[torqhead]

This winter I went through the process of adding A/C back on my car. This included a complete pulley set with an aftermarket aluminum bracket set up for A/C compressor, WP, PS and Alt. The day I got my A/C charged I decided to go for an afternoon test drive. Everything had seemed fine about a mile from my house and then my alternator smoked (literally was smoking). Fortunately I wasn't far from the house and made it home.

I ordered a new alternator 12SI 200 Amp, previous was a 120 Amp, and installed it. I run electric fans, fuel pump and a couple of amplifiers on a rare occasion as I like to hear the car so decided to go a little bigger to get more amperage at idle. Got the new one in, had taken the car to town and back one time no problems (10 miles round trip). Next time I went to take the car, the idiot light was on when I started it (meter check validated no charging). Had a 1 year warranty on it and got it exchanged. New one came it week later and installed it. I had the new one on the car for 2 months, estimating a couple of 100 miles. No idiot light but figured out there was a problem with charging due to my fuel pump pressure being low (another thread I had over in street if you're interested in more detail). Checked charging and discovered it was charging but not suffiently, it charges at 12.7 with my electric fans on and with them off it can't get past 13.2 ---- 2000+ RPM in both cases. Contacted the person with this info on the alternator and he indicated the first alternator was burned up (whatever that means), although it appears each alternator suffered a different failure.

First one smoked after many years of use and sounded like bearings were trashed on it.
Second one just stopped charging all together (idiot light turned on next start)
The last one charging was low but not enough to turn the idiot light on.

I was doing some searching to see what I can check for to ensure there's not something on the car that's causing these issues. For instance could it be when I use the A/C? What's some test I can pull to ensure there's not something in the car that's wiping these out or is it just bad luck as each alternator appears to have a different issue.

[torqhead]

Another question I had is what's the normal temp of the alternator on the outside?

[Bruce Meyer]

Sounds like bad luck. If a component was drawing too much current, the fuse should blow. Check all your fuses, including the one in the A/C harness, to make sure someone in the past didn't put the wrong one in or stuffed tin foil or something in its place.

[stellar]

If the 12 SI is made with a stock 94 amp rotor and is using a 200 amp stator, the volts will be low until higher rpm is applied. I would suggest (if using a 12si frame) going with a stator no higher than 140 amp and add a second battery. If you want to only use 1 battery I would suggest fiting a cs144 200 amp alt in. This unit will allow good voltage at lower rpm and is almost indestructable.

[stellar]

Hopefully the new pulleys are not a set of underdrive pulleys. If so you can expect low volts.

[gtofreek]

Originally Posted by torqhead

This winter I went through the process of adding A/C back on my car. This included a complete pulley set with an aftermarket aluminum bracket set up for A/C compressor, WP, PS and Alt. The day I got my A/C charged I decided to go for an afternoon test drive. Everything had seemed fine about a mile from my house and then my alternator smoked (literally was smoking). Fortunately I wasn't far from the house and made it home.

I ordered a new alternator 12SI 200 Amp, previous was a 120 Amp, and installed it. I run electric fans, fuel pump and a couple of amplifiers on a rare occasion as I like to hear the car so decided to go a little bigger to get more amperage at idle. Got the new one in, had taken the car to town and back one time no problems (10 miles round trip). Next time I went to take the car, the idiot light was on when I started it (meter check validated no charging). Had a 1 year warranty on it and got it exchanged. New one came it week later and installed it. I had the new one on the car for 2 months, estimating a couple of 100 miles. No idiot light but figured out there was a problem with charging due to my fuel pump pressure being low (another thread I had over in street if you're interested in more detail). Checked charging and discovered it was charging but not suffiently, it charges at 12.7 with my electric fans on and with them off it can't get past 13.2 ---- 2000+ RPM in both cases. Contacted the person with this info on the alternator and he indicated the first alternator was burned up (whatever that means), although it appears each alternator suffered a different failure.

First one smoked after many years of use and sounded like bearings were trashed on it.
Second one just stopped charging all together (idiot light turned on next start)
The last one charging was low but not enough to turn the idiot light on.

I was doing some searching to see what I can check for to ensure there's not something on the car that's causing these issues. For instance could it be when I use the A/C? What's some test I can pull to ensure there's not something in the car that's wiping these out or is it just bad luck as each alternator appears to have a different issue.

I used to rebuild alternators and diagnose starting, and charging systems for a living. When an alternator burns the diodes, or the stator, it will make a loud howling noise, much like bad bearings. The noise will get louder, the more load you put on it. Back in the 80's-early 90's, 110-120 amps was about all that could be made with a 12 SI alternator, with the stators, and rotors available then. Never seen one come close to 200 amps. We always built our higher amp alternators with diodes rated at twice the amperage as the stock alternators. If they are using standard diodes, that would explain why they keep burning up.

Other things that will cause an alternator to burn up is:
1. If it is left to charge up a dead battery.
2. You jump start someones car with your engine running. This puts an extreme load on the alternator. I charge their battery with my alternator for a couple minutes, then turn my car off, leaving the jumper cables hooked up, then start their car. This is the safest way to jump start someone.
3. High resistance in the main battery charge wire on the back off the alternator.

When it is charging low[the 12.7-13.2 you mentioned], try this. Add a temporary 10 gauge jumper wire from the alternator battery post, directly to the + post of the battery. If the charge rate goes up to 14 volts or better, you need to replace, or add another hot wire to the back of the alternator.

Also, the red wire in the alternator plug, is a battery sense wire. If it is bad, it will not sense the battery condition properly, and charge improperly. If it is attached to the hot post on the back of the alternator, I would try hooking it to the + post of the battery temporarily to see if it makes a difference in charging voltage.

These alternators are simple, and relatively fool proof. They are one of the best alternator designs ever, so it usually doesn't take much to make them charge right.

Also, higher amperage alternators tend to charge less at idle than lower amp alternators. Not in all cases, but depending on the type of stator used to get the high amperage, they usually don't charge as well at idle.

[gtofreek]

Also, just thought of another thing. If that is in fact a 12SI alternator, with an actual 12SI front housing, it has to have a plastic turbo fan on it. If it has the old style, steel fan on it, it will not cool properly, and overheat.

["QUICK-SILVER"]

Originally Posted by torqhead

Another question I had is what's the normal temp of the alternator on the outside?

That's something George K use to talk about.
The high amp converted 12's are bad about overheating. The case and fan isn't designed to do the kind of cooling needed for the work they're having to do. Thus causing overheating and early failure.

The CS144 that stellar mentioned is MADE to do the high amps. Better fan and better case venting.

[george kujanski]

Excess heat will kill alternators. they normally get hot anyway, but mismatched components, (rotor, stator) and fan, lower RPM operation such that there is not enuf cooling or a wrong fan will contribute to premature death.

The internal regulators are temperature compensated, i.e. will charge at slightly higher voltage when cold and lower voltage when hot; since it's at only 13.2 when hot, it may indicate that it's getting too hot.

Where are you buying the alts from? If they are OEM design, they should be reliable, but a 200 rating was not OEM from my knowledge.

The alt cools by drawing air from the rear case......sucking in heat from the exhaust manifolds will not be good, either.

I had a CS144 140A on my older Caddy 4.9L.....240K original miles, still going strong when I sold it recently.

George

[torqhead]

Thanks for all the feedback. Try to answer a few questions/comments. The alternator I picked up is this one:

https://www.amazon.com/LACTRICAL-ALT...ome+alternator

The guy I got the alternator from recommended to have a 4 gauge wire running from alt battery connection straight to the battery, which I did install. I also decided to run a 4 gauge wire from the ground bolt on the back of the alternator to where my negative battery cable connects to the front of the head behind the alternator. As far as heat on the back side, per George's comment, my alternator sits up high and in front of the valve cover. Needless to say it draws in heat but it's not right next to the header either.

[gtofreek]

The potential problem I see is the fan. That style of fan was used on 63 amp, and lower alternators. When GM went to the 12 SI alternator[the one pictured is actually a 10 SI], they upgraded the fan to a turbo style fan for better cooling. They also made the backside case with bigger air openings to get more air through it. The fan on the alternator you bought has uniform fan blades. If you look at the original GM steel fans, the fan blades were different sizes. I figure GM did that for a reason, probably cooled better. That fan they are using doesn't look like it will move much air. Just a thought. 200 amps is way pushing the limits of that case design. Chrome is not helping it dissipate heat either.

[george kujanski]

Looks Fancy..............but back in my day we tested our alts for extended periods in a temperature chamber to guarantee output and reliability. Unless the seller provides some detailed info about the performance and testing of their units, I personally wouldn't buy them.

Delco designs must meet performance and reliability considerations otherwise there would be nasty recalls that cost hundreds of millions of dollars...these aftermarket mfgrs probably don't have those issues.

The billet fan troubles me....Delco must have spent many thousands of dollars to design the best fan possible for their units...it sure looks pretty tho.

George

[george kujanski]

Just saw your comments Paul.......same conceerns.

George

[torqhead]

Interesting comments about the fans, wondering if that's where my issues started as the alternator I had run for years got a new fan that came with the rest of the brackets, etc. I got from the CVF Motorsports and I had installed it. The original fan was the blade style, although it had been chromed, 120 Amps, and had it for 20 years. I had replaced the diode trio about 5 years ago.

The new alternator off of Amazon is a 12SI based on the back has the bigger holes for cooling in that model, but the fan that comes on it I now tend to agree with you that's probably more so the issue on the new one.

If I'm not mistaken, correct me if I'm wrong, the alternator won't produce 200 Amps unless the regulator determines the car requires it. Is that how it works George?

["QUICK-SILVER"]

Originally Posted by torqhead

The new alternator off of Amazon is a 12SI based on the back has the bigger holes for cooling in that model, but the fan that comes on it I now tend to agree with you that's probably more so the issue on the new one.

Scroll down the pictures in this link to see the difference between 10SI and 12SI. Not only the rear case but the front case is different to make the turbo style fan more efficent.
http://www.madelectrical.com/electri...elcoremy.shtml
That whole little link from mad is a good read. It even covers the heat issue further down into it. That is an old link. I'm pretty sure it was George that has posted something like a 105 amp 12SI that came on some mid 80's car.

Originally Posted by torquhead

If I'm not mistaken, correct me if I'm wrong, the alternator won't produce 200 Amps unless the regulator determines the car requires it.

No.2 in the plastic plug is voltage sensing to the regulator. It does tell the alternator what to do. It's suppose to crank up the amp output to keep voltage at a preset range. More than 14 but less than 15 depending on who made the regulator.

Be interesting to hook an inductive pickup amp meter on the output of your alternator and just see how much difference between cold and hot operation.

[gtofreek]

Also, if the stator connections and other connections inside the alternator are not good enough to handle 200 amps, or whatever the car is needing, then those connections will also overheat, and burn up the alternator. A lot of stators for these type alternators do not have eyelets soldered to the stator wires. They are usually just crimped. That could be an issue with high amp stators.

[torqhead]

Originally Posted by "QUICK-SILVER"

Scroll down the pictures in this link to see the difference between 10SI and 12SI. Not only the rear case but the front case is different to make the turbo style fan more efficent.
http://www.madelectrical.com/electri...elcoremy.shtml
That whole little link from mad is a good read. It even covers the heat issue further down into it. That is an old link. I'm pretty sure it was George that has posted something like a 105 amp 12SI that came on some mid 80's car.


No.2 in the plastic plug is voltage sensing to the regulator. It does tell the alternator what to do. It's suppose to crank up the amp output to keep voltage at a preset range. More than 14 but less than 15 depending on who made the regulator.

Be interesting to hook an inductive pickup amp meter on the output of your alternator and just see how much difference between cold and hot operation.

When I went to pick up a 12SI that put out 74 amps the two they had in stock had different fans. One was the style in the pics and the ne had the metal fan like on the 10SI. Weird, or so they come both ways.

[george kujanski]

An alternator is designed to output current into a load at a regulated voltage of about 14.0 volts.

The load determines the current output.....example, not counting ignition, if you only have your radio on quietly the alt may produce say, 3 to 5 amps, some for the radio, some to actually charge the bat, (plus the ignition, of course).

Add some electric radiator fans, (heavier load), the alt may produce 50 or 60 amps, (it does that automatically) at a regulated voltage of 14.0 volts), but there's a catch......

The current output of an alt is based on the alt RPM.....max rated output usually occurs near 5000 shaft RPM. A well designed high output alt say around 94A rated will produce near 50 or 60 amps at engine idle (shaft speed of 2000 or so depending on pulley ratio).

If the load applied requires more than the alt can deliver at a certain speed, the alt output voltage drops from 14.0. (becomes unregulated). Once the system voltage drops to 12.6, the alt and battery combination are supplying current to the load, but the battery is discharging since the alt can't supply the load and charge the bat under those conditions.

If the system voltage is ABOVE 12.6 to 14.0, the alt is supplying current to the load AND charging the bat. Lower than 12.6 and the bat is being discharged.

So to summarize, the alt provides output current at a regulated voltage of 14.0 volts. The output current depends on the applied load up to a point where the load requires more than the alt can provide. At that point, the voltage drops. To get back into regulation, the alt speed needs to increase or the load needs to decrease.

Cooling is REALLY important...the diodes needs to be cooled, as does the stator and rotor. In high temp situations, we used to use wire that was rated for 200 degrees C....don't know what the aftermarket guys use.

Alts are also only about 50% efficient......a rated 94 A alt at 14 volts produces 1.3KW at full rating; that's 1.7HP and takes about 4 HP to drive. That xtra runs the fan and also ends up in internal heat that needs to be removed, probably near 1KW of internal heat by the math.........the belt(s) need to transfer about 4 HP mechanical to the alt.

Not simplistic.

George

[george kujanski]

here's the output curve

[torqhead]

Originally Posted by george kujanski

An alternator is designed to output current into a load at a regulated voltage of about 14.0 volts.

The load determines the current output.....example, not counting ignition, if you only have your radio on quietly the alt may produce say, 3 to 5 amps, some for the radio, some to actually charge the bat, (plus the ignition, of course).

Add some electric radiator fans, (heavier load), the alt may produce 50 or 60 amps, (it does that automatically) at a regulated voltage of 14.0 volts), but there's a catch......

The current output of an alt is based on the alt RPM.....max rated output usually occurs near 5000 shaft RPM. A well designed high output alt say around 94A rated will produce near 50 or 60 amps at engine idle (shaft speed of 2000 or so depending on pulley ratio).

If the load applied requires more than the alt can deliver at a certain speed, the alt output voltage drops from 14.0. (becomes unregulated). Once the system voltage drops to 12.6, the alt and battery combination are supplying current to the load, but the battery is discharging since the alt can't supply the load and charge the bat under those conditions.

If the system voltage is ABOVE 12.6 to 14.0, the alt is supplying current to the load AND charging the bat. Lower than 12.6 and the bat is being discharged.

So to summarize, the alt provides output current at a regulated voltage of 14.0 volts. The output current depends on the applied load up to a point where the load requires more than the alt can provide. At that point, the voltage drops. To get back into regulation, the alt speed needs to increase or the load needs to decrease.

Cooling is REALLY important...the diodes needs to be cooled, as does the stator and rotor. In high temp situations, we used to use wire that was rated for 200 degrees C....don't know what the aftermarket guys use.

Alts are also only about 50% efficient......a rated 94 A alt at 14 volts produces 1.3KW at full rating; that's 1.7HP and takes about 4 HP to drive. That xtra runs the fan and also ends up in internal heat that needs to be removed, probably near 1KW of internal heat by the math.........the belt(s) need to transfer about 4 HP mechanical to the alt.

Not simplistic.

George

Excellent info George, appreciate your insight!