VFR 750 Voltage issue, please help!

Hi all,

So the bike (vfr 750 '95) wouldn't start the other day due to the battery having run flat. As I have just replaced the reg/rec I assumed the battery had suffered and was not holding its charge, I tested it and confirmed this. So I went on my merry way to pick up a new battery at my local garage.

After they installed the battery we fired up the bike and tested the voltage which showed 15.5. The guys told me that was way to high (all lights were off) and that it should be showing 14.4v max. We assumed that the new reg/rec was faulty so tried another which also showed 15.5.

As the bike was in warranty at the dealer I bought it from I called them up and asked them what I should do as I had been advised not to ride it as I would burn out the new battery. I ended up having to fork out 80 quid for a van to get it over to the dealer. Two days later I get a call from the dealer telling me that the voltage is within normal limits and that the bike is fine.

I'm now down a new battery and 80 notes for the carriage, and the dealer is telling me there's nothing wrong with the bike. The warranty is up this month and I'm due to pick up the bike on Monday so before I do I just wanted to check if anyone has had this issue or can enlighten me as to what the correct voltage range should be on a '95 750 when running.

This has been a huge and costly ball ache and this is way above my home mechanic skills, I have one bike shop telling me one thing and another telling me the opposite. If anyone can help me out I'd be hugely appreciative!

Thanks in advance.

 

Congratulations, you got hosed. Welcome to the world of stupid mechanics. Download a copy of the manual.

The Honda manual lists the max voltage at 16V.

:crazy:

 

if you turn on the headlights the voltage will likely drop, especially at idle. Run it at idle with the lights on and measure, then rev up to 3000 to 5000 with lights on and measure voltage again. Report back the results.

The important parameter which you left out was at what rpm the 15.5 volts was measured. If at idle then you will boil the electrolyte out of a battery from overcharging, i.e. 14.4 or above is overcharging.

If it was measured at 3 to 5 krpm, then turning on the lights will likely bring it down to a more reasonable level.

Long story short--run your headlights all the time...It doesn't use anymore fuel since this is a permanent magnet alternator running all the time into the R/R which is making 25 amps of dc current--any excess or unused capacity is dumped into the frame as heat, so you might as well run the lights and even add some additional loads (heated grips/seat) and appliances (toaster/coffee maker, etc.) to use up the extra power.

 

You still got a great bike there mate! :cheers:

 

Thanks for all the replies.

Yes the voltage was showing 15.5 at idle. With lights on etc it was showing 15 or so, therefore still overcharging. As the bike is still within warranty should I get them to replace the stator?

Thanks

 

KB was bang on to bring up the RPM. Oops, I have to stop assuming that techs know how to do even the simplest tasks correctly.

I am a little curious on where he is getting his specs from though. According to the manual, the voltage at 5000rpm should be 13.5-16VDC, at a current rate of 5-9A. I don't believe the battery will actually start to overcharge until it gets up above 17 or 18 V.

Anyway, if it is at 15.5V at idle, chances are it will be above spec at 5000rpm. The faulty part to change would be the R/R, not the stator.

:crazy:

 

A dumb question, are you sure your voltmeter is accurate?
I do have to say 15.5 at idle is a bit high, I have 13.7V at idle, although on an 98 VFR .... Still, it should be close.

 

I ended up bying a new RR for my VFR, measured it to 18v at idle, turned out my multimeter was failing.

So I dont think your question is stupid at all!

 

Seems that you missed a crucial step as you needed to try a proppa recharge (1-2 amps for about 10 hours) on that battery FIRST before replacing it.