Packard Forum Index » Post-War (1946-54)

Today's problem is electrical! I've had little opportunity to drive my car since owning it but when I have it does not seem to charge the battery adequately. An alternator from Fifth Avenue Automotive was added by a previous owner. After some research I see that this alternator should charge even at idle but instead it seems to act like a six volt generator. when idling the gage is in the discharge area and I put a meter on it and it is indeed discharging at idle. Like a generator equipped car the gage goes up as the rpm's do. Am I incorrect in my assumption that it should charge all the time? Also the original voltage regulator was still wired in except for the battery wire that goes to the alternator. I disconnected it, the regulator, and it does not seem to make a difference. Is there anything that the old unit could affect?

Thanks Don

You might check with 5th avenue on their specs or see if they have a recommended wiring diagram. Some alternators are truly single wire with self excitation at a lower engine rpm and others will still work as a single wire but need a faster rpm before anything happens. Sometimes there are extra terminals that need a switched voltage input from the key or a jumper or some other arrangement to provide faster excitation to work at low engine rpms.

All alternators have a rpm where they start to work and that range vs engine rpm depends on pulley diameters. If there is a large diameter pulley on the alternator perhaps it is not getting to the needed alternator rpm until the engine is running faster.

Thanks Howard,
I tried to call for info but got no answer and I forgot to try again. The Fifth Ave site says these alternators charge at idle speed. I believe I have the correct pulley. I still have some things to check. I'll try the company again next week if I still have a problem.
Don

Roundsy;

If Fifth Avenue agrees that your alternator may be externally excited, then you can lower the 'cut-in' by installing an 'idiot light'. Sounds strange but it works because the bulb current creates a bit more magnetism inside the alternator while it's 'off-line'.

The information you need from Fifth Avenue is;
A.) Is the alternator configured for external excitation?
B.) What is the nominal and maximum current allowed in that circuit?

On your next posting let us know what the supplier's response, plus the voltage ( 6 or 12 ) and polarity ( negative ground or positive ground ) of your car.

I've 'fixed' one of my alternator equipped old cars using this method. You can use an incandescent bulb, or an LED and resistor. Since there is a limited amount of current adjustment with the single incandescent bulb configuration I used the LED & resistor method. I tried several different resistor combinations and settled on a resistance that allowed the 'cut-in' speed of the alternator to be close to the idle speed of the engine. I put one additional switch in the circuit, which allowed me to start the engine and establish a reasonably well idle, and then I would activate the alternator. You could really tell an extra load had just been put on the engine, but that was a low horsepower, low compression ratio original Model A engine.

DP

My 54 has a standard GM 10SI 3-wire alternator, and if I restart the engine after its already warmed up, then the GEN light will come on as the engine is at a hot idle and the rpms are too low to "excite" the alternator. If I goose the accelerator to bring up the rpms for a second or so, the alternator will kick on and stay on (GEN light turns off) even though the rpms drop back down. Most alternator need to reach a certain RPM to kick on, but they dont have to stay above that RPM to continue to work.

I've observed the two items that BigKev just talked about, namely, a bit of hysteresis between the 'cut-in' and 'cut-out' speed, and a slight delay in the response of the alternator.

I would say there was about a one second delay between me turning 'ON' the excitation circuit switch and the LED turning off. That would be at the 'normal' idle speed (throttle closed, timing at full advance). The delay was somewhat longer when the engine was at the ridiculously low idle (throttle closed, timing at full retard). Once the alternator was on-line I could turn OFF the circuit, and unless I went back into the ridiculous idle mode the alternator would stay on-line. By the way the Model A distributor does not feature centrifugal or vacuum advance, but there is a lever on the left side of the steering column to adjust the spark timing. There is a bit of 'high pilot workload' when driving that car, but that's why there can be more than one idle speed.

I suspect BigKev is using the standard #55 bulb, which should draw something like 1/3 ampere (perhaps less when fully warm . . . I've also assumed BigKev's car is 6 volt). My experience is with 1 ampere current flow, albeit I tried several lower currents. I used 4 - 100 ohm resistors in parallel which is equivalent to a single 12.5 ohm resistor ( the Model A was converted to 12 volt, which started this whole mess in the first place, so my resistor values are for a 12 volt application). My mini science project included using 3 and then 2 of the same resistors in parallel. That resulted in approximately 0.4 amperes for the 3 resistor configuration, and approximately 0.25 amperes for the 2 resistor configuration. More current resulted in a lower 'cut-in' speed, while less current resulted in a higher 'cut-in' speed.

As a test, a temporary parallel circuit with another #55 bulb could be used to see if the alternator could be convinced to work at the low hot idle condition . . . not there is anything wrong with the alternator not working at very low speed . . . I just have an aversion to seeing 'red lights'. I have an excerpt from a mid '70s Oldsmobile shop manual, it shows a resistor in parallel with the indicator bulb, so that manufacture was using parallel circuits to control the current flow to the alternator during periods of 'off-line' operation. I suspect the resistor was the control, while the light was just for us. That wiring diagram references the resistor as 10 ohms, which would result in approximately 1.25 ampere current (12 volt application). I would expect if BigKev doubles the current flow by adding a second #55 light bulb circuit he should see a difference in the hot idle 'cut-in' speed.

It's not clear to me if the generator/regulator indicating bulb in a '51-'54 Packard acts as a source of excitation, or is merely an indicator. If the intent was that of an indicator only the bulb size may not be optimized for the modern alternator excitation task. Even if the bulb was instrumental in the excitation of the generator I suspect optimization would still be in order for the Delco 10SI.

Since Roundsy's 23nd series car should have an ammeter, and not an 'idiot light', then some type of additional wiring will be in order to move the 'cut-in' speed to a lower value. I would be inclined to follow the GM design of using a parallel resistor & bulb circuit. I've used Radio Shack 12V LEDs on my 6 volt Packards, and the LEDs seem to work just fine and are available in several colors. Since the current flow of the LED is trivial the resistor should be sized to limit the excitation current to whatever Fifth Avenue suggests. For resistors I use Ohmite brand that are packaged in a fined aluminum housing.

DP

I spoke to someone at Fifth Ave this morning. He assured me that no extra, external excitation is needed. These alternators should charge from about 300 rpm. The alternator is either wired in wrong, which I don't believe to be the case or the pulley is too large. It may be the pulley. I thought it was correct but after further inspection I think it may be bigger than I thought. It's very difficult to see and I really wish I had undertaken this when the radiator was out recently. I'll try to get it apart one day soon and figure it out. The car still is a 6 volt system that has been converted to negative ground, probably for the purpose of installing this alternator.
The pulley that is on it now also drives the power steering pump so that is another concern if I need to change the pulley. The fun never stops!
Don

Reading about these alternators on their website, converting to negative ground is indeed required. As I recall from his blog, BigKev's 1954 Clipper was converted to 12v.

On a 3 wire alternator, the "Idiot" light is not an exciter. If the alternator is producing voltage then the light goes out, otherwise, that terminal is acting as a ground, and the light comes on as the power from the ignition switch ON is flowing through the filament to the that "ground".

Quote:
6V positive ground alternators are readily available although on the ones I have looked into the rated amp capacity seems to be less than the equivalent model in a negative ground configuration.