Alt or battery?
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Launching!
Joined: Jul 2016
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From: Martinsburg, WV
Alt or battery? Yesterday just as I left work I noticed my voltmeter drop below 13v while I was in traffic. I ended up making the trip which was 50 miles home though. It was dark so I had my headlights on as well as radio. While moving the volts stayed above 13v and if I came to a stop I'd give it a little gas so it wouldn't drop. Anyways I made it home and swapped the battery out and it seemed fine.
now this morning I saw the gauge drop below 13v a couple times as well but I made the trip ok. I had the current battery on a tender for 3 hrs this morning and it didn't turn green though my battery from yesterday did that was on a different charger.
thinking out loud since the battery only provides 12v to start and my gauge stayed just above 13v is it safe to say my alternator is good and I just replaced my battery with another bad one? I wouldve used my multimeter but it's battery is dead-go figure.
now this morning I saw the gauge drop below 13v a couple times as well but I made the trip ok. I had the current battery on a tender for 3 hrs this morning and it didn't turn green though my battery from yesterday did that was on a different charger.
thinking out loud since the battery only provides 12v to start and my gauge stayed just above 13v is it safe to say my alternator is good and I just replaced my battery with another bad one? I wouldve used my multimeter but it's battery is dead-go figure.
Last edited by sean byrd; Jan 4, 2017 at 06:16 AM.
TECH Junkie
Joined: Aug 2006
Posts: 3,911
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From: Western North Carolina
Hard to say because you didn't mention anything about the batteries. Are they old mongrel brands or new quality brands less than one year old? If it's old stuff, it's probably time to get a nice new fresh one. I've had good luck with the AC/Delco GM and with Interstate 'black top'. Yeah, well over $100 but worth it.
Thread Starter
Launching!
Joined: Jul 2016
Posts: 220
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From: Martinsburg, WV
First one was a redtop-not sure how old but after a few hours on the battery tender got a green light.
Current one is a no name battery that's a year old. After reading about the 145a truck alt I ordered one from a local LKQ for $42 just in case it does turn out to be my alternator.
Current one is a no name battery that's a year old. After reading about the 145a truck alt I ordered one from a local LKQ for $42 just in case it does turn out to be my alternator.
Last edited by sean byrd; Jan 4, 2017 at 11:18 AM.
I see nothing here that would indicate a battery problem, or really an alternator problem.
A/C and headlights will considerably create a voltage drop in the system. Does your voltage look off with the headlights off? If not, you could get the alternator tested.
(A battery or alt-battery connection problem would show up on start-up of the car. The alternator handles the lion's share of the loads when the car is running.)
A/C and headlights will considerably create a voltage drop in the system. Does your voltage look off with the headlights off? If not, you could get the alternator tested.
(A battery or alt-battery connection problem would show up on start-up of the car. The alternator handles the lion's share of the loads when the car is running.)
Thread Starter
Launching!
Joined: Jul 2016
Posts: 220
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From: Martinsburg, WV
Hey guys last night I put the battery (in the car) on the tender all night and had no issues all morning during my commute. Voltmeter was better and stayed around 13.8 with no drops even at idle.
To be safe I do have the truck alt on the way.
To be safe I do have the truck alt on the way.
the analog volt gauge in the dash cluster can sit just below the vertical mark of 13 volts and that does not mean a problem. It is not super accurate. Only when it sits down in the red at 10 volts and the check engine light is also on with an alternator related DTC should you trust it to go buy another alternator and/or battery.
but you should always use a digital multimeter you trust to report accurate voltage before making a decision to get a new alternator,
a fully charged battery is ~12.65 volts depending on temperature,
In hot weather on my car the volt gauge in the dash will sit just under the 13 volt vertical mark. This is normal.
what is possible is one of the six diodes in your alternator has died, it's what converts the AC voltage actually generated by the alternator (alternating current) into DC and is part of the rectifier circuit within the alternator. When less than 6 diodes are present the alternator has reduced output and is noticed most at lowest rpm's. Increase engine rpm alternator spins faster and is able to output what it needs and everything if fine. In this case you basically need a new alternator to fix this problem. This problem can happen to any model alternator.
but you should always use a digital multimeter you trust to report accurate voltage before making a decision to get a new alternator,
a fully charged battery is ~12.65 volts depending on temperature,
In hot weather on my car the volt gauge in the dash will sit just under the 13 volt vertical mark. This is normal.
what is possible is one of the six diodes in your alternator has died, it's what converts the AC voltage actually generated by the alternator (alternating current) into DC and is part of the rectifier circuit within the alternator. When less than 6 diodes are present the alternator has reduced output and is noticed most at lowest rpm's. Increase engine rpm alternator spins faster and is able to output what it needs and everything if fine. In this case you basically need a new alternator to fix this problem. This problem can happen to any model alternator.
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TECH Apprentice
Joined: Jan 2004
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I've noticed a couple times that my voltage measured a little low. But everything was fine and operated as normal. I did have an alternator go out on me while driving on a different Camaro I used to own. Engine just went to sleep and all the lights and gauges died. Coasted for a bit and just had enough momentum to bring it to the side of the road and out of traffic. I think your alternator is fine.
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When my alternator died I got a CHECK GAUGES light on the dash as well as the volt meter on the dash reading around 12, turned around and drove back to town and changed it in the parking lot of the autoparts store.
when the battery in the Trailblazer was bad (was bad when I bought the truck, used it to negotiate the price) the voltage stayed LOW on the dash but the battery got hot and started smoking (stinks really really bad), a typical sign of a bad battery in a F-body is after the car sitting over night when you crank it the gauges do a full sweep, if you are seeing that get a new battery.
when the battery in the Trailblazer was bad (was bad when I bought the truck, used it to negotiate the price) the voltage stayed LOW on the dash but the battery got hot and started smoking (stinks really really bad), a typical sign of a bad battery in a F-body is after the car sitting over night when you crank it the gauges do a full sweep, if you are seeing that get a new battery.