I have a new electrical fan that pulls 18 amps (Black magic Xtreme). When it kicks on, I get a 150-200rpm drop in egine rpms (in park).
I have a brand new powermaster alternator, 106 amps, 75amps at idle. It was label as a 1 wire, but, it had the provision for 3 (just a platic dust cover over the reg). So, at first I had it wired as one wire, and it would drop in RPM. Doh, I thought, I need to wire it as a 3, which I did. The regulator wire goes to my main power wire (off my power block). It still does it.
Now, one thing I have to say is this: my ignition box (6AL) has it's power wire hooked to the starter positive lug, and I have a car's main positive to that same spot.
Battery is in the trunk.
I thought having the regulator wire right at the block where the fan draws from would allow it to compensate, but, it doesn't look like it does, or, is the alternator puting that much drag on the engine?
Iginition if fine, doesn't break up nor is acting up.

It did not do this when I had a fan drawing 10 amps and the car was wired the same (the voltage reg wire was hooked to the back of the alternator though).
I am thinking the battery is just crap (it has sat for 3.5 years without running much if at all). Battery is a 1000 CCA

Yes, your battery is crap but that's another issue. The alternator is doing what it is supposed to and supplying the electrical energy that is required to keep the point of regulation at 14.2 V (usually at the horn relay). In order to do this it takes power from the engine. A fan at 18A and 14V is 252 watts, with alternator efficiency at 90% then 277W just to run the fan or about 0.37 HP. Not as bad as a compressor for A/C or a power steering pump (which should also drop the RPM when you turn the steering wheel) but enough to drop it some. 200 RPM is a bit surprising though. Do you have a fairly radical cam?
Three wire is the way to go in alternators....
Ron

Are you sure the alternator is actually working as a "3 wire"? Often, the 1 wire regulators have the 2 extra terminals on them but they aren't connected internally. It looks like a normal regulator, but doesn't operate like one.

Yes, your battery is crap but that's another issue. The alternator is doing what it is supposed to and supplying the electrical energy that is required to keep the point of regulation at 14.2 V (usually at the horn relay). In order to do this it takes power from the engine. A fan at 18A and 14V is 252 watts, with alternator efficiency at 90% then 277W just to run the fan or about 0.37 HP. Not as bad as a compressor for A/C or a power steering pump (which should also drop the RPM when you turn the steering wheel) but enough to drop it some. 200 RPM is a bit surprising though. Do you have a fairly radical cam?
Three wire is the way to go in alternators....
Ron

yea, cam is radical, 1250 idle in park, 1000 in drive, with 5" of vac. I suspect my tach might not be in its best of shape either but, I'm also having issues with idle air fuel ratio, which I'm sure also relates to some of my problems.

Are you sure the alternator is actually working as a "3 wire"? Often, the 1 wire regulators have the 2 extra terminals on them but they aren't connected internally. It looks like a normal regulator, but doesn't operate like one.

Do you know how to test the voltage reg??

Edit: I just checked with powermaster, and my alternator can be pluged either way. I have it as a 3 wire right now.

Do you know how to test the voltage reg??

Edit: I just checked with powermaster, and my alternator can be pluged either way. I have it as a 3 wire right now.

Hmmm, I'll need to look into that. I don't see how the regulator could work both ways. Where is the "voltage sense" wire connected? It's usually a red wire in the 2 wire connector and has power even with the ignition off.

As others have mentioned, the battery could also be weak. You'll want to test it first.

the sensing wire is connected to my dist block that I have on the rad support. I'm just about done re-wiring the engine bay (ignition box, fans, alt) so that everything gets power from the distribution block to which the sensing wire is hooked too.
The rear alternator wire goes to the main power wire of the factory harness, which is spliced and is also connected to the power block. Basically, it's wired per factory except my horn relay has been replaced by my distribution block.
Haven't had the chance to have the battery tested. tomorrow is another day:) probably will pick up an ultima red top.

the sensing wire is connected to my dist block that I have on the rad support. I'm just about done re-wiring the engine bay (ignition box, fans, alt) so that everything gets power from the distribution block to which the sensing wire is hooked too.
The rear alternator wire goes to the main power wire of the factory harness, which is spliced and is also connected to the power block. Basically, it's wired per factory except my horn relay has been replaced by my distribution block.
Haven't had the chance to have the battery tested. tomorrow is another day:) probably will pick up an ultima red top.

That sounds like you're doing it right.:beers:
I asked about the sense wire because many "kits" have it running right to the output stud on the alternator. It kinda defeats the purpose that way, dont'cha think? ;)

I just realized my thinking was backward. If the alt was operating as a "1 wire" you could have low voltage to your lights and accys. It would actually be less likely to load down the engine.

yeah, for years I had it looped back to the rear post of the alt. Never ever had a problem. I think the battery isn't very healthy, that's the only thing that could have changed.

yea, cam is radical, 1250 idle in park, 1000 in drive, with 5" of vac. I suspect my tach might not be in its best of shape either but, I'm also having issues with idle air fuel ratio, which I'm sure also relates to some of my problems.

Radical cams make problem of RPM dropping with additional load (alternator + fan) worse. EFI will fix this however. Expensive solution but there are other benefits too.
It won't hurt that the RPM drops unless it is causing a stall...

Ron

^ nah, doesn't hurt anything, but I'm prety sure the battery has something to do about it...

Yes, If the battery needs a lot of current it will suck up power from the alternator...but then it should not be able to start the car.
If the battery can start the car with no charger assistance then changing the battery won't make a difference.
You could find one of those old throttle solenoids that push the throttle up slightly when the A/C was turned on. In this case it would bump the throttle slightly when the fan comes on.
Ron

one more Q:
do I need a wire that goe directly from the back of the alternator to the battery?
Right now, my big gauge positive goes to the starter, then I have a 10gauge wire going from the starter to my dist block. Dist block has a wire to the back of the alt, and a wire to the internal reg, and of course, wires that goes to my MSD box, Fan relay, and one more for one relay under the dash for my tach and radio (I use the switched power slot available on the fuse box to activate that realay...cleaner, more reliable, I think)

Got the car fired back up, still have a drop when the fan kicks on, but doesn't seems as pronounced. headlights are nice and bright.
I'm going to slap on a new battery, this one is toast, been on the car 5 years, 3.5 of witch it ran a few times to move the car...so I can bet a buck it's nearly shot...it'll start the car though...but better hope it starts in a few sec of trying or you're SOL.

one more Q:
do I need a wire that goe directly from the back of the alternator to the battery?
...
I'm going to slap on a new battery, this one is toast, been on the car 5 years, 3.5 of witch it ran a few times to move the car...so I can bet a buck it's nearly shot...it'll start the car though...but better hope it starts in a few sec of trying or you're SOL.

The way it's wired should be just fine. Because your sense wire is at the terminal block, there "could" be conditions that would cause the battery to overcharge if the alternator output is connected directly to the battery.

I'll match your buck that the battery is bad.:) The last line above is a dead giveaway. The rest of your statement explains why.
5 years is actually pretty good for a battery even in everyday use unless it is a really good one. Your battery has actually been "abused", although you may not realize it.
Batteries don't like to sit idle in a partially or fully discharged state. Long periods of sitting, along with the resulting self discharge causes the plates to sulfate, lowering the current capacity. The more discharged, the more sulfation. I've seen brand new batteries ruined from sitting a year or more without charging them occasionally. There's no way to reverse the sulphation.

You might want to invest in a small trickle charger (battery tender). It won't make a battery last more than it's expected normal life, but it will help extend it's life until it is actually "used up".

Something to consider: I was told many years ago that the best place to store a fully charged lead-acid battery is in a freezer. It slows down the chemical reaction and self discharge and thus the sulfation. I do this with my motorcycle and lawn tractor batteries over winter and it seems to help them last much longer than just disconnecting them or storing them indoors. I just let them reach ambient temp before using them and charge at 3-5 amps for an hour or so. I've never tried it with a car battery, though. Just a thought.

^ cool, thanks for the info!
I'll go pick up a new battery sometime this week. I don't have a tender, but I plan on driving the car...if I don't, I'll make sure to put a 2A charge on it once a week if I don't drive it.