Squareback vs round back alternator?

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I'm thankful for all help, so it's never too late to chime in, thank you.

It was the first thing I checked if there's an electronic ignition after I couldn't find the ballast resistor. But it's a points ignition, check the pictures. Ballast resistor is necessary. The initial problem was that the fuse for the new "ignition relay" popped from time to time and the voltage at the battery contact was fluctuating heavily (btw 12 and 18 VDC) but with the engine running smooth. So we TS the reason. Once the Vreg was replaces by an electronic modell it was working very fine, exact 14,4 VDC at battery contact. Engine starts very well.


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You are right, on the key switch is only written IGN and not IGN1, I just wrote IGN1 because I thought it's easier to avoid misunderstandings.
Later into the trouble shooting we have seen the interconnection btw IGN and IGN2 just behind the key switch. I'm sure who ever worked here was smart and did the modifications for certain reason but also with the help of the other fellow forum users we couldn't find the reason for not having a ballast resistor except if the ign coil has already an internal one. THe coil didn't smell, nor was it looking overheated etc. So we decided to install a 0,6 Ohms.

As I wrote in post #72 the voltages measured at the ballast resistor (I modified the text and numbers as follows):

lower contact "A" (IGN from starter switch and IGN from Vreg)
engine off, key in RUN pos.: 11,7 Volts and dropping slowly
Engine cranking: 9-10 Volts
Engine idles and higher rotations: up to 14,4 Volts.

upper contact "B" (coil + and IGN 2 from key switch)
Engine off, key in RUN pos.: 7,5 Volts (means the voltage is reduced by the ballast resistor with engine off)
Engine cranking: 10 Volts
Engine idles and higher rotations: up to 13,8 Volts -> This I don't understand it should have lower voltage as well but it's math, Ohm's law...
We want the Voltage at the coil at max 8 Volts with engine running above idle were we have 14,4 VDC .
So it needs to drop 6,4 V. If I calculated right we need roughly a 2 Ohms resistor.


IMG-20220325-WA0002.jpeg
 
I used a square back on my 71 Polara in my avatar. It's a 440 with AC. The square part of the alternator is tight up against the head, I had to space it out a bit. I got an original round back with the 2 fields rebuilt, but haven't yet installed it. The guy at the rebuild shop said it shouldn't really be a problem- I have 15,000 miles on it that way. I was concerned that the heat transfer from the head would boil the grease out of the rear alt bearing.
 
The revised squarebacks are slightly larger than the regular ones.

CLBER said:
We want the Voltage at the coil at max 8 Volts
Click to expand...
Why?
Note the ballast resistor is meant to be a temperature sensitive device. The theory was that during highway speed driving it would be air cooled, and have less resistance so provide more current at these higher rpms. That would help compensate for the loss of time between sparks.
CLBER said:
This I don't understand it should have lower voltage as well but it's math, Ohm's law...
Click to expand...
The measurements at the ballast connection need to be compared with the supply voltage.
When the battery is turning the starter, the supply voltage is low. There also may be resistance in the circuit.

When the engine is running, the supply voltage at the alternator may be high. a little will be due to the regulator being temperature dependent. Cold engine compartment will result in slightly higher voltage. Often we find voltage of the alternator high due to resistance in the circuit. This is especially so immediately after starter because the high current supplied current for battery charging.

I don't know how you have rearranged the relays and extra fuses etc. So the following illustration is simply using the factory configuration. In this example there are two poor junctions and the rest of the wiring is perfect.
upload_2022-3-28_15-25-55.png

The alternator is producing power at 15.0 Volts.
WHY?
Because the regulator is sensing the system voltage is low. It brings the alternator voltage up enough so the regulator is at least seeing its minimum setpoint of 13.9 Volts.

The first voltage drop effects the entire system. All 12 amps flow through it. Voltage drops from 15 to 14.3 Volts.
change in V = I x R. 0.7 V = 12 amps x R
Therefore resistance is 0.06 Ohms.
It doesn't take much resistance to ruin our day.

As the battery charges, this voltage drop goes down.

The second voltage drop in this example is 0.4 Volts.
This will remain about the same since field and ignition requirements do not change significantly.

Troubleshoot by comparing voltages and/or directly measuring voltage drop between connections in the wiring.
The resistances are too small to read directly.

Also as Dana mentoned earlier, at idle speeds these alternators don't produce much power. With the engine around 700 to 800 rpm the power should be enough for most purposes. The shop manual load tests were at 1250 rpm.
 
Just to add to disussion . If you have a 360 with older Edelbrock aluminum heads squareback alternator won't fit. It is too wide at least on mine anyway
 
Wayne Rider said:
Just to add to disussion . If you have a 360 with older Edelbrock aluminum heads squareback alternator won't fit. It is too wide at least on mine anyway
Click to expand...
Do you instead mean "thick", i.e. in the axial direction of the engine? If so, that depends upon where the alternator's pulley needs to sit. Perhaps it was always on the innermost crankshaft pulley, with 2 belts used for factory AC. I have read that some aftermarket "racing" dampers are thicker so push the crank pulleys out. Anyway, many pulley and belt combinations, so not everyone will have the same issues. I thought the roundback and squareback alternators have almost the same max thickness, though the contours of the bodies vary, so a roundback might squeeze in better some places.
 
BillGrissom said:
Do you instead mean "thick", i.e. in the axial direction of the engine? If so, that depends upon where the alternator's pulley needs to sit. Perhaps it was always on the innermost crankshaft pulley, with 2 belts used for factory AC. I have read that some aftermarket "racing" dampers are thicker so push the crank pulleys out. Anyway, many pulley and belt combinations, so not everyone will have the same issues. I thought the roundback and squareback alternators have almost the same max thickness, though the contours of the bodies vary, so a roundback might squeeze in better some places.
Click to expand...
Yes I mean thick and I only have one pulley (no A/C ) i am not sure I am hoping roundback will fit . I am waiting on order to arrive. I was told roundback would work. The squareback will not set in place I am using aluminum mounts and have aluminum billet pulleys and it would not fit between head and brackets
 
Sounds like Wayne's problem is that the pivot ears are too wide on the square-back alternator. I don't recall that dimension being any different in the roundback alternators. Usually, the issue is the other way, where spacers are needed to fit the ears between head and brackets. I recall that spacers were used in many factory setups. When you do need spacers, Ace Hardware sells blingy chrome ones in various thicknesses.
 
Thanks and I received round back alternator today . Will try it this weekend . fingers crossed !
 
I have learned so much since starting this project ( 1975 Dodge Dart Sport ) .1) If you stroke a 360 and use Eagle H beam rods you have to notch cylinders for rods to clear . 2) if you use a cam that requires roller rockers you have to buy pushrod checker and get right length plus have machine shop elongate holes to clear push rods. 3) If you use Edelbrock aluminum heads a squareback alternator won't fit must use roundback. I am not done yet still lots to learn .
 
Wayne, Don't you have a thread going about this on your car? I ask because its very confusing in this thread, and it might be clearer if it was its own thread.
Your post follows a discussion with Christian about a very early A-body with a slant six in Germany, which in turn followed a discussion about operation and performance....

Yes as mentioned in the 'sticky' revised squarebacks are physically larger than previous squareback or roundback.
www.forabodiesonly.com

Identifying Chrysler Alternators (1960-1976)

Roundback and Squareback refer to the style of housing. Roundback through model year 1969. Roundback for model years 1970-71 usually has a slightly different rear housing Squareback Revised Squareback Is most easily differentiated by the thin middle between the housings. Overall these...
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Some other threads we've discussed various pulley issues including that some of the common replacement pulleys are not quite the same as originals. Aftermarket stuff can be a pain these days.

1975 has some unique power circuit wiring and differs from '74 and '76.
 
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