Would you suspect that the voltmeter wasn't lying though?Salsa Guy wrote:The alternator test while installed in the car is iffy at best. Battery test is ok but not perfect.
The voltage drop from 13.5v to 12.4 that you witnessed is normal. As far as the alternator load test you performed, when you turn on accessories and check voltage you always want to have the engine running at 2000 revolutions per minute. It is not uncommon to have low voltage at idle will all of the accessories on. Try the load test again with the engine at the proper RPM.wintersilke wrote:Vibe wouldn't start this morning and had to get a AAA jump. Started right up with boost.
Tech ran their test, which said the alternator was fine, but the battery had to be charged and tested again, so I drove it around for an hour, then went to O'Reilly's.
With the car on, O'Reilly tested the battery which came back as good but the voltage was dropping as he tested it. It started at 13.5 V but after 5 min. had dropped to 12.4 V.
After sitting for 4 hours in the cold, the battery voltage is sitting at 12.6 V. After starting the engine with all the electrical draws off, voltage reads at 14.2. Turning on the radio, A/C, headlights, fog lights, and all the wipers, voltage drops to 12.6. After 5 min. of monitoring it, voltage is now at 11.9.
Does that sound like an alternator that is on the verge of failing completely?
That still doesn't seem out of the ordinary. It wasn't designed to hold a full load at idle. You really just need to perform a proper alternator load test if you're worried about it.wintersilke wrote:But shouldn't the alternator mostly keep up with the load on it?
I reran the test later and after 20 min. the voltage had dropped to 11.1 V with everything on and the engine was sputtering.
Perform the whole test with the engine at approximately 2000rpm. First turn all the accessories off and check battery voltage. It should be around 14v. Now turn all the accessories on and check voltage again. It should be no less than 12v.wintersilke wrote:Okay...so now I've got to ask. What is considered a proper alternator load test? Is it something I can do with a simple voltmeter or do I need something more complicated?
Glad you got it fixed. For future reference, a fully charged battery is 12.6v or more. Any time the charging system is outputting less than 12.6v the battery is being discharged and that is NOT normal.wintersilke wrote:We replaced the alternator and with a full load with everything on in, the terminals show 14.1 V so I call that a success.
beemerphile1 wrote:Glad you got it fixed. For future reference, a fully charged battery is 12.6v or more. Any time the charging system is outputting less than 12.6v the battery is being discharged and that is NOT normal.wintersilke wrote:We replaced the alternator and with a full load with everything on in, the terminals show 14.1 V so I call that a success.