Bad batteries and implications for r/r and stator - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 07-10-2006, 06:58 AM Thread Starter
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Bad batteries and implications for r/r and stator

Hi, Folks - Now I've totally lost the thread from yesterday, but managed to get the info on the MF battery that's discussed in the first thread in this section. In response to my query about the bad cell in the battery, someone (VN750?) responded that I now need to check my r/r and my stator (if I got this right, "a bad r/r may ruin a stator, but a bad stator won't ruin an r/r"). Yikes! So if I get a new MF battery, I may *still* have to replace both the r/r and the stator? Because...?

Sorry, I'm still new to the mechanics of motorcycles -if someone could help, can you explain to me the relationship (briefly) between the r/r, battery, and stator/alternator? And was it my riding at low rpms in the heat that somehow may have mucked up all three? I recharged the maintenance battery, and everything seemed to work ok last night. But now I'm worried about riding too far from home...sounds like I could've screwed up a lot of important and costly parts!

Thanks!
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post #2 of 8 (permalink) Old 07-10-2006, 08:23 AM
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Get a volt meter (even a hand held one). Go for a ride a few times around the block (so the bike is warmed up). Take off the seat hook up the volt meter and see what the voltage is at idle, 3000 rpm, and 5000 rpm. If you get 13+ volts at 3000, you should be good to go.

Deuce (Loran Naperville IL)
1995 VN750 (Black w/ 2004 tins - no teal)
2003 VN750
Both have: - F&S Bags & brackets
- Corbin seat w backrest
- Progressive suspension.
- Kury iso goldwing grips
2 1983 V65 Magnas
2 1985 V65 Mangas (1 which is in many parts)
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post #3 of 8 (permalink) Old 07-10-2006, 01:33 PM
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Yep. Do what Loran says. If you don't get 13+ volts, it could be your r/r. From what others have said, any slow "parade like" riding on a 750 with stock exhaust can kill the r/r. The r/r gets very hot, even after being relocated where it can get air over its fins. The problem with the stock exhaust is the "goat's belly" - a pre-muffler that sits directly below the r/r and heats it further. So slow driving with absolutely no airflow is sure to kill the r/r like it would kill your computer if all your ventilation holes were plugged up.

The stator takes magnetic energy and converts it into electricity. The voltage varies depending on rpms, but I've heard somewhere between 40-70 volts AC. The voltage output is fed into the r/r, which is a passive device - meaning that it just converts voltage to another voltage. Similar to the transformer that you plug into the wall to charge your cell phone. So the r/r (regulator/rectifier) converts the 40-70 volts AC to something like 12.5-14.5 volts DC. The difference between your cell phone charger and the r/r is that the r/r puts out lots of current. The voltage conversion, along with the high current flow creates lots of heat. The output of the r/r charges your battery.

Anyhow, it was bad engineering design on Kawasaki's part with the placement of the r/r (under the battery, on top of the pre-muffler). If you don't have a maintenance free battery, this is an absolute must get. The battery alone will fix a multitude of the 750's problems. Check your voltage as Loran said. It could be your r/r is fried. Let us know...

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post #4 of 8 (permalink) Old 07-10-2006, 01:50 PM
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OH, if the r/r is fried, as in shorting out, it will cause the stator to "burn up" from the heat it creates from making electricity. This equation, V=IR, voltage = current X resistance, can be reconfigured as V/R=I, or voltage divided by resistance = current. One equation for watts (heat) is VI, voltage times current. If the r/r is shorted, the resistance of the r/r = 0 (shorted to ground), so the current from the stator is 50 volts divided by 0. By theory, this would mean that the current being produced by the stator would be infinite. Watts, then, would be infinite, or at least hotter than the sun. The wires and insulation making up the stator would melt, thus decreasing the voltage output to nil. And there you have it, a shorted r/r kills the stator. This is why it's important to do the modification of "fusing" your stator, so that a current output of more than 15 amps will kill the fuse, as opposed to killing the stator.

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relocated R/R
de-badged
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post #5 of 8 (permalink) Old 07-14-2006, 09:41 PM Thread Starter
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Voltage r/r fried

Hi, Folks -
I followed instructions, and definitely the r/r is cooked. Went from 12.79 v cold, rode around a few minutes, and then down to 12 v on the battery at idle. Tried to get the rpms up, but the engine died and wouldn't restart. Not enough juice, I guess!

Anyhow, have managed to fight my way under the battery and have pulled the r/r; is there an easy way to test the stator without pulling it (and the engine)? Or do I just have to suck this one up and hope I remember where everything goes?

Thanks for you guys' help so far - this is a great forum, and I appreciate everyone's "lessons learned"!

Cindy Robins
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post #6 of 8 (permalink) Old 07-14-2006, 09:59 PM
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hey cindy. sounds like you're in the boat as i am... just posted another charging system problem under the thread title 'introduction and diagnosing the charging system'.

from what i understand, there is a way to test the stator by using an ohmmeter on the three alternator leads coming out of the stator. you can do this without pulling the engine (of course, if the problem turns out to be a fried stator, you'll need to remove the engine (or at least cock it to the right) to replace the stator).

the procedure is described on page 15-18 of the service manual (if you have that)... otherwise, here is the procedure (reproduced from a file found on the vn750 yahoo groups forum (http://autos.groups.yahoo.com/group/VN750/).

-----
Remove the left side cover and find the stator/RR leads. They will be 3 yellow wires w/ bullet connectors that go from the stator to the RR (under the battery box if not relocated). After charging your battery FULLY, you can do 3 tests to check the stator, as well as voltage tests at the battery and resistance measurements at the RR.

Stator Coil Resistance
Set VOM to read ohms on lowest scale.
After disconnecting the bullets, check the resistance between any 2 yellow leads on the stator side....you will do 3 measurements total. All three should be roughly the same, and be in the range of 0.34 ~ 0.52 ohms. If the measurement is higher than the spec, the stator has an open winding and must be replaced. If the measurment is lower, the stator is shorted and must be replaced.

Stator Coil Isolation test
Set VOM to the highest ohms range, and test the 3 leads vs a good ground. Red lead on the yellow, black on the ground. There should be NO continuity..none, on any of the 3 readings. Any reading less than infinity means stator died and went to heaven....

If you're still in the game after these two (great!), then start the bike w/ the stator wires still disconnected (fully charged battery!).
Set you VOM to AC volts, and check any two legs of the yellow stator wires, just as above.
You should see IDENTICAL AC readings, varying with the throttle, ranging from maybe 13 ~15vAC at idle to possibly more than 50 vAC at 5000rpms.
If your stator does OK on these three tests...lucky you...you just may have a bad RR or a battery.
When you do these tests, remember to jiggle wires around a bit to try to locate shorts.
-----
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post #7 of 8 (permalink) Old 07-15-2006, 11:15 AM Thread Starter
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Checking the stator

Hi!
Seems like a lot of us are in this same boat! I'm definitely going to try to make some modifications (including moving the r/r and lower the amperage on teh stator fuses) once I get all the parts I need.

Okay, I pulled the r/r last night - after much non-Zen-like work - and checked the readings. I think I may have set the ohmmeter wrong, so I wanted to get a check on that before I try to check the stator. I set the ohms so that the meter read: 0L. and the to the side there was the "k" and then the omega. My readings were then up in the 200-300 range...whcih is what makes me think that I've either fused everything together or set the thing wrong. The manual says to set the meter at Rx100. Is the 0L. that? Or should i have set it differently? Any advice on that would be great.

As for the stator, I've now pulled my battery, various connections, *and* the r/r, so I have this terrible feeling I have to pull the stator anyway (and thus should replace it). Can I check the stator without all the other necessary parts, or should I just replace it and begin fresh?

By the time I've done all this, hopefully i can put Humpty back together again; if not, I'll part the _)@# out on eBay.

Thanks.
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post #8 of 8 (permalink) Old 04-06-2008, 11:05 PM
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This description was excellent. Simple but descriptive enough to actually use and make the measurements. Thanks. Rick
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