alt. question

smoker · Post by **smoker** » Fri Feb 10, 2006 8:12 pm

there is some debate here locally as to whether or not a high output alt...lets say a 200 amp that is replacing a stock alt. on a car will cause too much amperage to flow and fry stock electronics......now as i have never owned a high output alt. i dont know first hand that this info is right or wrong......i would assume its wrong but the guy made a very plausible case for it....i just wondered if there is any truth to this or not.....

joeyc · Post by **joeyc** » Fri Feb 10, 2006 8:46 pm

hmmmmmmmm, very interesting question!! unfortunately, I also am curious as to the answer!! lol

Bwcad1 · Post by **Bwcad1** » Fri Feb 10, 2006 9:00 pm

well smoker i can tell you this i have been running a high output alt for over 6 months and have no issues. but it sounds to me like the voltage is what would fry stuff not the amperage

JeremyC · Post by **JeremyC** » Sat Feb 11, 2006 1:03 am

Smoker an alternator only puts out the amout of amperage that is being drawn from it. Thats why you can ckeck an alt with no load and it will check fine, but if you load it up it can check bad.

That being said an alt will only put out its full amperage when the stereo is pulling it. If you leave the stereo off, then the alt will only put out enough amperage to supply the cars electronics, without going to far over the current load.

Keep in mind, I am not completly sure aout this, but I think thats the way it was explained in tech school.

Post by **GlassWolf** » Sat Feb 11, 2006 2:10 am

that is correct.
just like a computer power supply, the ratings on amps are peak ratings. the amount of current actually supplied is whatever the systems draw from it.
voltage stays a constant (more or less) and current varies based on load.. just like an amplifier.

whomever said a higher output alternator can damage a car's electronics, apparently has little understanding of electrical basics.

smoker · Post by **smoker** » Sat Feb 11, 2006 7:17 am

kinda what i thought..........when i was posed with this scenario my response was "what do you think the voltage regulator does?"

veggie-man · Post by **veggie-man** » Sat Feb 11, 2006 1:48 pm

yeah that makes perfect sense... when i turn up my A/C from off all the way to full blast the headlights dim for a second, then go back to full even when the A/C is sitll on

Jonathan · Post by **Jonathan** » Sat Feb 11, 2006 2:15 pm

"kinda what i thought..........when i was posed with this scenario my response was "what do you think the voltage regulator does?""

Exactly, when voltage falls below a predetermined level, the regulator increases rotor field current to strengthen inductance, and thus more output from the alternator. If it goes above a set level, it decreases field current and weakens inductance. Pretty simple.

smoker · Post by **smoker** » Sun Feb 12, 2006 7:09 am

part 2:

if you add additional batteries how is all this affected?

Post by **GlassWolf** » Sun Feb 12, 2006 6:01 pm

wel, if the batteries are charged, no real effect.
if you run down the isolated deep cycles, or drain the starter battery a bit on a cold day with a ahrd starting car, the alternator has to recharge the batteries by inducing a voltage across their terminals that's higher than their own chemically-generated voltage.. once the batteries are recharged, all is happy again.

while the batteries are connected, they act as a filter for any AC ripple that gets through the voltage regulator. the voltage regulator takes the AC output of the alternator and rectifies it to DC, but not perfectly, so the battery smooths that out.. capacitors help smooth it further, as well as helping to reduce that lag time between peak curent demand spikes, and the time it takes the voltage regulator to compensate by increasing the rotor field strength (that can take a second or so, thus the momentary light dimming you see when bass hits)

this is also why lights dimming briefly isn't an issue.. but when they dim down and stay that way, you have problems.