ELECTRICAL REBUILDER’S ASSOCIATION—Technical Document CS201411A www.electricalrebuilders.org STATOR “ N J N POSITIVE <~__ TRIO OUTPUT Figure 1—Delco-Remy Auto-Start trio with the terminals labeled. TRANSPO Testing The Auto-Start Trio BY BOB THOMAS he Delco-Remy Auto-Start trio was initially introduced with the 22SI alternator and has been around for over 17 years. However, many rebuilders may still not know how to test one. The Auto Start is basically a package of three components: a diode trio, a capacitor and an electronic circuit that senses stator voltage and applies excitation voltage to the field (see Figure 1). Operating much like AC-activated self-exciting regulators, Auto Start activates the field circuit through the trio once it senses any voltage on the stator. While stator voltage must exceed .7 volts in a normal trio before any current can get to the field, the Auto Start momentarily applies full battery voltage once stator voltage reaches a relatively low threshold—well below what a normal trio can manage. The result is a very fast alternator turn- on, even below engine idle speed. To test an Auto- Start trio, all you need is a voltage regulator ‘ » Ac tester with a output connection and stator ow POWER positive and negative rectifier legs on the Auto-Start trio. Attach the tester’s stator test lead to the stator leg closest to the Auto Start’s electronic package as shown. Connect your voltmeter between the negative leg and the trio-output leg of the Auto Start. The Auto Start contains a capacitor, so do not be alarmed if you see voltage before you turn on the regulator tester. Give it a few moments for the capacitor to discharge below one volt. Then turn on the regulator tester (see Figure 3). If you see a reading that is close to 12 volts, the Auto Start is functioning properly. In the event that you do not have a regulator tester, or if you would just like to test it as it works inside the alternator, you can hook it up to any alternator that allows access to a stator connection. Here we used a CS130D, because the back plastic cover is easily removed. We also removed the regulator from this alternator to ensure that no voltage could be applied to the rotor during the test. That way, we could be certain TRANSPO a voltmeter. In lieu of a 3 dies SHORT POSITIVE bigs STATOR regulator tester, you could PS}. een, 0 |% - also use an alternator on ue: your test bench. We will demonstrate both. If you have a regulator tester, simply hook up the trio as shown in Figure 2. Notice that the tester’s positive and negative leads are connected to the Figure 2—Auto Start connected to a regulator tester. Voltmeter shows voltage on the trio with tester off. Figure 3—With the tester on, trio voltage is over 10 volts and sufficient to excite the field circuit. 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 CS201411A www.electricalrebuilders.org that the Auto Start would operate from residual magnetism only. We connected the Auto Start to the alternator in the same way that we connected it to the regulator tester, using the positive, negative and stator connections on the trio (see Figure 4). The voltmeter on the right side in the photo is connected to the Auto Start between field and ground. You can see that we also used a second voltmeter set to AC voltage and connected it between the two unused stator leads on the alternator. The second meter provides the exact voltage in the stator during the test. You do not really need the second meter, but we wanted to watch the stator voltage build as we slowly increased the alternator’s shaft speed. Notice that when battery power is applied, even before spinning the alternator, there is .18v on the trio- output leg of the trio. That is the standby current, supplied to the field through a 1.4 mega-ohm resistor in the Auto Start. This is to ensure that there will be magnetism in the rotor for a quick start, but at the same time minimize parasitic drain to a few milliamperes. As we begin to turn the alternator, voltage builds in the stator (see Figure 5). Once the stator voltage reaches the threshold, it will apply battery voltage to the field (see Figure 6). Notice that this Auto Start turned on the field before the stator voltage even reached .4v with shaft speed of the test alternator below 200 rpm. Keep in mind that Auto-Start trios can be used in 21S] alternators, and there are several aftermarket versions available. Boa Figure 5— With the CS130D turning slowly, AC voltage builds in the stator but there is no change in output. Figure 4— Auto Start connected to CS130D at rest. The left meter shows stator volts, the right meter shows trio output. Figure 6-—Once stator voltage reaches the .35 volts threshold, battery voltage is applied to the trio. 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.