Is there a way to tap into raw pre-regulated alternator voltage?

[crazypete]

Whoa!

Ok, I just blew a 120 AMP breaker on a heavily underdriven stock 65 amp (verified) alternator!

How is this possible?

This breaker is toast. I mean I push reset and it said sproing and the handle is now hanging there limply: it's melted inside.

Tonight:

I pull to the top of the driveway and I'm idling for a few minutes lights on no problem, stereo playing on the resurrected kenwood amp (a single blown lead, I resoldered). I put it in drive and for that split second the backups flicker on, the radio/amp goes off but the voltage is full so the breaker was good. This still annoys me but I pull out and take off. I'm driving around and every once in a while when I _let off_ the brakes, the radio crackles and fades out for a few seconds. In the middle of the road a minute later, The stereo crackles again and starts to pulse off and on and I see the volts drop to about 4-5. I known the breaker somehow blew. Miraculously, the motor continues to run. I zoom home (1 mile away) and get it parked. I go up front and my poor circuit breaker is sitting there very blown. No blown fuses, on the amp or ignition. Just the 120 amp one on the 65 amp alternator.

What could possibly cause this? The amplifier is the only high amperage item so it is what senses power fluctuation the most.

 

[tmoss]

Sounds like you have an intermittant short on the alternator side of the breaker. My guess is the battery fed the short and burned up the breaker. a 65A alternator can't put out enough short circuit power to toast a 120amp breaker I'm thinking.

 

[crazypete]

Do alternators usually short internally or is it more likely the main power wire? I'm 99% sure that the main wire is ok since I just finished rewiring the car's enginebay and that wire was solid front to back.

The car has basically been sitting for 2 months getting a head swap/port done and the alternator has had no "stimulus" on it. It is a bit hotter under the hood due to a lean condition and it does take a little while before this starts to happen so it might be heat related.

I've been stalling on a 3G upgrade for a while but this is a great time to do it I guess. How much more of a load does a 3G produce than the stock alt?

 

[tmoss]

Alternators have a full wave bridge with diodes that can fail and a "return" blocking diode connected from ground to the bridge output that can fail also, but they normally fail and stay failed - they are not normally intermittant. Double check all the wiring.

 

[Idwitheld-1`]

Do alternators usually short internally or is it more likely the main power wire? I'm 99% sure that the main wire is ok since I just finished rewiring the car's enginebay and that wire was solid front to back.

The car has basically been sitting for 2 months getting a head swap/port done and the alternator has had no "stimulus" on it. It is a bit hotter under the hood due to a lean condition and it does take a little while before this starts to happen so it might be heat related.

I've been stalling on a 3G upgrade for a while but this is a great time to do it I guess. How much more of a load does a 3G produce than the stock alt?

My PA Performance 3G, 130 amp alt came with a load test report. It indicated 90 amps at 900 rpm's! That's 25 more than stock at full output.

 

[HISSIN50]

My PA Performance 3G, 130 amp alt came with a load test report. It indicated 90 amps at 900 rpm's! That's 25 more than stock at full output.

i would be happy to take it off your hands for Christmas.
i hope you and S are doin better bud. best wishes.

 

[crazypete]

The problem must be load related. I pulled the high juice device, the amplifier, the cd player and put the stock radio in with no stock amp (I might be funny in the head but it doesnt sound all that bad, just about the same as with the amp)

I drove around for over an hour last night. Apart from the dimming lights at idle when cold, I got no funny business. Lights on, blinkers, wipers, everything. I would see the volts drop at idle and the rpms would dip a bit too low for my tastes at times (looks like it was a rich condition and the car would load up at idle...time for a new o2 sensor, this one is obviously gummed up).

So it seems as if this is some of that "charging issues" that everyone told me I would have if I underdrove my alt. Oddly, absolutely none of this happened for the past 2 years and it's suddenly happeneing now that I changed the heads. Oh well, 3G for me! Thanks guys!

 

[HISSIN50]

Pete, im not that conversant with carb conversions - i have never seen someone run a lambda with a carb. is that for real? or do you have an A/F gauge or something. i cannot figure out how one would do anything for a carb with a lambda. LOL.
good luck.

 

[crazypete]

It's actually incredibly useful and I feel bad for all those that came before O2 sensors. I take the part of the EEC computer, screwdriver in hand, jets in box. Tuning a carb without this is ok for idle conditions but is a super pain in the rear for cruise or acceleration (shutting car as it is moving). With the stock O2 hooked up to an AF guage (autometer? Forgot the brand. They were available at summit a year back. They have 2 red, 2 yellow, 2 green, 2 more yellow and 2 more red bars. Not super accurate but then neither is a carb), I can now take it for a spin and I see the mixture change as I drive around. Or at least I did. Now it just shows 1 red bar or nothing so I'm pretty sure the thick black smoke shooting out the tailpipe after the rebuild contributed to this poor o2 sensor's gummy demise. I knew it was off when I was choking from fumes yet the sensor read 1 red bar and the rpms rose as I leaned it out at idle.

Reading some other posts, I also came to the realization that these are by no means wideband and jump between .2 and .6 volts which explains why I always get crappy readings and I am now wondering if a different type of O2 sensor would serve me better, maybe even a 1 wire wideband.