Alternator output

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Alternator output

Home > Discussion Forum > Mechanic's Corner - Electrical

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All Messages in Thread	Author	Date
Alternator output	john ogletree	10-22-03
My '87 Holiday Rambler Imperial CS Class A, 454, has a factory-installed Lestek 120 amp dual-output alternator. The voltmeter indicates about 13.7 volts when there are no other loads, such as lights, fans, etc, running. Turning on even the small cooling fan in front of the driver or passenger causes the meter to drop several volts and stay at the lower indication. Isn't the regulator supposed to sense loads and quickly adjust alternator output so that the most I should see is a short downward dip of the meter needle, which quickly returns to the previous level? I took the rig to an alternator shop and they blamed it on a wiring problem, not suggesting a regulator problem.
Re: Alternator output	john ogletree	10-22-03
I forgot to mention that when the voltmeter indication is reduced as described above, the fuel indicator also reads low. This seems to indicate that the voltmeter is telling the truth and the voltage really is low. Again, regulator problem?
Re: Alternator output	Chuckoc P30base batter if not isolator.	11-1-03
Wow, Dual output terminals on alt... is that the norm? I will have to check mine, Wow, How does your MH use only the couch batts and the engine use the isolator
Re: Alternator output	Chuck P30	10-23-03
I will asume you are talking at CRUISE RPM and not IDLE, If only at IDLE then bring it up to 1500 PLUS RPMS and see if that lights up the regulator../..alt. Also I recall reading something about a one volt differance before and after the dual batt isolator... so CHECK your OUTPUT VOLTAGE at both the alt output terminal (large 20ga. red wire attched to ONE stud on back of alt.) check output voltage there and at the house batteries and then at the engine batt. add that to the rpm above 1500 and you should see something like 14.7 // You said your LOW FUEL light came on when you were doing this as well, I can only say this I highly recomened that you CLEAN and maybe even add some NEW GROUNDS as that is Good ole GM FEEDBACK...(volatge) and it causes all kinds of little gemlins... CLEAN ALL GROUNDS, to frame, to battery, at any and all connections. You might find one that is highly corided thus blocking your ALT output and the actual prob... to all your woes.
Re: Alternator output	John Ogletree	10-24-03
Chuck P30 probably meant 8 gauge or larger. My alternator is dual output and there is no isolator. the two outputs are isolated from each other. Says so on the alternator. I don't have "idiot lights". I have a voltmeter and the low fuel indication is not a warning. I just mean that the indicated level reads lower when loads are added. I think this points to a regulator that isn't doing its job. The alternator bench tested at 130 amps on both output terminals so it seems that it is working fine. At least that's what the tech. said. The Holiday Rambler document calls it "Lestek 120 amp dual output". I still wonder why he didn't suspect the regulator, or more to the point, why do I suspect it? I'm not a pro.
Re: Alternator output	Chuck P30	10-27-03
Mesure volatge at 4 ga. wire, then mesure at ISOLATOR and then at battery.. asi have read it MIGHT be ONE volt higher on the side BEFORE ISOLATOR say 15.1 then after ISOLATOR it should read at the BATTERY 14.1 (one volt differance from back of alt.) in some cases.. Eitherway it is all done at some RPM above IDLE I like to use 1800-2200 rpm so as to be fair to the alt... You should be able to narrow it (the prob) down with these three points VOLATGE.. I do the test by myself I do it when the rig is on cold start so the choke hold the RPM range while I consentrat on volatge readings. Good luck, LET US know what you find so we all can learn.
Re: Alternator output	Sam Watson	10-22-03
The first thing I'd do is check the voltage at the alt output terminal with another voltmeter under the conditions you describe. If both meters agree, then I'd check the power supply going to the alt field. The voltage should remain constant, that's the regs job. Come back with what you find.
Re: Alternator output	Sam Watson	10-24-03
"large" 20 gauge wire???
Re: Alternator output	Chuck P30	10-25-03
Woops, I wentg the wrong way on the guage, What guage is the wire out of th eONE BATT lead from the alt? 14 Gauge? 12.... I now recall wire gauge is smaller number larger wire... I used double OO for long lenth of batt cable when installing trunk battery... I always get that gauge thing wrong of I am not looking at it.. Darn it... Thanks for pointing the error out..
Re: Alternator output	John Ogletree	10-26-03
According to a print I got from Holiday Rambler the wires from the alternator to the batteries is 4 ga. Remember, my alternator has dual isolated output terminals so I don't have a separate isolator.
Re: Alternator output	Sam Watson	10-26-03
Yep, Chuck, I always have to stop and remember that wire gauge is just the opposite of sheet metal gauge, why that's so I guess, is just to cause confusion.
Re: Alternator output	jd	10-26-03
Now I'm even more confused. Is NOT 12-gauge steel somewhere like.125" thick and auto body steel more like 22-gauge? God Bless, jd
Re: Alternator output	John Ogletree	10-28-03
Chuck P30, I DO NOT have an isolator. The alternator has two output terminals that are internally isolated from each other. When I find the answer I will post it here.
Re: Alternator output	koclieman2000a	1-27-04
I'n look for a rv magic home alternator