Rectifier

cc2larke

Joined
Jul 28, 2023
Messages
7
Age
53
Location
Washington
Bike
'91 ST1100
Had my rectifier grenade itself leaving me stranded. Was easy enough to see the problem with it billowing smoke out the side of the bike. Haven't checked all the continuities of the charging system yet--but is this likely a symptom of another problem, or just something that goes out after 30+ years? Have about 40k miles on the bike, it's been largely garaged all its life, and the wires seem good overall. Load wise, I put in a lithium battery, all LED lights, and heated grips (warm today, so theoretically not a factor), and haven't had any charging/electrical problems to date.

Thanks,
Christopher
 
Welcome to the forum.

We need more info, such as year and model, and what you're referring to as the rectifier.

Can you expose the part in question and post a pic or two?
 
'91 ST1100


This part definitely failed (was the smoking gun, has a leaking hole burned from the inside out), and I've ordered another genuine OEM. However, in searching for it, I came across this:

www.regulatorrectifier.com

1991-2004 Honda CB750 CB 750 Nighthawk Regulator Rectifier

Re-Designed and Improved heavy duty Honda CB750 CB 750 Nighthawk Regulator Rectifier has a higher power handling ability than the original OEM part. This regulator rectifier comes with a direct plug in connector. This unit is much more efficient than the OEM regulator rectifier because of its...
www.regulatorrectifier.com www.regulatorrectifier.com

Which is an aftermarket replacement that is engineered with additional cooling surfaces (and is significantly cheaper, as are all the aftermarket variants I found). Any have experience either with that brand or with adding a heat sink to the side of the unit? There's plenty of room under the plastic.

I've seen some info about the red socket bypass (all the pictures had some weird fuse in the place where the rectifier bolts in, same bolts), and in any case, the connectors look great--no corrosion or anything. I was considering removing the PAIR nonsense too, since the hoses for same are unavailable and pretty cooked from when my cooling system was leaking. Anyone have a lead on block off plates for the chrome tubes, or can it simply be disabled by plugging the line coming from the T connector coming from the carbs?
 
The police spec versions used a beefed up VRR featuring heat-sinks:

www.cmsnl.com

REGULATE (RECTI) for Honda - order at CMSNL

✓ Get the REGULATE (RECTI) ✓ Manufacturer Part Number: 31600-MZ9-901 ✓ Quality part
www.cmsnl.com www.cmsnl.com

the ST1100 specified VRR from your source is even listed at a lower price as the CB750 thing:

www.regulatorrectifier.com

1991-1995 Honda ST1100 ST1100A Pan European Regulator Rectifier

Re-Designed and Improved heavy duty Honda ST1100 ST 1100 ST1100A ST 1100A Pan European Regulator Rectifier has a higher power handling ability than the original OEM part. This regulator rectifier comes with a direct plug in connector. This unit is much more efficient than the OEM regulator...
www.regulatorrectifier.com www.regulatorrectifier.com

on the long run hard to tell how much of your wiring is already victim to corrosion and the resulting overheating...
Stiff cables with blackish strains are a definite sign...
It ain't the actual load causing a BBQ, its the increased resistance on a small contact patch (like a crimp point) due oxides/corrosion...
I'd also carefully measure the resistance of the stator windings (if possible also the AC output while engine is running) for being absolutely equal/balanced...
 
The OEM piece has a metal backing that sits against the step holder, which seems like a design feature to use it as a heat sink, since it appears to be a big piece of aluminum. Anyone tried a little thermal paste between them to encourage heat transfer?
 
Your model has the 28 amp alternator, its days are numbered. However it looks like you’re doing your best to ease the load.
That white connector to your rectifier is probably toast…you can replace the connector with individual female spade connectors just take note of the orientation of the wires in the connector to match it with the new rectifier.
Before going any further, check that the alternator isn’t leaking oil. Put a piece of paper under it overnight and monitor it. If there’s oil on the paper then start looking to get the parts for the 40 amp upgrade. If it’s dry, then spend the money on a rectifier.
There are three yellow wires coming from the alternator, follow them to the rectifier there. May be a red connector prior to going to the white connector to the rectifier. If there is, bypass the connector by soldering and heat shrink each yellow wire individually.
Also check the main relay connector. There are four wires going into that red connector. Check to see if it’s compromised, meaning melted or burned out. If it is replace with individual female insulated spade connectors. Again note the orientation of the wires from the connector. ( if you don’t match one of those green wires you will blow the clutch diode and your neutral light will stay on.
The clutch diode is located in the harness on the left side under the air filter
 
cc2larke said:
'91 ST1100

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This part definitely failed (was the smoking gun, has a leaking hole burned from the inside out), and I've ordered another genuine OEM. However, in searching for it, I came across this:

[/URL][/URL][/URL][/URL]

Which is an aftermarket replacement that is engineered with additional cooling surfaces (and is significantly cheaper, as are all the aftermarket variants I found). Any have experience either with that brand or with adding a heat sink to the side of the unit? There's plenty of room under the plastic.

I've seen some info about the red socket bypass (all the pictures had some weird fuse in the place where the rectifier bolts in, same bolts), and in any case, the connectors look great--no corrosion or anything. I was considering removing the PAIR nonsense too, since the hoses for same are unavailable and pretty cooked from when my cooling system was leaking. Anyone have a lead on block off plates for the chrome tubes, or can it simply be disabled by plugging the line coming from the T connector coming from the carbs?
Click to expand...
Jeez, dont buy the OEM R/R......look at getting an updated Shindengen model FH027AA, far less cost too.
https://roadstercycle.com/
 
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kiltman said:
Your model has the 28 amp alternator, its days are numbered. However it looks like you’re doing your best to ease the load.
That white connector to your rectifier is probably toast…you can replace the connector with individual female spade connectors just take note of the orientation of the wires in the connector to match it with the new rectifier.
Before going any further, check that the alternator isn’t leaking oil. Put a piece of paper under it overnight and monitor it. If there’s oil on the paper then start looking to get the parts for the 40 amp upgrade. If it’s dry, then spend the money on a rectifier.
There are three yellow wires coming from the alternator, follow them to the rectifier there. May be a red connector prior to going to the white connector to the rectifier. If there is, bypass the connector by soldering and heat shrink each yellow wire individually.
Also check the main relay connector. There are four wires going into that red connector. Check to see if it’s compromised, meaning melted or burned out. If it is replace with individual female insulated spade connectors. Again note the orientation of the wires from the connector. ( if you don’t match one of those green wires you will blow the clutch diode and your neutral light will stay on.
The clutch diode is located in the harness on the left side under the air filter
Click to expand...
Does it use engine oil for the cooling, or is it a separate self contained system in the older alternator? The bike doesn't leak at all (on the floor), if it's a slow leak with no path to ground, I'll check with the paper. When I unplugged the rectifier, the connector looked solid, but I haven't done all the continuity tests yet, nor had the opportunity to unplug the other connectors to check for obvious failure. The 30amp fuse next to the red connector is intact.
 
mello dude said:
Jeez, dont buy the OEM R/R......look at getting an updated Shindengen model FH027AA, far less cost too.
https://roadstercycle.com/
Click to expand...
I saw a couple different Mosfet choices--but none of them had the 6 wires. Is the solution the same for all--take all 3 of the yellow, and reroute them to this unit, then ignore the white/black/red & white wires, and plug directly to the battery instead?
 
cc2larke said:
Does it use engine oil for the cooling, or is it a separate self contained system in the older alternator?
Click to expand...
Yes, one oil system. Same oil lubes the engine, cools the clutch, cools the alternator and puddles on the floor (occasionally)
 
cc2larke said:
Does it use engine oil for the cooling, or is it a separate self contained system in the older alternator? The bike doesn't leak at all (on the floor), if it's a slow leak with no path to ground, I'll check with the paper. When I unplugged the rectifier, the connector looked solid, but I haven't done all the continuity tests yet, nor had the opportunity to unplug the other connectors to check for obvious failure. The 30amp fuse next to the red connector is intact.
Click to expand...
Yes it uses the engine oil. There’s also an oil cooler at the base of the oil filter.
If your white connector for the VR/R is still good just check the tightness of the internal connectors.
The green 30 amp fuse rarely blows, it is the red connector that can be of issue. I would take the time to take it apart and inspect it and make sure the contacts are clean and shiny.
The photos attached are from my 1990, they illustrate the compromised connections and the solution of individual connections in the event you experience the same issue in the future
 

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cc2larke said:
I saw a couple different Mosfet choices--but none of them had the 6 wires. Is the solution the same for all--take all 3 of the yellow, and reroute them to this unit, then ignore the white/black/red & white wires, and plug directly to the battery instead?
Click to expand...
Yes, wire direct to the battery with 40 amp capacity fuse holder...let me know if you want vender suggestions...Tape up the unused connector..
Circuit looks like... (this is a VFR example) The main thing is the stator and R/R connections...
(btw - those other R/Rs from your links are junk)
 
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cc2larke said:
The OEM piece has a metal backing that sits against the step holder, which seems like a design feature to use it as a heat sink, since it appears to be a big piece of aluminum. Anyone tried a little thermal paste between them to encourage heat transfer?
Click to expand...
Yep, in fact I always recommend doing so when working on the old, oil-cooled 26A system...
It however won't stop/cure any wire damage/connector overheating caused by corrosion...
 
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Ok--weather and time permitted tear down and fixing of immediate problem. All the connectors were in excellent shape, oxidation on any of the blades was minimal, and easily removed with a light filing. Resistances/continuity check out on everything except the resistance between white/black a little higher than the shop manual. Got everything back together, got bike started and warm, charging voltage about 14v across the battery. Added a little dialectic around exposed parts of the plugs, and thermal paste to the back of the rectifier.

The new rectifier is warm/hot to the touch after running for a couple of minutes--what is normal? I didn't take it out, as I didn't want to blow it up again.

Sadly, looks like I do have a small oil leak out of the alternator--not enough to make it to the ground, but enough to wet the exhaust pipe, noticeable as it cooks off. Looks like the alternator swap is in the future. For those of you that have done it, I've seen a wide rage of "compatible" alternators, though most of them look like Chinese junk. Where did you source yours, and were they genuine ND?
 
cc2larke said:
All the connectors were in excellent shape, oxidation on any of the blades was minimal, and easily removed with a light filing.
Click to expand...
Many connectors are plated to improve longevity and reduce corrosion due to dissimilar metals. Filing or sanding connectors can cut right through this plating. You might keep an eye on these connectors for future corrosion.

It is my understanding that parts for the alternator upgrade are becoming scarce. You might start collecting them now as they come available.
 
Someone was making new adapter plates for the 40A conversion, but I think his ad got lost in the Great Purge of 2025.
 
jdmccright said:
Someone was making new adapter plates for the 40A conversion, but I think his ad got lost in the Great Purge of 2025.
Click to expand...

Upgrade almost done… | ST1100-Alternator

Looks like a mess, and there’s still more to do, but the new 40 amp alternator upgrade is in! Seems to have gone very well. Question is, does the “new” sub-harness replace the old reg/rec stuff? ‍♂️ Gotta figure that out on the next decent weather day. 1991 Honda ST1100 CT, USA
www.st-owners.com www.st-owners.com
Some good info here
 
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