South West Bikers | Motorcycle Forum

A few weeks back, i rode my NC30 for about 45 mins or so around Plymouth (headlights on), and stopped at GT Motorcycles for a brew. When i went to set off again, the battery was dead. They jumped it for me, so i rode for another 45 mins or so to charge the battery, then stopped for some fuel. Once again, when i went to set off the battery was dead. A mate jumped it and i got home ok.

I checked the net for similar issues, and it sounded like my regulator/rectifier was screwed, so i tested it and yes, it seemed to be dead. The new one arrived in the post today, so i tested it and all seemed ok. I fitted it, fired up the bike and left the battery to charge. However, when i checked the voltage across the battery, it was only hitting 13.5v max, and with lights on was dropping to under 12. It should be around 14.5, both with and without lights on.

Can anyone suggest what it might be? Could the battery be dead (seems unlikely, it's 3 months old and has plenty of grunt to start the bike as long as it has some charge in it)? Could the alternator be dead? Could the new regulator/rectifier be a dud? Could there be some other issue with the wiring in the alternator circuit? I'm pretty new to all this so i don't know where to start really. All help is very gratefully received.

was it a like for like swap with the rec/reg? they usually have a voltage sensing circuit link to make sure that they are doing the job properly

failing that, check the outputs of the generator

3 yellows, multimeter on AC volts usually from my experience with the 400's you get about 20 volts at idle, and when revved 4-5k etc, you should be seeing 60-80v ac

just connect the meter across each combination of the yellows, 3 tests in all, make sure you dont short any, and see if any are drastically lower than the other

I found [url=http://www.electrosport.com/technical-r ... iagram.pdf]this diagnostic flowchart[/i] on another forum, and followed it. The thing is, it says that my charging system is fine, as the very first box essentially says "Is the voltage across the battery higher than 13.5v at 2500 rpm?" and the answer is yes, it's about 14v. It then says "is it lower than 14.8v at 5000 rpm, and agin the answer is yes, it's about 14.2v. So battery should be fine. However, i'm worried that as soon as i turn the lights on, the voltage drops to under 12 and keeps falling. This doesn't seem to be covered in the flow chart.

you could have a cell going down in the battery. riding around with a duff rectifier may have fooked the battery.

if you know someone who has a similar bike swap them over if not, take it to a battery shop, thay will be able to test it for you.

alternatively, get a new battery

Yeah agree with Simon, had that prob on my old Bandit, rectifier went down and took the battery with it, newish battery at the time too! Also check all your earth connections are clean and tight at the battery, might be a poor connection?

Cheers for the advice, here's an update:

With the new reg/rec fitted, i get a steady 14-14.3v reading across the battery at 2500-5000 rpm. This suggests the reg/rec is doing its job. The battery is alos holding its charge perfectly well, so i don't think the battery is at fault. What i did find however, was that instead of the 60/35w bulbs that my japanese 400 should have, someone had fitted 85/80w bulbs. I bought some 60/35s and fitted them today. Now the voltage across the battery is sitting at a constant 12.5v with dipped beams on, which is obviously still low, but not as low as the sub-12 and falling i was getting with the other bulbs.

nice one.

Definitely a short somewhere in the lighting circuit. Tested between the switches and the first connector, and is a fine, or it may well be buried somewhere in the frame. Damn. It's clearly exceeds my ability to reconnect all the bike, so I booked the next week is ordered.

VFR400s eat Reg/Rec for a past time. My NC24 had 4 swapped in 3 years, used to keep spares in the shed, at one stage I was swapping batteries every 2 days.

check the water/acid levels in the battery as 1 cell might be low and not working properly