Round Back Alternator Rebuilder

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I had mine rebuilt by Sound Starter and Alternator Rebuild. Been in Tacoma, WA since 1974. Excellent work, easy to work with. A one man shop and it's all he does. soundstarterandalternator.com It's a local business for me so if I can be of any help let me know. I specifically wanted a stock amperage alternator after a misadventure with a pretty alternator that turned out being over 100 amps. He tested all my cores, labelled them by output and rebuilt the one that I chose
What I'd really like to do is get the output at various rpms for some of the factory alternators.
Then we'ld have a baseline to judge others on.

FWIW I have a VAT 40 so can check output for an alternator that's on a running engine. If someone needs and is in the area, we can do that.
 
Difference... 2 groove was 3", 1 groove was 2.7", parts book calls for 2.5". It would probably charge with the headlights and brakes on at idle with a 2.5".
Pretty sure 2.7" OD might be 2.5" effective diameter.
I found the same OD on the factory type pulleys I have.

The V belt lengths are sometimes sized by effective length, and other times outside length.

Here's one got from OMM with the stamped number still visible.
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Just had to check. The stamped number is same as the part number for a 2 1/2" pulley
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according to my FSM for 1970:
alternator amps for 198 and 225 - 26 +/- 3amps
for V-8 - 34.5 +/- 3 amps
for vehicles with AC - 44.5 =/- 3 amps
for Special Equipment (fleets) - 51 +/- 3 amps
(NOTE- these vehicles had a factory bypass of the bulkhead connections for the main power wires, which were passed through the firewall in 2 grommets)
the +/- 3 amps is to recognize the variations in temperature. Current output is measured at 1250 rpm and 15 volts at the at the alternator. If measured at the battery current output will be approximately 5 amps lower than the above values.

good luck finding a replacement alternator that tests out under 90 amps. They think they are doing you a favor...
 
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Guess you'ld be surprised then.
Most parts store alternators will max out well below 90 amps, even at 2000 rpm and 14.0 Volts.
(discussing these Chrysler alternators not late model denso or anything like that).
There are various ways to make the output amperage higher, but there's only so much room inside a round back or even a regular squareback.

Getting higher output from a revised squareback is easier.
Here's a test sheet that came with a remanufactured '78 amp' revised squareback.
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A couple things to keep in mind when looking at the remanufacturers test results:
RPM is alternator rpm.
The load was applied while holding 13.2 Volts. (If it was regulated to 14 or 15 Volts, the output power would be the same and therefore the current output will be less)

Also notice the field current draw is 6.8 amps !
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So I guess this may leave you wondering why I'd want to measure some original or semi-original alternators.
A. Because its not clear how Chrysler rated their alternators. Most, but not all, years the Chrysler alternator ratings are higher than the 15 V, 1250 rpm test results. Ratings slapped on alternators seem to be based on whatever criteria a manufacturer wants to use. A Cardone 60 amp could be the same as a Chrysler 50 amp.

B. We know that some combinations of stator and rotors can produce more power at higher rpm, while reducing capacity at low rpm.

Here's set of output curves for GM's 10SI alternator which illustrates that.
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The '63 amp' can produce more power than the '40 amp' at all rpms.
On the other hand the '72 amp' alternator can not produce more power than the '63 amp' alternator at low rpms.

And here again we apparently have yet a different voltage used in an output test. I say 'apparently' because this is graphic is from their catalog so is unlikely an actual test of a specific alternator.
 
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Strangely, the square-back alternators in my 1982 Dodge Aries 2.5L would fail the diodes regularly. Only the 3 diodes on the rail hanging in the air (positive?), visible thru the openings. The other 3 diodes on the rail which clamped to the housing (negative?) never failed. Eventually, I would buy just the diode set from an auto electric supplier, and got good at splitting the alternator case and installing them, working underneath the AC compressor so I didn't have to unbolt the AC compressor. Figuring overheating was the culprit, I started cutting cooling fins in the rail, which seemed to last 2 years instead of the normal 1 year. The guy at the shop said those diodes regularly failed. I suspect the transverse engine mounting was the cause, since one never heard of them failing in RWD cars of the same time. The Aires still had a carburetor with mechanical fuel pump, but did have an electric radiator fan, so perhaps that load was a reason.
 
Strangely, the square-back alternators in my 1982 Dodge Aries 2.5L would fail the diodes regularly. Only the 3 diodes on the rail hanging in the air (positive?), visible thru the openings. The other 3 diodes on the rail which clamped to the housing (negative?) never failed. Eventually, I would buy just the diode set from an auto electric supplier, and got good at splitting the alternator case and installing them, working underneath the AC compressor so I didn't have to unbolt the AC compressor. Figuring overheating was the culprit, I started cutting cooling fins in the rail, which seemed to last 2 years instead of the normal 1 year. The guy at the shop said those diodes regularly failed. I suspect the transverse engine mounting was the cause, since one never heard of them failing in RWD cars of the same time. The Aires still had a carburetor with mechanical fuel pump, but did have an electric radiator fan, so perhaps that load was a reason.

thermal is the typical failure mechanism (or a large reverse voltage spike that could break them down backward).
 
The V belt lengths are sometimes sized by effective length, and other times outside length.
Just was looking through my notes
Dayco part number for v-belts consists of nominal top width followed by effective length.
For example. 15480 is 15/32 wide, 48.0 inches effective length, 48.6" overal length.

For the later water pump and pulleys, a non-a/c, non-p/s LA engine Dayco lists a 15475.
Chrysler books show a belt listed as 47.76" O.S.

For the early LA water pump and pulleys Dayco lists the 15470 belt.
The shop manuals show the belt length as 46.50" O.S.
 
Just was looking through my notes
Dayco part number for v-belts consists of nominal top width followed by effective length.
For example. 15480 is 15/32 wide, 48.0 inches effective length, 48.6" overal length.
...
Good info. People fret too much over factory belts. Long ago, I downloaded a belt catalog (Gates, Goodyear, forget). For V-belts, there are 3 basic widths and lengths in 2" increments, captured in the PN. Measuring the length you need is the trickiest part. Try marking on a stiff 1/4" poly rope. Once you get the PN, go to ebay and Amazon and also look at "alternate PN". Some belts are fancier, like Goodyear's Gatorback, some with angled teeth to run smoother and/or quieter. Carry your old belt in the trunk for emergencies.

For your newer engines, "serpentine" belts are termed "Multi-V" and come in several "number of V's" (count your pulley grooves) and lengths. Tip - if your underhood belt route label shows a non-AC option, smart to buy that belt for your AC car so you might bypass a seized AC pulley (clutch bearing) to avoid a tow.
 
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