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erratic voltage on my 2008 ST

2K views 12 replies 6 participants last post by  Oldman11 
#1 ·
I have blown two low beam headlamp bulbs over the last couple of month so decided to check if over-voltage may have been the issue (potential spikes or such)
Sure enough, on testing with a multimeter the static voltage was 13 volts at the battery but when starting the bike and running up the revs a little I found the multimeter was fluctuating with intermittent spikes well above the acceptable 15 volts, perhaps momentary spikes above 20 volts
My first thoughts were that it could be a faulty regulator / rectifier so just go and buy a new one. But then I know nothing about alternators other than they do have brushes in them that can wear out? My machine has done close on 40,000 kms so maybe they are in need of changing? Or could it be as simple as squirt some electrical contact cleaner into the wiring plug / socket and try the voltage test again?
I don't mind replacing the odd lamp but some of the electronics on board go way beyond that for replacement so I am reluctant to just fiddle without some guidance if there is a knowledge base out there that can help? I guess the lamps blowing were the "canary in the coal mine" sending me a message - everything else was going ok but now I do have a warning on the dash.
Any advice welcome [:(]
 
#2 ·
Noel

Do check the battery terminals too - intermittent on them will make the charge voltage go all over the place, but would probably guess the reg/rect isn't doing its 'short to ground' properly to limit the output voltage ... the F800s have a permanent magnet alternator, so the strength of the magnet can't be controlled like a car alternator (eg ones with brushes), the output is 'always on' full blast so at higher RPMs/ light load the standard reg/rect momentarily shorts the output to ground so the excess gets dissipated as heat in the stator windings (have a search for stator failures).

If you do go looking for another reg-rect would not suggest staying with a BMW unit - upgrade to a more modern MOSFET or 'series' regulator while you're in there anyway. Have a search for SH775, you'll find a lot of info around series regs and why they're supposed to be better.

HTH

Max
 
#3 ·
I agree with Max regarding the rectifier/regulator. The regulator/rectifier is what limits voltage output. Too high is a sure sign that it has a problem.

The stator works in unison and so replacing one means you should replace both. (And neither is expensive for the task they perform.) It's a very DIY project as no mechanical ability required - just patience.

https://f800riders.org/forum/showthread.php/315737-Replaced-stator-and-regulator-rectifier

As you are handy with a multi-meter, you can conduct a stator test. Follow the wires coming out of right side cover near your foot. These will lead to a connector. Notice the three yellow wires?

There are three primary wires coming from the stator yielding AC voltage. Set the meter to AC and you should have 40-80 volts AC between each of the three phases:

Y1...Y2....Y3

Measure between y1 and y2, then y2 and y3 and then y3 and y1. At idle is fine. If any of those three legs don`t yield AC then the stator is toast.

Now check for continuity. Turn the bike off. Use same 3 leads as measuring the AC voltage. This time the plug is disconnected (squeeze the sides of the connector.)

Any open measurement is bad as you test between y1 and y2, y2 and y3, etc. Those should be about 0.5 ohms. If they are open that means that circuit is bad. The take each of the legs and measure to ground. No continuity is good. You want an open circuit here. If you don`t that means that part of that coil is short circuited to ground.

Over voltage is a regulator issue, not a stator issue but they work as a team. Failure in one usually means a problem has occurred in the other, or the other is substantially weakened/damaged by the fault. It's all about voltage and heat between these two - very powerful forces when things go wrong.

Credit to ADVRider forum member ebrabaek.
 
#4 ·
Thanks to both of you, I like the sound of the modification, had already seen elsewhere that the SH775 was well recommended
As an Ex Kiwi myself who has also spent a couple of years (long time ago) in Alberta I feel among friends
Question for Max, you understanding the "extra" cost we pay down under for anything we import: where did you buy your parts and what was the approximate cost?
I am in my 70's, retired, so have time on my hands though I will dislike parking up the bike for an extended period if I have to wait for parts from the northern hemisphere.
Much better if I can purchase in Aussie (or NZ if required) just to hurry things along.
I also had a question about the plugs/ sockets required for any modification - how hard are they to come by and where to buy them?
My Rec/Reg has the number SH541G-12 which when I searched would indicate it came off a Honda perhaps?
And by the charge state of the battery it would "appear" to my unlearned self that the Stator is/was still doing its job?
 
#5 ·
Update: I just checked on line and both RR and stator can be purchased from right here in Aussie - Looks like $756.85
Oh well, its only money, and if I don't spend it, the "kids" will
I note the connectors look the same as original, nothing to modify with the Mosfet SH775 [:)]
 
#6 ·
Glad you've got it sorted. And what a surprise to hear you've lived in Alberta! You may be pleased to know Aussies remain well represented here, particularly in Banff and Jasper.

I've been to Perth, Melbourne and Sydney. Next time, I'll load my suitcase with motorcycle parts. Quite a price difference.[:)]
 
#7 ·
I would agree that the charge state of the battery indicates that the stator is fine. You can do the Y1, Y2, Y3 test as stated above to confirm this. Assuming that is the case, you only need a new R/R. I picked up a used Shindengen SH775 a couple years ago for $100 US on ebay. It bolts right on in 2 minutes, but did require some wiring because the connectors were different. I've replaced my stator 4 times over the past 7 years. It is not hard to do, but you do need a new gasket when reinstalling.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 
#8 ·
Steep learning curve here for me Guys, I am a "can do" sort of person, having done a full restoration on a now trophy winning '69 H1 hence my comment about the brushes (which it had)
Cramer, I am shocked to read the number of stators you have replaced, surely they must be of poor quality, but Max's thoughts about replacing both items at the same time and going the way of Mosfet R/R would have considerable logic to it?
At the prices we pay for this product it hurts but it would hurt a dam sight more if I had to do it all again in 18 months!
I will do a stator test in any event, now that I know how, but the logic that it may be damaged due to over heating (and fail down the track) makes a good argument for replacement.
A "tow" back home from some distant location would quickly swallow up any short term savings and then some
I do appreciate each and every comment because it gives balance to the advice so thank you one and all [:)]
 
#9 ·
My fist replacement was done by a BMW shop during a road trip 1000 miles from home. Cost me $1200! My second and 3rd replacement I did at home with cheap aftermarket parts (stators were about $200). My last one was a BMW part, at the same time that I swapped the R/R to a series style. Additionally, I changed the rotor to the newer design with more holes for oil cooling.

The rotor is a point worth mentioning. Around 2010 they changed the rotor design to improve cooling. It's not easy to remove, but plenty of heat and an impact wrench on a M22X1.5 R.H. External Thread puller got it off.

Hopefully I'll be good for a long time now that I have a new rotor, original brand stator and a series R/R.

Sent from my SAMSUNG-SM-G891A using Tapatalk
 
#10 ·
I have blown two low beam headlamp bulbs over the last couple of month
=======================================
I've got a 2013 GT with some 75,000 miles on it. I think it's fair to say i have never gone 6 months straight
with both bulbs lit. One after another they blow out. I've installed a high output twin LED light, so it's not
an issue anymore. For some reason I never had both bulbs out at the same time. It never occurred to me
to check on charging voltage, but the first time a bulb blew out twice in a couple of months it was still under the
warranty and I brought back to the dealer to look for a problem. It would hope the dealer mech. would be well
trained enough to have checked the voltage if that was a possible cause. FWIW I had a Honda ST1100 that
regularly charged at over 15 volts, usually 15.2, and never blew any H4 bulbs. So i've never found the problem
and I'm currently riding with the high beam out, but like I say I now rely on the LEDs I installed.

Bob
 
#11 ·
Job done. Replaced only the R/R with a new MOSFET type and did the stator tests - all OK so did not replace due to financial concerns.
I followed the advice that it is possible to replace the R/R without removal of the air box, is certainly possible but very fiddly and not sure how much time I might have saved.
Checked the charge rate at the battery post surgery and it is now a very stable 14 volts so have now replaced the headlight bulb, hopefully last time for a while?
I did note some minor corrosion inside one of the AC connector terminals, cleaned it up and lubed all connectors with the terminal grease supplied in the kit
Thanks to all for their contributions, a lump of money saved doing it myself and no new warnings on the dash- just the service indicator which has been there for a couple of years because I do my own servicing and don't have a reset tool. I should try a buy a second hand one?
 
#13 ·
Long term report:
More than 2 and a half years past since my R/R replacement - all still great, no problems - must be that MOSFET R/R? :)

What is also interensting. I had ordered a Cheap Chinese R/R($34 including postage) which duely arrived but I did not use
About a year ago a mate had just blown his R/R in an early Honda which appeared to be similar to my cheapy, which I gave him
Asked the other day and he tells me "It's still going fine thank you"
So there you are - two happy people, and the mysteries of the universe will remain that - just mysteries to me
 
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