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Battery at 10.5 volts, how to tell difference between battery problem & alternator problem

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Battery at full charge reads 12.8. recharge battery overnight and buy a battery hydrometer from an auto parts store. reading between cells should not be 50 or more point. for alternator:, connect a voltmeter with engine speed set at 1500-1800 rpm. turn on lights, a/c and other electrical loads. voltage should be over 12.8V. if not, alternator needs to be checked,and also the belt tension. instruction above should be done only when battery is fully charged.

Posted on Jul 11, 2009

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Disconnect positive battery cable with engine running, if the engine stays running it's the battery. if the engine dies it's the alternator.
or you can remove the alternator and take it to autozone or advance and have them test it for you. it's free

Posted on Jul 11, 2009


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High Output Alternator (240amp) with idle voltage at 13.7. How do I get past the PCM and bring voltage up to at least 14.4? 2013 Camry SE 4Cyl


The high output alternator you have puts out higher amps - not volts. 13.5 volts out is more than enough to keep your car battery charged. Excessive voltage will damage a battery.

If your car requires more amps than the original alternator was able to provide to (1) run the car and (2) all the electric accessories; then a higher output alternator is needed (the battery is only needed to start the engine, that's it - they are designed to provide a large amount of current (amps) for a short period of time as when starting). Otherwise, the battery would have to make up the difference between the what the alternator can provide and the actual amount of amps needed / used. Used this way, the battery lights would dim, engine slows and everything would just stop and go dark.

If you're running a powerful audio amplifier, the current it might need may be so much current that it may be too much for the alternator alone to provide - hence the high output style was installed. You can use one or more large value capacitors - or additional batteries to "fill" in whenever the amplifier briefly needs more current than the alternator can provide - without drawing on the main car battery.

Your alternator is probably just fine.

Apr 07, 2014 | Toyota Camry Cars & Trucks

3 Answers

2000 chevy silverado. alternator problems. start truck and meter shows about 11 to 12 amps for a few minutes then goes up over 14. Did this for several days. today started and went right to 14 amps then...

amps or volts
11 to 12 amps indicates nothing but if it is volts then it indicates that the alternator is not charging the battery
Battery voltage is 12 -13.5 volts and when charging is 14.5-14.8 volts dc
the rest of your statement indicates that the alternator or voltage regulator is faulty and you should have the charging system checked by an accredited auto electrician

Feb 26, 2018 | Cars & Trucks

1 Answer

How can you tell if the alternator is bad or if the belt has to be changed

The belt is obvious

You change that, as you always have on any vehicle
Every 4,5,6 years ,whatever you feel like

The Alternator, you put a volt meter across the battery
terminals & start the vehicle
You need 14 volts to charge a battery to 12.65 volts

Aug 06, 2011 | 2007 Cadillac SRX

1 Answer

How do i know if its the battery or alternator that is bad?

You would know how old the battery is

A battery can last 3 years or as much as 8 or 9,
as I usually get

The battery can be tested in a variety of ways
All you can do is go by age & put a Volt Meter
across the terminals
You need 12.5 to 12.68 volts
That doesn't tell you the condition inside
That is a load test that would have to be done
by a parts store or repair shop
A more recently used test is a capacitance test,
which I doubt few shop have the equip to do

The same with the Alternator
There, a volt meter across the battery terminals with
the engine runninng should give you 13.2 to 14.3
volts approx
It can also be tested in different ways to check for
actual amperage output

If your battery cables or other ground wires are corroded
or loose, then you can be tricked into thinking you have
problems with a battery or alt etc when they are okey

Jun 30, 2011 | Mitsubishi Eclipse Cars & Trucks

1 Answer

How to tell if the battery or the altenator is bad

Test the car battery & the alternator supply voltage. If the alternator voltage is around 14 Volts, engine idling and headlamps low beam turned ON, then the battery is bad. After engine stopping, the battery voltage should be at least 12,4 Volts. The battery could be too old and needs to be replaced. If the alternator voltage is below 13,8 Volts then you must check up first time the alternator belt & tensioner pulley. If everything is OK, then the alternator is out of order and needs to be repaired in a dedicated workshop: weared brushes, bad voltage regulator, ...

Oct 08, 2010 | 2003 Volkswagen Golf

3 Answers

Battery light comes on and off car dies with a quick boost it run again then dies battery good

this is caused by a failing alternator. Kragen auto and Autozone tests these for free.

Jun 03, 2010 | 1996 Mercury Sable

2 Answers

93 Buick LeSabre. Battery not charging

use a volt meter while the car is running to check the main wire or large red wire coming off the back of the alternator it should read a steady 14 volts, the volt meter must be set at dc 10 amp settings, ground the black wire to ground or a metal surface some where on the car and touch the red probe wire on the volt meter to the main terminal of the alternator as i said it should read a constant 14 volts if it doesn't the alternator is bad.

Sep 04, 2009 | 1993 Buick LeSabre

3 Answers

How do I check alternator amperage on a 2001 maxima?

  1. Check the gauges, if the car is equipped with them. If you have a volt/amp gauge, it will read the alternator output for you. Turn on the blower fan for the AC or Heater, the headlamps, and any other accessories that put a strain on the alternator, and watch the gauge to see if it decreases voltage or amperage. As a rule, if the voltmeter is higher when the engine is running then when the engine is not, you can confidently assume that the alternator is charging.
  2. Open the hood, and with the car engine off, loosen the negative battery cable so that it can be removed with little effort. With the battery cable still loosely attached to the terminal, crank the engine, then pull the battery cable completely free of the terminal. If the engine continues to run, the alternator is providing enough voltage to power the electric circuits that provide spark to the spark plugs, electric fuel pumps, etc. You can increase the demand on the alternator by turning on headlamps, heater blower fans, and other electrical accessories to determine the draw capability of your alternator. If the engine immediately dies when the cable is removed, the alternator is probably bad
1. Put a voltmeter as close to the alternator as possible. (Positive and Negative both.) If you can put the meter leads directly on or in the wire coming off the alternator that would be optimum.

2. Now start the car and turn all accessories off and check the voltage level. It should be between 13.5 and 15.1 volts. (depends on your make and model of car) It is a good idea to write down all voltage readings your taking. The main thing your looking for is a drop in voltage. Once you hit around 12.5, your alternator is not going to produce any additional amperage.

3. Now turn on one accessory at a time. Write down that accessories fuse rating. Keep turning on accessories and adding fuse ratings until the voltage falls to 12.5. Now add 15 amps if your electric cooling fans are on and 10 amps per battery in your system. Your numbers may look like this.

2 batteries- 20 amps
Cooling fan- 15 amps
Headlights - 10 amps
A/C blower - 10 amps
Rear Dfrst - 15 amps
High Beams - 10 amps
Fuel Pump - 10 amps

Aug 05, 2009 | 2001 Nissan Maxima

1 Answer

2003uburban not charging

make sure you have power to the back of the alternator and make sure you have power from the plug

Oct 22, 2008 | 2003 Chevrolet Suburban

1 Answer

86 Tercel 2wd wagon won't charge it's battery

clean battery terminals ,bring battery to be tested after charging, after reinstalling battery run car and test alternator output it should be a minimum of 13-14volts if it is under 13 replace alternator , use a voltmeter set on 12 volt 10 amp dc to check the wire to check is located on the back of the alternator covered with a rubber grommet of course hold negative wirw on volt meter to ground and touch red wire to big terminal on back of alternator while car is running should have 14 volts or at least 13 volts

Jul 27, 2008 | 1986 Toyota Tercel

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