onebadwagon

fact of the matter is it doesn't matter, unless you don't have enough juice.


get a good alternator, do some minor upgrades, and enjoy it.

sesand

The goal of my stereo isn't to cruise around at night with the windows down and stereo turned up, so I don't consider it an issue. I just turn it down a couple ticks to resolve the problem. The dimming is minor, but I don't want to put too much stress on the system (that's how things break). A high output alternator is on the list of upgrades if I find a more serious problem with the current setup.

NEEDAZ

Pay no attention to the man behind the volt meter. The dash volt meter is only good at tell you your alt is already dead. Get a DMM in there some place and drive around with it for a week.

ScrapMaker

here's my dmm... always in voltage mode...

makes the guage on the dash look like a politician...

sesand

Good to know. I'm glad GM put it there for a reason, just like those little rubber flaps on the door vents Good grief.....

ScrapMaker

oh, you can take apart the dash and clean up the connections on the meter, it should suffice then...

or get a new one.

89Vert

didn't quite read the whole thread but i'll mention a few points

I'm a semi truck mechanic and I specialize in electrical
and I deal with huge draws like 1000amps and 4/0 wire
I also am very knowlegdeable in car audio, I do installs on the side, custom boxes etc.

-watts=voltage x amps
12volts x 100 amps= 1200 watts
that is max its imposible to defy the laws of electricity

-don't expect your alt to continuosly put out 14.4 especialy a 15 year old Camaro with it high quality GM electrical system
you might maintain 13v with your system turned up if your lucky

-you can't expect your battery to keep up to your system, you'll kill your alt. regularly, you need a high output alt.
a 650 CCA batt means it'll put out 650 cranking amps with out falling below 9.6 volt

a cranking amp is nothing like the draw an amplifier loads
its quick and random not slow and constant

long story short unless you do some huge electrical upgrade don't expect much more than 70 amps from your car to power your stereo

especially if you leave the stock 10 gauge from the alt to the batt and the I belive 8 gauge ground to the cars chassis

ScrapMaker

yeah, hehe, I should upgrade the alternator power connection, and the engine ground...

my battery ground is 1 guage.

eh, 70 amps is good enough for me...

syc0path

A couple of general comments...

When using fuse rating to judge the power output of an amp, don't forget to take efficiency of the amp into account. Class D amps are about 80% efficient, while Class A/B amps are about 55% efficient. Fuse rating is the most accurate way to measure an amp's output (unless u have specialized test equipment), but u have to know the math and take efficiency into account.

Caps are useful in some situations, but not as many as they used to be. Most modern amps include enough capacitance as the amp needs, so separate caps are only helpful to the car's electical system. And they are only helpful in certain situations... figuring out which situations can get complicated.

Your alt produces higher voltage after startup so it can more quickly recharge the battery. It's probably something that's built into the voltage regulator... but in any event, it's perfectly normal.

89Vert

Alt. output is based on load,

after start up your alt puts out more because the discharged battery is putting a load on the alt and the alt is cold

as alt. heats up it has to work harder

I could go on all day about the inner workings of an alt. but it'll get kind of boring

alt. put out amps in AC current, generators put out volts DC current

sesand

Makes sense. I always feel better after a good explanation. Half of my problem was I didn't even pay attention to stuff like that before I installed the stereo, so I have no basis for comparison - I just thought it was something I did that needed to be fixed/upgraded. As always, I will keep an eye on it.
Thanks a bunch.

syc0path

U know, it always bothers me when someone professes to be an expert and then puts up a bunch of incorrect info. The fact that the battery is putting more of a load on the alt after startup would tend to reduce voltage, not increase it. And alts generate AC current, BUT then that current is rectified to DC before it's put out to the car's electrical system.

Your pt about the alt producing higher voltage when it's cold may have some merit, but it still doesn't explain why the voltage regulator would allow the voltage to go that high. A hot alternator turning at freeway speeds would certainly tend to produce higher volts than a cool alt at idle, if the regulator would allow it. But it doesn't -- it only seems to allow higher voltage right after start up.

89Vert

like I said I wasn't going to go into the inner workings of the alt.

yes the alt. A/C current is rectifeid to D/C in the diode trio, if thats the answer you were looking for

but alt out put is based on load, the regulator in an alt is not like the regulator in a gen, it doesn't control voltage it controls ampereage

the battery sets the voltage in the system, with out a battery an alt. can put out massive voltage way higher than 14.4

you can accually weld with your alt.

at start up your battery voltage is low and the alt. knows this so it increases the amp output, the battery is what allows the voltage to rise, not the alt the weaker the battery the higher it will rise

Like I said I do this stuff for a living, not tring to prove anyone wrong just letting you know what I've experienced

NEEDAZ

We need some work on ohms law here people.

89Vert

I got a few text books beside me I could bust open

do you want it in paragraph or point form?

NEEDAZ

Don't need it from a book, got it in my head....

syc0path

That can't be true... if the battery is discharged at startup, how could it cause the voltage to be higher? A discharged battery has lower voltage, not higher. Allowing more current to flow at a low voltage won't increase the voltage.

89Vert

yes it will if you put a battery on a charger that you plug into the wall the voltage will be like 14-18 right away depending on how weak the battery is not how discharged it is,

like i said I could go on for hours,

ALT. DOES NOT PUT OUT VOLTAGE IT PUTS OUT AMPEREAGE

you cab charge a battery to 13.2 in a second but until enough ampereage is put in it will not maintain that voltage

ScrapMaker

can anyone answer why the alt will output 14.4 on a cold start, but not CONTINUE this amazing voltage for when I actually need it?

I've seen it go up to 17 before

my brothers new f150 goes up to 18 volts all the time, and his average voltage is 16... not 13 like mine.

9177

On a cold start your engine rpms are usually higher. Most stock or stock type alts have low idle output. as for you brothers truck I would be willing to bet the gauge isn't very acurate. at that voltage you stand to burn out some electronics or the regulator is going bad with it.

NEEDAZ

Going back to ohm’s law, how are you getting current from the Alt. with no voltage from the alt.? (Note the use of the word current.)
I’ll add, if a car battery is 12Vdc, where is the 14.5Vdc coming from?

ScrapMaker

we checked his voltage at the digital dashboard all f150's have...

I've never seen a guage read so high like that... I could see it read LOW because of a bad connection.... but 16-18 volts... damn man... if his truck works fine on that... I wonder if a car audio amplifier would run fine too? I've heard of a lot that really love it up like that...

89Vert

I was wrong to say an alt doesn't put out voltage it just makes it easier to remember, the current is regulated not the voltage, in a generator, voltage is regulated

in an alt circuit the voltage isn't important, a bad alt can put out 14.4v and 2 amps

a fully car battery is really 13.2 volts, 6 cell battery 2.2volts per cell

just because a battery is 13.2 doesn't mean it limited to 13.2

ScrapMaker

so if a car battery is 13.2... how come when you turn off the car it typically drops right to 12.7, and settles at about 12.5 after a few hours....

13.2 is about what it settles at with the alternator running.

89Vert

how old is your battery, they get weaker over time,

does anything draw current when your car is off(deck, alarm etc)

what are you using to gauge this the voltmeter in your car?

the gauge on my dash with the car running says about 13

if I go look on my amp it says 14.5 usually(D class alpine has volt amp and temp gauge)

ScrapMaker

brand new yellowtop

I can play my stereo for about 5 hours on full blast without getting it below 11 volts... (which is when my entertainment computer starts my motor to recharge my battery)

syc0path

That doesn't make any sense.. the current is determined by the resistance of the circuits in the car. For example, if the car was running but almost everything was off, the resistance at the alt might be 1ohm, so roughly 13A of current would flow. The current is already limited by the draw (or non-draw) of the electrical devices in the car. So why would the current need to be regulated in the alt? On the other hand, I can't think of anything that would limit the voltage in the car's electrical system other than a voltage regulator in the alt.

NEEDAZ

You’re still not getting the point. Get a good high current amp meter or shunt. Disconnect the charge wire from the alt and place the amp meter or shunt in series. Start the car and with every thing off measure current and voltage. Then start turning things on and measure current and voltage. You will see the voltage stay more or less the same (it will drop some as the load increases, this is only because it’s not well regulated) but the current will increase dramatically. This is because the alt regulates voltage output, current is then determined by the load.
That’s how it works. Don’t believe me, run the test for yourself and you WILL prove you self wrong.
SycOpath got it dead on when he said VOLTAGE REGULATOR.
If the alt. regulated current, the electrical systems voltage would vary greatly (and make my life a PITA), but it doesn’t, it remains reasonably stable wile current varies considerably.
Like I said, don’t believe use, run the test for you’re self, please.

NEEDAZ

BTW, how are you going to put E=IR in paragraph form?

89Vert

you could explain E=IR in a paragrah

with the whole voltage=amperage x resistance

and give examples etc.

so if you have 2 fog lights at 6 ohms each in a 12 volt system what size fuse do you need

reminds me of good old BCIT tests

89Vert

so if voltage is regulated how come when you full feild an alt.(meaning ground out the regulator) you get maximum amperage output and the voltage doesn't go through the roof,

I'm sure I'm right but I'm goin to check at work tomorrow,
since it is a Delco-Remy certified warrenty center

NEEDAZ

I was hoping for something more, I just can't thing of a different way to explain my side of the fence here. Was hoping you would put down something that would trigger a different way to explain my thoughts. I'll keep thinking, after more coffee.

"full feild an alt.(meaning ground out the regulator)"

If you mean taking the output of the regulator (charge wire) to ground this would make perfect sense. That's what you're talking about right? If so I think I can form a sentence or two that will clear things up. Just want to make sure we're on the same page first.

89Vert

full feild is when you put a small peice of wire in the "D" whole at the back and ground to the alt. case this causes maximum amperage output

voltage is used to regulate current, the more voltage allowed the the magnets in the alt the more current output,

car engine slows down when a load is introduced at idle because it is harder for the alt to spin do to the increase in magnetic strength

syc0path

The more power u draw from a power supply, the more difficult it is to prevent the voltage from dropping. So if u ground out an alt, it's voltage output will drop, not go thru the roof.

Try this... turn on the water in your bathroom sink at full blast and get a feel for the water pressure coming out of the faucet. Then turn on your shower full blast. What happens to the pressure at the sink? It will drop off -- usually dramatically, or maybe not much if u have a strong water supply. The same thing happens w/ your alt... when u draw more current (equivalent to amount of water), the voltage (equivalent to the water pressure) drops.

Ideally, if the alt was perfectly regulated, it should always maintain about 13.8V no matter if the car is drawing .1A or 105A. There's no need to regulate the amps becuz the resistance in the circuit does that by default.

ScrapMaker

unfortunately my car only puts out 13.8 when everything is off.... when I turn the fan, fogs, headlights, radio on normal volume, and the AC on maximum blower setting... I get like 11.3 volts at a stop light

time for a new pulley! hope I don't break it

/lifetime AZ warranty!

the only reason I care is because my LED tailights tend to TURN off after a certain voltage... otherwise I could give a crap if my voltage was at 10 at a stoplight...

NEEDAZ

Brain spinning up. You're absolutely right about voltage (varying) to regulate current (back to ohms law), when current is being regulated. But I think the easiest thing here is to just try what I described above, it should clear it all up. I would hope if your working with that much current you have a shunt or some other way to measure/quantify current up to, say 100A, that should work (in most cars) for this test.
BTW, the effect of the alt slowing down the motor is called dynamic braking. This affect is often used in equipment that uses motors to slow/stop them.

ScrapMaker

cough:hybrids:cough

anyways, can someone explain why my alt will output 13.5 volts with everything on (when I start it in the morning)

yet when I'm doing that same load after my car is warmed up, it will be at like 12.5 volts...

why would the regulator do this? because clearly the alternator is capable of outputing enough volts, it's just being squeezed by something in the alternator....

unless... do the alternators heat up and become less efficient? is that why? because pretty much no matter how long I run my car, when I turn off the engine, my battery reads about 12.6 volts... so I could let my car sit for days and have a reading of 12.5, or I could run it for 6 hours, turn it off, and I instantly have a reading of 12.6-8... my battery really doesn't require much charging in the morning, so I really wonder if it's a heat thing.

89Vert

i'm talking about grounding out the regulator, not the alt output

the regulator regulates the volagte to the stator, which produces the current, the more voltage to the stator the more current out of the alt output

when you ground out the regulator full voltage is allowed to the stator inducing full current output

89Vert

i can read up to 4000amps

I have machines to test all this stuff, I just had to dig up the basic info from the back of my brain

i sometimes have trouble getting out what I'm trying to say over the intranet

NEEDAZ

I THINK I'VE GOT THE CAUSE OF YOUR CONFUSION. The voltage regulator in the alternator will vary (manipulate/ control/ not really 'regulate') the current in the in the rotor to maintain the voltage out of the stator. The voltage out of the stator is what is supplied to the car electrical system from the charge wire. The voltage regulator uses the ‘D’ input to monitor system voltage (usually back to the fuse panel, as at this point it can compensate for voltage drop up to the fuse panel). As this input voltage goes low, current through the rotor increases, but this is done to attempt to increase the voltage out of the stator, thus regulating the electrical systems VOLTAGE, not current. Thus the term ‘full field’, this refers to the magnetic field in/around the rotor, and the stronger this field is the more output voltage the stator will produce. Keep in mind that they control this to compensate for voltage DROP as current goes up to MAINTAIN a steady system VOLTAGE. You also made a statement that the voltage comes from the battery. That battery voltage is fed to the alt. to ‘excite’ the rotor, or start this field, the 14.5V comes from the alt/regulator (one package deal with the GMs).
So to say again, the alts stator (output) voltage is regulated by controlling the rotor current.

Clear as mud? Or do we need more?
Brain heart now bad.