Re: One Wire Alternators

Posted by Jon Hagen on September 03, 2016 at 11:48:45 from (64.68.4.241):

In Reply to: One Wire Alternators posted by Indiana Ken on September 03, 2016 at 06:21:53:

One big reason folks have trouble exciting a "1 wire " alternator on an old slow turning tractor engine is that they choose the wrong size "1 wire" alternator. The rotor poles on an alternator are much smaller than a generators pole shoes, so it needs to spin faster than a generator to induce enough voltage to excite the field rotor.

Most people try to use a very high output "1 wire" alternator, usually in the 60-72 or 100 amp range, to replace their 20-30 amp generator. Part of that fault may be with the parts store that stocks only very large output "1 wire" alternators to reduce inventory, as in many cases, a large alternator can replace a small one without problems.

My experience with the "1 wire" Delco SI series alternators is that the "small" stator windings of the 37 amp "1 wire" alternator will excite at less than half the rpm it takes to excite a 60-72-or 100 amp "1 wire" alternator. Thus making the 37 amp "1 wire" alt ideal for those old slow turning engines, plus if your using the original wiring harness, a 37 amp alternator will not overload / overheat the wiring that previously was connected to a 20-30 amp generator.

Also that old husbands / mechanics tale of a "1 wire" alternator draining your battery is false for any " 1 wire Delco built in the last 40 years. A modern "1 wire" Delco SI series alternator has the exact same internal wiring as the "3 wire" alternator, their is no added connection to battery power to discharge the battery. Very easy to confirm this fact, just disconnect the BAT wire from the alternators output stud and using your multimeter, measure the current flow to the alternator, be it "1 wire or "3 wire", you will find it to be exactly the same, a few miliamps lost through the rectifier diodes which are the exact same part in either "1 wire" or "3 wire " alternator.

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