HO Alternator Output/RPM Question

I purchased a 150-amp alternator from a rebuilder for my 1.6 ltr 93 Toyota Corrolla DX a few months back... the stock alt got whacked by a pair of JL amps in less than 48-hours. (I was actually rather proud..) Anywho, as I've played around with the charging system considerably in my car(big wires running everywhere, RedTop, 1.5 farad cap), I've noticed that the alt seems to drop down to a very low voltage... around 10 - 10.5 volts when the car is idling. If I leave it idling long enough (like to warm up in the morning), the battery light comes on and my voltmeter makes its annoying not-enough-power-beep. The SMALLEST INCREASE in engine speed will send the voltmeter straight to 12.5 and hold it there. Even the dash lights will suddenly brighten up. I can't say how fast the engine is going b/c I don't have a tachometer on that god-awful econobox. The idle is fairly rough so I'm guessing it is pretty low. Could I increase my idle speed a bit without risking damage to alt or the car? It seems to me it would require little more than a wrench and 30-seconds...? Is this common practice in the car audio world? I think I've seen competition rules that say engine RPM has to be below a certain point but I really dunno..

Whell, that is unusual , but common when you cheep out on the alternator.  A quality alternator will have the capacity to put out about 60% of its max output at idle.  Definately look into a smaller pully, altho a side affect is that the bearings on the alt will have a reduced life span.

DYohn: What could upping the idle 200 RPM's or so possibly do besides take a very modest bite out of fuel economy? 97Pathy: Yea I paid like $250 for the alt... But it was a direct bolt on and the shops around here all wanted like $700 just for an alt that'd I'd have to mod onto my car in some stupid and prolly expensive fashion. So I'm not the least bit unhappy.

sedate wrote: DYohn: What could upping the idle 200 RPM's or so possibly do besides take a very modest bite out of fuel economy? .

I don't know.  I'm not a mechanic, and that's why I suggested you ask. 

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Besides wearing out your motor prematurely? Higher rpm's at idle is not good. I would leave the idle alone and if you want more rpm's change the pulley size. That will turn the alternator faster at your same rpm's your motor is turning now. You will risk running the car hotter in summer also if you change the cars rpm's. '85 Toy

Ummm, here's a thought... leave the stereo OFF while it's warming up... There will be PLENTY of power provided to warm up your car and run the accessories as well... simple enough. Chances are, the idle is set by the CPU (or some would call it an ECU) in that car, so you won't be able to change it anyway... I recommend against the smaller pulley, ONLY because it will limit the maximum RPM you can run the car, and add additional load on the engine while driving. Also, as mentioned earlier, if you over-speed the alternator, it will cause premature wear on the bearings there as well... As DYohn said, check with a mechanic. If your idle is TAHT low, it is probably time for a tune-up anyway. And as a previous owner of a 93 Toyota Corolla, go to the dealer - they know what they are doing with the car...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst: No, see thats the problem.. the car has no accessories or opitions or anything. The ONLY thing it needs to run is the stereo... which I wouldn't be playing when I'm letting the car warm up while I'm inside my warm apartment. So if my battery will start my car... and then give me a low voltage warning after 20 minutes of idling, clearly something is amiss... Needless to say what happens to my sub-amp whenever I come to a stoplight.

ya, thats not acceptable.  Go back to the place you got it built and see what options you have.2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

sedate: That sounds exactly like what was happening to my HO alternator a while back. When I sent it back the company that built it, they fixed it and on the repair paperwork in the box had "repaired stator" listed as the bad part. Mine would charge fine all the time except when idleing. '85 Toy