I just canna do it captain, I dunt HAVE THE POWER!

Scotty hit the head on the nail for me. I am installing my under drive pulleys and I want to be able to run my stereo with them on...and AC...etc. I have a 360 watt amplifier hooked up, one sub (bridged) and a 1 farad capacitor. I need to save cash now (I just dropped a lot in the car) and was wondering what the best solution would be so that I could run the underdrives and not notice much of a difference with the stereo on at a decently loud level or not having to worry about my car shutting off, etc. Ideas? What's the amp rating for the stock alternator in a 92 Camaro RS? What output should I go for?
Thanks!

 

Get rid of the pullies first.

 

If it's stock, I believe yours would be 105 amperes. If you do get a new (different) alternator, remember that alternators should always be rated for well above your expected current load.

What output to strive for? I would think 140 amperes would be fine based on what you said and not knowing the exact total amperate load. See the following for a discussion you may be interested in.

1. In the General/Engine section; https://www.thirdgen.org/messgboard/...ML/009974.html .

2. In the Electronics section; https://www.thirdgen.org/messgboard/...ML/001748.html . You may get a chuckle when you read one of the lasts post's which stated "The only way a "high end" sound system uses more current than a conventinal sound system (a watt to watt compare) is if the amp is a Type A or Vacuum tube design." Lord only knows what "watt-to-watt compare" is all about. Input watts? Output watts?

Anyway, I'd try using a higher output alternator first. Spinning the alternator faster is generally only going to help you with more output current at the lower engine speeds - especially at idle. Once the engine gets up to ~1500 or more RPM, the difference is not really all that significant (IMO). The output curve for an alternator typically increases fairly rapidly, so the most benefit will come at the slower speeds (idle). The output will not be much different at highway speeds. I can't remember if www.premierpowerwelder.com has a graph to illustrate my point (you may also want to consider their alternators...). When selecting an alternator, it is important to know if an alternator is rated continuous and hot or not. (Continuous equals a 100% duty cycle.) This translates into real world conditions. The output will always drop when an alternator gets hot. The more it works (hence the "continuous" condition) the hotter it gets. If you rate it when it's cold, you can always get more output, but only for a short time (until it gets hot). Some manufactures often inflate this number to attract more customers playing the "numbers" game thinking that more is better.... just like the "boombox" makers claiming 800-or-more watts (PMPO! haha) from their stereo with only a few "D" cells powering it - all for $100. It all depends upon the type of measurement.

Personally, I'd look into the large case alternators (see the links above) which can produce current "easier" (for reasons too numerous for this post) than a small case.

If you ask that question ("continuous and hot") and get a blank stare in return, that'll be a good indication that he/they don't know what they're talking about and to move on to a professional (experienced) dealer.

EDIT:
Well, I went to the Preimer Power site, and they don't have the graph, but you could plot one from from the figures they give. Look at http://www.premierpowerwelder.com/specs/PP170CS.html for an '89 and newer (CS130 type) and, my favorite (take note Jason), the CS144 (GM/HUMMER) specs at http://www.premierpowerwelder.com/specs/CS144.html (beautiful) for a comparision.

Note the two columns - HOT and COLD, and see how much difference in amperage there is between these two conditions at any given rotor speed (remember - the speeds are not engine RPM speeds).

Now, look at one column and see how little difference there is at the faster speeds, but a dramatic difference at the lower speeds. Remember that the speeds given are alternator rotor speed, not engine speed. When the engine is at idle speeds the difference is 20-40 amperes (at 500RPM steps)! If you graph it, you'll clearly see the (relatively) steep slope.

They (Primer Power) want over $600 for the large case (CS144) alternator. Consider the first post for an "unmodified" CS144 (140 amperes I think) for <$200.).]

[This message has been edited by Stuart Moss (edited June 26, 2001).]

 

Thank you VERY much, Stuart. Your post was informative and very helpful. =D

 

More power = more drag. Get rid of the pully or send money on a alt that is deleting the point of the pully. I had a caddy with a 144 amp alt it ran 2)xtant 604x and 1) 1001x with 8) 1F caps and vola no problem. In my 00 T/A Xtant X604 120amp draw and 3 caps and no prob at idle. Try running a 1/0 from alt to batt and same for ground. Power is only as good as the ground.

 

Oh Lord, where do I start on this one... I'll try just one (the rest I couldn't decypher).

True. I agree 100%. BUT, the real question is "is this power needed?"

Sooner or later it will be. If you are spinning the alternator slower, or using a lower capacity alternator (to gain horsepower, for example), that just means that if the alternator cannot keep up with supplying ALL the electrical needs (this includes at idle), that just means that the battery will have to supply the difference. Now the alternator will just have to recharge the lost energy that the battery gave to fill this "gap" once it starts spinning faster. Sooner or later, it'll provide the power (if it's capable). Otherwise, you'll suffer from a less than ideal voltage (I'll define "ideal" as between 13.8-14.5). This can be important for a myriad of reasons - hottest spark, brightest headlamp output, less charge/discharge cycles on the battery (which will relate to its life...), and so on.

I hope I don't need to comment on using capacitors (at any size, even if you're towing one the size of a tanker trailer) to reduce alternator drag, current load or any other benefit that will allow the alternator to work less, because a capacitor, in and of itself, will not (at least according to the laws of physics as I know it).

 

In all honesty I don't think you need a new alt, unless the one you have is staring to die on you. A 360 watt amp does not draw that much current. check the fuse on the amp. It's probably around 50 Amps. That is the MAX amount of power your going to draw. i.e musical peaks etc. Most of the time you will be drawing at most half of what the fuse is rated at. You also have a 1 farad cap that will get you through those peaks even if are running a little close to the edge. I would save your money for other stuff.

BTW, I'm running a 2500 watt system off a 200 A alternator. Granted I do have 30 farads of capacitance, but I still don't expect any problems.

[This message has been edited by camaroguy99 (edited July 02, 2001).]