Re: Charging question

Posted by DavidPackard On 2018/10/29 11:52:46

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