How Do I Determine The Amps Of My Alternator?
- Thread starter kend
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Rapid Robert
Well-Known Member
pretty sure the 78 amper has the thin stator (in between the 2 case halves) as opposed to to wide one used on all of the earlier alts
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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You do a full-field test. If it blows the headlights out, she's a size large.
Kidding! of course
IIRC there are about a half dozen different sizes /types of passenger car units, up to the mid/late 80s ; A) early, non-isolated field roundbacks B) late, isolated field roundbacks, and C) squarebacks .The square/round refers to the diode heat exhaust openings.
Roundbacks
The early ones were small 35/45amp or so jobs. The later ones mighta pushed 60amps. The above mentioned thin stators refers to the exposed portion of the field coil cage. When you take them apart you find that the coil is actually bigger than the earlier lo-pos . The lo-pos are in the neighborhood of 1/2 inch to 5/8 worth of exposed laminations, while the hi-pos are less than half that. I've had lots of those apart.The small ones usually have only a single-groove pulley.
Squarebacks,
I can't recall much about these, cuz I haven't had much to do with them other than RnRs. They usually have two-groove pulleys.
These are heavy duty.I don't recall their ratings; maybe 75 to 100
This is what I recall
Oh and the chassis wiring for the squarebacks is much more robust.
Kidding! of course
IIRC there are about a half dozen different sizes /types of passenger car units, up to the mid/late 80s ; A) early, non-isolated field roundbacks B) late, isolated field roundbacks, and C) squarebacks .The square/round refers to the diode heat exhaust openings.
Roundbacks
The early ones were small 35/45amp or so jobs. The later ones mighta pushed 60amps. The above mentioned thin stators refers to the exposed portion of the field coil cage. When you take them apart you find that the coil is actually bigger than the earlier lo-pos . The lo-pos are in the neighborhood of 1/2 inch to 5/8 worth of exposed laminations, while the hi-pos are less than half that. I've had lots of those apart.The small ones usually have only a single-groove pulley.
Squarebacks,
I can't recall much about these, cuz I haven't had much to do with them other than RnRs. They usually have two-groove pulleys.
These are heavy duty.I don't recall their ratings; maybe 75 to 100
This is what I recall
Oh and the chassis wiring for the squarebacks is much more robust.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
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- 24,937
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- 12,287
Would that be an A/C car then?
The square back style alternator has 2 types. The easiest way to tell them apart is by the width of the stator ring. The narrow width type is rated at 78 amps, the other is rated around 60. The problem is if you have a rebuilt wide stator type, you don't know if the stators and rotors have been swapped with the lower power ones. The only way to know how much power you actually have is to have them tested with a carbon pile load tester such as a Sun VAT 10 through 60.
Cut it in half and count the rings....
I don't have one handy but is there a part number on them somewhere?
Yes
There are some numbers on it but I'll have to clean it up a bit and take a better look.
The shop manual has a test you can do when its in the car. It's a test done at 1250 rpm but requires the heavy 'carbon pile' resistance to simulate load, an ammeter and voltmeter.
1968 Plymouth alternator Current Output specs from page 8-96
Standard w/ slant 6, 26 Amps
Standard all others, 34.5 Amps
Heavy Duty or with A/C, 44 Amps
Special Equipment, 51 Amps
All above are allowed plus minus 3 Amps for temperature variation.
Current Output above is measured at the alternator with the engine at 1250 RPM and 15 Volts. If current is measured at Battery, output is expected to be approximately 5 Amps less. Voltage is controlled by a variable load (carbon pile) across the battery.
Know that the outputs above are test specs, not the maximum current. The factory test spec and the parts store rating will not match. Ratings are almost always based on maximum output (higher rpm) and with voltage anywhere from 13.5 to 15 V. Later shop manuals did sometimes equate the test output to the alternator 'ratings'.
1968 Plymouth alternator Current Output specs from page 8-96
Standard w/ slant 6, 26 Amps
Standard all others, 34.5 Amps
Heavy Duty or with A/C, 44 Amps
Special Equipment, 51 Amps
All above are allowed plus minus 3 Amps for temperature variation.
Current Output above is measured at the alternator with the engine at 1250 RPM and 15 Volts. If current is measured at Battery, output is expected to be approximately 5 Amps less. Voltage is controlled by a variable load (carbon pile) across the battery.
Know that the outputs above are test specs, not the maximum current. The factory test spec and the parts store rating will not match. Ratings are almost always based on maximum output (higher rpm) and with voltage anywhere from 13.5 to 15 V. Later shop manuals did sometimes equate the test output to the alternator 'ratings'.
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