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Battery/Alternator check
From: "RG" > To: "Ralph" > Subject: Fw: How to test Battery/alternating testing Date: Saturday, November 27, 2004 9:48 PM ----- Original Message ----- From: "Ackerman" > Newsgroups: alt.autos.lexus Sent: Sunday, November 07, 2004 6:28 PM Subject: How to test Battery/alternating testing |I thought I'd layout the procedure to check your battery and charging | system. First, the battery has to be fully charged. Then take a voltage | reading, which should be about 12.5 volts. Next start the engine and the | voltage reading should go to 14.5 or so. This tells you the alternator is | putting out. The last question is whether it is putting out sufficiently. | So, turn on the headlights and see if the voltage stays about 14.5. If so, | the charging circuit is OK. | | Next you need to verify whether there is drain back from the battery when | the engine is off. To do this, disconnect one of the battery terminals and | place an ammeter in series with the battery terminal and the removed cable. | There may be an initial surge of current, but should quickly stabilize to | less than 50 milliamps. Make sure you close the car door and have all | lights off. On some cars this reading can be as high as 80 milliamps, but | any higher than this will cause a dead battery after a few days. If higher | you need to remove fuses one at a time or check for leakback through the | alternator. Sometimes something as simple as a trunk light switch can cause | the problem. | | Lastly, you need to check the battery to see if it can hold a charge and | whether it can provide enough power to start the engine. To do this, again, | the battery must be fully charged. Take a voltage reading (should be about | 12.5). Disable the engine so it will not start. This is best done by | removing the fuse for the fuel pump. Crank the engine for 5 seconds (use a | watch). Wait 15 seconds and do again. Repeat this several times. You | should be able to do this 10 or more times before the battery goes dead. If | it fails sooner, the battery is defective (assuming you don't have excessive | current draw problem with your starter). | | Lastly again starting with a fully charged battery, disconnect either | battery terminal. Take a voltage reading. Wait 12 hours and read again. | Repeat this for two days. The voltage should no drop more than.1 volt. | Reconnect the battery and crank the engine. If it cranks, battery is OK. | | | John Ackerman | | | |
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