Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Charging system issues

Discussion in 'Technical and Troubleshooting Torque' started by Tim., May 9, 2012.

  1. Occasionally my bike is going flat. I checked the electrical system, the only issue I can find is if I test the current made by the alternator between 2 of the 3 fields I get a good reading, but the 3rd only gives me 5-6v (I.E. in fields a, b and c: a-b = good; a-c = good; b-c = bad)

    All tests on the alt come up fine, the windings all have less than 1ohm resistance and no shorts to ground and the field coil seems good and strong.

    Anyone know anything that might be wrong or should I just get a replacement alt and be done with it?

  2. Hi Tim, I assume you did these voltage tests with no load on the alternator? If it was still connected to the reg/rec then it could be pulling one phase down. What's the bike? Lots of bikes now days have permanent magnet alternators and shunt regulators. Shunt regs short across the alternator phases as their method of voltage control. A failure could leave this shorting one winding although they generally blow open and allow the voltage to rise and cook your battery :)
  3. Yeah no load. The bike is a 15 year old CBR thou and the regulator is just a Bosch RE 55 and it's rectified by a bank of rectifier bridges. (last time the reg/rec died it was going to take a few weeks for the new one and I wanted to ride that weekend so I had to build my own). It doesn't have a perm. magnet and when I bypass the regulator it doesn't make any difference.

  4. Ok, if not a permanent magnet alternator then something from the reg must drive the rotor field coil??? I am leaning towards your original diagnosis of alternator though.