Possible electrical issue

[release_the_bees]

On Saturday I went to go for a ride only to find that my battery was flat. As the battery was only a couple of months old, I put the battery on charge and put the old battery in the bike to see if it would start, which it did. I went for a decent ride (about 30 kilometres of motorway riding) and then went back home.

On Sunday I went to start the bike and the old battery was flat again. By that time, the two month old battery was fully charged, so I put this battery back in the bike and did a few tests.

1. I checked if the alternator was working by starting the bike and disconnecting the battery. No problem there. The bike kept running with the battery disconnected.

2. I checked the battery voltage with the engine off (12.8v) and compared this to the engine on (12.6v). I revved the engine a bit (3-5k) and checked again while the engine was revving (12.7v).

From my limited experience of this process (IE what I have found online), when the battery is charging, the voltage across the battery should be somewhere between 13.5 and 14.5v.

I am a little bit confused about what to try next. Test 1 seems to indicate that the alternator is working fine, as the headlights and the bike continue running happily with no battery connected. However my second test seems to indicate that the battery might not be charging. Is there any way, short of me taking the bike for a longish ride that I can confirm this (and if so, are there any likely faults that would cause this)?

I am planning on going on a 1200 kilometre journey this weekend, so would like some peace of mind before I set off.

Not that it probably matters, but my bike is a 2007 Hyosung GT650R.

[YellowDog]

Surely the old battery was knackered and hence it failed after the long journey.

Now new battery has been charged, if that again loses charge then you have a drain somewhere. Some alarms have this effect if you don't use the bike a much thriough the winter.

What was the last bit of electrical work done on ther bike?

Hopefully the two month old battery is fine and you don't have a problem.

[release_the_bees]

Thanks for the response.

I figured that was probably the case with the old battery. When I bought the bike a couple of months back, the pre-purchase inspection indicated that although the existing battery was working fine, it needed replacing, hence the reason I got the new battery. I gave the old battery a charge and then it has been sitting ever since, which is hardly conducive to a healthy battery.

The only electrical work that I know of is the tail-light wiring, which has been replaced due to a broken connector. The previous owner got this fixed professionally the week before I bought the bike.

I usually ride the bike once or twice a week, which usually works out at about 60-120km of riding a week).

[Juzz976]

Charge voltage 12.7V (engine running/revving) seems a bit low, was there any electrical load switched on at the time (hand grips, headlights....)?

[release_the_bees]

The low beam was on. There is no off switch, so the lights run whenever the engine is running.

[Juzz976]

2. I checked the battery voltage with the engine off (12.8v) and compared this to the engine on (12.6v). I revved the engine a bit (3-5k) and checked again while the engine was revving (12.7v).
.

Voltage while running should be QUOTE "From my limited experience of this process (IE what I have found online), when the battery is charging, the voltage across the battery should be somewhere between 13.5 and 14.5v. "

Regulator/rectifier should be regulating to this voltage, may be a bad earth or other connection, dud reg/rec or an alternator fault.
Check connections first, if still not enough charge voltage might need to take to shop.

[avgas]

Yep you have an electrical fault.
No need to check tyre pressure.

[release_the_bees]

Okay thanks guys. I'll look into things further and report back once I find out what the cause is.

[Squiggles]

There's a pretty good flow chart here

[willytheekid]

Great flow chart Squiggles !

Ive learnt to always check your earths are doing the job, some times there just not "quite" earthing properly (cause's more problems than you would think)

[release_the_bees]

Thanks for the link to the diagram! I think that will be most useful.