Mystery Charging Issue

[supersim65]

I'm having problems with the charging system, but I'm not really sure what it is. Not terrible problems, just slightly frustrating ones. Does anyone have any experience with the following issues?

Symptoms:
Engine running, headlight off, things seem fine, good charging voltage.
Headlight on, and I need to do about 5000 rpm to get the charging voltage up to over 13V. Which I do not do unless I'm on the motorway, so night driving drains the battery.

So far:
- New battery.
- Rectifier diodes tested with a multi-meter. Fine.
- Resistance around each coil is a consistent 1 ohm tested under the side panel at the connector. Spec says 0.2-0.3 ohms. But it's consistent across all three, so I suspect the cable run between the connector and the coil might be the other 0.7 ohms.
- AC measured at the connector while the engine is running: 15V at idle rising to around 55V at 5000 rpm consistent across all three coils.

Do these stators wear out progressively and consistently across all three phases? Or should I be thinking about replacing the wiring to the rectifier. Why is the rectifier so far away from the battery anyway Yamaha? I don't feel like a £90 new stator is a worthy spend unless I'm sure.

Is the charging system on the 3YF just a bit rubbish? Should I consider upgrading if I want to ride at night below 4000 rpm?

[charliext1vj]

You would get these measurements even with part defective cables. If you have truely sorted out the generating components i would like at cabling and connections especially at bends etc. If a 32 strand cable had 2/3 of the strands broken it would still provide the results but only a fraction of the charging current. worth a check - you can slave a wire across to check.

[motorang]

Not to forget: every bulb or other electrical component has more or less its own positive wire, but they all share a common single ground wire. So it makes sense to have an additional ground wire from the negative terminal to the front fairing to at least connect the two headlamps.

Same symptoms may occur if the fuse is not 100% up to its job (or its connectors), as all current has to pass through that as well.

Andy

[dzl]

- AC measured at the connector while the engine is running: 15V at idle rising to around 55V at 5000 rpm consistent across all three coils.

Is this AC voltage open circuit/ unplugged from bike or when plugged in to bike and with headlight on etc?

Ensure that the red wire going into voltage reg is actually sensing the actual + voltage at the battery. This wire should have zero resistance from voltage reg to battery. Ensure the negative/ earth wire that runs up to the voltage reg mounting also has good connection.

If the loaded AC voltage is getting to 55VAC then that is good and I would try another voltage reg regardless of the results of your diode test. I have had voltage regs that diode test ok with meter not work correctly.

Charging Voltage should easily be over 13.5 V with new battery at all revs

[supersim65]

Thank you all. I decided to do a bit of a sort out and service on the wiring in the charging system as part of the investigation. A lot of the connectors we're quite corroded as to be expected with age so hopefully that will help.

However I think I've spotted something, the black plastic connector that clips the AC feed and battery into the rectifier appears to have melted a bit in the past. It doesn't look like anything shorted out. But I'm not getting continuity from two of the AC cables near the stator to the rectifier connector. The connectors inside the slightly melted housing seem badly corroded and a bit bent out of shape.

Does anyone know if I can get a replacement connector? I'm not sure how unique it is to Yamaha.

[supersim65]

Connector in question...

[motorang]

Usually the inner metal connectors are standard an can be changed.
They can be clipped into a new 4-bay connector (if you change them on both cables).
There is a little metal tongue you have to push back, then you can remove the plug/socket bits from the plastic housing.
I find any small electronic screwdriver works well for that.

check "spade connector housing" (picture search)

Here is how to remove them: https://www.americanautowire.com/view-f ... or-cavity/
As an alternative you could color code which goes where and plug them into their respective sockets one by one, without the housing, just for a test.

Andy

[supersim65]

Thanks Andy. I had tried getting them out, but unfortunately they were well and truly stuck, probably because the housing had melted a bit in the past. And replacing the connector with another generic 4-way was difficult because on the '91 here, the connector pictured goes straight into the rectifier, it's not on an extension.

I took risk on a connector that looked pretty similar on the internet though, hoping they'd be standardised (https://www.mandp.co.uk/es127-connector ... 4inch.html). They were! I had to cut the old connector into pieces (wanting to keep a much length on the cables as possible) to remove it. But the new connector is a great fit into the rectifier!

Results at 1500rpm with all lights on and the GPS charger plugged in: 13.7v across the battery.

[scottieh]

Nicely done! I too have fried my rectifier connectors before and that, as you well know, caused all sorts of electrical issues with lights and charging. Congratulations on a good fix!