posted
I was once 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 design and function of an alternator. They just repair factory alternators by replacing parts. 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 with 8 gage? 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 loading. (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
Post edited to add alternator testing procedure.
Ok, I guess I forgot to actually explain how to test an alternator.
I will explain it two different ways. One is how to test your own alternator and make sure its producing current and the other is how an alternator shop should test your alternator.
1. Put a voltmeter as close to the alternator as possible. (Positive and Negative both.) If you can put the meter leads directly on or in the wire coming off the alternator that would be optimum.
2. Now start the car and turn all accessories off and check the voltage level. It should be between 13.5 and 15.1 volts. (depends on your make and model of car) It is a good idea to write down all voltage readings your taking. The main thing your looking for is a drop in voltage. Once you hit around 12.5, your alternator is not going to produce any additional amperage.
3. Now turn on one accessory at a time. Write down that accessories fuse rating. Keep turning on accessories and adding fuse ratings until the voltage falls to 12.5. Now add 15 amps if your electric cooling fans are on and 10 amps per battery in your system. Your numbers may look like this.
2 batteries- 20 amps Cooling fan- 15 amps Headlights - 10 amps A/C blower - 10 amps Rear Dfrst - 15 amps High Beams - 10 amps Fuel Pump - 10 amps --------------------- Total not including stereo system 90 amps.
If you can turn on all these accessories and your voltage does not fall below 12.8 your alternator is capable of producing more than 90 amps of current. You can now turn on your system and start slow on the volume. Its hard to say how much current your system pulls unless you know how much power your amps are producing at a given volume level.
You will need to do all these measurments at idle and at 2000 rpm. This way you can test idle output and max.
NOTE: When testing output at idle your numbers may appear a little low. It is probably because your alternator is making your motor bog down and when you spin an alternator slower it can not produce as much amperage.
-------------------- 2006 Bass Race 149.9 World Finals 2nd place H.O. Alts FI If you dont like what I have to say, just contact Boomingcreation he will erase it for you Posts: 16072 | From: tx | Registered: Dec 2003
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Ya thanks..I took my Alternator over to a local shop and the guy told me it cant possibly work or put out the amps you say it does..He told me to my Face I was full of **** no alternator can put out more than 160 amps..I laughed at him..He didnt like that at all..Told me to F Off..
-------------------- Team SoundStream Team Atomic Team Iraggi Alternators 2005 Spring Break Nationals Champ Meca M2 155.2 2005 Florida State Champ Meca M2 157.0 with one sub. 2005 Meca M2 World Champion 2 SS XXX 6500Ds 2 Atomic APX 10s 2006 Street A Participant Posts: 754 | From: Tequesta Fl | Registered: Jan 2004
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couldnt have thought of a better person to have answer the topic at hand btw dom your alternators suck hehe that 260amp of yours i put on the blazer today made me see how much that 280 amp ohio wasnt doing its job think that confermed what alternators are going on my truck ill be in touch
-------------------- --Chris Crane-- 2004 MECA M1 State Champion 2004 MECA MR1 State Champion 2004 MECA Finals 2nd Place MR1 2004 MECA Finals 2nd Place MQ1 Posts: 225 | From: Bedford In | Registered: Oct 2004
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we will not dom but all i have to say is dzamn man just got my package from you and all i can say is wow thanks man ..if you go to sbn i gotta shake your hand now time to get installed on there and hook it up ..
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Interesting, I was given a PG 140 amp HO alt by a friend of my dad's who was an old competitor. I took it into this alt repair shop where the guy laughed at me when I told him it was suposed to be 140amp, he gave me his spheel on how that's impossible and so on, but then tested it.
He told me it put out 6 amps, and that 3 of the diodes were blown. Now I didn't know what he was talking about, and just assumed he did. Is there anyway short of sending the alt someplace to see if it actually works?
-------------------- North Dakota MECA Event Director Posts: 622 | From: Bismarck, North Dakota | Registered: May 2005
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Everyone gets Ohio's numbers mixed up. From what I have seen, their numbers are Cold/Hot, not Max/Idle. The 188 is hot and the 212 is cold. I may be mistaken, but im almost positive thats the way they rate them.
I wouldnt trust Autozone to test an alt..... Unless I was using their equipment. LOL
Dom
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i still dont see how this tells me how to test my alt...
can i just hook up my true rms DC ammeter to the alt charging lead and burp my system?
-------------------- Team Art of Noyze DiRtY SoUtH DEAF SqUaD Elemental Designs Representative 150+ Nissan pickup and 150+ Rex United States Marine Posts: 2110 | From: Atlanta,GA,USA | Registered: Dec 2000
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Hey Dom, I have a few questions? Whats the difference between your dominator and amputator series alts?
Also what # is most important? the idle amperage?
I was wondering because I was looking at your alts on ebay and noticed that the lower rated alts put out more power at idle:
220 amp alt - 175@idle 280 amp alt - 145@idle 300 amp alt - 145@idle
why is that? is it best to just look at the idle rating?
I'm planning on buying one from you by this spring, which one should i get for a 6kwatt system? I'll have 2 extra batteries too, not sure what kind though.
Posts: 1340 | From: Cleveland, Ohio | Registered: May 1999
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I have seen a lot of local shops that test the alternator's output with a volt meter only and not a DC current clamp. If the voltage rises with the car running they assume that it is charging the battery. Some of my customers have been told by such places (parts stores & even car dealer "electronics techs") that the alternator charges the system by increasing the voltage going out the battery, not supplying it with current. It's frustrating. Stick with the pros not the parts changers! I've accumulated too many grey hairs arguing with parts changers about even the most basic dc electrical principals.
-------------------- Stereo West Auto Toys 2006-7 Mobile Electronics Magazine Retailer of the Year! SWAT Team 2006 USACi SS 301-900 World Champion 159.4db Posts: 134 | From: omaha, ne | Registered: Aug 2002
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I was an assistant manager at Advance Auto Parts. The reason they put the clamp on the negative wire is because the sticker on the test equipment instructs them too for some stupid reason Im un aware of... However I told my team to put it on the positive lead Why in the world would the sticker on the equipment state to put the clamp on the negative terminal?
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2 DD3515s for when I blow the dustcaps off my MT's Posts: 253 | From: Fayetteville Tennessee | Registered: Nov 2003
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quote:Originally posted by AudioFaNaTiC: I was an assistant manager at Advance Auto Parts. The reason they put the clamp on the negative wire is because the sticker on the test equipment instructs them too for some stupid reason Im un aware of... However I told my team to put it on the positive lead Why in the world would the sticker on the equipment state to put the clamp on the negative terminal?
Putting the clamp on the battery negative is fine if your just testing the battery. Not the alternator. You can also not test the battery when the car is running. I think they just dont know what they are doing or they want your alternator to look bad so you buy one.
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2002 UsaCi Super Modified 0-1000 World Champion 173.6 2002 UsaCi Legal World Record Holder Expert 0-600 (B&K) 171.0 (171.4) 2003 Meca XX-Class Record Holder 172.0 (backed
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