91 st not charging with headlamp fuse installed

[stratosflyer]

Hi all,

I have a 91 st1100 28 amp alternator. recently found the insulator going into the main fuse/starter relay melted so I replaced that wiring and added 4 new insulated terminals. What I am finding now is the charging system does not work with the headlamp fuse in. I have done a regulated voltage test - shows from 12.61-14.30 with the headlamp fuse out. as soon as the fuse completes the headlamp circuit it stops charging and will only run off the battery. Looking for some ideas - I am currently checking the wiring harness and grounds. Thanks.

 

[stratosflyer]

a little history related to the above post.
75k - replaced the voltage regulator - no issues until alternator failure below
103k - replaced the stator housing - no issues until the problem with the wiring in my original post

the only auxiliary electrical items I have are a trunk tail light and volt meter knowing how anemic the system is. I was originally thinking I might have a short or bad ground but all the systems work independently from each other. Of course I am unsure what caused the issues with the insulator to begin with and maybe that is somehow related to my current charging issue. I have pulled the fuse and run the regulated voltage test several times as each time as soon as the fuse is pulled the multi-meter shows the system putting out between 12.61-14.30. Even rode it with no headlight and it showed 12.39-13.19 on the meter. Put headlamp fuse back when I turned around and immediately stopped charging. Another note I just rebuilt the forks, brakes and added handlebar risers. None of the wiring was not pinched but I am going to look at that again nonetheless since I am searching.

 

[dwalby]

Since the fuse in question doesn't blow, it wouldn't appear that you have a direct short. That being the case, it would seem that perhaps the alternator output is marginal, and when you add the headlight load it exceeds the available alternator output. Just a guess, if your fuses are holding, then your loads are either normal, or near normal, unless you somehow put a higher amperage fuse in. Haven't had to troubleshoot the ST alternator, don't know how much work it is to get to the individual wires from the alternator, but taking ohm readings on the various wires associated with the alternator would be a good next step. Since you replaced the stator, but not the rotor, it may be that the rotor has degraded and is causing the marginal output.

 

[stratosflyer]

thanks for the reply. Just got done going thru all the wiring behind the left side panel and all the ground and power connections were good and all the wiring had no cuts or nicks in it. just for kicks pulled the connectors off the back of the headlamps and ran the standard regulated voltage test without the fuse and again it ran up into the 14.3 range. While it was running put the fuse in (no lamps) and it continued to show 14.3 @ 5000 rpm. Connected 1 headlamp and it would show about 12.4 volts with some rpm, same if that side was disconnected and the other side connected. Going to go mess with it some more and do some of the additional electrical system checks in the manual. Just trying to document as I go. I do have the recommended 20 amp fuse in the headlight circuit. Seems odd to me that it would pass the voltage test with such good numbers and all the other bike systems running and just fall flat with headlamps connected.

 

[ST1100Y]

Well, the 28A unit has a '3-phase stator', if one 'phase' is missing you still get some juice, but the avail/delivered current is significantly lower; thus adding larger consumers will lead to fatal voltage drop (BDDT, limped home on '2 phases' once; only position lights avail, everything more like stereo, brake lights, yet even turn-signals would bring the system down -> engine stalling. Battery would barely charge, ST required a 'bump start' every morning or refuelling stop... nice with full luggage for two folks, but doable in 3rd gear...)
I'd start by checking if all 3 stator coils are conductive or open (also not short to ground) and also check the VRR to see if any diodes have suffered a meltdown/short.

 

[Doodaa]

+1.....best place to start. JMHO

Well, the 28A unit has a '3-phase stator', if one 'phase' is missing you still get some juice, but the avail/delivered current is significantly lower; thus adding larger consumers will lead to fatal voltage drop (BDDT, limped home on '2 phases' once; only position lights avail, everything more like stereo, brake lights, yet even turn-signals would bring the system down -> engine stalling. Battery would barely charge, ST required a 'bump start' every morning or refuelling stop... nice with full luggage for two folks, but doable in 3rd gear...)
I'd start by checking if all 3 stator coils are conductive or open (also not short to ground) and also check the VRR to see if any diodes have suffered a meltdown/short.

 

[sofawizard]

+1 from me to

+1.....best place to start. JMHO

 

[stratosflyer]

going thru the results of the tests in the manual at operating temperature
voltage at 12.6-14.3
charging amperage -
regulator/rectifier harness - charge coils read .6 ohms x 3 (0-1.0 ohms spec)
- field coil reads 3.5 ohms (0-4.0 ohms spec)
alternator harness red connector - charge coils .6 ohms x 3 (0-1.0 ohms spec)
- no continuity per manual checked against ground
alternator harness black connector - field coil 3.3 ohms (0-4.0 ohms spec)
- no continuity per manual checked against ground

 

[ST1100Y]

I'd also make the grid-measurements on the VRR diodes... melting crimp connectors there are never a good sign... silicone components don't appreciate temps >120?C...

.6 ohms on the charge coils appear OK, however is this reading taken without any load. I've seen windings open/short under load or temperature...

The 28A unit of my refurbed '94 ST did also read absolutely fine and within specs on the multimeter, engine ran perfect, all lights OK, perfect ~15V @5000rpm and 12,6V on idle, what more could you ask...
While taking it to the MOT the bugger suddenly perished like 300 feet from the workshop door, cough-cough-splutter-bang... the pointer of the OEM P-spec voltmeter dead on the zero, not a single light in the dash, nada...
In the ~15 minute ride the stator had suffered a sudden short to ground, thus no current for the bike's consumers left...
Disconnected the stator and the bike ran perfectly... on battery power... passed the MOT with flying flags though... <phew!> :roll:

 

[stratosflyer]

unfortunately my multi-meter won't read my vrr. I had actually purchased another vrr before I replaced the stator last time since the symptoms were the same as when I had originally had the vrr failure at 75k. I installed it in this bout of diagnostics with no change to any of the symptoms or operating readings. I am leaning toward it being a stator issue since it falls out under load but I hate to spend that cash on what amounts to my best guess at the holidays. Last time my stator failed at least it gave me the benefit of failing the field coil so I could confirm my suspicions it by testing. I was hoping to match the 98k from the original with the replacement but if it indeed has failed it only made it 23k and well short of 2 years. I ride close to every day and with multiple tours planned this calendar year it may be time to suck it up and put a 40 amp on the old girl.....

 

[Doodaa]

Thought I'd read on the forums here just lately of a different brand being used successfully, with an adapter plate. Think this mod was from the Eastern side of the Atlantic, where they go thru this problem with greater frequency. Just throwin' it out there, might be in the same boat someday. I think the mod was from a Suzuki Bandit at a reduced cost and probably easier to find.
D.C. ammeters are easier to find at a good old auto shop or a place that repairs/rebuilds starters and generators (for your load testing).

 

[stratosflyer]

I did some reading on the Bandit mod and it seemed that it would be necessary to already have a 40 amp on the machine if I processed what I read correctly although I certainly could have interpreted it incorrectly. Also just finished an ac voltage check at the alternator 3 pin connector and came up with 25.2v from all three terminals @ 1200 rpm idle warm and 70.2v from all three terminals @ 4000 rpm warm. I am leaning toward voltage regulator at this point but wouldn't mind another opinion with this additional information from this post in mind.

 

[stratosflyer]

and in my continued documentation I also noticed this time after the bike was warmed to enough operating temp that fan operation began the wires on either side of the 3 pin red connector were very warm. Also once the fan started cycling the max voltage output was 13.02 and would no longer get to 14.6.

 

[dwalby]

I did some reading on the Bandit mod and it seemed that it would be necessary to already have a 40 amp on the machine if I processed what I read correctly although I certainly could have interpreted it incorrectly. Also just finished an ac voltage check at the alternator 3 pin connector and came up with 25.2v from all three terminals @ 1200 rpm idle warm and 70.2v from all three terminals @ 4000 rpm warm. I am leaning toward voltage regulator at this point but wouldn't mind another opinion with this additional information from this post in mind.

Its been a long time since I had to trouble shoot alternator issues, and it wasn't on an ST, so don't quote me on this, but I think your AC voltage should be more like 90-100v, 70v sounds kind of low. That would also be consistent with your symptoms of it not being able to hold 14v with the headlight load, but its otherwise OK without the headlight. Seems like you'd see a low resistance somewhere though along with the low AC output, and I think your resistance measurements were all within spec, weren't they? Since the AC voltage is prior to the regulator, perhaps its possible that your regulator is somehow sucking too much power from the alternator. Is it possible to disconnect the regulator and see if your AC voltage goes up?

 

[Doodaa]

and in my continued documentation I also noticed this time after the bike was warmed to enough operating temp that fan operation began the wires on either side of the 3 pin red connector were very warm. Also once the fan started cycling the max voltage output was 13.02 and would no longer get to 14.6.

Connectors should not get warm. That is electrical energy converted to heat. If you don't have a friend with an electrical background to look at the connections, replace/bypass those connections before doing anything else, please. Electrical energy converted to heat cannot provide any other useful function, like charging a battery or operating headlights. The local power company here scans their large distribution lines with an infrared camera to detect upcoming problems before they occur, that tell you anything ?
And, agree about the bandit conversion, not a go for the 28 amp.
keep updating, you'll get it fixed before spring....at least Yankee spring

 

[stratosflyer]

I'll keep posting and hopefully my own experience will help someone else down the line. I did go ahead a remove the red 3 pin connector this morning and actually was reading 14.85 volts now at operating temp. After it got hot enough for the fan to come on it would maintain about 12.8v. what I did check this time after it was hot as a follow up to the wiring was to check the vrr as well. While engine running the yellow wires to the rectifier were still hot while running as soon as I shut it off the were cool immediately (as I thought they would be no longer carrying current) but the vrr was very hot to the touch as it had been loaded. I guess at the end of the day I have talked myself into it being a vrr issue (even though a new in box unit is in it) although I think removing the connector will save me some trouble somewhere along the line and ultimately it would have been removed when I do the 40 amp conversion anyway. Now it's just a matter of getting ahold of a known good vrr soon and confirm my suspicions. of course any additional input to my own diagnostics is always welcome and thanks for all the input so far.

 

[kiltman]

The question is how hot does the VRR get that is considered normal operating temperature. I have seen some aftermarket units with cooling fins to address the heat issue. I still wouldn't rule out the possibility of a faulty VRR......

 

[stratosflyer]

good question about the heat. What is installed on the bike is an Electrosport with the cooling fins.

 

[Doodaa]

I'll keep posting and hopefully my own experience will help someone else down the line. I did go ahead a remove the red 3 pin connector this morning and actually was reading 14.85 volts now at operating temp. After it got hot enough for the fan to come on it would maintain about 12.8v. what I did check this time after it was hot as a follow up to the wiring was to check the vrr as well. While engine running the yellow wires to the rectifier were still hot while running as soon as I shut it off the were cool immediately (as I thought they would be no longer carrying current) but the vrr was very hot to the touch as it had been loaded. I guess at the end of the day I have talked myself into it being a vrr issue (even though a new in box unit is in it) although I think removing the connector will save me some trouble somewhere along the line and ultimately it would have been removed when I do the 40 amp conversion anyway. Now it's just a matter of getting ahold of a known good vrr soon and confirm my suspicions. of course any additional input to my own diagnostics is always welcome and thanks for all the input so far.

Are the yellow wires themselves warmer than the VRR ? If so, look for connections to change there. It's normal for the VRR to get warm, that's the "regulating" part of it. BOLT it down, additional physical contact helps draw the heat away. If you're running 12.8 with the fan on, that's still good enough to keep charging the battery. If you have the headlights connected when you got this barely marginally charging volt reading, I think that's close to normal. Maybe not Honda specs, but livable, for a 20 some year old machine. Mine gets "marginal" with higher wattage headlights when the cooling fan comes on, but otherwise charges O.K. I have a small 3 color LED voltage monitoring unit mounted on mine to keep an eye on my changes in power consumption and simply look at the color for charging operation.
I'd run it and see if the battery holds a charge. Keep posting, I think you've about solved it.

 

[ST1100Y]

It's normal for the VRR to get warm, that's the "regulating" part of it. BOLT it down, additional physical contact helps draw the heat away.

I actually apply some CPU cooler paste on the surface its contacting the footrest plate, aiding the heat transfer/cooling.