Greetings all. I went to ride my 91 ST1100 last weekend and the battery was flat. After charging, the battery maintained a 13.1V charge while sitting on the workbench for a couple of days, so I think that it is okay. I installed the battery and while at idle (1100 to 1200 rpm) I was reading 14.4 V across the battery, and at 3000 rpm I was reading over 15.5 V. I deduce that the R/R is in need of replacement. Ron Ayers has the OEM unit listed for $225, YIKES! Does anyone know of an equivalent after-market unit that is more wallet friendly? Thanks!
Rectifier help
- Thread starter KSRider11
- Start date
kiltman
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- Apr 27, 2013
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- 3,287
- Age
- 68
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- Stratford, Ontario Canada
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- 2002,ST1100ABS
- STOC #
- 8826
The 28 amp unit does produce between 14.7 and 15.2 volts at the battery, so yes it’s possible your VR/R May be faulty. Check your connectors in that area. The three yellow wire red connector coming from the alternator to the VR/R, the main relay connector with the red wire and the connector to the VR/R. Make sure all are clean with no burn or melting marks on them.
You can get an aftermarket VR/R for considerably less on eBay. If one is needed
I would also check your alternator to see it it’s leaking oil, if it is, there’s no sense in buying a new VR/R, use that money to upgrade to the 40 amp unit with a built in VR/R
You can get an aftermarket VR/R for considerably less on eBay. If one is needed
I would also check your alternator to see it it’s leaking oil, if it is, there’s no sense in buying a new VR/R, use that money to upgrade to the 40 amp unit with a built in VR/R
Last edited:
IndyRob
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I have two of them listed in the For Sale section.... an OEM one that I would deal with you on (used all of 10 days before I went all in and did the 40A upgrade) and a never installed BD Electric aftermarket one....
Before going for a new VRR, how old is the battery? Living in a warm climate, as you do, is harder on batteries actually. I would have the battery load tested first. The VRR is certainly giving enough voltage to charge the battery and I would not suspect it as being bad.
Do check all the wiring too, as Kiltman suggests.
Do check all the wiring too, as Kiltman suggests.
years ago I had a similar issue with a Yamaha sport bike. Turned out the problem wasn't in the alternator, or the regulator, there was corrosion in the main path between the battery and the ignition switch that was causing a pretty large voltage drop. The theory of operation of charging systems isn't generally spelled out in the service manuals, but the basic idea is the charging system will monitor the system voltage downstream from the ignition switch and try to keep that voltage within a particular range. If there's an unusual voltage drop in that path, the monitored voltage level will be lower than normal, and the alternator will increase the charging voltage upstream to whatever level is necessary to bring the monitored voltage back into the desired range.
For example, let's say a normal voltage drop from the battery to the monitor point is 0.7v, and the charging system wants to see 13.5v at the monitor point, that means the battery voltage would be 14.2v. If the corrosion increases that voltage drop to 1.5v, now the charging system will put out 15.0v at the battery to keep the monitor point at 13.5v.
I've never had to trace this out on the ST1100, so I can't give specifics, but if you look at the wiring diagram and find a convenient place downstream of the ignition switch to measure the voltage you can see what the voltage drop is from the battery to that point. If the drop is more than 0.7-1.0v, it would be worth looking at the connectors in the path for possible corrosion.
For example, let's say a normal voltage drop from the battery to the monitor point is 0.7v, and the charging system wants to see 13.5v at the monitor point, that means the battery voltage would be 14.2v. If the corrosion increases that voltage drop to 1.5v, now the charging system will put out 15.0v at the battery to keep the monitor point at 13.5v.
I've never had to trace this out on the ST1100, so I can't give specifics, but if you look at the wiring diagram and find a convenient place downstream of the ignition switch to measure the voltage you can see what the voltage drop is from the battery to that point. If the drop is more than 0.7-1.0v, it would be worth looking at the connectors in the path for possible corrosion.