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Old 09-01-2014, 03:34 PM   #1
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Alternator check?

Noticing that my alternator seldom puts out more than 25A even after running my small, 6" foam insulated, danfoss, reefer overnight. I began to wonder if the alternator had lost it's ability to put out it's rated 100A at all. The ammeter does jump up and up as I turn on more loads and the voltage is 13-14.2 while running. The battery is nicely charged after a days run, still it would be impossible, at this rate, to recharge on the hook.

I decided to put my battery load tester on the alternator (200A) on the alternator to force it to put out full amperage and naturally I connected it after the ammeter shunt so it would register on the ammeter. It only went to 50A... Altho I didn't expect 100A I did expect better than 50A.

I have a smart regulator on this which I originally set for 90A because I only have a single belt to drive the alternator.
Could this regulator have "reset" itself?
Could the regulator have been in some other mode (other than bulk) which reduced the amperage output?
Can an alternator be 1/2 gone (not working)?
Ideas?
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Old 09-01-2014, 04:45 PM   #2
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What alternator and regulator are you using?

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Old 09-01-2014, 05:21 PM   #3
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What alternator and regulator are you using?

David
It's a Delco SA10 type I think and stamped 135 amps made for 60-79 vintage GM's

The regulator Hehr Power Systems 10-82 multistep older but like their 10HD series now.
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Old 09-01-2014, 06:23 PM   #4
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Could be the regulator not telling the field to go gangbusters. Could be the pulley on the alternator was not well chosen for the typical rpm of the engine and not spinning fast enough (what rpm do you cruise/wot and did you test the alternator at). Could be partially blown diodes in the alternator rectifier circuit and you are only getting a fraction of the charging waveform.

Lots to check here. It might be easiest to check on a bench. If it checks out, then come back and figure out whether its the pulley ratio or regulator. You can manually power the field to trick the alternator into going full out.

A quick search found this: Smells pretty close to correct and most alternators work the same theory.
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Old 09-01-2014, 08:10 PM   #5
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You didn't say what engine rpm you were testing at, but no alternator will put out its max at low rpm.

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Old 09-01-2014, 08:17 PM   #6
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Ghost, thanks. I checked at various rpm's but even with the 150A battery teater load on it, still max 50A (actually 45). If I recall, you can remover the plug from the alternator (2 prongs 1=tach, 1=field) and put full bat voltage to the field for a moment and expect the alt to put out full amps. I'd like to confirm this b/4 I try it though.

If it fails that test it needs repair, if it passes, maybe it's the regulator.
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Old 09-01-2014, 08:53 PM   #7
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Quote:
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If it fails that test it needs repair, if it passes, maybe it's the regulator.
This may have been mentioned, but have you checked the settings on your smart regulator? Some will allow adjustment settings.
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Old 09-01-2014, 09:31 PM   #8
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How big is the battery bank? How many amp-hrs was it down when the charge started? What was the battery voltage prior to charging? Just trying to get a better picture of what the alternator is being asked to recover.
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Old 09-01-2014, 10:25 PM   #9
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When in doubt take it to a generator shop (I've used Auto Zone) for a load test.
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Old 09-02-2014, 04:38 AM   #10
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This may have been mentioned, but have you checked the settings on your smart regulator? Some will allow adjustment settings.
Yes this reglator does have such a setting and as mentioned was set for 90A when installed (2003)
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Old 09-02-2014, 04:44 AM   #11
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How big is the battery bank? How many amp-hrs was it down when the charge started? What was the battery voltage prior to charging? Just trying to get a better picture of what the alternator is being asked to recover.
No b/4 measurements taken just the observation that ammeter used to show high rates 50-70 sometimes and now never does more than 25 (45 with the 150A load tester on it)
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Old 09-02-2014, 04:53 AM   #12
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When in doubt take it to a generator shop (I've used Auto Zone) for a load test.
I have used Auto Zone too for car stuff but their tester, judged by the gauge of the test lead and the feeble belt drive, couldn't handle 135A if it had to IMO. If I pull the alt I'll take it to a ahop that can give me a real test. I thought I was doing that myself with the load tester but too many variables I guess. For one, my "smart" regulator may have been out of the bulk mode when I ran the test, I think that could do it right there.
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Old 09-02-2014, 06:09 AM   #13
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and put full bat voltage to the field for a moment

You will produce way over 12v , as much as 150V , so turn as much off as you can.

Best is still the free checkup at Auto Zone .
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Old 09-02-2014, 01:39 PM   #14
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Try Autozone. If they can't do it then take it to a proper rebuilder and get them to check it..

Be absolutely sure about the cabling and connections between the alternator and the batteries including the negatives. All it takes is one lousy connection to screw it all up.

If the alternator is working, good voltage, but the current output is low then it could simply be connections. If the voltage rises on the alt. main output terminal then the alt. would appear to be working.

As suggested though the failure of a diode set would reduce the output substantially. If they fail shorted you will have a path to ground from the batteries which can be checked for with a DMM or VOM. If they fail open the alternator simply loses output which is harder to detect. Frequency might be helpfull but you would have to know how many poles there are and the revs [alt.] to know what freq. to expect.

Check that the output from the regulator to the alternator is actually working. Measure the current with partly discharged batteries AND the load tester again. Maybe the regulator is not calling for full current or its connection is poor. On my Ample Power controlling a Delco 22SI the control current is ~ 6A with partly down batteries at idle or higher revs. The alt. current output then is dependent upon revs. I do have mine turned down also so you would have to do a bit of sleuthing to find the full regulator output current. The manual should tell you. If, with partly down batts., you only see 1 or 2 o3A than maybe the regulator is the problem.

Keep in mind that the regulator sensing connections and power connections must also be good or it too cannot do its job.

Get it [alter.] checked OR depending upon mounting style maybe it would be easier and cheaper to simply get a replacement, new or rebuilt. But be sure about the cabling or the problem will still be there.

Sorry can't be more help
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Old 09-02-2014, 02:04 PM   #15
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Brooksie- So you load test the batt bank with alt being spun by engine and concerned that ammeter shows low amps. Big question from me is what is batt terminal voltage during this test? If still around 14v, alt and reg are doing their job regardless of what ammeter displays.
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Old 09-02-2014, 03:55 PM   #16
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All of the above are good suggestions. The "full field" test will tell you quickly if the alternator is putting out to spec.

Run the engine to decent rpms, at least 2,000. Put the 200 amp test load on it. Then jumper from the big starter terminal to the field terminal for few seconds. You obviously have a way of measuring net alternator current. If it is below spec then:

1. Blown diodes
2. Bad connection from alternator output to battery/load.
3. Slipping belt
4. Pulley ratio not spinning it fast enough. Most need to go 4,000 for full output.

I can't think of anything internal to the alternator that would allow partial output other than diodes.

If the output is near spec, then it is the regulator or its wiring. Measure its field current output with a clamp on ammeter with the load on as in above. Should be 5-10 amps.

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Old 09-02-2014, 05:33 PM   #17
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Brooksie- So you load test the batt bank with alt being spun by engine and concerned that ammeter shows low amps. Big question from me is what is batt terminal voltage during this test? If still around 14v, alt and reg are doing their job regardless of what ammeter displays.
Ski, thanks, I must recheck that with my digital VM attached, I didn't do that, just looked for amps output, Nor did I make note of the bat state of charge b/4 I just put the 150A load on the battery and expected the 135A alt to respond with more than a 45A output.
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Old 09-02-2014, 05:41 PM   #18
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All of the above are good suggestions. The "full field" test will tell you quickly if the alternator is putting out to spec.

Run the engine to decent rpms, at least 2,000. Put the 200 amp test load on it. Then jumper from the big starter terminal to the field terminal for few seconds. You obviously have a way of measuring net alternator current. If it is below spec then:

1. Blown diodes
2. Bad connection from alternator output to battery/load.
3. Slipping belt
4. Pulley ratio not spinning it fast enough. Most need to go 4,000 for full output.

I can't think of anything internal to the alternator that would allow partial output other than diodes.

If the output is near spec, then it is the regulator or its wiring. Measure its field current output with a clamp on ammeter with the load on as in above. Should be 5-10 amps.

David
Understand... I need more equipment and time next time I go to the boat to do the tests you (&others) suggest. The belt and pulley ratio (almost 4:1) are fine but I'll check belt again. with the load on, there was no rise in amps beyond 2000 engine rpm.
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Old 09-02-2014, 05:59 PM   #19
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Your battery was dumping into the tester at the same time as the alt so I don't think you really tested the alt. I suspect all is well.
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Old 09-02-2014, 09:18 PM   #20
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Your battery was dumping into the tester at the same time as the alt so I don't think you really tested the alt. I suspect all is well.
Good point. You mean 1/2 the power was coming from the bat & 1/2 from the alt. My understanding is that the alt supplies the load in addition to the bat, but maybe not
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