Born again Biker with Charging problems!

Hello all.
Had a drunken night out a couple of months ago and made up a bucket list. The main part was to buy a couple of bikes with my brother and go to the Isle of Man TT in 2012. A biker for many year but gave it up " so I thought" quite a while ago. Bought a VFR750 1996 a couple of months ago and love the thing. The bikes great but seems to have a slight problem. If I ride it with both headlights on / Main beam the battery goes flat and the bike will stop and have to be pushed started.
The service books say it has a charging current of 5-9 amps yet also says 350 watts?
Using both front lights which are 60 watts each and then other lights ignition etc I recon 150-200 watts in total. both lights alone using 120 watts would use up 10 amps? The Haynes service book can't be right at 5-9 amps only? Surely I can ride with both lights on without a problem? Checked out charging and it seems OK at about 13.5 at tick over and 14.5 at 5,000rpm. So whats right. 5-9 amps or 350 watts which would be at 12 volts almost 30 amps??? Do other 96 vfr750 owners have the same problem?

Bob

 

Well... 350 watts is probably the max output, and you shouldn't be having a problem running with your high beams on.

13.5V at idle is a little higher than I would expect; but may not be a problem. Measure the battery voltage a) with the key off ... and b) with the key on and the engine stopped. This will tell us where to look next.

 

Thanks for that. I'm an ex motor mechanic and would think 13.5 at tick over was about right. The reading with the ignition off wouldn't really help as it would only show if the battery was faulty. The battery is fine at about 13v. The problem is only when the charging system is under load. At 5000rpm under full load it shows 14.5 volts with everything switched on. I would expect the alternator to be able to cope under full load and still put a charge in to the battery.

Bob

 

If one was to use 14V as an average charging voltage, that works out to 25A total current at 350W. Perhaps the manual is rating it per phase, as it is a 3 phase stator (assumption on my part; most bikes are). That would give you 8.3A per phase.

All that aside, the only thing I can think of is checking the R/R connectors on both ends and the battery connections. It might be they are borderline when they get hot.

 

+1 to Lgn's post. Another aspect of this 'classic' Honda V-4 trouble area is that if the connections between the stator and the R/R aren't consistent, the result will be less than efficient charging because the 3 phases won't be 'balanced'. In any case, you should probably just pull those connectors apart, clean them thoroughly, and put them back together. A small amount of corrosion will cause a lot of voltage drop when large currents are flowing (translating into a lot of heat) in there. This is one of the most common causes of fried R/R's in these bikes.

 

It occurred to me out of nowhere (you can tell I'm bored today) that this specification might be referring to how much current is available to charge the battery once all the other electrical loads are accounted for (lights, ignition, etc.). Just a thought.