Batt light...Smoked my alternator (1360w rms)

[Liquid_force]

For anyone interested...
For a couple weeks I had seen my batt light coming on once in a while, usually only for a matter of minutes. Didn't think a whole lot of it.

On a 200 mi round trip this weekend it came on about 50 miles from home and never went off. When I got home I checked V with the engine off -- 12.0. Started it and checked again - 11.65.

Pulled the alt and took it to a good auto electric shop. By the way - thought it was a 130A -- it's 110A. They said they'd rebuild it for about $90 by the end of the day (reman replacement is $180). I said go for it. Got a call in about an hour and the tech said the alt was so torched it wasn't worth rebuilding.

Told him I have a high power sound system and he said when I get the new one in to come by and he'd test it for me.

I have 1000w class D sub amp and 180x2 a/b for the fronts.

Voltage w/engine off was 12.6, at idle it was about 13.7 (battery had been pretty badly discharged before I got the new alt in -- it turned over slow). I put in some bass mekanik w/volume close to or at the edge of clipping (I rarely listen that loud). Voltage sagged to 12.5-12.8 and current was varying between 30-60. The tech seemed a little wowed. Older guy. Seemed cool w/audio but I don't think he had any idea people are running that kind of power.
He seemed to be as worried about the weak battery eating current as the amps.
He also pointed out a smell like burned plastic and said it was due to the alt charging so hard it was burning the coatings off its internal parts, and the alt would probably be hot enough to physically burn you if you touched it.

Dude told me a cap might help (!?!?!) I wanted to ask his logic on that one, but it was 10 min before close so I just let it go.
Anyway - just an interesting learning experience regarding current draw and its effect on the charging system. I thought some of you running a lot of amp power might be interested in.

I guess the lesson is if you're running ~1200w or so and you pound on it very often your alt is probably on borrowed time.
I got one with a lifetime warranty, so even if I have to change it every year or so I'm ok w/that vs big charging system mods.
I'll look into a good battery when this one dies -- that's about it.

 

[Dyoel182]

Caps are great and pretty cheap insurance for this kinda thing.

 

[pre98zetec]

i ran almost 2000wrms for over a year with a single yellow top up front and a 2400 kinetik in the back. You must be doing something wrong or your alternator was just destined to go anyways.

 

[Liquid_force]

Caps are great and pretty cheap insurance for this kinda thing.

I've read, and often been involved in HUGE threads re: the never ending cap debate probably 20 times. I know what they do, I know how they work.
What it comes down to is a cap is a storage device and as such has to be charged. Why/how does adding a storage device to an electrical system that has very little excess current to spare help the situation?

A 1F cap stores 98 Joules at 14v, but since it is only usable down to 12v or so only 28J is available. That's 28 watt-seconds. A 1000w amp drawing, let's say 1000w on a big bass note means that cap is useful for <0.03 sec, after that it's just another load. That's assuming we have a perfect capacitor with no esr/esl losses.
They serve two purposes - peace of mind for people who've never considered the math, and to make money for salespeople.
They don't do anything for an alt at its limits.
20 years ago when they were introduced, and 200w was a BIG system I can see how they might have been some of some very small benefit. Now, with 1000w being typical they are useless.

i ran almost 2000wrms for over a year with a single yellow top up front and a 2400 kinetik in the back. You must be doing something wrong or your alternator was just destined to go anyways.

It may have been, but I think a cheap, older battery had an impact as well.

 

[Dyoel182]

I've read, and often been involved in HUGE threads re: the never ending cap debate probably 20 times. I know what they do, I know how they work.

What it comes down to is a cap is a storage device and as such has to be charged. Why/how does adding a storage device to an electrical system that has very little excess current to spare help the situation?

It may have been, but I think a cheap, older battery had an impact as well.

If they didnt work you wouldnt see them in professional setups. The way they were explained to me by a pro audio guys years ago was that the cap is there for instant power use just like the battery but you dont automatically need one. On a system where your alternator is up to the task you probably dont need one but when your lights dim as the sub plays you'll know you might need one and you might want to look at a better battery and then at a better alternator.

 

[Liquid_force]

pro audio guys...

Probably a sponsorship - it's their job to promote the gear they run.

If they REALLY worked you'd see all the accessory companies like streetwires, stinger etc with demos at comps showing you exactly what they do and why we all need one -- you know - side by side demos, one with, one without a cap and all the great things they do...AKA proof.
The problem is THEY know, and a lot of consumers know they don't do squat except make them money -- THAT'S why you see them in sponsored comp cars and the cars of those who have never really taken the time to understand them, and there's the few that just think they're cool.

Yes, they store energy that can be quickly discharged in tiny little bursts, then they load the alt while they recharge.

They can help dimming lights in just the right situation, but if that is the objective they should be installed at the front of the car near the headlights.

 

[Dyoel182]

pro audio guys...

Probably a sponsorship - it's their job to promote the gear they run.

Yes, they store energy that can be quickly discharged in tiny little bursts, then they load the alt while they recharge.

They can help dimming lights in just the right situation, but if that is the objective they should be installed at the front of the car near the headlights.

This was a personal friend that wasnt trying to sell me anything and was just answering a question I had. The theory behind them is sound though and they do exactly what they say they're supposed do. I've seen people with a second battery in the trunk instead of a capacitor and be perfectly happy. But as you said and I agreed to before, its really a moot point if the charging system cant handle it in the first place.

 

[pre98zetec]

caps are in show cars because they look cool, thats all. Fashion over function in a show car. In real world situations your better off with a second battery, which cost just as much as most caps if you really look into it.