Why am i losing volts?
Discussion
Bike has let me down recently by not starting. Symptoms are:
Battery was discharged. Recharged and left for 5 days, still had 12.6v in it after standing (was still connected to bike but not started).
Started up with lights off, rand at a solid 14.4v, no issues.
Switched lights on, voltage sank like a stone. Turned lights off, bike re-charged battery.
Yes, i know it’s my lights, bit does anyone have any experience of sorting this sort of thing. Bike is usually 100% reliable.
Battery was discharged. Recharged and left for 5 days, still had 12.6v in it after standing (was still connected to bike but not started).
Started up with lights off, rand at a solid 14.4v, no issues.
Switched lights on, voltage sank like a stone. Turned lights off, bike re-charged battery.
Yes, i know it’s my lights, bit does anyone have any experience of sorting this sort of thing. Bike is usually 100% reliable.
darkyoung1000 said:
My thought would be battery. It sounds like it has enough to start and run the bike, but when you ask it to do more than that (lights), it gives up.
Do you know how old it is?
Fiver on this from me as well. Friend had a VFR1200 with similar. Started perfectly after being on charge, charged the battery when running, but if you put a multimeter on it once you turned the trickle charger off it lost 2 volts in a few minutes.Do you know how old it is?
I immediately thought battery too, and since they're so cheap (as long as not lithium) may be worth throwing a new one on for peace of mind anyway... but...
If the voltage dropped from 14.4v whilst running as soon as you put the lights on then really the charging system should've supported that load, how much are we talking in terms of a drop? I don't think it's your rectifier cos your voltage is sound but maybe your stator is on its way out hence why voltage is fine under no load but falls flat on its face when any demand is put on it.
If the voltage dropped from 14.4v whilst running as soon as you put the lights on then really the charging system should've supported that load, how much are we talking in terms of a drop? I don't think it's your rectifier cos your voltage is sound but maybe your stator is on its way out hence why voltage is fine under no load but falls flat on its face when any demand is put on it.
Edited by Yazza54 on Thursday 14th July 21:04
Tricky one this innit? A bit more background…
Bike is a 1990 vfr750; theyre known for charging issues which is why years ago when i bought it i redid all the charging wiring, put a mosfet rr on it, an uprated stator and a new battery. It’s been unbelievably reliable until this week.
I guess next step now is check all wiring from battery, through rr and back to stator. Took rr off earlier and no burnt contacts in plugs so that’s next step i guess.
I think diagnostically the thing that’s thrown me is thinking the lights draining it means it’s the lights that are the cause, not something just showing up as a symptom of another problem?
Bike is a 1990 vfr750; theyre known for charging issues which is why years ago when i bought it i redid all the charging wiring, put a mosfet rr on it, an uprated stator and a new battery. It’s been unbelievably reliable until this week.
I guess next step now is check all wiring from battery, through rr and back to stator. Took rr off earlier and no burnt contacts in plugs so that’s next step i guess.
I think diagnostically the thing that’s thrown me is thinking the lights draining it means it’s the lights that are the cause, not something just showing up as a symptom of another problem?
Hugo Stiglitz said:
It's possibly the regulator/rectifier
It was kicking out 14.4v so its unlikely to be that. It's much more likely the battery is u/s having been left discharged. Biggest killer of cells. One will have gone down and it won't hold charge.Pop a proper load tester across the fully charged battery (off bike) and see how it holds up on test then.
V1nce Fox said:
Bike has let me down recently by not starting. Symptoms are:
Battery was discharged. Recharged and left for 5 days, still had 12.6v in it after standing (was still connected to bike but not started).
Started up with lights off, rand at a solid 14.4v, no issues.
Switched lights on, voltage sank like a stone. Turned lights off, bike re-charged battery.
Yes, i know it’s my lights, bit does anyone have any experience of sorting this sort of thing. Bike is usually 100% reliable.
Fully charged battery should run say 100W of lights for quite a while before the volts go down below 12VBattery was discharged. Recharged and left for 5 days, still had 12.6v in it after standing (was still connected to bike but not started).
Started up with lights off, rand at a solid 14.4v, no issues.
Switched lights on, voltage sank like a stone. Turned lights off, bike re-charged battery.
Yes, i know it’s my lights, bit does anyone have any experience of sorting this sort of thing. Bike is usually 100% reliable.
Alternator/reg/ rectifier may need some RPM to provide enough for the lights.
Test the battery.
Does it start the bike? Tick?
Does it have proper capacity? with the engine off, if it's been charged fully, how long will it run the headlamp before dropping to 11V or something?
Test the charging circuit.
At some reasonable RPM, it should deliver a charging voltage of >13.8V while powering the lights.
I'm used to Italian so this can be a bit sketchy, some bikes are marginal with the lights on at 'pottering' revs.
If we were talking about a car, once the engine is running , it should not depend on the battery to run the lights, even at 1200RPM. A lot of bikes are not like that. A workshop manual should have a test procedure.
Voltage is easy to measure but really you need to know how many amps it has stored
You can buy a CCA meter on ebay for £15ish but if after it's fully charged, it won't start the bike at least 10 times in a row then it's duff
Recently I've had bikes start and run fine but then they die after an hour or so... dead cell etc as the RAC man said to me
"I don't know anything about bikes but 99% of the time it's the battery"
He's not wrong
I find Tayna very good
You can buy a CCA meter on ebay for £15ish but if after it's fully charged, it won't start the bike at least 10 times in a row then it's duff
Recently I've had bikes start and run fine but then they die after an hour or so... dead cell etc as the RAC man said to me
"I don't know anything about bikes but 99% of the time it's the battery"
He's not wrong
I find Tayna very good
I'd still expect the charging system to support a load increase as minimal as switching the lights on. If it's running at 14.4v and then drops under any electrical load that to me points more to the stator than the battery.
My race car (cbr1000rr engine) for example, happily ticks over at 14.4V while powering up lights, data logger, dash, camera and a high output electric water pump, and a fan as and when required... I am still running a bike battery.
The only problem I've ever had was when the stator was slowly on its way out. It still ran and charged but it was only managing 13.2-13.5V.
I suppose your battery could be absolutely shagged to the point where it isn't really absorbing any of the fluctuation in load but I feel like your stator should cope with putting the lights on without the voltage dropping much or at all.
My race car (cbr1000rr engine) for example, happily ticks over at 14.4V while powering up lights, data logger, dash, camera and a high output electric water pump, and a fan as and when required... I am still running a bike battery.
The only problem I've ever had was when the stator was slowly on its way out. It still ran and charged but it was only managing 13.2-13.5V.
I suppose your battery could be absolutely shagged to the point where it isn't really absorbing any of the fluctuation in load but I feel like your stator should cope with putting the lights on without the voltage dropping much or at all.
Edited by Yazza54 on Friday 15th July 09:30
Yazza54 said:
I'd still expect the charging system to support a load increase as minimal as switching the lights on. If it's running at 14.4v and then drops under any electrical load that to me points more to the stator than the battery.
Possibly but I had a Tiger 955 that came in with a dead battery and making 11v, cut out a burnt connector 13v, cleaned up the earth and battery conections 13.7v upgraded the undersized (by a PO) wiring 14.4v 
It's frequently a few things combined
Hugo Stiglitz said:
It's possibly the regulator/rectifier
I would assume this and check it first. Doubly so now that I've seen the model. Hondas pre-2009 (including my CBF1000) do have issues with regulator/recifiers overheating and eventually letting go over the period of years. I've had it. Was a £100 job and back on the road in no time. Suggest checking that.The clue for me is in the original post that the battery was discharged. Just because it was then recharged and showed 12 6v means nothing, it could be a faulty cell.
Start with the easiest thing and put a load tester straight across the battery and kill it or cure it before you look elsewhere. Doesn't matter what voltage comes put of the alternator /reg if there's a faulty or damaged cell in the battery.
How old is it, how long was it left discharged etc ?
Start with the easiest thing and put a load tester straight across the battery and kill it or cure it before you look elsewhere. Doesn't matter what voltage comes put of the alternator /reg if there's a faulty or damaged cell in the battery.
How old is it, how long was it left discharged etc ?
Ah, the old vfr charging issues .
Put the electrex reg/rect with the long leads direct to battery.
A professional word of advise though. A honda reg/rect usually fails because of a poor connecter somewhere creating a high resistance. The connectors on the right side of the bike above the rad are usually to blame on a VFR. They are Ignition switch, right switchgear, and regulator connectors.
I've fixed many many hondas, and other bikes without the need for the internet 'Its the regulator, mate' advise.
Also check the bulbs are 60/55 and not 100W ;-)
Put the electrex reg/rect with the long leads direct to battery.
A professional word of advise though. A honda reg/rect usually fails because of a poor connecter somewhere creating a high resistance. The connectors on the right side of the bike above the rad are usually to blame on a VFR. They are Ignition switch, right switchgear, and regulator connectors.
I've fixed many many hondas, and other bikes without the need for the internet 'Its the regulator, mate' advise.
Also check the bulbs are 60/55 and not 100W ;-)
fred bloggs said:
Ah, the old vfr charging issues .
Put the electrex reg/rect with the long leads direct to battery.
A professional word of advise though. A honda reg/rect usually fails because of a poor connecter somewhere creating a high resistance. The connectors on the right side of the bike above the rad are usually to blame on a VFR. They are Ignition switch, right switchgear, and regulator connectors.
I've fixed many many hondas, and other bikes without the need for the internet 'Its the regulator, mate' advise.
Also check the bulbs are 60/55 and not 100W ;-)
All of this is familiar. I did the whole mosfet/vfrness/multiplug delete when i first got the bike and as said above it’s been ultra reliable since until this. Put the electrex reg/rect with the long leads direct to battery.
A professional word of advise though. A honda reg/rect usually fails because of a poor connecter somewhere creating a high resistance. The connectors on the right side of the bike above the rad are usually to blame on a VFR. They are Ignition switch, right switchgear, and regulator connectors.
I've fixed many many hondas, and other bikes without the need for the internet 'Its the regulator, mate' advise.
Also check the bulbs are 60/55 and not 100W ;-)
Gassing Station | Biker Banter | Top of Page | What's New | My Stuff