Allpar Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
885 Posts
Discussion Starter #1
Is there any way to determine the amperage size of a '70s square back alternator other than the color tag - which is often absent?
FSM says they were anywhere from 34 to 65 Amp (34, 41, 50, 60, 65). This is for my '74 Cuda project. What is different between them - stator? rectifier?
The alternator that was on the car when I got it (some years ago) has no tag. Looks to me to be a rebuild / replaced - I think the date on it is '76.
Then I have a '73 50 amp unit that I picked up at a wreckers some time ago also - it still had the green tag on it. Unfortunately one of the stator terminals is damaged - might be able to fix - but not sure if 50A is good enough or what would have been original to the car. I would guess probably 50 or 60 - no power options - has rear defog, 3 spd wiper - not sure what else is extra - No A/C. I do plan to go EFI so pump will add load - but that will be offset by LED headlights.
I also have another one that is dual pulley - not sure where I got it - probably junk yard too or maybe swap meet. Case is a little different on it from the other two and what the FSM seems to show - the stator laminations are set into the front and rear housing unlike the other two which are just sandwiched between.
I might just buy a rebuilt 60A from Rockauto (Remy or Pure Energy are quite reasonable) to be sure I have a working unit. These appear to be ones with stator set into front and rear housings also.
I see you can also buy stators reasonably priced so I could rebuild one of the old ones with a new stator - but not sure which stator number I would need. The one ad I saw on ebay states one number in the description 3438754 and another on the box 3438768 - both of which appear in the '74 parts book. The parts book lists different alternator numbers but I don't see that it identifies which is which. I don't see any part numbers on the old stators and the alternator case numbers do not seem to be rating specific if I got that right.
Any knowledge appreciated. Thanks
 

·
Registered
Joined
·
885 Posts
Discussion Starter #2
So I did find a table in the parts book that listed ampacity for each alternator number and then the internal parts below that. So it looks like in '74 anyway everything up to and including the 50A used all the same parts! Same rotor, same stator, same rectifier - and all other components listed. Was this just a marketing thing? 60 and 65A have distinct parts. And that ebay listing must be one or the other - probably 60A per the box. 60A unit used the same rectifier as the 50- but different stator and rotor - so the rectifier must be good to 60. I think I'll make one good 50 from the two I have with new brushes and maybe buy a rebuilt 60 as a back up. Can't see the car is going to need anything more than 60.
 

·
Registered
Joined
·
4,729 Posts
. . . Then I have a '73 50 amp unit that I picked up at a wreckers some time ago also - it still had the green tag on it. Unfortunately one of the stator terminals is damaged - might be able to fix - but not sure if 50A is good enough or what would have been original to the car. I would guess probably 50 or 60 - no power options - has rear defog, 3 spd wiper - not sure what else is extra - No A/C. I do plan to go EFI so pump will add load - but that will be offset by LED headlights. . . . .
If you are going to install EFI then a 60 amp alternator is going to be very marginal with engine idling. At 500 - 600 engine rpm you are only going to produce about 1/3 of the alternator rated maximum output. So that makes about 20 amps available which is insufficient with EFI and expect to have anything left over for other electrical functions on the vehicle.

In the 1980s when Chrysler started equipping vehicles with EFI typical alternator capacity was raised to about 90 amp output. Also you need to consider using a 6 gauge wire to carry the electrical current at maximum alternator charging capacity to the battery.
 

·
THE MAD DUCK
Joined
·
2,386 Posts
A Warning if you put a Bigger Alternator in your Project Car make sure you put in Larger Sized Wire from the Alternator to where it goes electrical system.
I went from a 45 Amp Alt. Round Style to a 78or 80 Amp Square Back one and Promptly Toasted the Wire.
 

·
Registered
Joined
·
885 Posts
Discussion Starter #5
Good advice for sure - when I redid the wiring harnesses I did put in a #8 direct to battery in parallel with the original wire - the #8 will carry most of the current - the original wire still runs through the bulkhead and ammeter carrying a little and hopefully give me some indication of + / - current flow. If needed I could save 5 amp by changing brake, turn and reverse to LED - and markers. That with the LED H4 Headlights should offset the EFI I think. FiTech also says they modulate the pump current under light engine load. In the 80's the cars also got current sucking rear window and mirror defog and other accessories. I am going to try it with the 60 - if it does not work well I can hear the I told you so :).
 
1 - 5 of 5 Posts
Top