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Discussion Starter #1
I bought a new battery (Optima Redtop) about 3 months ago. Everything worked fine up until now. The past two times I have tried to start the car, it won't crank. Won't start unless I jump it with my truck. What is the best way to diagnose the problem? Could it be the alternator or is it probably the battery? Any help would be great, thanks!
 

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Jump start the car and put a volt meter on the back of the altenator. It should be 14 - 14.5 volts. If so, the battery is probably bad. It is not uncomon for the red tops to go bad. I've stopped buying them. They are only really needed if you are worried about battry rupture or you don't mount it up-right.
 

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Jump start the car and put a volt meter on the back of the altenator. It should be 14 - 14.5 volts. If so, the battery is probably bad. It is not uncomon for the red tops to go bad. I've stopped buying them. They are only really needed if you are worried about battry rupture or you don't mount it up-right.
well that blows for me! i'll check the alternator. is it possible the alternator is bad and isn't charging the battery properly? if so, how do i check that?
 

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most car parts places will check both the battery and the alternator.

To check your alternator youself, is fairly simple and straight forward.

put a volt meter across the battery with the car running. You should have somewhere between 14 and 15VDC... personally I don't like to see over 15 but some say 15.5 is ok.. I say BS. Anything under 14 is also BS.
 

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i swapped out the battery for another, and the car started right up. gettin the alternator and battery tested tomorrow. see if the alternator isn't charging the battery enough, might need to bump up the amps, or if the battery is just shot. i'm hoping it's the battery, free replacement :)
 

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I got the battery tested today, and Monument says the battery is bad. No description on what caused it though. Still could be the alternator not fully charging it. Called Summit, they are sending me a new one for free, thank god. Should I get a new higher output alternator to insure full charging is taking place? With the old battery, and the alternator that's on there now, when I pull up to a stoplight, and it's idling at 7-800rpms the voltmeter reads 12volts, when I start to drive it goes up to 13.6ish. Is this enough to keep it fully charged, or should the alternator be around 13.6 the whole time the car is running? I'm not too knowledgeable in the electrical department, hope someone can chime in and help out a bit, thanks guys!
 

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If you have an SI altenator and you are measuring voltage at the battery, it is close to normal. If you are measuring at the altenator, then the readings are low. You should measure at the altenator so you don't have to calculate voltage drops. voltage at the battery is highly dependent on the load on the system, wire size and wire lengths.

If you are running a CS130 altenator, the idle voltage is too low.
 

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the readings are inside the car, on the voltmeter (gauge). so i believe it is the battery voltage. as for the alternator, i believe it is an SI, 60amp. i talked it over with my dad and he says there was more than likely a bad cell in the battery. i watched the test they ran on my battery, and the battery reached 10volts and then dropped down to 6. so i am assuming the battery is shot. anyway the battery can become useless if it isn't being charged correctly (not rechargeable or anything)?
 

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the readings are inside the car, on the voltmeter (gauge). so i believe it is the battery voltage. as for the alternator, i believe it is an SI, 60amp. i talked it over with my dad and he says there was more than likely a bad cell in the battery. i watched the test they ran on my battery, and the battery reached 10volts and then dropped down to 6. so i am assuming the battery is shot. anyway the battery can become useless if it isn't being charged correctly (not rechargeable or anything)?
Unless you are running a big electric fan and A/C, 60 amps is usually enough. When you are checking your altenator, always measure at the back of the altenator. If your checking the charging system, check at the battery. a vehicles electrical system has too many sources of voltaged drop to measure any other way. You voltmeter is only as accurate as the point at which it is connected, but it is a very good indicator of the overall charging system condition.
 

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a normal car battery should read anywhere from 13.8-14.6 at idle if its young. if it drops to the 12s replace it. the way to check if hte alt is going is easy....start the car, let it run for a few, then disconnect the battery. if the car stalls or shuts down its the alt. the battery is only used primarily for starting the engine anyway. and whoever said you should have at least 15 volts across teh batt must have an external reg. alt. the only way ive ever been able to get mine to stay that hight is with what we call teh "big 3" upgrade and an external reg alt capable of setting it to roughly 16 volts
 

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and on that note...optima red tops are designed soley for starting applications where as their yellow and blues are less for starting and more for deep cell capabilities...ive never had a problem with em, theyre not the best battery out there i could recommend better but the only time you should run into trouble with these batts is if you mix diff colors....
 

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i have a 3000cfm electric fan, aftermarket radio (w/amp & sub), headlights. that's the most i have going at once. other times=minus headlights. i'm pretty sure the battery is just trashed, hopefully the new one holds up longer than 6 months. or receiving a brand new one, i could sell it for as much as i can, and buy a better battery. any suggestions on that?
 

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i have a 3000cfm electric fan, aftermarket radio (w/amp & sub), headlights. that's the most i have going at once. other times=minus headlights. i'm pretty sure the battery is just trashed, hopefully the new one holds up longer than 6 months. or receiving a brand new one, i could sell it for as much as i can, and buy a better battery. any suggestions on that?
ok the amp is the big problem. red tops were not made for audio purposes in any way. the only way ive found to fix this is get a high output alt for the system. my personal preference when dealing with any system watsoever is a deep cycle in front and another in back.
 

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ok the amp is the big problem. red tops were not made for audio purposes in any way. the only way ive found to fix this is get a high output alt for the system. my personal preference when dealing with any system watsoever is a deep cycle in front and another in back.
i was planning on getting a 100amp alternator anyways, so no problems there (i hope). the amp has been unplugged for awhile now, i stopped using it until i get the new alternator. even then i might not hook it back up. i like some bass with my rock! but oh well. i'd rather have the car running and charging properly than bass.
 

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You could mount a capacitor in-line with the amp. That is usually sufficient for one amp. As far as battery's; Interstate are some of the best battery's, but Autozone's and Advanced Auto Parts' batterys are pretty decent for the money.
 

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The 100 amp alt. will do just fine, even with the amplifier. 14-14.5 is the golden voltage range to keep the battery alive, any higher will kill it in a matter of months! If the voltage stays around 14V with everything on, you should be fine.
 

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You could mount a capacitor in-line with the amp. That is usually sufficient for one amp. As far as battery's; Interstate are some of the best battery's, but Autozone's and Advanced Auto Parts' batterys are pretty decent for the money.
An inline cap won't magically create power.

Thevanin's theorum states: power in = power out.

Feel free to disprove it, but the theorum has stood for a hundred years already.

All the cap will do is release 'instantaneous' pulse, preventing a voltage loss at the amp when the bass hits. This momentary pulse of power from the cap allows the alternator time to boost voltage.

BUT.. your battery charge is all about AVERAGE power.. if the amp, and other electrical loads provide a greater ( average ) demand upon the system than the alternator can provide, then the battery becomes you 'boom cap' and the battery drains.

long story made a tad shorter: if the amp is overloading the circuit, then adding a boom cap won't fix it.
 

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An inline cap won't magically create power.

Thevanin's theorum states: power in = power out.

Feel free to disprove it, but the theorum has stood for a hundred years already.

All the cap will do is release 'instantaneous' pulse, preventing a voltage loss at the amp when the bass hits. This momentary pulse of power from the cap allows the alternator time to boost voltage.

BUT.. your battery charge is all about AVERAGE power.. if the amp, and other electrical loads provide a greater ( average ) demand upon the system than the alternator can provide, then the battery becomes you 'boom cap' and the battery drains.

long story made a tad shorter: if the amp is overloading the circuit, then adding a boom cap won't fix it.
absolutely right. its been long known in the audio world that a cap will NOT, against popular belief, make your system louder or create more power. it does its job in buffering the voltage drops but puts another strain on the electrical system. i never have and never will use a cap. if something extra is needed, always go to a secondary batt, and upgrade the "big 3" wires to 0 gauge. best course of action for keeping voltage drop. my .02
 
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