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Discussion Starter #1 (Edited)
Issues with charging - voltage drops with rpm

My 98 GSXR 750 doesn't charge the battery. When rpm increase, the voltage goes down. The voltage on the battery is a little higher when the engine is running, than it is when the ignition is off.

This is what I've looked at so far:

- I've measured the resistance of the lead wires coming from the stator, and they all read 0.5-0.6 ohm. Ground test is good, and VAC test from the three leads is also good (~25 vac at idle, 70+ vac at higher rpm).I've opened up the stator housing, and the stator looked fine (I have pictures, but don't know how to upload them). This leads me to believe that the stator is not the cause of my issues.

- I used the diode function on my mulit meter to check the R/R. It gave a consistent reading on all wires, measuring from the positive lead and the negative lead onto all three leads from the stator. Resistance between the positive and negative lead was around 1000 Ohm, and about half of that between the positive/negative and the three leads from the stator.

- I've measured the current directly onto the lead going to the battery. I dosconnected the leads from the battery after starting the engine. This makes the idle rpm rise. I guess the ECU notice the lack of current, and increase rpm in an effort to charge more? Anyway, the current measured at the battery leads is too low (12 and lower), and decrease when with higher rpm. This leads me to believe it's not the battery that is the cause.

- With all connectors pluged in, and the battery connected, I the measured the voltage at the connector from the R/R, by probing it form the backside of the connector. On the R/R side of the connector, the voltage was around 14.4-14.5 when idling. Good right? But it dropped to ~13 when I increased rpm to 5000. I held 5000 rpm for a few seconds, and the voltage continued to drop, about 0.01 volt every second. When measuring from the battery side of the connector, the voltage was a little lower than on the other side. But the voltage was all over the place when I increased rpm. It would jump from 6 volts to 12, and everything in between.

Is that normal? Is the R/R damaged? Is the connector? Is it the harness, or the leads?

Thanks in advance for any help. I'm really at a loss here.
 

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You mention a lot of measurements (which is a good thing!), but you aren't always very specific about what exactly was measured and what the readings were compared against. For instance, you mention getting "consistent reading on all wires" when testing the diodes in the R/R, but that doesn't say much about what it was consistent with. Did you compare the figures you got with the table of expected ranges in the service manual? Then you go on to mention readings of "resistance" across positive/negative leads and getting values of 1000Ω, but resistance measurements aren't specified anywhere and there is no expected value. I'm also fairly certain that you shouldn't be getting measurable resistances at those leads, but perhaps you mean that you've probed the +/- leads in diode test mode and got 1.0V back (as diode mode measures the voltage drop accross the diode(s) between the probed points).

At any rate, if you've measured the stator and R/R *as described in the service manual* and got back values within the normal ranges, then your problem is probably related to voltage drops across couplers and wiring. Inspect the couplers of the R/R (and other couplers on the way to the battery) looking for signs of overheating, grime, rust, looseness and other issues that might be deteriorating the connection.

Finally, a word of caution: It's generally not a good idea to disconnect the battery, or any other large load, while the engine is running. The sharp disconitnuity in the current (especially when the disconnected battery was drained and therefore drawing a large current) causes the voltage to spike faster than the R/R can handle, potentially causing damage to wiring and attached devices. Furthermore, testing the current through the battery leads while the engine is working doesn't really say much unless you have some sort of expected result. (For instance, why would "12 and lower", assuming we're talking about amps, be "too low"? If anything, it would see curiously high to me.)
 

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+1 on not disconnecting the battery while the engine is running. I don't have a service manual for your bike but the TLR manual and all subsequent manuals says:

Removing any battery terminal of a running engine is strictly prohibited.
The moment such removal is made, damaging counter electromotive force will be applied to the ECM which may result in serious damage.

To measure the current in the battery leads requires special meters or shunts. Few people have such equipment and there's very little information about what those values should be. You're venturing into uncharted waters. For example, I've wondered what the starter motor current is but never bothered to try to measure it.
 

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Discussion Starter #4
Thanks for your reply, guys. I appreciate any feedback, as I'm completely green at this stuff.

I disconnected the battery leads in an effor to isolate the voltage readings coming from the stator/RR. I figured if the leads read 13.5-14.5 VDC, it was the battery that was at fault, but I realize that was foolish. It goes without saying I don't know what I'm refrencing - hence why the measurements I mentioned are a little vague.

When I say "consistent readings" I mean that the value measured from each lead was more or less the same. I don't know what measurment the diode setting on the multi meter measures, be it wattage, volts, amps or ohm. But I was getting more or less the same number on all three leads (around 550 - 560 if I recall). The service manual say I should be getting values of "approx. 1.5" with the diode setting on a multi meter. So my values are way off spec? However, I've watched some videos on YT, and they had numbers similar to mine. They seemed to indicate that those number are normal, only when you do not get any readings it means there is a fault somewhere.
 

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The manual has a table that lists the value you should be getting when probing all pairs of leads in the R/R connectors. Pay attention to where the + probe goes and where the - probe goes, since its important given that you're measuring diodes. (Also make sure you attach the probes properly to the DMM.) If you get off-spec readings, let us know where you get them and how exactly you measure (where you put each probe). Generally, if all readings are off-spec, you're likely doing it wrong; if one or two are, some of the diodes inside the R/R have failed.
 

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What leads you to believe that the battery isn't charging? Does the battery die often? A lot of the tests that you did are what are described in the manual and those tests look normal. Those resistance tests you did, that were already mentioned, mean nothing. FOr the diode test on the R/R, you didn't mention values, just that they are consistent. What, exactly, are they?

Like was said, never disconnect a battery from the engine when running. The battery is part of the circuit and when it is disconnected, then the rest of the circuit will be smashed in the face with higher values. If you ever want to measure current at the battery, just disconnect ONE lead, put the ammeter in series by putting one alligator clip on the lead, the other on the battery, THEN start it.

As for battery going down with RPM, that is a more sticky issue. There are lots of reasons why it could go down when the system is under load and that is because as rpm increases, so does the load on the electrical system and that is why the SPECIFIC rpm of 5k is where one measures the voltage across the terminals.

The jumping around of the voltage from the battery side of your connector could be twofold. One, your leads were contacting the wires intermittently or not strongly, or there is corrosion/bad connection.

At 5000 rpm, with everything connected, what is the voltage at the battery terminals? What exact values are you getting with the diode tests at the R/R.

I do not know what specific values you should be getting for everything since your bike is carbed vs. FI, but it would be worthwhile for you to buy a manual for that specific info.
 

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What makes You think stator is all right? Did You measure it on both idle and 5000 rpm on all couples?
 

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QUOTE=Kartel;9558884]What makes You think stator is all right? Did You measure it on both idle and 5000 rpm on all couples?[/QUOTE]

:I've measured the resistance of the lead wires coming from the stator, and they all read 0.5-0.6 ohm. Ground test is good, and VAC test from the three leads is also good (~25 vac at idle, 70+ vac at higher rpm).I've opened up the stator housing, and the stator looked fine (I have pictures, but don't know how to upload them). This leads me to believe that the stator is not the cause of my issues.
 
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