Hi i have the problem where my car 12v battery run down after a day or two.I checked my alternator(output okay) and charging circuits but that test okay.I looked for any short circuited wires but can't find any.Currently i have the option of a 2nd battery+charger.But it's a nuisance i can live without.Any suggestions as to what i can look for and what circuits i can still test?
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Hi , you need to have the battery checked for condition, it may not be retaining charge because one or more of the cells is in bad condition. Assuming you have a 12v battery, it should be producing rather more than that while the engine is running and the charging circuit is performaing it's task of keeping it charged. Ideally this value will be around the 14 v mark. If the value is below the 12v the battery requires then the battery will not charge but slowly become depleted. Somebody should check the battery output with the engine running , with a multimeter, to establish whether this is the case.
If the output is below 12v have the alternator checked, check the drive belt is appropriately tensioned so that the alternator can be properly driven. It may be that the alternator itself is faultyand needs servicing or replacement.
It might be that there is a fault with one of the components in the electrical system that is the battery to drain, this is not very unusual and can sometimes be traced to components such as the BCM, (body control module,) an electrician can establish this for you.
It should be a fairly straightforward task to track the cause of this problem in the case the battery/belt/alternator are at fault.
Check if the alternator output is 13 volts to 14 volts or when the engine runs try to disconnect the negative (- ) terminal from the battery, if it still runs your alternator is okay. Just to check if that new alternator works.
If the procedure that I have told you is working, the battery must be brought to the nearest battery center, they have a load tester that will definintely assess the battery's condition if it really good or needs to be replace.
You either have a bad battery or a bad alternator. Most alternator shops and Advance auto parts store will check both for free. It is possible for an alternator to charge the battery while the car is running but kill it when it is switched off because of a bad diode in the alternator.
There seems to be a no charge state in this case. I recommend checking the charging system. use the procedure below to isolate this issue.
Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a +positive terminal (red), - negative terminal (black). Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. (Note: never disconnect the battery while the engine is running. If the battery cable is disconnected from the battery a spark can be generated which can cause the battery to explode or a major electrical malfunction to occur.)
To check a battery surface voltage, remove the positive terminal protective cover. Connect the +positive side meter lead (red) to the positive side battery terminal. Connect the - negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts.(You will need to use a voltmeter for this testing procedure)
The alternator is rotated by a drive belt driven by the vehicles engine while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running.(most non charge states will be the cause of a loose belt or a low tension rate, due to a mis-adjusted alternator. make sure you have enough tension in the belt for full rotation of the alt pulley)
Next, you will need to check the alternators output with the Amp meter.
Testing the amperage output of the alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage. Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter is needed. Once the meter is connected start the engine. Next turn on all electrical accessories and raise the engine idle to about 1200 RPM. The alternator should output the max amperage it was designed to produce. Example: a 90 amp alternator should output about 88 amps. Note: An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail. An alternator is designed to operate at max amperage output only for a reasonable amount of time.
((Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive) at engine idle the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing.)))
sounds like the alternator is shot and is not supplying sufficient power to the engine or even enough to charge the battery, try replacing it, and you said the dash light for the alternator is on so its most likely the alternator
Check the voltage regulator if there's coming out of it. you may have a good alternator but if nothing goes at the alternator, then, it results to a drained battery. Just replace your regulator, if this is not working.
the regulator is in the alternator. it sounds like it isn't charging the battery anymore. battery voltage should be around 14 volts with engine running. also check connections at alternator to battery. have seen corrosion here keep the battery from charging