ELECTRICAL REBUILDER’S ASSOCIATION—Technical Document CS201411B www.electricalrebuilders.org Rectifying The Wye Connection BY BOB THOMAS L the September issue I wrote about a CS121 conversion alternator for a Model T that came into my shop for rebuilding. It had a stator that had been reconfigured from delta-wound to wye- wound. I mistakenly stated that Delco’s 1ODN, 10SI and Chrysler’s early alternators all had delta-wound stators. I was wrong, a price I often pay nowadays when I trust my memory. Those stators were in fact all wye-wound, and I apologize for the error. Since then, I have inspected many stators, paying particular attention to their configuration. I believe that the 27SI Type 100 may have actually been the first Delco automotive alternator to not use a Y-configured stator. Application data shows that it was introduced in 1974 as part of a towing-package option, and later it became standard equipment on many Cadillac models. In that same article, we explained the charging characteristics of both stator configurations. A delta- wound stator will produce more amperage at high rotor speeds, but the same stator in wye configuration will produce better amperage at low rotor speed. That may explain why most of the heavy duty alternators are delta-wound—for use on over-the-road trucks that spend most of their time at a constant speed. At the same time, many of those early automotive applications were wye-wound, to better carry the loads in city driving conditions. It certainly explained the reason the stator in the CS121 Model T conversion alternator had been changed to wye configuration. Some manufacturers have used the wye terminal to power electric choke heaters, among other things. When used in this way, the wye terminal provides about one half of the system voltage if tested with a meter set to DC or AC. In reality, the voltage you are measuring is actually half AC and half DC, because the return path is through a diode. The reason the “wye” output is half voltage is that it is half phase, generated within a single stator coil. As you can see in Figure 1, a full phase is comprised of two coils in Y-configured stators. If the voltage of each phase is 14 volts, the voltage on the wye connection should be about 7 volts. Incidentally, that wye terminal’s AC voltage also has a frequency that is three times higher than a phase terminal, because it is connected to all three phases. This produces the extra output, but it also produces a different waveform at the B+ terminal. The ripple of the two waveforms are added to each other. If your test bench measures AC or ripple voltage, you will always notice higher ripple readings when testing alternators that have rectified wye terminals. Rectifying the “wye” reduces a stator’s resistance, therefore the alternator has good high-speed output along with the wye’s low-speed output. The stator will perform as a “wye” until the resistance or voltage drop of the diodes connected to the “wye” are overcome. We suspect that it may have been Denso who first rectified the wye connection. They did it in a few of their last external fan alternators in the early 1980s. To determine just how much amperage can be gained by rectifying the wye connection, we conducted an experiment. We selected a 65-amp internal fan Denso alternator that was originally used on Honda Accords and Preludes from 1984 to 1989, Denso part number 100211-2140 or Lester 14680 (see Figure 1). If you look at any internal fan Denso stator, the wye terminal is easy to pick out (see Figure 2). You will notice that our test alternator’s wye terminal has three wire ends, and the other three stator (phase) leads have one each. Ifa stator happens to be double-wound, there would be six leads on the wye connection and two each on the phase terminals (see Figure 3). All internal-fan Denso alternators prior to the introduction of hairpin stators have used Y-configured stators, so far as we can tell. However, the presence of a wye connection does not mean that it is being rectified. DIODES NEG POS CONNECTOR Figure 2—This is our Denso 100211-2140 test alternator with the rear cover removed. Note that the rectifier is secured to ground, and ring terminals have been added to the stator connections for test purposes. An ERA Publication. ©2014, Electrical Rebuilder’s Association. All rights reserved. No portion of the guide may be reproduced in any way, or stored in any electronic retrieval system without the prior written consent of the Electrical Rebuilder’s Association. Page 1 ELECTRICAL REBUILDER’S ASSOCIATION—Technical Document CS201411B www.electricalrebuilders.org This particular alternator has eight diodes in the rectifier—which indicates that the wye connection is being rectified. After removing the back cover and securing the rectifier on the ground studs, we were able to operate it on the test bench and take voltage measurements directly from the stator. We installed ring terminals where each lead is connected to the rectifier to ensure accurate readings. While operating the alternator at a moderate load, we measured AC voltage between two of the phase terminals at 13.49 volts (see Figure 4). Then we measured AC voltage between one phase connection and the wye terminal to get half-phase voltage of 7.53 volts (see Figure 5). You may think that the “wye” voltage is too high, but remember that these readings were taken at the stator. All stator connections are joined on the other side of the diodes which is connected to a battery. Remember that the half-phase “wye” produces three times the frequency. Figure 3—This is a double-wound Denso stator with six coils connected to form We also tested this alternator for maximum output. the wye connection. When it was cold, it produced 70 amps. Then we removed Figure 2—This is a typical single-wound Denso stator with one end of each of Figure 4—Here we are measuring the AC voltage of a single phase by reading the three coils joined to form the wye connection. between two of the phase terminals. An ERA Publication. ©2014, Electrical Rebuilder’s Association. All rights reserved. No portion of the guide may be reproduced Page 2 in any way, or stored in any electronic retrieval system without the prior written consent of the Electrical Rebuilder’s Association.