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Old 06-25-2019, 10:42 AM   #1
Merc Cruzer
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Default Amp test on the generator

Preliminary test seem to show that the battery is not charging when the rpm's are increased to 2000.

As you can see I would like to perform an AMP test on my generator with my Sears engine analyzer (that I have had forever). The question is what terminal do I put the the "shunt" on: red arrow post, white arrow post or black arrow post?

If additional photos are needed to answer, let me know.

Found this on Utube, interesting: https://www.youtube.com/watch?v=RjLW_eb3D-c

Thank you,

Merc Cruzer
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Old 06-25-2019, 10:52 AM   #2
WABOOM
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Default Re: Amp test on the generator

subscribed for future reference
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Old 06-25-2019, 11:07 AM   #3
Kurt in NJ
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Default Re: Amp test on the generator

Whatever wire is"armature "
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Old 06-25-2019, 11:24 AM   #4
tubman
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Default Re: Amp test on the generator

That unit looks very similar to an Aacron tester I bought many years ago for a quarter at a garage sale. I went looking on the intenet and quite easily found a manual for it that I was able to download and print out. Once I had that, I found out what a handy little device it is. All of the functions still seem to work too.
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Old 06-25-2019, 11:43 AM   #5
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Default Re: Amp test on the generator

I had one once upon a time. No idea what happened to it or when!
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Old 06-25-2019, 12:00 PM   #6
Merc Cruzer
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Default Re: Amp test on the generator

Quote:
Originally Posted by Kurt in NJ View Post
Whatever wire is"armature "
Black arrow post would be the armature, the red arrow post would be the field and the white arrow post would be the ground, if I am reading the diagrams correctly.
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Old 06-25-2019, 01:06 PM   #7
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Default Re: Amp test on the generator

The field is power input so the generator gets the magnetism for it to generate power. The armature terminal is the output for power. Keep in mind that a generator is a controled unit with that control provided by the voltage regulator with current limiter. The output generated will only be what is necessary to charge the battery and provide power for the system. If the battery is fully charged, it won't have any output. The test for output is usually done with a jumper to the field so that it will put out an uncontrolled amount of amperage for the brief test. Only test the generator long enough to see that it will go to it's max output then stop the test. You don't want to damage anything. It doesn't take long for a good generator to get up to 30 or 35 amps when control is bypassed.

Many test amp meters have the shunt built in but yours is an older unit that doesn't seem to have that option. I'd say a person should disconnect the armature terminal wire from the generator then attach the shunt as illustrated. This will allow it to read the amperage as designed. The shunt allows the amp meter to only get a sample and not full force amperage.
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Old 06-25-2019, 01:15 PM   #8
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Default Re: Amp test on the generator

As stated shunt goes between armature on the back and the cable...the instrument is reading the voltage drop over the shunt to see how many amps pass through it.
You really need a load to perform a more extensive test...old style is a "carbon stack"
basicly a large variable resistor to load the generator.
Modern style is an electronic load which you can program for a set load or voltage...
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Old 06-25-2019, 01:17 PM   #9
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Default Re: Amp test on the generator

The easiest generator output test is to use a "clamp on" tool to read the output level at the battery cable. Ours is a professional "Amprobe". Most well equipped shops have them. For hobbyists, there are accessories for volt-ohm meters. We like ours because no disconnecting is required. Often, simply disturbing a connection can mask the cause of the problem.
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Old 06-25-2019, 02:10 PM   #10
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Default Re: Amp test on the generator

This basically what the loop ammeter is doing, measuring current flow from the generator to the battery. With a charged battery the ammeter will show only a small current flow.
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Old 06-25-2019, 06:20 PM   #11
Merc Cruzer
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Default Re: Amp test on the generator

Completed the test on the generator with the Sears engine analyzer, and it showed a less than maximum amperage output. So I took it out and took it to the local Carquest and they confirmed that it was only putting out only 20.7 amps. Voltage was right on at 7.2. The voltage regulator also passed. Suggestion was to clean and polish the commutator and clean the brushes.

Last edited by Merc Cruzer; 06-25-2019 at 08:18 PM.
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Old 06-25-2019, 07:16 PM   #12
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Default Re: Amp test on the generator

"CarQuest" tested it, told you what was wrong, and how to fix it? WOW! What is this world coming to? Usually they just try to sell you new parts. Sounds like a "keeper" as a parts store!
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Old 06-25-2019, 07:33 PM   #13
Merc Cruzer
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Default Re: Amp test on the generator

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"CarQuest" tested it, told you what was wrong, and how to fix it? WOW! What is this world coming to? Usually they just try to sell you new parts. Sounds like a "keeper" as a parts store!
Definitely a keeper. He wouldn't even let me pay him for the testing. The owners car was parked out side when Google took the picture of the store, it is a 31'.

https://www.google.com/maps/place/Ca...4d-105.3362368

Last edited by Merc Cruzer; 06-28-2019 at 07:08 AM.
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Old 06-25-2019, 10:26 PM   #14
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Default Re: Amp test on the generator

Quote:
Originally Posted by rotorwrench View Post
The field is power input so the generator gets the magnetism for it to generate power. The armature terminal is the output for power. Keep in mind that a generator is a controled unit with that control provided by the voltage regulator with current limiter. The output generated will only be what is necessary to charge the battery and provide power for the system. If the battery is fully charged, it won't have any output. The test for output is usually done with a jumper to the field so that it will put out an uncontrolled amount of amperage for the brief test. Only test the generator long enough to see that it will go to it's max output then stop the test. You don't want to damage anything. It doesn't take long for a good generator to get up to 30 or 35 amps when control is bypassed.

Many test amp meters have the shunt built in but yours is an older unit that doesn't seem to have that option. I'd say a person should disconnect the armature terminal wire from the generator then attach the shunt as illustrated. This will allow it to read the amperage as designed. The shunt allows the amp meter to only get a sample and not full force amperage.

Good explanation. Generators produce power, it's what they do. The more they turn the better. Why cutouts and voltage regulars are necessary. They are not alternators.


Amps draw from battery power on a normal system, gens kick in to supply voltage usage/ or an alternator. Less you are putting in 22" kickers, not sure why amps would be an issue?




.

Last edited by Tinker; 06-25-2019 at 11:42 PM.
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Old 06-26-2019, 09:11 AM   #15
Merc Cruzer
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Default Re: Amp test on the generator

The original reason for the amp test was: a while back when I got up early, before the sun came up, to go to a show, the generator would not keep up with the lights, especially when they were on bright, driving down the unlit mountain roads. Never had an issue driving during the day. Now I have a good idea as to why.

Last edited by Merc Cruzer; 06-26-2019 at 11:35 AM.
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Old 06-26-2019, 03:46 PM   #16
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Default Re: Amp test on the generator

I'm glad you posted this; just another thing to keep your eye on (as if we don't have enough the way it is).
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Old 06-26-2019, 04:12 PM   #17
Merc Cruzer
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Default Re: Amp test on the generator

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I'm glad you posted this; just another thing to keep your eye on (as if we don't have enough the way it is).
Now thinking of looking for a backup generator, just to put on the shelf. You know if you have one you will never need it, but if you don't...
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Old 06-26-2019, 04:35 PM   #18
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Default Re: Amp test on the generator

My 49 thru 51 shop manual states that the units should put out at least 33 amps for the Mercury that is set up to generate 35-amps. It's probably just tired and in need of a refresh.
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Old 06-26-2019, 07:45 PM   #19
Merc Cruzer
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Default Re: Amp test on the generator

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Originally Posted by rotorwrench View Post
My 49 thru 51 shop manual states that the units should put out at least 33 amps for the Mercury that is set up to generate 35-amps. It's probably just tired and in need of a refresh.
Define "refresh". I am about to take it of of the car and clean and polish the communicator and brushes. Any other suggestions while I am in there. It was fully serviced about 10 years ago, after I bought the car, by a older auto electrical shop in Denver.

Last edited by Merc Cruzer; 06-26-2019 at 08:19 PM.
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Old 06-26-2019, 07:52 PM   #20
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Default Re: Amp test on the generator

Did you ask CarQuest how they tested your generator and arrive at 22 amps output ? To test for maximum output the generator needs to be run up in a generator test bench that can rev it up to 3000 RPM plus, with the voltage regulator not connected. To do this the field terminal is connected to the armature terminal with a jumper wire and the battery connected across the armature and ground terminals. You should get 33 amps or more on this test depending on the revs. You could also do this test on the car for a few seconds to prove the generator is up to specs. Maybe CARQUEST ran it up with the regulator connected in the circuit or their test bench electric motor did not have the power to rev the generator hard enough. You need to get the facts. Most automotive generator test benches have a variable speed electric drive motor of at least three horsepower. An auto electrical repair shop would be the best people to do this test, not a spare parts store who may not have the expertise. Regards, Kevin.
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