Question about alternators and electric fans

[Mastiff]

I know you already ordered a new one, but I have seen some high output 12SI alternators that would quit charging at low idle speeds. It is an inherent problem with the 12SI. That is why lots have gone CS130. Hopefully this fixes yours.

If that happens I'll return it. The sites I was looking at mostly boasted about how much extra charge their units provided at idle.

It says it makes 80 amps at 2400 RPM and has a max RPM of 18000. The question is how to convert from engine RPM to alternator RPM. Just looking at the size of the pulley, it must be at least 4:1. My guess is they spec'd the 80 amps because that's the "idle" value. My existing alternator is probably less than 80 at full speed, so this should be a significant boost.

 

[thearborbarber]

Measure the diameter of the crank pulley and alternator pulley and divide the two. So if your crank pulley is 9 inches and the alternator pulley is 3 inches. That's a 3 to 1 ration. So if your engine is at 1000 rpms the alternator is at 3000 rpms.

 

[Krusty78]

Wasn't there something on Pirate about guys swapping to a chevy caprice alternator and not having to change a thing?

 

[Heavyleft]

I changed to a Caprice alternator. I dont have the specs handy on my phone but I can post it when I get home if needed. Best bang for the buck in my opinion.

 

[Krusty78]

I changed to a Caprice alternator. I dont have the specs handy on my phone but I can post it when I get home if needed. Best bang for the buck in my opinion.

If you could please sir. Direct bolt on? Did you have to change what belt you ran?

 

[Heavyleft]

I had done a write up for another group so its a bit over the top but here it is.

 

[WJACKSON11X]

Nice write up! I'm assuming this is the same alternator as the Pontiac Transport?

 

[Heavyleft]

To be honest Ive never heard anything about the Pontiac Transport alternators but if its the same model number, then it would be safe to assume its the same alternator.

 

[WJACKSON11X]

I'm pretty sure it's the same alternator, came in the Transport, caprice, Buick roadmaster, and some other vehicles. Thanks for the write up, I'll be doing this soon.

 

[Mastiff]

Is there a reason to go that route instead of with a 140 amp unit in the original size case? I just got my Powermaster in the mail and it's identical to the original size/connector wise. Looks good and was tested at 80 amps idle and 160+ at driving speed.

 

[WJACKSON11X]

I think price would be the only advantage. I picked one up for $50 from the local junkyard. Here are the factory applications if anyone is interested.

 

[Krusty78]

You think this would still work on a 78 w/ a 350?

 

[WJACKSON11X]

You think this would still work on a 78 w/ a 350?

I dont see why not. You may have to swap pulleys if you have a v belt pulley setup now. Not sure about the wiring.

 

[Mastiff]

Well, the Powermaster dropped right in, direct replacement. It keeps about 13 volts at idle with both fans and all four headlights on. I was hoping for 14.5 volts, but I guess not. The batteries may have been charging a little on top of everything else.

The little card that came with the alternator says this unit provided 97 amps at idle (2500 alternator RPM). I'm not sure how that squares with it dropping voltage in this case. With all four headlights I could be pulling 25 amps, plus maybe as much as 60 amps for both fans? Plus everything else, maybe I'm getting there...

 

[DizturbedOne]

I was going to say, before upgrading alternators... You should place a large gauge ground strap from motor to frame, and a nice negative cable from negative to somewhere close to the alt and bare metal. Make sure the positive is really solid from battery to starter.

Just the upgraded ground strap (I replaced the braided one with a short section of negative battery cable with bolt-hole tabs on each end) solved huge problems in my Camaro after a high power stereo system I had installed

If you want to go the extra mile, check this guy out, http://www.innovativewiring.com/ he will do it custom, however you want. EXCELLENT QUALITY. Got a custom set for my Camaro with an extra accessory rail for the stereo and other interior extras.

 

[Mastiff]

I have a giant welding cable from negative battery to the block. I guess the alternator ground just has to get to the block through the brackets. Could be suspect. I'll double check.

 

[WJACKSON11X]

Decided to do the swap today, but I'm confused on the wiring. Here is a pic of the stock wiring. The wire that has the fusible link goes to the BAT terminal on back of the alternator? I'm assuming the small black wire that comes from the harness goes to the small red wire on the new plug. I've got a volt gauge if that matters. I think I'm correct in the wiring, just want to make sure.

Here is a pic of how I have it at the moment. The black wire with the yellow insulation is going to Battery.

 

[WJACKSON11X]

Double post

 

[WJACKSON11X]

I figured out the wiring and everything seems to be working properly. I can now run headlights, rocklights, and spotlights and voltage doesn't drop much. I haven't checked with a meter yet, but i will. I did have to bend the upper bracket a little to get it to fit, but nothing major. I'm still a little confused if I need to run diodes or not. I have a voltage gauge and no idiot light. Can anyone help on this?

 

[WJACKSON11X]

Would it be easier to just install a light on the dash for resistance and help to monitor voltage drop? Does anyone know how to wire in a light? I'm guessing I would have to tap into the brown wire coming from the dash area and ground it on the other side.