Just guessing that you had this problem before you installed the new alternator. Is that a 3-wire alternator from someone like Powermaster? If so, once that alternator gets going it shouldn't drop down.
Once the car has been brought up to 2000 RPM, drop it back down to idle. Take some readings off the back of the alternator, horn relay, junction block, and battery. See if there is a difference between those readings. They should all be the same or close to the same. What you are looking for is a voltage drop indicating that one of the connections isn't clean or tight.
If you used a 3-wire alternator, see where you hooked up the sense line to. Having it tied next to the alternator may give you a problem. Read this article about the sense line. Look under the paragragh titled REMOTE VOLTAGE SENSING, a THREE-WIRE advantage. Moving the sense line may help. http://www.madelectrical.com/electricaltech/onewire-threewire.shtml
Not that this is really relevant to you I guess... but I just put in my one wire Magnum alternator last summer. When I first got it, I was worried because I had heard stories of low rpm charging problems with the one-wire units. When I got the alternator, the pulley actually had a larger diameter than the old one, which worried me more. However, while the old charging system left the lights dimming every time I stopped, the one wire keeps them bright constantly.
All of my wiring and relays are all still original. I read over the MAD Enterprises documentation again last night. They recommend replacing the main power charging wire when using an alternator larger than 63 amps. I went ahead and rewired the main charging wire and also used a larger wire for the #2 connector to the charging wire.
After looking over the horn relay and some of the other connections I am going to replace them as well. My amp meters batteries were dead so I am going to replace them today and check each point in the system.
Just my opinion and it seems to be shared by MAD:
I am not a fan of true one-wire alternators. They don't have the best regulator circuit in there for a car. Actually I prefer the 10 SI and the 12 SI style of alternator because you can get a replacement just about anywhere. Fixing cars on the road isn't fun and having special parts in there makes it rough. Again just my preference.
I haven't read anywhere, including Mr. Wes Vann's tech reference articles, that you need to change pulley diameters going from a DN alternator. (external regulator) to a SI alternator.
I don't remember seeing that in the MAD articles either. Some aftermarket alternators probably do have a different size pulley. The manufacturers probably felt their design needed it.
The point I was trying to make was to check the alternator output voltage at idle and check the junction block (or horn relay) at idle. As the MAD article points out, there could be a voltage drop between these 2 depending on how things are hooked up and the load the car is seeing. Wes Vann's information says to jumper the sense line to the back of the alternator. He is referring to a car that hasn't been modified with a lot of aftermarket items.
By moving the sense line further away from the alternator, the regulator sense circuit still tries to control at around 14 volts. If you tie the sense line at the horn relay, for example, it will take its reading at that junction. The voltage, on the back of the alternator, will be higher but you really only care about the junction where the wire leading inside the car is tied to. Chevy likes to tie this to the horn relay.
the best way to set up an alternator circuit is to jump the sense wire to the back of the alternator, then run a rather large wire from the back of the alternator directly to the positive terminal on the battery. try to get about an 8 gauge or so wire- a little overkill here is a good thing. later model gm cars use this setup, and it works killer. i have it on my Nova, and never a problem with power.
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik
Mine is the CS alternator example that Wes has in the Tech Referance section. The car uses a larger Z/28 type deep-groove pulley and has A/C, high-power stereo, aftermarket electronic ignition, etc. It does have a very heavy gauge (6 or 8, I can't remember) main buss from the alternator to the battery. I also replaced the main + buss to the firewall plug with a stock-gauge wire since the original was a bit crusty. To re-do the wiring so it looks really nice will take the better part of a day by the time you re-wrap all of the harnesses.
Replacing the main buss from the alternator to the battery will cause the factory ampmeter gauge to be useless. It's better to replace the factory ampmeter gauge movement with an aftermarket voltmeter gauge. It can be done easily and is much more usefull. Just take an aftermarket voltmeter gauge with the same needle sweep angle and adapt it to the stock ampmeter gauge face.
I also like the idea of using an off-the-shelf part that can be bought at any auto parts store. The modifications necessary to make them work is minimal. You can also find pics of the installation on my website.
Well, I was skeptical about one wires myself until a few years ago and more and more quality manufacturers came along and made the market. The product has improved tremendously. I have had nothing but outstanding luck with them.
I do like the sensing ability of the other types, however I have found with then new fangled wiring kits and the bigger capicity wires and better quality (meaning the voltage drops are not as prevalent), the one-wire works as good as any other and is inherently simple. I have used/installed/recommended dozens of either Powermaster or Tuffstuff units without a failure to date. Just my experience...so far.
MOst one-wires need 1750 rpms of shaft speed to turn on and stay on. So, this could mean several things depending on crank pully diameter. MOst aftermarket pulleys are the same size, but the crank pulleys are the ones that vary a bit! Check this out if you have charging problems or the turning off and on issue.
One last but important recommendation, always..and I mean always...upgrade your wiring/feed/charging wires when upgrading the alternator's capacity or risk blowing fusible links or worse...burning the harness up!
STEVE JACK ConceptOne Pulleys and Brackets Northern/Southern Rodder Magazine's "Jack'Stands" author and creator
Techical forum/links at www.inccn.net/techforum.htm
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