Understanding stator resistance reading
 

Hi again. I'd appreciate some help in understanding the readings I'm getting from my stator so I avoid making an expensive mistake. I've got some flaky charging issues that only show up after I've been riding for three hours or so. The VR is new so I'm trying to figure out if the stator is faulty. The manual says the reading across the contacts should be between 0.52 and 0.78 ohms. Mine is reading at 1.3 but it is at the highest setting of sensitivity (200 ohms). Is this enough to confirm sick stator? Thank you.

Hi, make sure you subtract the resistance of the meter leads. Touch the leads together and deduct amount from the reading. Also make sure you have a very good contact with the connector as those resistance values are quite small and are easily swamped out by poor connections.
You can also check the voltage being produced from the stator coils when engine is running (which will be an AC voltage) to get an idea of how the charging circuit is performing.

As dblunn says, take a 'zero reading' of your meter with leads and take that away from your stator reading.

There are two further things.

You should also take a resistance reading from one of your stator connectors to 'earth' (battery negative terminal or any clean bit of metal). This should be 'hi resistance' say, over 2,000 ohms.

You say that it only acts up when the engine is warm.
This is when you want to take your resistance readings.
You should also check that the battery is not boiled dry (how hot is it when the problem occurs?)
And the rectifier/regulator .. how hot is that when the problem occurs?

Thanks guys for the very helpful advice. I'm fairly new to this so hadn't thought to check the zero resistance but it explains the discrepancy - touching the leads gave me 0.6 ohms which makes up the difference. So I guess the stator is ok but I'm running out of ideas on where to look for the source of the problem. What's happening is that after a few hours riding (with lights on) the battery voltage suddenly starts dropping. I turn the lights off and it climbs again. I've tried everything I can think of - changed the rectifier/regulator and finally rewired the whole bike to eliminate any possibility of shorts or earth leakage. But it's still there grrrrrr

Fault finding chart
 

Try this chart to compare your specific symptoms for their fault finding flow chart - without following the logic of such charts, electricary is tricky stuff!!
http://www.electrosport.com/media/pd...ng-diagram.pdf

Thanks for that link. It was very helpful. I've gone through the whole flow chart and everything seems to check out ok. But I'm still getting this voltage drop when riding with the lights on. With my old rectifier it would drop from the charging voltage of 14.6 to around 12.6 as soon as I turned the lights on while riding. With the new one the voltage stays steady at 14.6 until half an hour or so into the ride and then drops by around 1.5 v.

Is it normal for the voltage to drop like this? I've spent many hours searching for an answer but have not found it yet.

Do some 'measurements'. This will give you some information that may indicate where the problem is.

How hot

is the rectifier/regulator?
is the battery?


At, say, 1 hour into the ride and then when the voltage falls.


What is the voltage coming out of the stator - again at various timings.

Thinking about it only gets you so far. Then you need more information to isolate the fault, the thinking should indicate where that information should be obtained.

Is the front bulb stock? Just so you dont chase deaons beacuse someone fitted a 100w bulb or something...

Thanks for the excellent advice on going through those checks after running the bike for a while. I did that and got markedly different numbers on two of the checks.

When hot the resistance between the three wires coming from the stator is 2.6 ohms as opposed to 1.5 when cold. I guess this means the stator is somehow malfunctioning when hot and I need to fork out for a new one.

But I was wondering if it was possible, or likely, that the faulty stator could have cooked my newly fitted rectifier/regulator (I though the old one could be causing the problem)? When testing the diodes on the RR with the black multimeter lead on earth and the red touching each of the three input contacts in turn I get an OL result on two of them and a reading of just over a volt on the third. Can anyone advise me on whether this is a sign of a cooked diode?

Thank again for all your generous help. It's two steps forward and one step back but I'm getting there slowly.

It is unlikely that all 3 stator windings have the same fault.
Was the system working at the time you made these reading?
What were they before the system failed ... but the system was hot? (e.g. at 1 hour rather than 1.5 hours)

The stator windings are copper - copper has a 'positive temperature coefficient' meaning as temperature rises they get more resistance

Same question for the rec/reg.

Thank you Warin for your input. I'm just trying to avoid making the expensive mistake of unnecessarily replacing the stator and RR (again) so your advice is really useful to me. I thought I had the problem pinned to the stator but from what you say I've probably got that wrong. Everything was working fine when I stopped the bike and made the readings but there was not enough charge reaching the battery, unless I turned the lights off when the charging voltage would climb to 14V + again. The battery wasn't hot and neither was the rectifier.

The weird and inexplicable thing for my limited knowledge is that when I first fitted the new RR the bike ran fine for a seven hour ride (voltage with lights on steady at around 14.5V). Then on the way home the following day it stayed the same until four hours into the ride and then suddenly dropped 2V. When I turned the lights off it climbed again and went back down as soon as I turned them back on.

The next ride this happened after just half an hour, and today it happened as soon as I turned the lights on. So something is getting worse and I just can't figure out what it is. The headlight is aftermarket but the bulb is 45 W max so I'm running out of ideas.

New parts do fail.

I'd be very carefully checking the connections to the reg/reg .. the ends of the wire to the crimp/solder connection to the metal socket. They should be solid - no movement between wire and the metal socket socket.

Is there no one you can swap parts with? Put your rec/reg on their bike and see if the fault goes to their bike?

It is good that it is getting worse .. makes it easier to find.

My best bet so far is that something on the bike is causing the rec/reg to fail so I'd be concerned about borrowing someone else's in case I messed theirs up as well. The only other conclusion I can come to is that the old rec/reg was indeed bad and I've been unlucky enough to replace it with a faulty new one.

Can I ask - what other component or cause could be responsible for rec/eg failure?