rpm’s drop when car is in idle
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=10660
Printed Date: June 08, 2024 at 7:46 AM
Topic: rpm’s drop when car is in idle
Posted By: bni1029
Subject: rpm’s drop when car is in idle
Date Posted: March 09, 2003 at 7:40 PM
recently i installed a punch500s and a kicker l5 in my car. i have a 03 galant. a day or two after i noticed that every time i stopped at a red light my rpm's would drop really low, and my car would even turn off. i have a 1 farad cap, and a yellow top dry cell optima battery. what can i do to make this problem stop? anyones help is greatly appreciated. brian
Replies:
Posted By: wu_187
Date Posted: March 10, 2003 at 7:01 AM
you might need a higher output alternator. newer cars seem to be very sensitive when it comes to a drop in current, and will even shut off sometimes for safety.
Posted By: bberman1
Date Posted: March 10, 2003 at 12:17 PM
What size power and ground cable are you using?
Posted By: bberman1
Date Posted: March 10, 2003 at 12:27 PM
That amp should use about 36 amps at full power. Your alternator puts out 90 amps (auto transmission) or 75 amps (manual transmission). Now are you running any aftermarket accessories? Also turn off everything except the engine like your lights ac etc and let me know if the rpms still drop. One ore thing do they drop at low volumes middle or high?
Posted By: Big Purds
Date Posted: March 10, 2003 at 12:41 PM
buy a larger alternator and ditch the cap...
Posted By: Big Purds
Date Posted: March 10, 2003 at 12:43 PM
buy a larger alternator and ditch the cap...upgrade your wires on your alternator (at least a 4ga wire for charging lead from alt to battery and 4 ga for the ground wire from your battery to the frame of the car) and make sure you have sufficient size wire for the amp...
Posted By: bni1029
Date Posted: March 10, 2003 at 10:23 PM
i am using 4 ga wire for both power and ground. i noticed problem only occurs when radio is on, and car is in drive. while car is in park i can play my radio without a problem. i was told that the problem might go away if i get a smaller pulley for my alternator. is this true?
Posted By: bberman1
Date Posted: March 10, 2003 at 11:01 PM
If you get a smaller pulley it might solve the problem. But if you do that then it will generate more heat and possibly shorten the life of the alternator. What is happening is your alternator will only put out its full load at higher rpms. So if your car idles between 800-1000 rpms you might only be getting half of the current as you would at a higher rpm. So by getting a smaller pulley you are making the alternator spin faster and it will generate more current at a low rpm. Now if your going to swap out the pulley you should just do it right. Replace it with a high out put alternator that is built to put its max current at a low rpm.
Posted By: Durango9
Date Posted: March 11, 2003 at 8:14 PM
I also have the dimming/ shut off problem. I have a 2000 Durango and Im running 1/0 gauge to my MTX81000D. The lights dim and rpms drop when parked. Then after driving around for a while with it up loud, and i put it in park it sometimes shuts off. I dont yet have a new battery and i hope that this is all i need.
Posted By: bberman1
Date Posted: March 12, 2003 at 9:28 AM
Running that amp alone at full power will use about 108 amps. I don’t think that a new battery will help you out. You will need to get a high output alternator that can handle your trucks load as will as your amps. You will also need to upgrade your cables from the alternator to the battery and chassis.
Posted By: Durango9
Date Posted: March 12, 2003 at 4:04 PM
Do you happen to know about the size of my alternator at the moment? Becasue I dont know what size i should be looking for.
Posted By: bberman1
Date Posted: March 12, 2003 at 4:30 PM
There are three different alternators that came form the factory (1) Bosh 136 Amps (2) Nippondenso 136 amps (3) Nippondenso 117 amps. I would suggest that you call around and find the largest alternator you can. But at the very least don’t get anything under 200 amps. Might want to call this guy C.S.A nathanpeddicord@yahoo.com or call at 1-334-712-9955 or 1-334-791-6272I have never dealt with him but I hear that he makes some of the largest amp alternators out there and has good pricing. He builds a lot of alternators for comp.
Posted By: IronCy
Date Posted: March 12, 2003 at 9:09 PM
Most high output alternators, like everyone is suggesting, put out full power at around 1200-1500 rpm, problem is, most cars idle below 1000 rpm. I have learned this since purchasing a $500 alternator for my 01 durango. My volt meter (instrument cluster) drops when I really beat on my system, no shutting off......yet. The voltage gauge goes back up once the car is moving. Another thing is that most new cars have external voltage regulators in the body computer, which can also affect performance. -Cy
Posted By: IronCy
Date Posted: March 12, 2003 at 9:13 PM
-btw, My alternator was a direct bolt on replacement for the nippondenso 136A, it is a Ohio Generator 200A alternator. It is going to get extremely difficult to get find a bigger one. And if you do, you will prob have do some extensive mods to get it in. -Cy
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