentage of change compared to your average idle speed, nearly undetectable audibly, than it is 3 to 4k rpm. A much more powerful and consistent delivery of volts and amps. Hopefully that sounded smart. I'm in need of being smart.

Brant · Oct 29, 2016

Having a bit of noticeable idle fluxuation if idle set at the normal 1100rpm,is initially out of sync carb bank

.

TerryS · Oct 29, 2016

Brant said:
Having a bit of noticeable idle fluxuation if idle set at the normal 1100rpm,is initially out of sync carb bank.

The carb synch is spot on at present, and most of the time the idle is rock solid. However for whatever reason I'm getting a cyclical voltage occasionally and that causes the idle to fluctuate as well.

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Brant · Oct 29, 2016

TerryS said:
The carb synch is spot on at present, and most of the time the idle is rock solid. However for whatever reason I'm getting a cyclical voltage occasionally and that causes the idle to fluctuate as well.

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May wanna' pull that left-side tupperware, un-plug that large connector next to battery, clean both ends contacts with electrical spray cleaner and plug back in. That may resolve the erratic charging rate

.

TerryS · Oct 30, 2016

CYYJ said:
Terry:

Don't rule out the possibility that what you have is an indication problem, rather than a problem with the alternator. You stated that you just installed additional electrical equipment (the LED lights) - it is quite possible that you may have nudged or loosened the wires that lead to your voltage indicator during the process of installing the lights.

I'm not saying that this is the most probable cause, I'm just saying 'keep an open mind' and don't jump to conclusions about the alternator. One way of checking the accuracy of your voltage indicator is to put a separate, known-good voltmeter across the battery terminals when the engine is running, and see if you see the same voltage reading on it as you see on the permanently installed voltage indicator.

Michael

I installed the voltmeter (a Honda marine unit) with a direct feed from the battery, through a fused relay, just couple of months back, and checked the reading vs my multimeter when I did that, both very close together.

TerryS · Oct 30, 2016

Brant said:
May wanna' pull that left-side tupperware, un-plug that large connector next to battery, clean both ends contacts with electrical spray cleaner and plug back in. That may resolve the erratic charging rate.

Good suggestion Brant, but I have been right through all connectors about 6 months ago when I was restoring the bike to a runner, cleaned and greased. I'm fairly sure what I'm seeing is the RR feeding back to the alternator secondary coils and varying the load on the alternator and hence the idle.

Brant · Oct 30, 2016

TerryS said:
Good suggestion Brant, but I have been right through all connectors about 6 months ago when I was restoring the bike to a runner, cleaned and greased. I'm fairly sure what I'm seeing is the RR feeding back to the alternator secondary coils and varying the load on the alternator and hence the idle.

Well,,,,,possibly least narrowed down to that, with VR voltage feed being the culprit.

Fluctuating idle/voltage

TerryS

kiltman

CYYJ

Michael

vinny

Blrfl

Natural Rider Enhancement

ST1100Y

TerryS

moddy

the mod

Brant

TerryS

Brant

TerryS

TerryS

Brant