Unused alternator winding - Page 1
Forum section: electronics / beginners

author: EEBlackSheep
author_rank: Contributor
timestamp: March 03, 2014, 03:13:44 am
content: I have a motorcycle that is being converted to a race bike. It has two independent windings in the alternator, one for the electronic ignition, another high current winding for lights etc. It is *not* a typical three phase motorcycle alternator 0- just two independent windings. Since it is being converted to a race bike, there is no need for the high current winding (there will be no lights, battery or electric start, just the electronic ignition).What do I do with the unused winding? One schematic shows that it should be shorted out; but a number of people on the motorcycle forums says the circuit should be left open. I would like to understand why - one way or the other.thanks for the help.

author: c4757p
author_rank: Super Contributor
timestamp: March 03, 2014, 03:44:28 am
content: The winding is a power supply. If you short it out, it will attempt to supply power to the wire with which you have done that.Bad. Best case, it makes the alternator act as a brake. Medium, the wire melts. Worst, the wire in the alternator melts.If you leave it open, it simply won't supply power. Everyone's happy.The outlets in your house are supplied by a winding on a transformer, too. You don't short those out when not in use, do you?

author: CodeDog
author_rank: Contributor
timestamp: March 03, 2014, 04:32:02 am
content: is it a permanent magnet alternator?if so, their windings can be shorted/earthed with no ill effect ... otherwise the shunt regulatorson most motorcycles wouldn't work ...leaving them open cct is feasible but for safety take care to insulate the floating connector as reasonably large voltages are likely to be generated at high RPMsit would be good if someone knowledgeable on the subject of permanent magnet alternators could explainthe counter-intuitive result that the output can safely be shorted

author: G7PSK
author_rank: Super Contributor
timestamp: March 03, 2014, 08:58:39 am
content: If its a flywheel type alternator just remove the whole coil.

author: Richard Head
author_rank: Frequent Contributor
timestamp: March 03, 2014, 09:09:36 am
content: If you short it it will act as an electromagnetic brake and sap power from the engine. The power loss will appear as heat in the flywheel and the windings.Dick

author: tautech
author_rank: Super Contributor
timestamp: March 03, 2014, 09:26:39 am
content: Often there are 3 windings, power, ignition exciter and ignition trigger windings. They are commonly on a single stator. You could possibly un-wind the one you don't need, but I would leave it open circuit, unless the little extra weight worries you. If you leave it there, just be sure any remaining leads are well insulated.

author: Dave Turner
author_rank: Frequent Contributor
timestamp: March 04, 2014, 12:23:33 am
content: All else being equal leave it alone. Removing will probably cause unwanted effects.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 04, 2014, 06:05:16 pm
content: Short it out, and never win any racesLeave it open, and maybe you will...

author: IanB
author_rank: Super Contributor
timestamp: March 04, 2014, 06:14:24 pm
content: Quote from: CodeDog on March 03, 2014, 04:32:02 amI don't think the output can safely be shorted. If you short the output then current will flow through the short, the wiring and alternator will get hot, and the short circuit will act as a magnetic brake on the engine.The output must be left open, and the output wires must be carefully tied off and insulated so they don't accidentally short against anything else.