twister360
Well-Known Member
Advantage/disadvantage?
Explain square back alternator
- Thread starter twister360
- Start date
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71DodgeDemon340
Well-Known Member
Square back?
CudaJunction
Well-Known Member
70 up use a square back better because it uses dual fields. 69 down use a round back alt 1 field.
71DodgeDemon340
Well-Known Member
Oh gotcha lol idk older style is easier to wire right
twister360
Well-Known Member
Thanks, I thought there might be a slight difference regarding clearance. I suppose they are not interchangeable.
It has a square back, not a round back.
Pete in NH
Well-Known Member
Hi,
In the 60's and 70's Chrysler used three basic styles of alternators. Up to 1969 they were round back, single field terminal alternators. One field brush was internally grounded, used an electro-mechanical regulator and the diodes were pressed fit into heat sinks in the rear of the alternator. These alternators did not produce much output at idle and were good for 30 to 45 amps depending on engine size and whether A/C was installed on the car.
1970 and 71 saw the introduction of electronic voltage regulation and the round back alternator now had both brushes brought out to insulated terminals. One brush was connected to 12 volts with the ignition on and the other brush connected to the regulator which provided a variable path the ground.
1972 and up saw the square back alternator introduced. It had a higher output at engine idle and was available in versions up to 60 amps. The big change was in the rear casting of the alternator which was redesigned to use a cheaper pellet diode rectifier assemblies rather than the older press fit diodes and heat sinks.
In many cases if it will physically fit the square back unit will give you a better output at idle and a little more maximum output. They are completely electrically interchangeable with the 70 and 71 round backs and can be used on 69 and earlier cars if you ground one brush terminal. This assumes you don't care too much about original appearance.
In the 60's and 70's Chrysler used three basic styles of alternators. Up to 1969 they were round back, single field terminal alternators. One field brush was internally grounded, used an electro-mechanical regulator and the diodes were pressed fit into heat sinks in the rear of the alternator. These alternators did not produce much output at idle and were good for 30 to 45 amps depending on engine size and whether A/C was installed on the car.
1970 and 71 saw the introduction of electronic voltage regulation and the round back alternator now had both brushes brought out to insulated terminals. One brush was connected to 12 volts with the ignition on and the other brush connected to the regulator which provided a variable path the ground.
1972 and up saw the square back alternator introduced. It had a higher output at engine idle and was available in versions up to 60 amps. The big change was in the rear casting of the alternator which was redesigned to use a cheaper pellet diode rectifier assemblies rather than the older press fit diodes and heat sinks.
In many cases if it will physically fit the square back unit will give you a better output at idle and a little more maximum output. They are completely electrically interchangeable with the 70 and 71 round backs and can be used on 69 and earlier cars if you ground one brush terminal. This assumes you don't care too much about original appearance.
The Neens
Well-Known Member
Pete in NH just solved my current (pun intended) issue...Thanks 
BillGrissom
Well-Known Member
Search posts by 67Dart273 on alternators. He has photos and descriptions of all types and how you can wire them. If a square-back will fit (usually), it is preferable. You can easily wire it to work w/ 1969- regulator wiring. Most 2000+ Chrysler alternators still have the same "external regulator" design, so can be wired similar.
I'll simply add that these worked fine in RWD cars, but when they continued them in FWD (like my 1982 Aries), the diodes regularly failed, probably from not enough air flow. I got good at splitting the alternator open under the AC compressor (so didn't have to remove that) and changing the "floating diodes" that vaporized every year. By cutting cooling slots, I could get them to last 2 years.
I'll simply add that these worked fine in RWD cars, but when they continued them in FWD (like my 1982 Aries), the diodes regularly failed, probably from not enough air flow. I got good at splitting the alternator open under the AC compressor (so didn't have to remove that) and changing the "floating diodes" that vaporized every year. By cutting cooling slots, I could get them to last 2 years.
Integrating the square back alternator, and the newer style voltage regulator is super easy in these old cars! The 2 voltage reg wires are the same color from early to late, so a quick splice in of the newer style plug is a snap, and adding the 2nd field wire is a snap too, right into the same splice!!! Boom, upgrade, and electronic ready if you're still running points!! Geof
It's better than the hunchback...
67Dart273
Well-Known Member
Don't confuse "square back" with "isolated field." The "dual field" (wrong terminology) isolated field alternator came out in 1970 with the newer style electronic regulator The "square back" didn't come out until a year or two later.
(The isolated field round back is still pictured in the 71 shop manual, squareback in 72)
You can ground one field terminal of any isolated field unit and use a 69/ earlier style regulator.
Other than being electronic, there is no real advantage to changing the circuit. That is, grounded or isolated, you can build good regulators either way. You CAN BUY good regulators for the older grounded field.
The advantage, then, of a "square back" is what?
The advantage is, that the square back marks a design change that puts out more amperage at lower RPM.
If you are willing to run some of the newer Mopar or Denso stuff, it gets even better in that regard.
THE THINGS YOU MUST WATCH FOR
Below is a "back woods rebuilder special." Do not ever accept one of these unless you are "stuck on the road." Rebuilders do "these" all the time. See the hole at 12 o'clock? A rebuilder drilled that so that they could CONVERT a 69 alternator into an isolated field 70
Below shows a CONVERTIBLE round back and a newer square back. This (round) one is a mystery to me. It may have been production "near the end" before the square back came out. It has been MADE with BOTH grounded and isolated brushes. The empty hole you see at 3 o'clock is for the isolated brush, the grounded brush being installed at 9 o'clock and the remaining insulated / isolated brush at 12 o'clock. This casting was made to be used either as a 69 or as a 70 / later
A quick shot showing 69 /earlier mechanical regulator and 70 / later electronic / isolated field
(The isolated field round back is still pictured in the 71 shop manual, squareback in 72)
You can ground one field terminal of any isolated field unit and use a 69/ earlier style regulator.
Other than being electronic, there is no real advantage to changing the circuit. That is, grounded or isolated, you can build good regulators either way. You CAN BUY good regulators for the older grounded field.
The advantage, then, of a "square back" is what?
The advantage is, that the square back marks a design change that puts out more amperage at lower RPM.
If you are willing to run some of the newer Mopar or Denso stuff, it gets even better in that regard.
THE THINGS YOU MUST WATCH FOR
Below is a "back woods rebuilder special." Do not ever accept one of these unless you are "stuck on the road." Rebuilders do "these" all the time. See the hole at 12 o'clock? A rebuilder drilled that so that they could CONVERT a 69 alternator into an isolated field 70
Below shows a CONVERTIBLE round back and a newer square back. This (round) one is a mystery to me. It may have been production "near the end" before the square back came out. It has been MADE with BOTH grounded and isolated brushes. The empty hole you see at 3 o'clock is for the isolated brush, the grounded brush being installed at 9 o'clock and the remaining insulated / isolated brush at 12 o'clock. This casting was made to be used either as a 69 or as a 70 / later
A quick shot showing 69 /earlier mechanical regulator and 70 / later electronic / isolated field
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