Ever since installing an electrical fan on my sported I've noticed a strange problem. My engine idols somewhere around 900 RPM and that this RPM I see the alternator outputs about 12 V. if I increase the throttle even a tiny bit too maybe 1000 RPM or 1100 the voltage increases to 14 V which is where I would expected to be anyway.

I'm wondering if this car would benefit with a slightly smaller pulley on the alternator that would make its been slightly faster when the engine is idle, or I'm not actually sure if my engine is even idling at the right speed does 900 RPM sound about right?

nothing wrong with the alternator or the battery they both are new and in fact the alternator is a high output alternator outputs I think 140 amps instead of 70 A like the stock one and it did this with the old alternator as well.

advice? has anyone else explored options for improving the system voltage at idle speeds?

I would try the smallest pulley you can get and see if that helps.
I would also look at the main cable from the alternator to battery/fuse/relay. I added and extra cable.
Hope this helps.
Everet

Do you happen to have a part number for the smaller pulley, or its dimensions etc?

Or maybe I can change the pulley on my alternator?

I can't seem to find the information about the pulley dimensions. If I can't find that info, I guess I'll be taking measurements of my pulley tonight and try to look up online and find a pulley that will fit but is smaller <img src="/forums/images/graemlins/kewl.gif" alt="" />

I THINK that the stock pulley is about 2.5" in diameter but I don't know the size of the shaft and other information that I'd need. I also am not sure what the main drive pulley size is on the engine.

I was reading that if the idle speed is 800 RPM then you want the pulley ratio to be at least 3:1 so tthat the alternator can spin at 2400 RPM, so it can keep up with electrical system demands.

I bet the stock Sportage alternator ratio is lower than 3:1? That could explain the problems I'm seeing. I mean, it doesn't matter if your alternator is capable of 140 amps or 70 amps or 30 amps, if you're not spinning it fast enough it won't supply anywhere near that much. I'll find out tonight!

Update:

I looked all over and didn't find a smaller pulley that would fit.

However, I got in touch with the company that I bought my alternator from, here:
http://www.qualitypowerauto.com/item_342/Kia-Sportage.htm

It turns out I'm in luck. They sell a 140 Amp alternator for our Sportages. They just recently started also selling a 200 Amp alternator for them (it's so new it's not even on their website yet). For the 200 Amp alternator, they have a smaller (1.8") pulley custom-machined just for our vehicles. The catch is you have to remove a little lip from the alternator chassis to make it fit.

So, for $40 they sold me the pulley, and I will remove the front of my alternator case, grind off the lip, and install the smaller pulley. That should spin the alternator a bit faster and let me maintain a solid 14v at idle even with my electric fan on fully blast!
<img src="/forums/images/graemlins/kewl.gif" alt="" />

I highly recommend these guys for anyone looking for a high-output alternator, but I'd buy the 200 Amp model now that they are selling it! You'd need to call them to order it, I guess, because it's NOT listed on their website / online store yet <img src="/forums/images/graemlins/notooth.gif" alt="" />

I guess $40 probably sounds expensive for a pulley, but IMO it's not, when you consider that they had to have them custom-machined out of billet aluminum for this vehicle. There is no mass-produced overdrive pulley that will fit this vehicle's stock alternator. If I was starting over buying a high-output alternator I'd order the 200Amp model from these guys because it's a drop-in replacement, no custom work needed. But that might be less fun for some people <img src="/forums/images/graemlins/wink.gif" alt="" />

Ok here you can see the modification I had to do to the alternator case to make the smaller pulley fit. High output alternator that I modified is on top!

http://imgur.com/0dhRLst

http://imgur.com/HuL7fZ0

http://imgur.com/hEGeQAZ

Voltage is now rock solid under all conditions and fan controller totally reliable <img src="/forums/images/graemlins/kewl.gif" alt="" />

Ok here you can see the modification I had to do to the alternator case to make the smaller pulley fit. High output alternator that I modified is on top!

Voltage is now rock solid under all conditions and fan controller totally reliable <img src="/forums/images/graemlins/kewl.gif" alt="" />

http://imgur.com/0dhRLst.jpg

http://imgur.com/HuL7fZ0.jpg

http://imgur.com/hEGeQAZ.jpg

OK well my electrical system is VERY stable now. Voltage at the battery while the engine is running never changes. It's the same at idle, or revving the engine. This is a great improvement!

However, I noticed something. Even with perfect, large, well-conducting cables connecting the battery to the alternator, the voltage at the battery terminals is always 13.8v, not 14v or higher.

I think this is fine, because now, it doesn't sag down to 12v or lower at idle, like it used to, it stays solid.

I actually was just reading about AGM batteries (which is what I have) and it says that the best charging voltage for them is 2.3v per cell, which comes to 13.8v, so this is actually good. It says 14v or higher can degrade the lifetime of the battery.

Just for your information though, if anybody wanted to maintain at least 14v all the time (for example, maybe for car audio amplifiers or something where that makes a difference), you can do that.

I used to have a Zener diode wired inline between the alternator sense wire and battery positive. This bumped up my output voltage to about 14.5v, and with the smaller pulley, it stayed that high all the time, even at idle with the fan on, headlights on, and other electric accessories.

I took the zener diode out though because 13.8v is plenty.

There does seem to be some drop in voltage though, probably due to crappy wiring, at the cigarette lighter. I only see around 13.4v at the cigarette lighter. I think that's OK though.

Main thing is, now my alternator can maintain high enough voltage at idle to keep the battery charged even under heavier electrical load <img src="/forums/images/graemlins/kewl.gif" alt="" />

Well, as long as you don't buy 14V cigarettes, you're good to go... <img src="/forums/images/graemlins/shiner.gif" alt="" />