Honda CBF125 battery not charging

[Savage3000]

Hi all!

Just got into the world of biking, and in an effort to not spend too much money I think I’ve ended up buying a turd.

I haven’t owned the bike long and I broke down, but got lucky that someone stopped and helped me, chucked my bike in the back of his van and dropped me and the bike home.

Since then ive had the multimeter out, battery was testing fine, stator was testing fine, but I had an issue with the regulator/rectifier. It seemed to be a loose connection issue, but it wouldn’t go away, so I ordered a new rectifier, and hey presto, problem seemed to be solved. With the new rectifier I was recording 14.something volts across the battery terminals.

Then next issue….

Me being a div/ the fuel gauge being WILDLY inaccurate, I pretty much ran out of fuel a couple of miles from home, managed to get it home, but when I topped up with fuel and attempted to restart it, I couldn’t get anything to happen. I read somewhere about repriming the fuel tank, which I did, along with putting the battery on a trickle charge overnight.

Next day I managed to get it started again fine, however I can’t get a reading above 12.4V on the battery.

In fact, when I test the battery with the ignition off, I’m getting 12.7V, but it now goes down when the ignition is on.

I’m not getting any of the same issues I was getting with the old regulator/rectifier where the lights would dim as soon as I put some power through the engine, in fact, the bike seems otherwise completely fine and I went on a 20 minute test ride with no issues at all, except I know that the battery isn’t charging up because I’m not getting the higher voltage reading that I require. I’m very reluctant to try and ride again at the risk of breaking down with a dead battery.

Any ideas?!?!

Also, my dipped headlight bulb seems to also not be working after this kerfuffle, might just need a new bulb, unless a fuse or something else could be an issue. That wouldn’t affect the battery not charging though would it?

[jaffa90]

Ok you are testing the battery but is the battery connected to the bike ?

[Robby]

You're looking at two separate things.

From memory, the CBF125 runs an AC headlight. Direct feed off the alternator, doesn't go anywhere near the reg/rec. So headlight performance doesn't tell you a thing about the reg/rec, all it should be telling you is engine speed - getting a bit brighter as the revs increase.

Seeing as there bikes do suffer from corrosion a bit, it's worth checking the headlight connections for corrosion, particularly any points where it has an earthing connection to the frame. Honda usually use green wire for earth.

To test the reg/rec, the only test is to get a multimeter on the battery, set to volts.
With the engine off, you are looking for about 12.6v - a healthy battery.
At tickover you are looking for 13-13.5v
At 4000rpm, you are looking for 14.5v

If the voltage is going down as the revs increase, chances are your new reg/rec is already knackered. If it was a cheap one off ebay, this is likely, because the cheap ones are shit. Even the genuine ones are fairly shit.