Charging System Help

[Andrew Shadow]

I take voltage readings every spring when I fire up my ST1300. The voltage drop when you are starting the engine seems quite normal but I have never seen voltage readings as low as what you have reported when the engine is running. I have never seen less than 13.9 V at idle, and at anything above idle I always see 14.2 V or above. If the battery is good, and if there is not a wiring problem (e.g. loose connections, corrosion, etc.) I fear that you have an alternator problem. Unfortunately if it is only the voltage regulator it is about the same amount of work as if it was the alternator.

It isn't still under warranty from Michael? (Kidding of course.)

 

[dwalby]

I have never seen voltage readings as low as what you have reported when the engine is running. I have never seen less than 13.9 V at idle, and at anything above idle I always see 14.2 V or above. If the battery is good, and if there is not a wiring problem (e.g. loose connections, corrosion, etc.) I fear that you have an alternator problem.

I don't have a lot of experience with failed alternators (fortunately!) but back in the old UJM days when I had a failed alternator it shorted out completely. Just curious if alternators typically fail altogether like my experience, or if there are varying degrees of failure that might explain the OP's situation.

 

[Andrew Shadow]

I don't have a lot of experience with failed alternators (fortunately!) but back in the old UJM days when I had a failed alternator it shorted out completely. Just curious if alternators typically fail altogether like my experience, or if there are varying degrees of failure that might explain the OP's situation.

The ST1300 has an automotive style alternator so the failures can be the same.
e.g. The failure can be the voltage regulator, the diode set, the brushes, the rotor windings, the stator windings, as well as mechanical failures like bearings.

The problem with the ST1300 is that considering the effort to get it out and back in many people opt to replace it rather than to risk the failure of another aged and possibly tired component later on.

 

[Andrew Shadow]

To add to my above response what I forgot to include, and in answer to your question, is that in my experience the most common failures with this type of alternator are the voltage regulator and the diodes. Unfortunately, as I previously stated, getting to those requires removing the alternator.

 

[JamieE]

Thanks @Andrew Shadow ! I read through the service manual and the work involved is out of my league. I’m going to try to find someone local to help. Is rebuilding it an option? Here in Canada I’m looking at over a grand for a new one (not sure how new).

 

[Andrew Shadow]

Rebuilding it is no different than rebuilding an automotive alternator. All of the parts are listed in the parts diagram individually. If they are ALL still available and how many might be back order is something that you will need to check in to with your favourite parts supplier.

If this is something that you don't want to tackle yourself any alternator/starter motor repair shop can easily do it. The problem with finding somewhere to rebuild these is not the complexity of it, it is not much different than an automotive alternator of the same era. The problem is that they all have test rigs designed for automotive alternators that have a pulley on them. Consequently they can not put it on their test bed. Because they can't test it most don't want to bother with it. Adapting something to allow them to spin the alternator on their test bed is not an insurmountable obstacle but it is not worth the effort for them in order to be able to test and rebuild one alternator, so they just say that they can't do it. If you are willing to pay for their time and energy to do this you might find a shop that is willing. One of those scenarios where you never know until you ask.

If you find an automotive place that is willing to do this you may also have to supply them with the parts because they may not have a relationship with any motorcycle parts departments, but that is not an issue once they tell you what they need.

It might well be worth your while to ask on here if anyone knows of somewhere who will do this. I remember at least one thread where a member on here found a shop that adapted their test rig so that they could repair and test it but I have no idea who that was. I have never looked for one bit it seems to me that there must be shops somewhere that rebuild motorcycle alternators.