#21  
Old 05-08-2012, 10:52 PM
george kujanski's Avatar
george kujanski george kujanski is offline
Ultimate Warrior
 
Join Date: Jan 2000
Location: palatine, il. USA
Posts: 7,832
Default

Here are the specs for the Delco 12SI 94A. As you can see, full rated output is 94 A, slightly over 5000 shaft RPM. This is typical for alternators.....the output maxes out in that range. At 2000 shaft RPM you get about 50A, which will correspond to about 1000 engine RPM if your pulley ratio is 1:2. (alt =1/2 the size of the crank pulley)

With a larger pulley ratio, you will get more output at the same engine RPM; the output curve is fairly steep in that range, so a small change in engine RPM or pulley ratio will make a big difference.

The curve is usually done at 14.0 volts out, alternator temperature stabilized. I don't recall what ambient temperature is used, but the important thing is the output will increase if the air temp is cooler and therefore the alt temp is also less.

The test conditions probably are similar to underhood operation with A/C on, running for an extended length of time so the alt temp has stabilized.

When comparing output ratings, the temperature conditions should be known, since an alt can output substantially more current when the machine is not stabilized at normal operating temp.

George
Attached Thumbnails
Click image for larger version

Name:	delco_12SI_specs.jpg
Views:	68
Size:	51.4 KB
ID:	283984  

__________________
"...out to my ol'55, I pulled away slowly, feeling so holy, god knows i was feeling alive"....written by Tom Wait from the Eagles' Live From The Forum
The Following User Says Thank You to george kujanski For This Useful Post:
  #22  
Old 05-09-2012, 08:08 AM
highrisk's Avatar
highrisk highrisk is offline
Ultimate Warrior
 
Join Date: Mar 2004
Location: Jackson, MO
Posts: 1,276
Default

Quote:
Originally Posted by george kujanski View Post
Here are the specs for the Delco 12SI 94A. As you can see, full rated output is 94 A, slightly over 5000 shaft RPM. This is typical for alternators.....the output maxes out in that range. At 2000 shaft RPM you get about 50A, which will correspond to about 1000 engine RPM if your pulley ratio is 1:2. (alt =1/2 the size of the crank pulley)

With a larger pulley ratio, you will get more output at the same engine RPM; the output curve is fairly steep in that range, so a small change in engine RPM or pulley ratio will make a big difference.

The curve is usually done at 14.0 volts out, alternator temperature stabilized. I don't recall what ambient temperature is used, but the important thing is the output will increase if the air temp is cooler and therefore the alt temp is also less.

The test conditions probably are similar to underhood operation with A/C on, running for an extended length of time so the alt temp has stabilized.

When comparing output ratings, the temperature conditions should be known, since an alt can output substantially more current when the machine is not stabilized at normal operating temp.

George
George,
Thank you for that information. So if you are running the 8" AC crank pulley and a stock size alternator pulley you would actually have close to 60 to 65 amps at an idle of 900 to 1000. That should handle all of my current requirements, maybe even an electric fan as long as I am careful not to get a power hog.
Thanks again for your time and experience.
Dale

  #23  
Old 05-09-2012, 10:21 AM
highrisk's Avatar
highrisk highrisk is offline
Ultimate Warrior
 
Join Date: Mar 2004
Location: Jackson, MO
Posts: 1,276
Default

George,
One other question.
I plan on upgrading the cable from the battery to the starter to a 2GA. I am also going to run a 6GA or 8GA from the alternator directly to the battery. Should I also leave the stock 10GA wire from the alternator to the starter or disconnect it from the alternator? I know this wire will need to be connected to the starter because it runs all of the cars electrical needs.
Thanks again,
Dale

  #24  
Old 09-26-2022, 07:39 PM
Hotrodjohn71 Hotrodjohn71 is offline
Senior Member
 
Join Date: Oct 2020
Location: Fair oaks Ca 95628
Posts: 223
Default

Highrisk,
I know it's been a while but in #12, you mentioned possibly leaving your stock alternator wire in place and adding an 8ga wire beside it to handle the new highest output of the new alternator..
Did having those 2 output wires together work out ok?

  #25  
Old 09-26-2022, 07:45 PM
highrisk's Avatar
highrisk highrisk is offline
Ultimate Warrior
 
Join Date: Mar 2004
Location: Jackson, MO
Posts: 1,276
Default

Yes it did, it worked great. I ran the extra wire directly to the battery.

Dale

__________________
1969 428
Tremec 5 Speed
U.S. Army Retired
Retired Helicopter Pilot
The Following User Says Thank You to highrisk For This Useful Post:
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 03:05 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017