Diagnose my 'lectrics (again)...

[Captain Starfish]

A friend's GSXR 750 (bout 10 years old?) has been playing up and I'm giving them a hand to try and get it back on the road.

First thing when the fairing came off: the classic melted plug between stator and loom. Fine, cut the puppy off and I've replaced the wire back to the reg/rec plug.

Next question - what's rooted?

All windings measure around 0.8Ω winding to winding on the stator.
Winding to winding voltage at 5000RPM around 65V ± 5V when open circuit.
Plug it in, winding to ground voltage around 12.5V and stays put.
Battery voltage 13.4V off, 12.5V ignition on, 11.8V start, then sits at 12.5-13.5V regardless of RPM. Actually, the highest voltage seems to be near idle.

I'm expecting it to sit around 13V at idle and then march up with RPM to around 4500RPM where it clips at around 14.5V. This ain't happening.

So: reg/rec stuffed? Stator stuffed? Both? Any other checks I can do? Grr: both were replaced 13 months ago.

[I Fancy Holidays]

Its the battery.

Not sure how helpful but can you measure the current in/out of the battery?

[Captain Starfish]

I doubt it, not on the pissy little fuse multimeter I have...

[potato]

its a jap bike and a "modern" one, its past its use by date.

oh fuck its not the one that needs the rear cover painted?

runs off and hides

[Captain Starfish]

At least it's spent some portion of its life actually running.

[potato]

true ! ive got nearly 95k on the 900ss,its fouling plugs so i bought a box of em and replace them every 3rd ride........

still carnt bump start the fucker................

[SpeedTrip]

So Mr.*Fish
What's the actual problem?
Is it not starting?
Not running (I doubt it coz you said you measured the voltage at idle)
So what is the actual problem we're chasing?

Edit:
It's a Suzuki, should have told them to trade it on a Kawasaki

[Nero Diablo]

I'd track the main charge wire back to the battery check every connector it passes through make sure none are corroded/broken/melted. Also the bolts that hold the reg to the frame these often earth the regulator via the case clean good metal to metal contact. Main earth lead where it bolts to the frame clean free of corrosion. If problem persists its most likely the regulator the numbers coming out of the stator seem to be ok to me.

[Captain Starfish]

Spedtrip: It's struggling to start, now with a freshly charged battery is ok again but with the wiring fried I'm concerned the subsequent short may have fried stator or reg/rec. If, when I'd redone the wiring this afternoon, it fired up and held anything over 14V at revs I'd be happy. It's not, so I'm not.

At least it's not a krapasake though: thanks for pointing out the silver lining

Nero: good stinking on the charge wire. This model earths the reg/rec with a separate lead but I'll check that tomorrow, too.

I guess my worry is that, though the stator may be generating the right volts open circuit, it looks like it might be shitting itself under load when hooked up to the rest of the bike. Whether that's the reg/rec or the stator, though, I can't tell...

[likefry]

Can you try measuring the voltage of the stator with the reg/rec hooked up?

My battery voltage was doing the same thing when I had a no earth, ie the reg/rec was not bolted on the frame. Put it back in it's place and all was good.

[Captain Starfish]

Good to know, thanks!

Tomorrow (next time I'll see it), then:
1. Check voltage across stator coils under load.
2. Check both earth and +ve wires from reg/rec to battery, and look at whether it needs frame earthing as well.

Cheers guys.

[K1GxR]

suzuki gsxrs do stators and regulator / rectifiers. common problem with them.

[Ducfreak]

As mentioned above stator numbers semm good, and at .8R theres no high resistance joint to kill it on load. My bet is Reg/Rec has dropped one diode, replace and smile again .
And Potato run the SS on NON PULP fuel with Flashlube or similar and it WONT foul plugs, My 78 darmah fouls 'em in no time flat when run on premium, runs forever on 2 cyclinders on standard unleaded or E10

[Captain Starfish]

K1GxR - hence the "only 13 months since replaced". Trying to work out which/if both are fried and what to do next.

Thanks Ducman - might see if I can check diodes to +ve on these units or something.

[Ducfreak]

3 phase alternator, so 3 inputs , 6 diodes 3 positive in form alternator 3 positive in from earth to the Batt out.
Hope that helps

[Captain Starfish]

It does help. I'd forgotten about the bottom end diodes.

So it's a bridge rectifier with 3 phases instead of the usual 2 found in AC/DC supplies. And I'm assuming the regulator just sits open circuit until some nominal voltage is reached - so using a diode checker I should see 0.7V drop or so from each phase to +ve and from earth to each phase.

The regulator should do nothing unless I put one of the phases to a benchtop supply with another phase to 0v on the supply in which case the voltage + to gnd should sit about 1.4V lower than the supply output as it comes up from 0V until about 14-15V somewhere when the output voltage should clip.

Amidoinitright?

[Ducfreak]

You may not get acess to all of it, depends how the actaul reg is set up, some "crowbar" the output to regulate others are a controlled bridge with 3 x SCR's and 3 x diodes, but the basics are close, at least it'll give ya an idea

[Captain Starfish]

I did wonder how intertwined it would get - but gives me something to work with. Thanks, ducman!

[Ducfreak]

[GSX IN SHED]

Hey Capn' H/Duty 3 phase reg's for big Suzi's don't come cheap (unless I've been Ripped off!!)
bike tyre city has 'em in stock (?) SH-548 12v/3 phase/27 amp.... more than up to the task...
Did you check stator for short to earth ( burnt wiring)??
Good luck man....Greg