I’m putting vintage air on my wagon and the compressor bracket necessitates a GM alternator. I need about 100amps, I don’t know anything about GM alternators, What do I need, 1 wire? 3 wire? is there one I can buy at the local parts store? thanks for the education!
The is basically three types of alternators working on how many amps output and what RPM of the "" alternator speed" Most Older Gm between 35 & 65 amp (example) @ 1,000 rpms around 15 amps Above 3,000 rpms 65 amp ish This is Rpm's of alternator Not engine Rpms , Example Some alternator are 3 stage , 3 different amperage output 3,000 35amp , then 6,000 65 amp Then 12,000 100 amp One place You can read about this at Power masters website. The more amps alternator puts out the bigger awg wire size required From alternator back to battery
If the car has an idiot light, you might want a 3 wire, so the light will work. The old design 10SI alternator was used from 1969 into the mid 80s, and is my "go to" for most retrofits. I prefer the standard design (used in cars, not tractors) 3 wire style, for one thing it's still available in stock at local parts stores, and for another is the cheapest alternator there is, usually. and it's pretty easy to adapt to lots of different engines. The current rating...hmmm....how do you know how many amps you need? It's usually a guess, based on what accessories you have. A big electric fan will drive up the current requirement.
thanks! Current is a guess, but I had a 60amp alternator and it couldn’t keep up at idle with the electric fan and headlights on. I switched to a 95amp alternator that I had and my charging problems went away. I’m estimating that with AC, electric fan and headlights 100amp would be sufficient give or take a little.
lots to read here about 1 vs 3 wire, 10si vs 12si, remote sensing, etc. and even has part numbers to make things easier MadElectrical.com - Electrical Tech -rick
@AldeanFan My self I ran into a problem alternator Not keeping up , My issue was because I needed a small compact size , 100 amp Denso , My electric fan itself Pulled 35 ish amps . @ engine rpm's of 1,000 & alt speed of 2,500 ish the alt only put out 36 amps , plus the extra 20 amps @ night my electrical needs ( 55 amp), this was only a issue @ engine Idle with a 2-1/4 alt pulley & Fan On , Batt would drain in 10 mints @ Idle from 14v to 12.2 v with Yellow top witch higher reserve amp per hour then Red top Above 1,500 engine Rpms no issue. I installed a 2 stage alt , 65 amps below 3,000 rpm's of Alt speed Above the 3,000 Alt rpm's speed 150 amps & needed to use # 4 awg charge wire
I used a single wire 100 amp GM alternator with my heat & air in our wagon. HRP Sometimes you just gotta use a few GM parts. HRP
I had issues with the fan and headlights at idle. I went to newer relays...I had an old relay set up for the headlights. made a difference. I use a one wire 100 amp at idle
Denso 2 stage Alternator , 2 functions .. Not meaning Stage 2 Its 150 amp above 3,000 Rpms of Alt Speed , Below 3,000 Rpms its 65 amps . All alternators have a Spec of Amps out put @ what Alternator Rpms speed, Most are 2 stage Most are based On 3,000 Rpm' The split between 1st and 2nd stage. For Example if not understanding the way I write , 100 amp Alternator Is above the 3,000 ish Rpm's 2nd stage The 1st stage Below 3,000 could be as low as 20 amp out put
I remember being told to get one for an 80's car with a rear window defroster element to get the highest amp output. Don't know if this is fact or not. Gary
Thanks for all the great advice. I’ve decided on an AC Delco 335-1094 It’s a 94amp 12si that came on some 80’s cars. I’ll post an update when it’s installed and working.
I understand sizing for worst case situation, but are you really going to be driving in hot weather (A/C, fan) with the lights on? If so, might as well add that sound system and wipers. FLA does crazy stuff.
last summer we got caught in the rain at the beach and stuck in traffic. The windshield was completely fogged up and it was over 30°C out, so I had the headlights and radiator fan on and would have had the defrost on if I’d had it. the cost difference between a 60amp and a 90 amp alternator is $20 so I’ll definitely go bigger.
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