Abnormal charging..alternator or?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

spspspspoon · 03-06-2022, 02:49 AM

65 C10 82 V8
10/12si Alternator
For years Alternator worked great it finally died
Readings from Mech volt gauge are noticable but maybe slightly off
And VOM clipped to volt gauge hot and is what I'm reading it on

First remanufactured replacement from Napa
Same Remy Delco alternator appears to be slightly smaller pulley but closer together so I'm not sure that the revolutions are any different
Constantly took its slow time to charge fully to 14+
Almost every time

Second remanufactured same AC Remy Delco alternator Napa
At idle it takes it slow Time charging up to 13.9
At idle at 13.9 turning on parking lights drops it to 13.4 or so
Turning on lights drop it to right below 13
And it will slowly drop at idle from there if I drive it will slowly drop until I put my foot in the clutch and let it idle and then it will slowly go back up a little bit

Any load results In an immediate and seemingly drastic drop in Voltage

Never had that variable issue with an alternator before

Thoughts??

**Getter-Done** · 03-06-2022, 10:36 AM

Are both your battery cables good?

**TJ's Chevy** · 03-06-2022, 01:45 PM

Is it still externally regulated? Could be a bad regulator.

ACK · 03-06-2022, 02:57 PM

10 and 12SI alternators are internally regulated. I strongly suggest taking it to a local shop to bench test it. If it fails, have them perform a rebuild, it should cost about the same as a replacement. To save cash, you can purchase a rebuild kit and do it yourself if it fails the bench test.

The down side to rebuilds, a pile of 10 and 12SIs are taken apart and everything put in a big pile, parts replaced, and what ever fits together is reassembled to make the finished product (eg: mine has a 10SI back and a 12SI front). Makes ya' feel that QC isn't a high priority.

LVPhotos · 03-06-2022, 10:35 PM

Is battery good? Are the wire in good condition and properly sized? Good grounds... motor to frame, alt to battery. Wires should be equal size positive and negative. Enough amp output for amp used? Consider a higher output alternator like Mechman.

SidsChopShop · 03-06-2022, 11:14 PM

FWIW I wouldn't be surprised if the Napa alt. are bad. I went thru a handful of them before they claimed aiming for 75% reliability on their alternators. I went with another parts store brand and have had good luck. But you could test diodes and do a full field test on your current one to see if its in good shape. However my initial thought is to try a different regulator first before trying another alternator, that may set you in the right direction.

**The Rocknrod** · 03-07-2022, 08:27 AM

How is the Alt wired?

forestb · 03-07-2022, 04:33 PM

x2 as far as grounds go. I grounded my engine to the frame with a one inch ground strap from the bolt hole that the battery ground is bolted to the engine. I also grounded my battery to the frame at the back of the engine and cab to the frame with the same one inch ground straps. It helped tremendously with keeping my voltage up. I also increased my battery cable size to a one gauge wire.

03-06-2022, 02:49 AM	#1
spspspspoon Registered User Join Date: Sep 2018 Location: New Orleans Posts: 30	Abnormal charging..alternator or?? 65 C10 82 V8 10/12si Alternator For years Alternator worked great it finally died Readings from Mech volt gauge are noticable but maybe slightly off And VOM clipped to volt gauge hot and is what I'm reading it on First remanufactured replacement from Napa Same Remy Delco alternator appears to be slightly smaller pulley but closer together so I'm not sure that the revolutions are any different Constantly took its slow time to charge fully to 14+ Almost every time Second remanufactured same AC Remy Delco alternator Napa At idle it takes it slow Time charging up to 13.9 At idle at 13.9 turning on parking lights drops it to 13.4 or so Turning on lights drop it to right below 13 And it will slowly drop at idle from there if I drive it will slowly drop until I put my foot in the clutch and let it idle and then it will slowly go back up a little bit Any load results In an immediate and seemingly drastic drop in Voltage Never had that variable issue with an alternator before Thoughts??

03-06-2022, 10:36 AM	#2
Getter-Done Senior Member Join Date: Dec 2009 Location: TN. Posts: 7,832	Re: Abnormal charging..alternator or?? Are both your battery cables good? __________________ ________________________________________________________________________________________ ____________________________________________ 84 Chevy K-20 63 Impala (my high school car) http://67-72chevytrucks.com/vboard/s...Crew Cab Build

03-06-2022, 01:45 PM	#3
TJ's Chevy Post Whore Join Date: Mar 2013 Location: Southern Oregon Posts: 10,384	Re: Abnormal charging..alternator or?? Is it still externally regulated? Could be a bad regulator. __________________ 1966 Chevy C10 "Project Two Tone" http://67-72chevytrucks.com/vboard/s...d.php?t=596643 1964 GMC "Crustine" semi-build:http://67-72chevytrucks.com/vboard/s...d.php?t=665056 My youtube channel. Username "Military Chevy": https://www.youtube.com/channel/UC_h...fzpcUXyK_5-uiw

03-06-2022, 02:57 PM	#4
ACK Registered User Join Date: Oct 2012 Location: Philly, PA Posts: 537	Re: Abnormal charging..alternator or?? 10 and 12SI alternators are internally regulated. I strongly suggest taking it to a local shop to bench test it. If it fails, have them perform a rebuild, it should cost about the same as a replacement. To save cash, you can purchase a rebuild kit and do it yourself if it fails the bench test. The down side to rebuilds, a pile of 10 and 12SIs are taken apart and everything put in a big pile, parts replaced, and what ever fits together is reassembled to make the finished product (eg: mine has a 10SI back and a 12SI front). Makes ya' feel that QC isn't a high priority. __________________ My truck ain't dead, it just smells funny.

03-06-2022, 10:35 PM	#5
LVPhotos Registered User Join Date: Jan 2013 Location: Las Vegas, NV Posts: 1,853	Re: Abnormal charging..alternator or?? Is battery good? Are the wire in good condition and properly sized? Good grounds... motor to frame, alt to battery. Wires should be equal size positive and negative. Enough amp output for amp used? Consider a higher output alternator like Mechman. __________________ 1962 shortbed 408cui small block, TKO 600 5-speed, bagged Porterbuilt suspension. 18" Salt Flats http://www.cardomain.com/ride/332579...t-c-k-pick-up/ http://67-72chevytrucks.com/vboard/s...d.php?t=560081

03-06-2022, 11:14 PM	#6
SidsChopShop Registered User Join Date: Apr 2014 Location: Harlan, IN Posts: 61	Re: Abnormal charging..alternator or?? FWIW I wouldn't be surprised if the Napa alt. are bad. I went thru a handful of them before they claimed aiming for 75% reliability on their alternators. I went with another parts store brand and have had good luck. But you could test diodes and do a full field test on your current one to see if its in good shape. However my initial thought is to try a different regulator first before trying another alternator, that may set you in the right direction.

03-07-2022, 08:27 AM	#7
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Abnormal charging..alternator or?? How is the Alt wired? __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

03-07-2022, 04:33 PM	#8
forestb Registered User Join Date: Jan 2009 Location: Burbank, CA Posts: 3,590	Re: Abnormal charging..alternator or?? x2 as far as grounds go. I grounded my engine to the frame with a one inch ground strap from the bolt hole that the battery ground is bolted to the engine. I also grounded my battery to the frame at the back of the engine and cab to the frame with the same one inch ground straps. It helped tremendously with keeping my voltage up. I also increased my battery cable size to a one gauge wire.



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