Voltage Goes Down as RPMs Go Up? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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Where does this wire go?
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post #1 of 26 (permalink) Old 02-26-2014, 09:40 PM Thread Starter
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Voltage Goes Down as RPMs Go Up?

I just wanted to ask real quick before I set off on a full set of tests from the guide. I recently acquired a Vulcan. I haven't ridden more than a block yet. I'm still waiting for decent weather and for parts to arrive. I want to get all the maintenance up to date (oil change, clean air filters, lube the drive line, change the plugs, etc.). After reading about charging problems that come up with these bikes, I thought I'd better do quick test and see if I'm charging before sinking anymore money in this thing.

I connected my meter to the battery terminals. I keep all my bikes on a trickle charger so the the resting voltage at the time was about 13.2. I started the bike. At an idle (~1000 - 1100 RPM) I get 14.4 volts at the battery. As I rev the engine up the voltage drops to about 13.5 at 5K RPM.

This is a$$ backwards to everything I've read. The fan was off during the tests, just didn't run it enough for it to come on since it was less than 20F in the garage at the time.

It's a stock 89, no mods, no extra lights. About 26K miles. I imagine the ignition system is pulling the voltage down as the RPMs qo up. But shouldn't the regulator compensate for that (if it's functional)? It seems the stator is capable of making over 14 volts.

I wouldn't be worried if I only had battery voltage or maybe a little less at an idle and the voltage increased along with the RPMs. But this is really weird.

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post #2 of 26 (permalink) Old 02-26-2014, 09:58 PM
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The voltage regulator isn't dependent on engine RPMs...only the stator is.

So your stator output seems a bit wonky. But good news is it is putting out enough power to charge the battery even at 5k RPMs.
I'd check (and clean) all your stator connections, your ground and the R/R connector.

There's a test somewhere here on checking your stator output. If do that after the above if you're still getting "backward" readings....but again if you're not going under 13.4 volts I'm not sure I'd be too worried.

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post #3 of 26 (permalink) Old 02-26-2014, 10:39 PM Thread Starter
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I'm hoping a good cleaning may help. I'm by no means knowledgeable about electricity, but I would think that poor connections could cause the voltage reading to go down as current goes up. Isn't that why bad connections seem to get hot - resistance?

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post #4 of 26 (permalink) Old 02-26-2014, 11:53 PM
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That's a short test ride to be testing the stator, specially since you started with a topped off battery.

Start by pulling the charger offline and wait at least 2 hrs. With engine off test battery voltage. 12.4-12.7v would be what you should see with a freshly charged battery after being off the charger for an hour. Start and ride (or rev over 2000 rpm for 5 minutes) for 3-5 miles. When you finish the ride or high speed idol with the bike at 1000 rpm you should still be seeing at least 12.3v and at 2500 rpm at least 13.8v ( I would hope to see 14v+) If you don't you've got a problem. If you do see these voltages ride on and enjoy the hell out if the bike.

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Last edited by Spencer1; 02-26-2014 at 11:56 PM.
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post #5 of 26 (permalink) Old 02-27-2014, 12:31 AM
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...all the testing stuff starts at 15-17 in the manual....diagrams, tables, etc...15-17, 15-18, 15-19....



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post #6 of 26 (permalink) Old 02-27-2014, 04:06 AM
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I have seen readings like these right before the stator let loose

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post #7 of 26 (permalink) Old 02-27-2014, 09:04 AM
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Quote:
Originally Posted by slimvulcanrider View Post
I have seen readings like these right before the stator let loose

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Well, maybe his stator is about to go. Damn that's a lot of work to fix.

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post #8 of 26 (permalink) Old 02-27-2014, 02:51 PM
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I had readings like this once too, but the system is fine.
In my case it had to do with LED's that were installed and causing cross-bleeding in the lighting system.

If the battery is not rested after a charge, you will see some screwy numbers (which is what Fool was eluding to). it has to do with balancing the cells internally...some balancing of loads...ying...yang...yada yada.
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post #9 of 26 (permalink) Old 02-27-2014, 09:15 PM
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Quote:
Originally Posted by kc2dgq View Post
I had readings like this once too, but the system is fine.
In my case it had to do with LED's that were installed and causing cross-bleeding in the lighting system.

If the battery is not rested after a charge, you will see some screwy numbers (which is what Fool was eluding to). it has to do with balancing the cells internally...some balancing of loads...ying...yang...yada yada.

Wow ! New & Good Experienced info here !

Read & head !


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post #10 of 26 (permalink) Old 03-06-2014, 04:43 PM
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Just a note. This got my attention so I waited till is was above 20 F to check. I know my bike is charging at all revs. Never had even a low battery, and even today it has not ran in 2 weeks, stored in the cold. Prestart was 12.7 V. Fired up with one crank, temp was 36F. The only electrical thing different is turn signals in saddle bags. These are my readings; 1100=14.34 1600=13.8 3000=13.6 3500=13.4 I had a thought, maybe with the R/R in the cold air it may dump voltage more efficiently?
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