Bad battery or bad rectifier/regulator?

[Degsy]

You cooked the shit out of the RR when you left it idling on a hot summers day with no airflow. It hiccuped. It might have some internal damage, it might not. If it's the original, I'd replace it anyway. They go, as they say.

[number9]

I got to the "idled the bike for 25 minutes outside" and that was as far as I got. Fyi, Don't do that.

To be fair, when it was idling outside I checked it every few minutes and the bike was in the shade. Also, I had the rear fairing off, which I had ASSumed would give it enough airflow.

Check voltage across legs of stator at about 5000rom. You'll be looking for 60VAC or so.

I'm confused. You're not draining battery, bike starts fine. Your only issue is a 0.1vdc drop at 5000 rpm? I'd say operating within design perameters, captain.

Or did I miss something?

You missed something, but only because I wasn't clear on where I was back to. The bike will start fine, and idle fine at ~14VDC. Once the bike is up to temperature, it still shows ~14V. Once I bring the RPMs to 5,000 or so the voltage will drop out of the R/R to <12VDC and never recover. If I ride the bike like that, the battery will of course eventually go flat.

The last time this happened, the stator was showing well under 20VAC at the time that the battery was seeing <12VDC at 5k rpm. I haven't done that same test recently, though.

You cooked the shit out of the RR when you left it idling on a hot summers day with no airflow. It hiccuped. It might have some internal damage, it might not. If it's the original, I'd replace it anyway. They go, as they say.

Should I not follow Occam's Razor and change the battery first? It only shows about 12.3VDC when fully charged, and I don't know how old it is other than to say "more than 6 years".

[Degsy]

Probably, yes. That does sound logical.

But......bad R/R's damage batteries.

If you have the cash-ola, change them both at the same time. If the stator output is correct, it's good. They don't get affected by heat etc.

[nhbubba]

If the stator output is correct, it's good. They don't get affected by heat etc.

Really?

[Degsy]

Ok.

[number9]

Probably, yes. That does sound logical.

But......bad R/R's damage batteries.

Will a bad battery "refuse" a charge, perhaps by making the R/R shunt the excess current (while charging) and have it dissipate as heat?

[Degsy]

Yep. Bad battery will cause the RR to get hot. That's how a regulator works. That's why they are affected by even more heat. That's why they are usually (not always) placed somewhere in airflow and are just one big heatsink.

As opposed to stators, which I'm told are sensitive to heat even though they spend their lives inside an engine, basted in hot oil for hours at a time, yet rarely fail.

[Stromper]

There are many instances where the control of electronics fail at a certain voltage (short) not before

[nhbubba]

Re: Stators. My understanding is that they are bathed in oil to help cool them. Run your oil level just a little bit low in some machines (ex: SV/DL650) and there isn't enough oil to keep it cool. Combine with the right load conditions and the stator can burn through the coil insulation and short.

Mine had a short. Not across the whole coil, but somewhere in the middle. Its resistance was close to spec. It did not put out the spec'ed voltage on 1 of the 3 coils. I opened it up to find what you see in the photo above.

Procedure to test the stator was pretty simple:
- Disconnect from R/R
- Engine off, check resistance of each coil using multi-meter
- Engine on turning at ~4-5k RPM, check AC voltage across each coil

Or something like that. Consult your trusty shop manual for details. In my case the hardest part was getting to the stator <-> R/R plug. Once it failed the voltage test I pulled the stator cover and it was clear it had failed.

My symptoms were different though. I had a weak charging circuit. Voltage at idle was well below 12VDC. At speed it topped out at mid 12VDC or something. It never got above 13V.

Lately I have problems again. Looks like voltage at 4-5k RPM is in the ~13-14VDC range. However it drops into the low 12VDC and sometimes lower range at idle, depending on load. It also drops below 12VDC if I use high beams. I suspect a new battery is called for. This battery is original (2011 bike).

[Danz19899]

Judging by your test results I'd also have to say it sounds like the R/R is toast. My last Zx-6r had a bad one that would only mess up when hot.

Usually if the stator is bad the resistance test would show it.

As others have stated you may also need a battery. Little motorcycle batteries don't like crazy voltage drops much

You've got to starts somewhere put a R/R in it and see what happens. Also a lot easier to replace then the stator

[number9]

Part of my frustration stems from the fact that the problem is intermittent. At 7:30pm it was the same scenario as before. My DMM shows >13VDC at the battery when the bike is idling cold. Once the bike is warmed up and I take it to 5,000rpm or so, the voltage at the battery drops to <12VDC and keeps going below 11V.

At 5,000rpm, the output side of the stator is showing ~11VAC between terminals 1 and 3 and around 6.3VAC between terminals 2 and 3. I think it shows around 6VAC between terminals 1 and 2, too. I remember seeing well over 40VAC at high rpm when the bike was healthy. I didn't bother checking the output side of the R/R.

I wait about half an hour, then repeat the test. This time it's >13VDC at idle, and stays around 14VDC above 5,000rpm. But even at that rpm, the A/C output of the stator is barely 12VAC. So in this case, the battery is charging even though the stator output seems weak.

There's about 0.03Ω between each of the stator terminals, and my DMM thinks its own resistance is 0.1Ω. There is an open circuit between the stator terminals and battery ground.

Interestingly the factory service manual says a good battery should show 13.0-13.2V when fully charged. Mine is not much above 12.4V.

[Danz19899]

Ok well judging by the new readings I change my mind lol That stator is toast "intermittently" lol It should always be producing more then 12V when running as far as I know.

[number9]

Pulled the stator this morning. I think it's fried. Right?

[juha_teuvonnen]

Pulled the stator this morning. I think it's fried. Right?

One of the things that I learned the hard way: never judge the electrical component by its looks. Always measure. Certain bikes (80s vintage Suzuki GS for example) have crappy R/R by design. To make long story short, they will sink excess current into both the stator and R/R itself, eventually overheating and frying one of the components. Sometimes it will fry both. Some R/R's will fail and take the battery with them by overcharging the crap out of it. I would replace the R/R with MOSFET type. This will make future R/R and stator failures extremely unlikely. The MOSFET type is inherently superior than shunt type by design. That's why bike manufacturers have largely abandoned the shunt type.

[number9]

One of the things that I learned the hard way: never judge the electrical component by its looks. Always measure. Certain bikes (80s vintage Suzuki GS for example) have crappy R/R by design. To make long story short, they will sink excess current into both the stator and R/R itself, eventually overheating and frying one of the components. Sometimes it will fry both. Some R/R's will fail and take the battery with them by overcharging the crap out of it. I would replace the R/R with MOSFET type. This will make future R/R and stator failures extremely unlikely. The MOSFET type is inherently superior than shunt type by design. That's why bike manufacturers have largely abandoned the shunt type.

I know a little (emphasis on little) about transistors and yeah, MOSFETs are quite superior. This stator actually tested fine but it turned out to be bad; I replaced it and the bike runs great.

[duganc1717]

Just as a reference, this pic is from when I was having electrical issues and determined my Stator was okay.

[juha_teuvonnen]

For future reference, "shindengen fh020aa mosfet regulator" seems to be the fix for bikes that have chronic R/R problems. Certain Ducs, Hyosung, 80s Suzuki GS and certain Hondas can all be cured by replacing the stock R/R with this unit.