Re: Stewart's 1955 Packard 400

Posted by DavidPackard On 2024/1/26 0:01:36

Stewart, I’ve added a few thoughts if you elect to change to an alternator. The 12- / 12+ question was asked to help guide discussion later in the process.

The ‘problem statement’ of swapping from a generator to an alternator has been done perhaps hundreds of thousands of times . . . well maybe not that many, but enough so there are few unknowns at this point.

First let’s start at which brand of alternator to choose:
All of the ‘big three’ products had unique to the brand alternators, but I would suggest the Delco units found on GM products. From a financial standpoint the 10SI or 12SI units are the smart choice (opinion). The difference between the two models is the self-cooling ability. The early 10SI units were cooling limited to about 60A output (likely twice the output of your generator). The 12SI added additional inlet area on the rear face of the unit, and the cooling fan that had a vane shroud. The 12SI output could be at least twice of the older design, or four times the output of your generator. The extra capacity was needed when continuous high current features were added. One of the first of these features was rear window heat. The alternator for cars so equipped had a higher output alternator than cars without the rear window heat. I don’t know of any ‘downside’ of having reserve current capacity. In the OEM configurations the capacity of the charging system is matched to the load that is expected to be continuous (with little positive margin). If all of the continuous loads are powered there is little left to charge the battery or operate the transient loads (horns). So if the headlights and heater blower loads are off, technically you’re operating with reserve capacity, therefore having a bit more won’t hurt (opinion). I think a 60 A 10SI alternator will be more than enough.

The mounting of the 10SI and 12SI are identical, and there are many brackets that would be direct replacement for your generator mount. Mounting will not likely be a problem. Pulleys for most of the standard belt widths are available (and are easily changed), and there is a selection of pulley diameter available, so matching the alternator minimum speed should not be a problem.

The next subject is whether you expect to find a replacement alternator if you’re away from home on some type of a tour. Since your car is 12-volt negative ground you have a pretty good chance of finding a replacement . . . 12-volt positive ground not so much. One more consideration, that is, whether the alternator is electrically similar to the OEM configuration, or a different wiring scheme is used. Finally, we’ve arrived at the ‘one-wire’ / ‘three-wire’ conversation.
Both the 10SI and 12SI alternators are internally regulated . . . somewhat a standalone unit. These internal regulators come in several flavors that are referred to one-wire or three-wire. The OEM used the ‘three-wire’ scheme, but it wasn’t called that at the time. The first wire connection, normally a threaded post pointing straight aft, is the output of the alternator (BAT on your current regulator). Both 1 & 3 wire configurations will have the output pole. The next two connections are ¼ inch male blade connections and only apply to the 3-wire scheme. One of the connections has two functions; first it is the connection for an ‘idiot light’, while the second function is to provide external excitation to improve low speed alternator performance. The external excitation current is actually the current lighting the bulb, however there are GM designs that had a resistor in parallel with the bulb. I believe the design intent is to current limit the excitation to approximately 1 amp. The final ¼ inch male connection needs a bit of explanation. In the automotive industry there is sufficient motivation to match the design to meet the need with minimum margin. It the case of the charging system there was a desire to minimize the wire gauge size when possible, and the output of the alternator was subject to these pressures. GM (Delco-Remy being a division of same) made a lot of cars, with many different circuit lengths between the battery and alternator, and the scheme to regulate the alternators output to the battery voltage was invented. With the addition of one small circuit between the battery and the alternator the battery could be held at 13.4 volts (nominal) even with some variable voltage drop between the two. The corrector plug for the two-blade connection are available.

If you value being able to maintain your car far from home, then wiring your car the same way GM did would be a plus. If you would like to monitor the system the minimum would be an ‘idiot light’, followed by either a voltmeter, or ammeter. For my 6+ cars I bought a few digital voltmeters on EBay and wired them to a plug appropriate for the cigar lighter socket. One of the cars has a light, while the other has an ammeter . . . both have the EBay voltmeters (easily removed when the critics arrive).

Finally, if maintaining the correct under hood look is a consideration there are PowerMaster alternators that look almost like a generator. The 12-volt negative ground unit (they don’t make a 12+) is available with and without a connection for the ‘idiot light’. I have a 6+ PowerMaster on my ’48 (ammeter). I drilled the aft case to install a phony field winding connection, and added an Autolite generator tag completed the ‘look’. The only missing items are the ‘oil caps’, otherwise it’s an adequate facsimile. I left the voltage regulator on the firewall. It doesn’t do anything now, but as I think about it, that regulator didn’t do anything the last time in was trying to control the generator.
I agree with the comments about the adequacy of the OEM generator equipped charging system until your continuous load exceeds 30A. If the OEM system is complete junk adding an alternator is an easy way to return the car to service while the availability and $$ of restoring the OEM system is being investigated/accomplished. My ’54 has the OEM system that is working just fine. When I purchased the ’48 I would say the OEM system was on its last legs a few years before I bought the car.

You mentioned a Painless wiring harness. Is the car functioning now, or are you in the process of swapping the harness? If you’re installing the new harness, I would investigate what you would need if on day two you installed an alternator. As a minimum I think you’ll need a 8 – 10 gauge wire from the alternator output to the BAT connection on the regulator, and if it is a 3-wire alternator the ‘idiot light’ wire (I believe it’s tan) on the GEN (perhaps ARM) connection removed from the regulator and extended to the alternator. The other blade on the 3 wire is attached to either the battery or the large connection on the starter solenoid. The armature and field wires connected to the generator will be insulated and folded-back on the harness. I think all of that wire harness modification and additions could be added when needed. Since the alternators are internally regulated, I don’t believe the wire bonding the generator and regulator together is required but bonding the alternator housing to a ‘good ground’ would be a ‘best practice’ subject.

dp