'93 st1100A charging problems... :/

Hello all. I'm having heaps of trouble diagnosing what is wrong with my ST. I had previously done a RWB on the main red wire, and found it was still melting fuses. Not blowing, but melting the plastic shell. So I swapped out the main starter relay and it stopped doing that. Then 4 months ago I went to ride home from work and my battery was dead, I quickly found out that it was not charging my battery. I have since swapped the old relay in and out to know avail.

First of all, the bike is putting out a charge, but it's not enough to charge the battery. Around 11.5 volts at 1000 RPM and up to 12.4 at 3000 rpm. I have since checked the alternator voltages (around 70ish volts on all 3 phases), resistance tests are with in spec. continuity on the wires seems fine.

I have tested and replaced the rectifier, thinking that was the problem, the first 2 cheap chinese rectifiers I have received have not worked for bad quality reasons, so while I wait on the 3rd from a different seller to arrive what else could it be? Ideally I don't want to dismantle the back 2/3s the bike to replace the 28A alternator if there is nothing wrong with it.

Any help would be appreciated. I am dying to get out and ride again while the weather here in Oz is good.

Check the three yellow wire connector that comes out of the alternator to the rectifier/regulator. Some have done away with the connector and soldered and heat shrink tubed the corresponding wires. What condition is the white connector to the rectifier? Any burnout? If you’re blowing fuses you have a short, check the integrity of the RWB, it may be grounding.
is the alternator leaking oil?

Since your dynamic testing of the alternator (at 70V. each phase) seems normal, as do the other tests, one would logically suspect the rectifier. You may want to consider spending the bigger bucks for the Honda unit, since you have already had bad luck with the aftermarket variety.

However, I would double check all the alternator tests first, especially the dynamic test of the coil's outputs. Those readings should all be very close to each other.

Kiltman's suggestion of inspecting the red 3P connector and the white 6P connector for corrosion, usually hard to see within the connectors, is a worthwhile time investment too.

Karen, I am running with the stock 28A alt.

I've not seen any oil leaks, and the connectors look fine, but I'll have another good look in the day light. Dropping $150au on a new rectifier isn't optimal but it's better then twice that for a new alternator and a week of pain.

Thanks for the input so far everyone.

BennyBones said:

Karen, I am running with the stock 28A alt.

I've not seen any oil leaks, and the connectors look fine, but I'll have another good look in the day light. Dropping $150au on a new rectifier isn't optimal but it's better then twice that for a new alternator and a week of pain.

Thanks for the input so far everyone.

Click to expand...

Bear in mind too that although your dynamic test showed around 70V at the three coils in the alt, there could be overheated, melted varnish in there causing a short in one or more coils that only connects/shows up when they are fully heated up by the engine, dropping the output of one or more coils. The 28 Amper has a long history of failures, especially when they have experienced too high a demand because of too many added electrical accessories. There is only about 10 amps to spare with that alternator. That's why I suggested another thorough test of the alternator.

A couple of thoughts...

Redoing the dynamic AC comparison checks between the three legs' combinations on a well warmed up engine is a good idea.

Before you buy a new VRR, check the continuity and resistance of the yellow AC leads between the red 3P connector and the white 6P connector. I know of one case of a bad wire there that confounded an STrider until the fault was found.

FWIW Good luck. BTW, there is a cheaper (than new stock Honda) aftermarket 40amp replacement alternator that was recently brought to the attention of the community. Makes the upgrade more palatable.

John

Hi this post is been long, seem am experiencing something similar, read through the comments and am getting something, pls how do I check optimum power supply from the rectifier, looks like that's where my problem is

All you can really do is measure the charging voltage at the battery at, I think at 5000 RPM, for the 28A model. You should see high 14 to low 15 volts. If you're seeing battery voltage or less you'll have to dig deeper. There's no way to test the VRR without the specific meter called out in the Honda repair manual, but this meter seems to be vaporware, not even the dealers have one. You can infer the VRR is bad by testing the stator directly at the 3P connector. You should be seeing around 30V on each winding of the stator if it's working properly in such case you can infer that the VRR is bad. Unfortunately, these charging issued have been much more likely due to a faulty stator.

+1 ^^what Jeff says^^

Controlled substitution with a known-good VRR is the only way to really confirm it’s the VRR, absent obvious burned/melted spots.

John