reg/rec problem 125cc help

[eddie011]

ok so i have a

125cc
08 plate
4 stroke
moto mornini engine

the problem is i have to charge the battery every couple days because it is draining and its not charging its self
the main comes on when i start the bike and gets a hell of a lot brighter when the bike is being revved or used and dims down again when bike inst being revved or used but when battery dies all other lights and electrical items don't work but main light stays on

I'm wondering if the reg/rec could of be wired wrong and the main feed that charges the battery is going to the light instead of the battery if anyone could help that would be a really big help#
thanks

[Efes123]

You could just have a screwed battery that's not holding a charge. Or it could be your rec/reg is fried, but I seriously doubt it wired wrongly.

Check the battery with a multimeter with ig off, on, running, and reving
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[RhynoCZ]

[P.]

Check the voltage across the battery when bike is running...

[unitynotsocri...]

Reg/regulator problem or , if fitted a ballast resistor that's used to dump excess electricity.
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[Teflon-Mike]

It sounds to me, like a fukken-shrunk battery.

Batteries loose charge capacity with age and heavy use. They get 'smaller' in effect.

Bigger batteries on bigger bikes are bigger, physically, and in charge capacity, but they still work at the same volts; so getting 12v on the terminals doesn't tell you how much charge capacity they have or whether the battery is 'good' or not.

If the electrical equipment uses more electric than the generator can supply, difference has to come from the battery. Only if the generator is making more power than equipment is using, will the battery charge.

It's possible, you have an AC-Direct lighting system; which powers the lamps directly off un-rectified AC current from the generator; that does make lamps dim and bright with revs, especially if a higher wattage bulb's been fitted; but if that doesn't happen when you have charged the battery, implies you have regulated DC lighting. AND fact that lights are behaving like AC-Direct, brighting and dimming with engine revs, implies that there's probably nothing wrong with your reg-rect; lights are getting power, so genny is making it, and it is getting to the battery, (which is probably 'robbing' a fair bit, if it's kerfuckered, acting as a resistor, taking amps, not providing them) and what's making it to the lights is just not enough to keep-em lit.

But tells you even if battery were good, at lower revs; battery will be powering lights, not the engine....

So, if you do lots of short journeys at slower speeds, short shifting, never reving the engine over maybe 3,000rpm, and you have the head-lamp constantly on, even in day-light... good chance that the light is taking almost all of its power out of the battery, and the generator is never making enough 'spare' to top it back up.

And if the battery is old, and harder used, the 'reserve' the battery has to keep making up the difference will be getting ever smaller and smaller, until the battery simply doesn't hold ANY charge... and you get what you have seen.

As suggested, try a new battery. A good battery, probably only has a 2-3 year life anyway; and this is most likely cause of problem you are seeing.

BUT, heavy load on the battery, using Day-Time-Running-Lights, and not revving the engine to give it a chance to charge, is likely to be making the problem appear. And if its electric start, and you are doing shorter journeys, not giving genny chance to put charge back in the battery between starts, could be even worse.

And; if using Day-Time-Running-Lights for 'conspicuous'... if you can turn them off... do so. Using the side-light in day-light can still provide desired conspicuity, lighting up the head-lamp bowl. And give the bike a chance to charge; use the revs more, ride for response around town, dont make work for yourself, short shifting up too many gears when you dont need to, demanding more unnecessary down shifts when you dont need them, and keeping revs low and choking generators chances to charge the battery; Use the Revs... and take it out for a good thrashing once a week; good half hour or hour long blast on country roads, get the speeds up, and give the genny a chance to make some spare amps to keep battery topped up; circulate some oil and wash fuel through the main jets 'Blow out the Cob-webs' as we say. Bikes actually likely to appreciate it.
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