# Do I really need to remove my alternator to have it properly tested? **URL:** \ **Category:** Factual Questions\ **Created:** [June 28, 2011, 1:05am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082 "2011-06-28T01:05:06Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![I\_Know\_Nothing](https://avatars.discourse-cdn.com/v4/letter/i/f04885/32.png) [@I\_Know\_Nothing](https://boards.straightdope.com/u/I_Know_Nothing)\ **Post date:** [June 28, 2011, 1:05am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/1 "2011-06-28T01:05:06Z")
I took my 2001 Jeep Cherokee to Autozone(auto parts store) to have the alternator tested. I am suspicious that it just overcharged and ruined my last battery. The guy at Autozone said I would need to remove the alternator to have it tested. Oh man, is this really necessary? Is there no way to verify whether or not its overcharging with it still in my car? ---
**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\ **Post date:** [June 28, 2011, 1:15am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/2 "2011-06-28T01:15:25Z")
> [@I\_Know\_Nothing](#): > > I took my 2001 Jeep Cherokee to Autozone(auto parts store) to have the alternator tested. I am suspicious that it just overcharged and ruined my last battery. The guy at Autozone said I would need to remove the alternator to have it tested. Oh man, is this really necessary? Is there no way to verify whether or not its overcharging with it still in my car? I’ve always just put a meter on the battery to test the alternator. You should get around 14 volts with the car running, much more or less and it’s a pretty good indication you need to investigate further. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [June 28, 2011, 2:34am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/3 "2011-06-28T02:34:55Z")
You need to remove it to have it tested with their type of test equipment. It can be tested on the car by a repair shop, which they’re not – they’re a parts store. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 28, 2011, 3:55am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/4 "2011-06-28T03:55:53Z")
> [@boytyperanma](#): > > I’ve always just put a meter on the battery to test the alternator. You should get around 14 volts with the car running, much more or less and it’s a pretty good indication you need to investigate further. This is actually a very marginal test. The diode bridge in the alternator can become defective in a way that allows perfect voltage at normal load conditions, but fails under heavy load (headlights and AC on). When the parts store test the alternator, they test it under load. ---
**Author:** ![Al\_Bundy](https://avatars.discourse-cdn.com/v4/letter/a/e79b87/32.png) [@Al\_Bundy](https://boards.straightdope.com/u/Al_Bundy)\ **Post date:** [June 28, 2011, 11:22am UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/5 "2011-06-28T11:22:10Z")
> [@beowulff](#): > > This is actually a very marginal test. The diode bridge in the alternator can become defective in a way that allows perfect voltage at normal load conditions, but fails under heavy load (headlights and AC on). When the parts store test the alternator, they test it under load. But you can apply that substantial load by turning all he accessories on including heater, lights, radio, etc. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [June 28, 2011, 12:32pm UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/6 "2011-06-28T12:32:37Z")
The standard procedure for on-car alternator testing includes measuring the charging voltage at idle with headlights on and blower on high. Those two items are considered to provide sufficient load. ---
**Author:** ![TurboNuke](https://avatars.discourse-cdn.com/v4/letter/t/f19dbf/32.png) [@TurboNuke](https://boards.straightdope.com/u/TurboNuke)\ **Post date:** [June 28, 2011, 6:20pm UTC](https://boards.straightdope.com/t/do-i-really-need-to-remove-my-alternator-to-have-it-properly-tested/587082/7 "2011-06-28T18:20:12Z")
With the car off, a charged battery should read about 12.7v. With the car running, the voltage should read 13.5-14.5 volts. Check the voltages with the car off, and running with little electrical load and with a lot of load (ie. headlights and blower on high). The two times I’ve seen failed voltage regulators the alternators put out about 18 volts so it was easy to tell.