Honda xr Battery not charging

Hello All

I'm calling in from Ibiza where I evade the summer madness of drunk and drugged drivers by zooming around the backroads on my trusty Honda XR125. Trouble is, it's just started NOT charging the battery and I hope someone out there can help me out.

I've put my multi-meter across each of the three yellow wires coming out of the alternator to the rectifier (to a good earth point) and each reads +/- 2.8v at medium revs . So i took off the alternator cover to see what was what. I can't see what there is to go wrong in there and from experience these issues usually stem from something more obvious/likely to go wrong, like a loose connection, so I put it back together and started looking elsewhere.

The wiring diagram shows a lead going from the alternator to the ECM. Could it be the ECM that's faulty? I have no idea why ECM and alternator should be connected but electrics was never my strong hand. How do I test the ECM?

It's hard to check the rectifier when there's so little going into it. So I'm kind of stuck between the alternator and the ECM.

Surely the alternator should be throwing out around 18v (3 x 6v) as soon as it's turning at any speed? I've known car alternators to pack up but never a bike's.

There's a very odd little earthing point behind and below the front sprocket, which I've cleaned, still to no avail.

I'll stop there. Any advice gratefully received and thanks for reading thus far.

Hi, welcome to the forum.

Moved topic here.

If you would like to introduce yourself please post in newbies.

Ibiza......lucky you! Es Cana is one of my favourite places

Hello All

I'm calling in from Ibiza where I evade the summer madness of drunk and drugged drivers by zooming around the backroads on my trusty Honda XR125. Trouble is, it's just started NOT charging the battery and I hope someone out there can help me out.

I've put my multi-meter across each of the three yellow wires coming out of the alternator to the rectifier (to a good earth point) and each reads +/- 2.8v at medium revs . So i took off the alternator cover to see what was what. I can't see what there is to go wrong in there and from experience these issues usually stem from something more obvious/likely to go wrong, like a loose connection, so I put it back together and started looking elsewhere.

The wiring diagram shows a lead going from the alternator to the ECM. Could it be the ECM that's faulty? I have no idea why ECM and alternator should be connected but electrics was never my strong hand. How do I test the ECM?

It's hard to check the rectifier when there's so little going into it. So I'm kind of stuck between the alternator and the ECM.

Surely the alternator should be throwing out around 18v (3 x 6v) as soon as it's turning at any speed? I've known car alternators to pack up but never a bike's.

There's a very odd little earthing point behind and below the front sprocket, which I've cleaned, still to no avail.

I'll stop there. Any advice gratefully received and thanks for reading thus far.

test the voltage between the yellow wires , set the meter on AC volts

you get quite a high voltage when there is no load on the alternator,

Yeah...as FredC says, the alternator will be putting out AC volts so you need the meter set to AC Volts. How about the DC voltage actually across the battery when the engine is running? And also when the ignition is off? Are you sure it's not just a duff battery that's not taking a charge?

Good luck mate.....

AC...OK, alternator...alternating current...should have guessed that....maybe

Across the battery terminals there's only what ever is in the battery, ignition on or off, engine running or not, never more that 12.8v. The battery's brand new. I've just come back to the bike after 6 months (stored in dry garage) and the battery, very tired at the end of last year, wouldn't charge up. Now the new one won't so I don't actually know when this issue began.

I'll come back after checking with AC.

Thanks guys.

OK, alternator is putting out around 6v on each of the yellows (phew). So 18v AC going into the rectifier and around 2.5vDC coming out.

All connectors are clean so it must be the rectifier then. I've never known one of these to go wrong either. Can anyone enlighten me as to whether this is common or not, and is there a cause generally?

Many thanks

Reg/Recs can be very fragile......I had one fail a week before I sold my Sprint. .... And it was meant to be a super duper mosfet one too! So I wouldn't be surprised if the one on your bike has died.

OK, alternator is putting out around 6v on each of the yellows (phew). So 18v AC going into the rectifier and around 2.5vDC coming out.

The alternator should be putting out more volts

Did you measure from yellow to yellow (right) or yellow to ground (wrong)

6v on each of the yellows is still only 6v output not 18v

When you rev it the voltage could reach 40 - 50v between any 2 yellow wires

Personal experince here, but could be wrong, last thursday my battery would not charge while "reving" but would pump 13.2 or so while idle, the alternator i did not check, but the regulator needed replacing which fixed the issue, personally i would go with the gamble of the reg/rec due to the fact that fixed my issue, but as you already are testing the alt keep doing that for now.

had same problem as you it turned out to be a corroded connection at the junction between the regulator and the battery, just pull the connecter apart and check the pins