Battery Charging system check
02-09-2004, 11:57 AM
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Join Date: May 2003
Location: Pennsylvania
Posts: 149
Car Info: 2002 WRX
Battery Charging system check
This is the way to check your battery / charging system.
First alittle battery info:
1-a DEAD car battery without a load on it is 12volts
2-a FULLY CHARGED battery without a load is 13.4 volts
3-in order to charge a battery you have to "push" in more volts than what the battery has. i.e. 13.7-14.?
OK make sure everything is off and put your voltmeter across the positive and ground on the battery. It should be 13.4 for a fully charged GOOD battery. If its less then its in some sort of discharged state untill it gets to 12 volts then its discharged fully.
(Now if its discharged and the eloctrolite is frozen then your gonna have to thaw it out and hope the freeze action did not warp/ruin the plates/battery.)
OK so it reads lets say 12.5. Its pretty discharged. It wont have enough ummph to crank your engine over.
So you put it on a charger for awhile and then you get the engine started..
Now while its running, with all accessories turned off, you measure the voltage again and now its 13.7-14.?
What this tells you is that your charging system system is working while not under a load. Perhaps now turn on the lights. Adding a load. The voltage should still be in the 13.7-14.? area. Assuming that its ideling fast enough. Now if you have one of thoes 300W steroes and have the bass turned up you can watch the voltage fluctuate with the music. This may ON ADVERAGE, while ideling, take more away from the battery than the alternator can replenish. Thus after a few weeks your battery is discharged. i.e. car wont start.
Another possibility is a dirty connection =, i.e. battery terminal. Make sure they are clean, otherwise the charging currant wont make it to the battery resullting in a discharged battery over time.
So there you have it: You can determine if its your battery or your charging system at fault.
REF: I dont recall what the upper voltage is on a subaru voltage regulator so I left that 14.? .... Maybe somebody can fill that in?
Batterys have acid in them. Do not get it on you or your clothes. *L* Get it on your clothes and when you wash them you'll have holes
Batterys give off hydrogen while charging. So there is a potential for explosion when working with something that may cause a spark near a battery. Remember the Hindenburg.... BOOM
First alittle battery info:
1-a DEAD car battery without a load on it is 12volts
2-a FULLY CHARGED battery without a load is 13.4 volts
3-in order to charge a battery you have to "push" in more volts than what the battery has. i.e. 13.7-14.?
OK make sure everything is off and put your voltmeter across the positive and ground on the battery. It should be 13.4 for a fully charged GOOD battery. If its less then its in some sort of discharged state untill it gets to 12 volts then its discharged fully.
(Now if its discharged and the eloctrolite is frozen then your gonna have to thaw it out and hope the freeze action did not warp/ruin the plates/battery.)
OK so it reads lets say 12.5. Its pretty discharged. It wont have enough ummph to crank your engine over.
So you put it on a charger for awhile and then you get the engine started..
Now while its running, with all accessories turned off, you measure the voltage again and now its 13.7-14.?
What this tells you is that your charging system system is working while not under a load. Perhaps now turn on the lights. Adding a load. The voltage should still be in the 13.7-14.? area. Assuming that its ideling fast enough. Now if you have one of thoes 300W steroes and have the bass turned up you can watch the voltage fluctuate with the music. This may ON ADVERAGE, while ideling, take more away from the battery than the alternator can replenish. Thus after a few weeks your battery is discharged. i.e. car wont start.
Another possibility is a dirty connection =, i.e. battery terminal. Make sure they are clean, otherwise the charging currant wont make it to the battery resullting in a discharged battery over time.
So there you have it: You can determine if its your battery or your charging system at fault.
REF: I dont recall what the upper voltage is on a subaru voltage regulator so I left that 14.? .... Maybe somebody can fill that in?
Batterys have acid in them. Do not get it on you or your clothes. *L* Get it on your clothes and when you wash them you'll have holes
Batterys give off hydrogen while charging. So there is a potential for explosion when working with something that may cause a spark near a battery. Remember the Hindenburg.... BOOM
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