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Louie
Louie, Technician
Category: Motorcycle
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Experience:  25+ yrs. experience
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How would I troubleshoot a voltage drop that happens after a

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How would I troubleshoot a voltage drop that happens after a while of riding?
The problem appears when the motorcycle is hot (within 5-15 minutes typically). If I haven't ridden it the voltage is ok, then starts dropping (i have a voltage reader on my dash).
Eventually the battery discharges.

Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, is a standalone volt/multi-meter available?

Customer: replied 2 months ago.

Let's try check and review the basics. Proposed preliminary tries (if have not been done):

  • • re-inspect the battery, its ground lines to the harness, frame & engine, and/or re-check and re-clean the battery cables + terminals, connectors and wiring ;
  • • more importantly, have the battery externally charged; and
  • • then also have the battery LOAD TESTed (even if new/charged and just for the purpose of eliminating it as a suspect);
  • • disconnect regulator/regulator combo (may be challenging to some);
  • • check resistance between any/all pairings of the 3 stator output wires - very low ~ 1Ω or less;
  • • but no reading from any of these 3 wires to the engine ground;
  • • reconnect regulator;
  • • start/idle the Triumph and check DC voltage between the battery terminals - not less than 12.7V;
  • • rev the Triumph to 4,000RPM and re-check DC voltage between the battery terminals - 13.5 to 14.5V;
  • • but not to exceed 15.0V.

In most instances, it would be a regulator that has failed.

However, if left unchecked and over time, the stator gets cooked causing a short to ground with any of the 3 or all of its windings.

The end result would be a replacement of the stator and regulator combo.

Customer: replied 2 months ago.
Hi, thanks for the info. So I did all this. There's a new battery, a new regulator/rectifier, and the stator checks out (passes the resistance test and puts out the voltage necessary).
I'm not sure where the connection to ground is but a shop said it was fine. I measured battery neg to ground voltage difference while running and it was very low.
The tests you mention it passes when it's cold. But after a few minutes of riding it fails as the voltage drops.
Any idea what else I could investigate?

The regulator would still be a suspect then.

On:

  • stator...puts out the voltage necessary - what is the AC Voltage output idling and when @ 4K RPM;
  • battery neg to ground voltage - should always read read 0V;
  • passes when it's cold...riding it fails - for tests purposes how about stationary (on stand).

Also and even if just for test purposes, consider hardwiring a secondary ground line from the battery's - terminal to the frame, then also to the engine and to the harness ground/black wires.

And perhaps the article HERE may provide insight.

Customer: replied 2 months ago.
The voltage I'm getting out of the stator is fine (ranges mentioned in the article you linked).
Battery to neg is 0. I tried hardwiring a secondary ground connectoin and that didn't do anything.
Whether riding or stationary I get the same results. It seems to be about how hot the engine is or how long it's been running.
Customer: replied 2 months ago.
I found one thing that's different when it's working and failing: the AC voltage between stator out and ground is in the proper range when working (17-70 volts) and very low when the problem appears (around 1 volt).
What could cause that?

Very significant findings!

Possibilities:

  • magnetic field (least likely);
  • stator wiring/connectors (likely);
  • stator winding/insulation (most likely).
Customer: replied 2 months ago.
How would I figure this out?
For the most likely case it would mean the stator grounds out when hot?
Or the connectors?
The AC voltage out of the stator is still in the proper range (19-70) when it fails.

Interesting...

In both cases:

  • voltage between stator out and ground is in the proper range when working (17-70 volts) and very low when the problem appears (around 1 volt);

and

  • AC voltage out of the stator is still in the proper range (19-70) when it fails

...were the stator wires connected to the regulator?

Customer: replied 2 months ago.
Some voltage readings:
connected wires: stator: 11.7, at battery: 13.6
with the headlight:
stator: 10.8, at battery: 12.2With wire between stator and battery disconnected:
at stator: 18.5 (idling), battery 12.2 (drops to 11.4 with headlight).

...now confusing:

  • connected wires: stator: 11.7 - my understanding was "...17-70 volts..."

Can you please provide clear closeup pictures of:

  • wires from the stator;
  • wires to / from regulator.

Click HERE.

Customer: replied 1 month ago.
Yeah I don't get 17-70 range at the stator when it's connected to the regulator and it's all working as expected.
If I disconnect it though it jumps back up to that.
Today it took about 5 minutes of idling stationnary before failing.
Here are the pics: https://goo.gl/photos/n2UMcFeUx1Dba2yT9
I also ran the experiment with another R/R going directly from the stator without the extra wire and it didn't change anything.

Appreciate the pictures.
And would appear several connectors? ...extension wires?
Let's go back and re-trace our steps/checks:

  • • when cold/no problem:
  • - AC Voltage on 3 pairing of the three (3) black wires directly from the stator = __??__ACV;
  • - AC Voltage on 3 pairing of the three (3) yellow wires directly to the regulator = __??__ACV;
  • - DC Voltage between the red & black wires from the regulator = __??__DCV;
  • - DC Voltage between the brown & black wires from the connector = __??__DCV;
  • - DC Voltage between the battery's + and - terminals = __??__DCV.
  • ...........................................................
  • • when hot/not charging:
  • - AC Voltage on 3 pairing of the three (3) black wires directly from the stator = __??__ACV;
  • - AC Voltage on 3 pairing of the three (3) yellow wires directly to the regulator = __??__ACV;
  • - DC Voltage between the red & black wires from the regulator = __??__DCV;
  • - DC Voltage between the brown & black wires from the connector = __??__DCV;
  • - DC Voltage between the battery's + and - terminals = __??__DCV.

To ensure that the readings are taken from the wires themselves and not at the pins/terminals of the connectors, carefully use safety pins as extensions of the multi-meter test probes to be able to puncture the wire insulation.

Customer: replied 1 month ago.
I'm actually on a trip for a week so won't be able to do this. So from what I've said nothing presents itself as a possible culprit?As for the pictures, the one with 'extension wires' is the test I ran to circumvent the wire between stator and R/R. One less connection. But that didn't change anything. Otherwise the setup is standard.

I understand; when able.

Actually, I am inclined to suspect:

  • • stator (least likely);
  • • regulator (likely);
  • • connector(s) (most likely). Hence the above test using safety pins to the wires.
Louie and other Motorcycle Specialists are ready to help you
Customer: replied 1 month ago.
I did the measurements and one thing puzzled me: there's a difference of .5V between R/R out and battery positive. Is that because there are a few things on the circuit using the electricity?Otherwise for failing scenario I'm getting 11V at stator out AC, and 12.6 at RR out (without head light in circuit).

On:

  • there's a difference of .5V between R/R out and battery positive;
  • - Is that because there are a few things on the circuit using the electricity? - not necessarily as it could mean a slightly loose/poor connection;
  • - or the wire is a bit small;
  • failing scenario I'm getting 11V at stator out AC;
  • - too low as expected would be "...17-70 volts..." proportionate to the engine RPM;
  • - 12.6 at RR out - during idling would be acceptable but should increase together with the RPM proportionately to ~14.5V but not to exceed 15.0V
Customer: replied 1 month ago.
If the difference in voltage RR to battery is because of a poor connection, isn't that a big deal and something I should investigate?

If there is a resulting over heating of the wire(s) and/or connector/terminals, then yes to the further investigation.

However, if the heating up is normal (you can still touch/hold), then should/would be acceptable

Customer: replied 1 month ago.
I could still touch it.
So here is what I measured. It took a few minutes running before failure this morning.• when cold/no problem:
- AC Voltage on 3 pairing of the three (3) black wires directly from the stator = __17__ACV;
- AC Voltage on 3 pairing of the three (3) yellow wires directly to the regulator = __17__ACV;
- DC Voltage between the red & black wires from the regulator = __14.2__DCV;
- DC Voltage between the brown & black wires from the connector = __??__DCV;
- DC Voltage between the battery's + and - terminals = __13.5__DCV.
...........................................................
• when hot/not charging:
- AC Voltage on 3 pairing of the three (3) black wires directly from the stator = __11__ACV;
- AC Voltage on 3 pairing of the three (3) yellow wires directly to the regulator = __11__ACV;
- DC Voltage between the red & black wires from the regulator = __11.6__DCV;
- DC Voltage between the brown & black wires from the connector = __??__DCV;
- DC Voltage between the battery's + and - terminals = __11.9__DCV.battery when bike off after hot/not charging: 12.45

That:

  • when cold/no problem: - AC Voltage on 3 pairing of the three (3) black wires directly from the stator = __17__ACV;
  • when hot/not charging: - AC Voltage... = __11__ACV.

would again point to a stator issue.

...the alternative is a failing alternator rotor. Item # 1 HERE.

Customer: replied 1 month ago.
I see. When I disconenct the stator though, the AC voltage is what you would expect.

"... disconenct the stator though, the AC voltage is what you would expect..." = 'ghost' or technically, no-load voltage.

The regulator was ruled out since:

could still touch it;

when hot/not charging...three (3) yellow wires directly to the regulator = __11__ACV hence too low already at its input, therefore/expectedly the output would also be low.

By process of elimination and more importantly "...hot/not charging...stator...AC Voltage... = __11__ACV...", then stator and/or rotor are the only suspects left.

Customer: replied 1 month ago.
That makes sense but what I don't understand is why it would be 17 volts when disconnected and go down to 11V when connected to the R/R.

As posted, no-load voltage; i.e. a condition when there is 0 current flow and the voltage would tend to go up.

This is a universal constant condition. Technically and if mathematically interested, part of Thevenin's Theorem. Please click HERE.

Customer: replied 1 month ago.
I changed the stator but the behavior is the same. At this point I've tried a different stator, different regulator, connecting the stator directly to the regulator.
Wouldn't that mean we can rule out stator, regulator, and connection from the stator to the regulator?

By process of elimination, that would leave us just with the rotor.

Customer: replied 1 month ago.
I took a look at the rotor and I didn't see anything out of hte ordinary. Those don't fail a lot, do they?

Yes, not that often.

Known causes would be if dropped and/or if there a cracks no matter how small.

Customer: replied 10 days ago.
What would be a way to test this assumption?

Compare its magnetic strength with a known good rotor

...or better yet, swap even if just for test purposes.

Customer: replied 10 days ago.
Would it be possible and make sense to connect a running motorcycle's stator AC out to my R/R in? Or vice versa?

Have not tried that approach. , But if ever, aside from the 3 stator wires, engine/frame/battery ground wire would have to be hooked up as well.

And yes, it may be simpler/easier to connect the Triple's regulator to another motorcycle with known good stator output.