hey everyone,
i{m the proud owner of a cheap chinese 250cc bike which i'm using to travel in south america.
lately i've been having a mysterious electrical problem- when i ride at night and turn on the lights, after around 20-25 minutes the bike loses electrical power- the high beams don't work, then the lights turn off, then the indicators stop working, then the dials, and when i switch off the bike it completely dies and when i turn the ignition to "on" nothing happens. after a perios of time between 5 minutes-2 hours the bike returns to normal and works perfectly.
i've checked the battery and it has sufficient voltage(14V when idle, 12.8 when everything is off) so that's not the problem.
the problem has occured twice so far- first time i looked and found that the cheap chinese light bulbs melted in their cheap chinese housing and short-circuited the electrical system, so i replaced them. the second time it happened i could find no fault at all- battery fine, fuse fine, light housings whole and good.
i'm thinking perhaps because my bike has two front headlights(they copied the front off an old KLR) the headlights are draining the battery and when it has no power left it dies and after some time the battery regains it's power to start up the bike. could that be possible?
any other ideas would be welcome. thanks!

Odd sure enough

Check all the earth connections. It seems unlikely to be a charging issue.
Other thing it could be an intermittent short circuit which when it occurs it takes the voltage away from where it is supposed to be..
Do you have any accessories wired in that could be an issue?

Its a start, keep us posted.

hmm, i checked all the electrical connections on the bike and they all seem to be fine. last two days i drove around with the lights on and everything worked. i haven't connected any accessories, but i have changed the front headlights though i doubt that is the problem because i connected everything according to the same colors.
after running it yesterday with the lights on for an hour i checked the voltage and found without lights when idle i have 14V, with low beams only one headlight works and i have 13.5 volts, and when idle with bothe high beams on i have 12.5V. is this okay?
i also have burnt through a few headlights already (6-7) and they all burn out the low beams but the high beams work. could that be a sign the headlights are getting to much electricity?
i hope the problem will repeat itself soon when i'm in a normal place so i could look into it again.
thanks!

Hi,

Your charging voltages sound OK to me.

I wonder if the extra current being drawn when the head lights are on is too much for the main fuse holder, main wiring connectors or contacts in the ignition switch. If so the problem would get worse over time as they get hotter and drop more voltage, possibly causing the symptoms you describe.
I would suggest feeling for any of these areas getting hot when the problem starts to appear. Also try before problem appears but after bike has run a while so that you know how warm is normal.
If this is the problem you could use a relay to feed the headlights straight from the battery (with in line fuse as near to battery as possible), so removing quite a bit of current from the main wiring, fuse & ignition switch. And an added bonus of brighter head lights.

As for blowing headlight bulbs, it might be worth checking the charging voltage over the whole engine rev range. If it goes over 14.5V a charging problem could be the cause.

Good luck

Mark

Sounds tricky. For me the key piece of info is that it fixes itself after some time - that means it has to be heat thing. There's quite a few things which can overheat and act funky, but my guess would be the voltage regulator - the lights are probably the biggest prolonged source of current draw on the bike. So find and check whether it's your regulator getting hot..... At least that's what I'd look at.

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I think that the 14V @ idle is a starting point for your problem. At idle you should not be that high. Charging for 'almost' any bike isn't until around 3K RPM.
Check the voltage throughout the RPM range and see if it goes over 15V. If it does...bad Reg/Rec.

1) a drained battery will not self recover over time. Well not that much.

Felling for heat is a good idea... don't forget to check the battery temperature.. AND use the back of your hand ... if it is really hot then the burn won't be over so many nerve ends there!

14v at idle is a concern .. check battery temperature - if hot = bad rect/reg.