Bumpin' Yota

this came from a thread http://audioforum.termpro.com/ubb/ul.../t/003982.html over on termpro.com and is the email conversation btwn one of the forum members and dominick irragi... I was asked why can a rebuilder or store like Autozone not properly test an alternator.. I figured this would be a good place to post.. Here was the question Dom If you don't mind, I'd like to ask your explanation of why it is difficult to test alternators and how one can go about getting one properly tested? I know you're busy with work, but your contributions in the electrical arena could greatly help increase the knowledge base on this forum. Thanks! No problem, I would love to answer this question.. Here are the main reasons for each party that tries to test an alternator. Your hometown rebuilder. 1. They are just that, a rebuilder. They know very little about the ins and outs of an alternator. They just make a broke stock one work again. They also will tell you your crazy when you tell them an alternator can do 200 amps. They dont understand what they dont know. 2. When they do test an alternator,(on their bench), they almost always use small aligator clips to the battery post of the alternator. Probably 8 or 6 gage. Would you connect your 2000 watt amplifier to your battery this way? I dont think so....for obvious reasons. 3.On their bench test, they more than likely will never go over 3500 to 4000 rpm. Dont freak out, this is alternator rpm, not engine rpm. An alternator should spin atleast 3 times faster than your motor. The industry standard for max output is to be tested at 6000 rpm. Approximately 1500-2000 engine rpm. 3500-4000 is just above idle. 4.When a load is applied, it should be gradual. 75% of the test stations that are common to rebuild shops are either on.... or off when it comes to loads. (typically 300 amps) There is no way to ramp up the load presented to the alternator. When you load an alternator with an instantaneous 300 amps, the regulator does not have time to react and the reading will be substantially lower. It also depends on the type of regulator used. Some vehicles must have a time delay type regulator due to the car either being so new or aftermarket not available yet. When you load the alternator down, you keep going until the voltage level falls to that of the battery. Which is typically 13.0-13.5 This way all current being pulled is is being produced by the alternator, not the battery. You then take the current reading off the battery post of the alternator. Your local "Autozone" or "Advanced" I have taken my personal vehicle to both of these parts stores just to see why I get so many calls and emails stating "I had my alternator tested and it doesnt work or only does 20 amps". Both companies are improperly trained in how to test your alternator. 1.The first thing they do is roll out their tester and connect it wrong. They put the current clamp on the battery negative. Why they want to know how much current is going through your negative battery terminal is beyond me..... I personally like to know how much current is coming out the alternator OUTPUT terminal...which is the positive one. While your sitting there at idle, before the test even begins, the tester is telling you how much current is going through the negative battery terminal. This is how much charging current your battery is pulling. They all confuse this with how much current your alternator is doing at idle. You need to first load the alternator down before you can determine how much current your alternator is capable of producing. Just for example....I have 3-300 amp alternators on my Suburban. They told me I was doing 55 amps at idle and 168 amps max. He did admit tho after seeing under the hood, he didnt really know anything about setups like mine. I would type more, but I gotta go. If anybody would like some explanation of other issues, let me know. Hope this post helps. Thanks, Dominick Iraggi Dom If you don't mind, I'd like to ask your explanation of why it is difficult to test alternators and how one can go about getting one properly tested? I know you're busy with work, but your contributions in the electrical arena could greatly help increase the knowledge base on this forum. Thanks!

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3vze, 4x4, sr5, 90, auto, LSD
2x dB Drag World Finalist
2003 Nopi Nat. Street B champ
2004 SBN Street C champ
2004 SBN Advncd NW Champ
2004 Former WR Holder in NW.
SPL: 159.8db @ 42hz

In loving memory of Jamie Riggs 5/15/85 - 10/8/04

Blair

GREAT Post. This should go in the "Tips and Tricks" section so we can get it when we need it. Thanks for the edification. You learn something new every day!

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91 4Runner, 5 spd, with the Mighty 3.0!
0 to 60 in 2.5 liters.

snap-on

I have a few issues with the above.

1) generally im trying to get my alternator tested because i think its not working ie its output is nearly 0 amps. so even a puny 20 amps at idle is more than 0 and at least SOME indication that the alternator is working.

2) he talks about instantiously applying a (test) load to the alternator and some how this is unreaslitic? ummmmm oddly enough its JUST like when i flip the switch on my 4 140w daylighters! there is no, they dont come on kinda dim then finally get bright, BOOOM they are on and drawing 40 amps. THe regulator CIRUCUT (ie electrionics) is just that, electronics, capable of "responding" in fractions of a second. So why there may be a fraction of a sec that the lights draw off the battery, the alternator SHOULD be able to ramp up output with in a sec or less.


I have always considered autozone/advance whatever that test alternators as is it DOA? not "is it still capable of putting out full design rated current"

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94 EX cab, 5speed, V6, locked, ARB bar, NWOR headers
92 4runner, auto, V6, OME suspension, Downey headers

Bumpin' Yota

Well how I am able to tell is with a DMM measuring the voltage at the battery. If the voltage with the engine off is around 12.9v, then you fire up the engine and the voltage increases to say, 13.5v, then yes your alt is working.

I think what dom was referring to as far as load testing the alt is not a meager 40 or 80 amp draw, but rather a draw that is much higher than what the 160+ amp alt can provide. If one monitors the system voltage during testing and has a good clamp meter to measure current flow you can determine at what point the alt cant put out any more current. He was saying that such a severe load should be applied gradually not all at once. The same concept would hold true for a manual tranny truck...do you bounce off the revlimiter and dump the clutch all at once while towing a 20,000lb trailer with your tacoma to see how far you can move it? (God I hope not...lol)

__________________
3vze, 4x4, sr5, 90, auto, LSD
2x dB Drag World Finalist
2003 Nopi Nat. Street B champ
2004 SBN Street C champ
2004 SBN Advncd NW Champ
2004 Former WR Holder in NW.
SPL: 159.8db @ 42hz

In loving memory of Jamie Riggs 5/15/85 - 10/8/04