KSP Posted May 27, 2015 Share Posted May 27, 2015 I have a shop and the customer complains the bike runs fine until he shuts it off then it won't start. I disconnected the headlight then he says the bike acts normally and will start up after being shut off. I have checked the 3 legs on the stator and am getting continuity between all three and no continuity to ground. I'm also getting approx. 65VAC coming out of the stator at 5,000 RPM (all three legs). The battery appears good (I load tested it). What seems strange is when I start the bike at idle I'm getting maybe 13.9V at the battery however even if I rev it slightly (2KRPM) the voltage goes down to about 13, and when I rev it to 5K it goes down to like 12.8 or so. This sounds like a bad regulator/rectifier to me, anybody had any experience with this? Any help appreciated. Thanks Ken Link to comment Share on other sites More sharing options...
Beck Posted May 27, 2015 Share Posted May 27, 2015 Yes, that's the backwards voltage syndrome that many VFRs seem to suffer from. Voltage Good/OK at Idle, but rev the motor up and the voltage dips. I heard and read that it's a bad thing, but I never did see any definitive explanation on what might be causing it..... Link to comment Share on other sites More sharing options...
Auspanyol Posted May 27, 2015 Share Posted May 27, 2015 5th gens are known for frying R/Rs so that's statistically more likely to be the Problem. I have seen a ratio of cases of well over 100:1 R/Rs to Stators firsthand on 5th gens and Probably the Inverse Applies to 6th gens. Either way, you should Assure thEre is between 0.1-1.0 Ohms between each pair of yellow Cables with the Motor cold (20°C), just to be sure but I would Hazard a Guess your most likely Looking at regulator failure. Link to comment Share on other sites More sharing options...
Member Contributer Egg on Leggs Posted May 27, 2015 Member Contributer Share Posted May 27, 2015 Yes, that's the backwards voltage syndrome that many VFRs seem to suffer from. Voltage Good/OK at Idle, but rev the motor up and the voltage dips. I heard and read that it's a bad thing, but I never did see any definitive explanation on what might be causing it..... Simples, engine needs more electricity to run the faster it goes. If the charging system is not putting anything into the battery the voltage will fall with the rise in engine speed. Link to comment Share on other sites More sharing options...
Beck Posted May 27, 2015 Share Posted May 27, 2015 Yes, that's the backwards voltage syndrome that many VFRs seem to suffer from. Voltage Good/OK at Idle, but rev the motor up and the voltage dips. I heard and read that it's a bad thing, but I never did see any definitive explanation on what might be causing it..... Simples, engine needs more electricity to run the faster it goes. If the charging system is not putting anything into the battery the voltage will fall with the rise in engine speed. I always understood that it was the engine that might be "sucking up the voltage", but what is the root cause of this. Too much shunting from possibly a faling RR, if that can even happen, or a failing stator that cannot provide enough juice tot he system?? Link to comment Share on other sites More sharing options...
Member Contributer Egg on Leggs Posted May 27, 2015 Member Contributer Share Posted May 27, 2015 Yes, that's the backwards voltage syndrome that many VFRs seem to suffer from. Voltage Good/OK at Idle, but rev the motor up and the voltage dips. I heard and read that it's a bad thing, but I never did see any definitive explanation on what might be causing it..... Simples, engine needs more electricity to run the faster it goes. If the charging system is not putting anything into the battery the voltage will fall with the rise in engine speed. I always understood that it was the engine that might be "sucking up the voltage", but what is the root cause of this. Too much shunting from possibly a faling RR, if that can even happen, or a failing stator that cannot provide enough juice tot he system?? I am not an electronics person so I can't do a detailed explanation. I have had 2 failures. One was a partial where it was getting some voltage through to the battery. I suspect the partial failure of the alternator took out the regulator. The second was a total failure of the replacement regulator 2 years later. I have now fitted a Mosfet regulator. Link to comment Share on other sites More sharing options...
checksix Posted May 27, 2015 Share Posted May 27, 2015 I always understood that it was the engine that might be "sucking up the voltage", but what is the root cause of this. Conjecture: more revs = more sparks per second = more current consumption, but the failing regulator/stator can't deliver the required current, so the output voltage starts to drop. ? Link to comment Share on other sites More sharing options...
Member Contributer Cogswell Posted May 28, 2015 Member Contributer Share Posted May 28, 2015 Dropping voltage is what my 5th gen was doing prior to replacing the R/R. Here's a thread about R/R's on the Superhawk forum that provides some explanation (see post #3) of why and how R/R's fail. It's not definitive, but it's interesting reading. http://www.superhawkforum.com/forums/knowledge-base-40/mosfet-regulator-rectifiers-why-how-25117/ Link to comment Share on other sites More sharing options...
KSP Posted May 28, 2015 Author Share Posted May 28, 2015 Hmmm, Mosfet regulator? I have not heard of that. How long has it been in for and what kind of voltage readings are you getting with it? I may be willing to try it if it has good reviews. Ken Link to comment Share on other sites More sharing options...
Member Contributer SCguy Posted May 28, 2015 Member Contributer Share Posted May 28, 2015 KSP, I replaced the RR on mine with a kit from Roadstercycle.com It's been great so far, 14.3 V at idle and all the way though the rev range. Link to comment Share on other sites More sharing options...
KSP Posted May 28, 2015 Author Share Posted May 28, 2015 How long have you had it in and how many miles? Ken Link to comment Share on other sites More sharing options...
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