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Volts not increasing with RPMs

7K views 30 replies 5 participants last post by  mulumbo 
#1 ·
First time poster.

I am following the Clymer manual and at idle my vulcan 900 is averaging around 14amps. When I increase the RPMs it stays at 14amps. 14amps is within the range for the 3000rpm test, however the amps did not increase as they should.

According to the Clymer manual, the next step is to test the alternator, which requires removing the outer cover and Alternator cover. That appears to take removing the floor board and shifter. Ugh! :eek:

According to this youtube guy (https://www.youtube.com/watch?v=5v2LtHlvcqI) there is a way to test the stator without all that removal.

My question: does this method apply to a 08 Vulcan 900? Do I do exactly as he did it in the video?
 
#3 ·
Yes, the stator can be tested without removal.

Like Sfair said; are you sure "amps" is what you're looking for? Set your meter to DC volts and check it at the battery. Then we can progress from there.

What symptoms led you to doing this test?
 
#6 ·
I dislike the word "fine" because testing should involve numbers. "Fine" is how you rate a chicken salad, not an electrical component! But I digress.

Okay, so you're in luck, Sfair is in this thread and he's the electrical guru. But for our benefit; a couple of questions. We'll call this our diagnostic inventory that will help us ask you the NEXT set of questions. But, stay patient, use your meter, and we'll get the problem diagnosed without the need to purchase unnecessary parts.

1) How many miles on the bike
2) Has the problem happened again
3) ANY variation in charging voltage? (Was it 14.00 the entire time?)
4) ANY other symptoms or strange behaviors on the bike?
5) What happens if you don't ride every day?

If you'd like to test your stator, the procedure follows. Though 14 volts is within range. 13.5-15v at speed is the spec, and you're within that spec; which, at face value, makes it appear nothing is wrong. But of course, this is electrical, and problems can be intermittent!

Down on the front of your bike, at the bottom, you'll see the regulator/rectifier unit, which has a plug with 6 wires in it and is covered by a small metal protector. Remove that plug. You might find some water or grit falls out; wouldn't hurt to spray with electronic cleaner and di-electric grease while you're down there.

You'll notice six wires, three of them white.

Set your meter to AC Volts. Your alternator produces AC volts which are converted to DC. Touch a black probe to one of the pins associated with a black wire and the red probe to one of the white wires. Start the bike. Record the number at idle, and bring the engine up to about 3,000 RPM's (Use the idle adjust screw on one side and bring it up to about what it sounds like cruising down a 55mph road). Record the numbers, and repeat for all three white wires. I don't recall the spec and no longer have a VN900 service manual. However, idle is typically around 36v and at speed around 50v. Post your numbers and we can research further. Low voltage or voltages being significantly different than one another can indicate a problem. There's a procedure for testing the regulator/rectifier unit as well but with good charging voltage that doesn't seem necessary (unless sfair tells you to do it; always do what sfair tells you to do!)

One last parting thought. On the 900, it is possible to turn the key back unknowingly to the "parking light" position, which is BEHIND the "off" position, and then remove the key. Which will leave the rear running lights on, and all other systems off. The intention of this position is to be used when the bike needs to be left on the side of the road in an emergency, such as a roadside mechanical failure. Is it at all possible that this is what has happened?
 
#7 ·
1) How many miles on the bike
2) Has the problem happened again
3) ANY variation in charging voltage? (Was it 14.00 the entire time?)
4) ANY other symptoms or strange behaviors on the bike?
5) What happens if you don't ride every day?
1) 18k
2) Not since the first time, which was almost 2 weeks ago.
3) It varied small amounts (14.XX) but never dipped below 14.
4) Right now? No. When it happened a couple weeks ago, I was getting low battery symptoms (bike cutting off when coming to a stop, display resetting, not starting)
5) It is my only vehicle. Most I won't ride is one day. So this question is hard to answer.

One last parting thought. On the 900, it is possible to turn the key back unknowingly to the "parking light" position, which is BEHIND the "off" position, and then remove the key. Which will leave the rear running lights on, and all other systems off. The intention of this position is to be used when the bike needs to be left on the side of the road in an emergency, such as a roadside mechanical failure. Is it at all possible that this is what has happened?
I can't be 100% sure, but I am 98% sure this wasn't the case.

I will do the other testing tomorrow and get back to you with the results.
 
#8 · (Edited)
If you're getting 14 volts across the battery with the engine running, that should be enough to charge it, especially if you're riding daily.

When you say the battery went dead, do you mean that it really was dead, meaning it was reading well below 12 volts on a meter, or that the bike wouldn't start? I'm wondering if you've got a goofy starter, solenoid, starter button, etc?

If you can eliminate the possibility of starting system problems, I'd bet you're going to find that the battery is faulty. I've seen this happen many times, the battery will charge and work fine most of the time, but every once in a while, phht! The battery has numerous internal connections, and if one of them is skitzy you'll get an intermittent dead battery.

You've got to rule out faulty connections, missing or loose frame grounds, etc. of course. Those things will also cause intermittent charging or starting problems.
 
#10 ·
Something isn't right here; you're getting ample charging voltage so 0 volts on the white wires is impossible.

The problem is, the dummy who gave you the instructions (me) gave you bad instructions. I was thinking of something else and gave you bad info.

Let's try this again.

Pretend the 3 while wires are A, B, C

Take your black and red probe, still AC volts, and put the probes:

A-B
A-C
B-C

Then report the voltages; same deal, at both idle and at speed.
 
#12 ·
Stator checks out. The voltages are a smidge lower than what I got on my Rick's motorsport stator, but they are consistent and within range.

Electrical issues can sometimes be intermittent, which is a royal pain. Next test is the regulator/rectifier unit.

The test is as follows:

First, remove the regulator/rectifier from the bike, Noting the red, black, and white wire positions. On mine, I used a pencil and marked "R, B, W1, W2, W3" above each location a wire would be plugged into.

Set your regulator down and grab out your trusty meter, once again set to ohms. Zero the meter. Set to X1K resistance if the option is available to you.

Black probe to Black, Red probe to White 1
Black probe to Black, Red probe to White 2
Black probe to Black, Red probe to White 3
Note the readings.

Repeat the tests, this time reversing the probes (Red to black, black to white)
Repeat the tests one more time, but this time, in places where you tested using the black pin you noted, use the red. You should have 12 readings noted.

If your rectifier is working properly, you are looking for low resistance in one direction, and infinite resistance in the opposite direction.

Bear in mind that your charging voltage IS within range so I am NOT expecting the reg/rect unit to show a failure. As frustrating as intermittent issues are, I've yet to see anything that indicates anything is wrong with your bike. Lights surging at idle with a dead battery isn't unusual, given the low output of the stator. The battery is designed to take over in that case.
 
#13 ·
So my tester had Ohm settings for 200 or 2,000. I did both.
When the probes aren't touching anything a "1" shows on the screen. I did all twelve combinations and a "1" showed the whole time. It didn't not show a reading like it does when you touch both probes together to zero it out.
 
#14 ·
@sfair Any input?

To my eyes, it appears that the regulator/rectifier unit is done for. It should be replaced immediately, as it can damage the stator; was it tested when the stator was originally replaced?
 
#16 ·
My bad, sorry. I've got a couple of these threads open.

A couple of inventory questions

1) What year?
2) How many miles?
3) Any mods?

Very unusual. The numbers for the resistance test for the reg/rect unit don't match up with the good charging voltage you're getting at the battery. A head scratcher!
 
#21 ·
Starting two weeks ago I was leaving a gas station when my motorcycle died (I was at near idle speeds with the clutch pulled in). It wouldn't restart until I turned the key to the off position then back to the on position. The display reset during the process.

It happened again a few days later, except I did not need to turn the key to the off position to restart it.

A few days later the bike starts acting weird (speed isn't consistent and display is resetting). The next morning, the bike would not start, the battery was dead.

I took the battery into the place i purchased it from to have it charged and tested. The shop said the battery is good.

They suggested I bring in the bike to have the charging system tested, hence why I took it upon myself to test it.
 
#25 ·
The OP measured infinity in both directions, and was advised that it sounded like a bad rectifier. In all probability, that rectifier is fine since most of the time when a rectifier fails it will short. As you say, that is easily detectable with an ohm meter.

But if it has opened, The OP's method is inconclusive... that's when the proper diode check is needed. I doubt this is the case, because if it was open he wouldn't be seeing anywhere near 14v.
 
#27 ·
It happened one time, and that was 2 weeks ago of every day riding. He took the battery in to have it tested and then reinstalled and has not had a problem since. Test not showing an issue and his voltage is good. I'm guessing it was a bad connection (loose wire, corrosion on the terminal, etc.) that he "fixed" when he reinstalled it. Either that, or he didn't realize that he had left something on that drained the battery.
 
#31 ·
Sorry about the confusion. Here are the readings you requested:

1. Take voltage reading across battery. (12.69)
2. Key on, take another reading. (12.37)
3. Leave key on for a full 5 minutes and then take another reading. (12.32)
4. Key off for 5 minutes, take another reading. (12.60)
 
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