voltage at 12.1 volts normal?

[iceteebone 5,000+ posts]

i just went to autozone to get my alternator and battery checked. The worker say everything was fine. I notice that when i turn my headlights on the battery voltage stay at 13.4 or so but without headlights the battery voltage goes down to 12.1.

Are you still going by your headunit? Did he test the battery or the alternator? Here you have to bring the alternator in to have it checked out. An alternator should always maintain at least 13.5 volts constant. Fluctuating a volt and a half tells me you have alternator problems.

 

[themommyvan 10+ year member]

Did you get a DMM? If you did what did it say?

 

[thaster 10+ year member]

the worker check both alternator and battery. he say the battery was somewhere at 12.5 volts(car wasn't on) and the alternator(engine on) was around 13.9-14.0.

 

[iceteebone 5,000+ posts]

the worker check both alternator and battery. he say the battery was somewhere at 12.5 volts(car wasn't on) and the alternator(engine on) was around 13.9-14.0.

If it stayed constant 13.9 then you are good.

 

[thaster 10+ year member]

probably the voltmeter on the headunit is wrong or something but imma try to get my hands on a dmm.

 

[fbi90909 5,000+ posts]

Wrong.
At idle and after the car is warmed up your voltage should still be above 13 volts. 13.5-14.5 like iceetee said.

if i leave the car parked in idle with the stereo off yes i would get a voltage of about 13.0 - .5, but if i'm driving around after the engine warms up(for instance when i go to work) and waiting at red lights my voltage stays around 12.1 - .3

i've been staring at my voltage since i purchased my car and driving with my h.u that has a voltage meter (which is off by .2, checked with DMM and i run a Stinger digi voltage meter now) to a point where the LCD screen has the voltage display burned into the h.u.

realistically i spend most of the time driving my car. not parked at the lot sitting with the car idle listening to music. so the idle parked voltage figure stays out of my head.

also put into mind that not every vehicle is the same. i have only watched this with honda/acuras.

also in theory these vehicles are somewhat "efficient". so if the engine only needs a level of voltage to be operational then why would it produce energy that is not needed for the vehicle at the time when nothing is being used, i.e. the a/c or the headlights?

why would my voltage jump from a 12.1 - .5 to a 13.9-14.2 after i turn on my headlights while driving 25mph at 1.5krpms?

note that there is nothing wrong with my alt nor my battery even when i drove my car around for the first half year with only my H.u installed with no sub.

early next year i will be getting an h.o alt and hope there is a difference with a more higher stable voltage.

 

[tommyk90 5,000+ posts]

if i leave the car parked in idle with the stereo off yes i would get a voltage of about 13.0 - .5, but if i'm driving around after the engine warms up(for instance when i go to work) and waiting at red lights my voltage stays around 12.1 - .3i've been staring at my voltage since i purchased my car and driving with my h.u that has a voltage meter (which is off by .2, checked with DMM and i run a Stinger digi voltage meter now) to a point where the LCD screen has the voltage display burned into the h.u.

realistically i spend most of the time driving my car. not parked at the lot sitting with the car idle listening to music. so the idle parked voltage figure stays out of my head.

also put into mind that not every vehicle is the same. i have only watched this with honda/acuras.

also in theory these vehicles are somewhat "efficient". so if the engine only needs a level of voltage to be operational then why would it produce energy that is not needed for the vehicle at the time when nothing is being used, i.e. the a/c or the headlights?

why would my voltage jump from a 12.1 - .5 to a 13.9-14.2 after i turn on my headlights while driving 25mph at 1.5krpms?

note that there is nothing wrong with my alt nor my battery even when i drove my car around for the first half year with only my H.u installed with no sub.

early next year i will be getting an h.o alt and hope there is a difference with a more higher stable voltage.

Well, if your car is idling at 12.1 volts, that means that alternator is not charging and your car is running off the battery, which is not good. Doing that will end up killing your battery from the constant strain.

That's odd for a stock alternator to not charge at lower RPM's though. Usually thats something that happens with a H.O. alt.

 

[fbi90909 5,000+ posts]

Well, if your car is idling at 12.1 volts, that means that alternator is not charging and your car is running off the battery, which is not good. Doing that will end up killing your battery from the constant strain.
That's odd for a stock alternator to not charge at lower RPM's though. Usually thats something that happens with a H.O. alt.

as i drive per say at 25mph with 1.5krpm myv oltage would jump every once in a while like Thaster had mentioned his vehicle does. jump from 12.1-.2 to a 13.9 for a few secs then drop back down to 12.1-.2 which is why i mentioned that it is normal for his car to do that.

when it does this voltage jump the alt kicks in and well produces the loss energy that the engine has consumed to a stable point where the engine/car does not need any excessive amount but to just maintain what the car is demanding. which basically is not much at all.

now lets say i was doing 25mph at 1.5 krpms then slammed on the accelerator and accelerated from 2.5krpm to a redline of 7krpm my voltage would jump from a 12.1-.5 to a 13.0-14.0. note that THAT is where a demand in power would come in and cause the alt to kick on(even with the rise in RPMS) and produce the energy needed that the car is demanding. then just drop back down to a 12.5 and slowly drop.

also look at the fact that his stock alt is probrably only 70-90 amps. which at low rpms produces crap.

now i'm no expert in this feild or anything but i'm just saying from what i have experienced.

 

[tommyk90 5,000+ posts]

as i drive per say at 25mph with 1.5krpm myv oltage would jump every once in a while like Thaster had mentioned his vehicle does. jump from 12.1-.2 to a 13.9 for a few secs then drop back down to 12.1-.2 which is why i mentioned that it is normal for his car to do that.when it does this voltage jump the alt kicks in and well produces the loss energy that the engine has consumed to a stable point where the engine/car does not need any excessive amount but to just maintain what the car is demanding. which basically is not much at all.

now lets say i was doing 25mph at 1.5 krpms then slammed on the accelerator and accelerated from 2.5krpm to a redline of 7krpm my voltage would jump from a 12.1-.5 to a 13.0-14.0. note that THAT is where a demand in power would come in and cause the alt to kick on(even with the rise in RPMS) and produce the energy needed that the car is demanding. then just drop back down to a 12.5 and slowly drop.

also look at the fact that his stock alt is probrably only 70-90 amps. which at low rpms produces crap.

now i'm no expert in this feild or anything but i'm just saying from what i have experienced.

An alternator only produces energy as needed, even when it's on. //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

Just because an alternator is rated for 80 amps at idle and 200 amps at 2k RPM, does NOT mean it's constantly doing that. It only puts out the current the car demands.

Therefore, having the alternator turn off during low demand periods will not increase it's efficiency.

Either way, having the voltage dip that low while driving or at idle signifies that the car is running off the battery, which is not good.

 

[fbi90909 5,000+ posts]

i can see that running the engine off the battery may not be good but i know that the alt is producing a small amount of energy even at low rpms while driving. which is why the battery never drops under 12.1. (with nothing on) which is why i don't see a 14.0 while driving, all because it's not in demand for it.

if it did just run off the battery i'm sure it would drop even lower or even be dead by now from the strain. though i've had my car for 2 years and still have the stock g51 size batt which had to be jumped once from having my car off and running my stereo for 5 hours(note: no subs only H.U). ran a pca2000d to my XXX for about 6 months on that single stock bat, never had any issues starting my car either or having a dead battery, then swiitched to a saz1500d in febuary with a red top(keeping voltage more stable) and i still have that battery going.

i know that just cause the alts rated at per say 80 amps it's not always producing 80 amps. but your looking at a little alt only pumping out small(per say 30 amps) amounts of energy for only what the car is demanding.

i wouldn't say that the alts purposely shut off the alt to improve on effeciency i was stating that being these vehicles are not as demanding and are not needing that excess of 14v to operate. which is why they keep the car at such a low voltage.

now saying that the car is running off the battery while driving or at idle is something i would say the car is not doing, why would honda/acura do something like that? if so then sooooooooooo manyf people with hondas/acuras would be having bad batteries.

 

[tommyk90 5,000+ posts]

i can see that running the engine off the battery may not be good but i know that the alt is producing a small amount of energy even at low rpms while driving. which is why the battery never drops under 12.1. (with nothing on) which is why i don't see a 14.0 while driving, all because it's not in demand for it.
if it did just run off the battery i'm sure it would drop even lower or even be dead by now from the strain. though i've had my car for 2 years and still have the stock g51 size batt which had to be jumped once from having my car off and running my stereo for 5 hours(note: no subs only H.U). ran a pca2000d to my XXX for about 6 months on that single stock bat, never had any issues starting my car either or having a dead battery, then swiitched to a saz1500d in febuary with a red top(keeping voltage more stable) and i still have that battery going.

i know that just cause the alts rated at per say 80 amps it's not always producing 80 amps. but your looking at a little alt only pumping out small(per say 30 amps) amounts of energy for only what the car is demanding.

i wouldn't say that the alts purposely shut off the alt to improve on effeciency i was stating that being these vehicles are not as demanding and are not needing that excess of 14v to operate. which is why they keep the car at such a low voltage.

now saying that the car is running off the battery while driving or at idle is something i would say the car is not doing, why would honda/acura do something like that? if so then sooooooooooo manyf people with hondas/acuras would be having bad batteries.

Low voltage and low amperage are two different things.

Even with the car OFF, your battery should be floating at 12.6 or better. So if your voltage is sitting at 12.1 with the car RUNNING that means it is only running off the battery....period. Any alternator that is functioning properly will put out more than 13 volts as long as the engine is turning it fast enough. To go any more below that is just putting strain on the battery.

If your car's voltage is dipping below 12.5 with the car on and nothing else on, something is wrong with the alternator whether the alternator is not turning on or the car is just not spinning fast enough.

A plain battery, taken off the shelf anywhere, should read at least 12.6 volts if it's been properly maintained or not been sitting around for 2 years.

 

[theothermike 10+ year member]

when i start my car my voltage goes to 14.2 volts on my headunit (880 prs, seems to be off by .1 volts from my crappy dmm) it then settles around 13.3 - 13.5 @ idle with nothing on in park. and 12.9 - 13.2 @ idle when in drive. With my system on 48 ( mid - loud volume im getting 12.7 - 12.9 volts at idle in drive and around 12.9 - 13.1 in park. I get 13.4 - 6 when in drive around 1600 - 2000 rpms and around 13.2 around 1300 rpms.

This normal for 3 amps, 2 have 90 amp rating 1 has 60 amp rating. i have kinetik 2400, 1800, and a 200 amp iraggi ho alt. with big 3 1/0 gauge and a 1/0 gauge pos and neg run.

Mike-

 

[fbi90909 5,000+ posts]

Any alternator that is functioning properly will put out more than 13 volts as long as the engine is turning it fast enough.

which is why at low rpms i'm not seeing 14v.

if something would be wrong with this alt or this battery then why would the OP be having the same voltage of 12.1-12.2 while driving? even after he just recently took his car to an auto parts and had them check the battery plus alt and give him the O.K??

it's how these cars work.. it's a honda.

 

[tommyk90 5,000+ posts]

which is why at low rpms i'm not seeing 14v.
if something would be wrong with this alt or this battery then why would the OP be having the same voltage of 12.1-12.2 while driving? even after he just recently took his car to an auto parts and had them check the battery plus alt and give him the O.K??

it's how these cars work.. it's a honda.

Well, then its a stupid *** design if the alternator puts out less voltage during idle than the battery, don't you think?

Even at idle the car should be producing more than 12.5 volts, unless the car has a H.O. alt with a higher idle speed.

 

[fbi90909 5,000+ posts]

Well, then its a stupid *** design if the alternator puts out less voltage during idle than the battery, don't you think?
Even at idle the car should be producing more than 12.5 volts, unless the car has a H.O. alt with a higher idle speed.

i'm sure it could be producing more than 12.5 at idle but could be being drained at that same time from having the engine running. i don't know?

i'd like to get a h.o alt soon but also sketchy that reading about those alts not really producing much untill after 2krpm which it could become useless.

where i live in the city the highest speed limit is 35mph. if i drive up the keys it's 55mph, but being in the city i rarely ever drive over 1.5-2krpms unless if it's taking off from a stop or driving aggressively.

what i really need is a bigger/different car with good gas mileage. :/