Dubstep Shep

This last weekend I made it out to my first HPDE in my 07 Z06.

The car ran great, no overheating of any kind on the oil and coolant. Oil temps were 230-240 and coolant was 220-230 after a 20 minute session. I wasn't pushing the limits as much as I could, but it was a hot weekend as well, over 90 for sure.

The problem is, I think I'm roasting my alternator.

First session out in the morning, the car ran fine. Second session, I noticed the ABS acting up and then my voltage started dropping. By the end of the session the car was running on battery power. I charged the car up and swapped the alternator out for a new one and the issue mostly went away, but the car was idling at about 13.0-13.4 volts with the A/C on instead of the normal 14.2 volts. At 1,000rpm with the A/C on I was getting the full 14.2 volts though, and with the A/C off it would do that at idle, so I went ahead and ran the last session of the day. Sure enough, same thing happened.

I swapped on my buddies alternator from his car and that didn't solve the problem, so I assumed the alternator wasn't the issue.

Went home that night and messed with the car some. Tried testing voltage on all four connections on the alternator and couldn't figure out what was wrong with it.

I had NGK spark plugs and MSD plug wires, so I swapped those out for some AC Delco units. That didn't fix the issue.

I went ahead and touched my battery terminals together for 30 seconds to reset everything. That didn't fix the issue.

I also pulled the code from the tune so the computer wouldn't even recognize it. That didn't fix the issue.

Finally I went to O'Reilly and tested the system. Battery was good, but the starter AND alternator failed according to their tool. The car started and the battery voltage was really low, so it seemed like the starter failing might be a false reading. Took the alternator off and had it tested in the store and it failed. Got another alternator and put it on and the issue was semi fixed again. The car would idle with the A/C on at 13.0-13.4 volts and 14.2v with the A/C off.

I ran the next session and sure enough, same set of symptoms. This time though I waited for the car to cool off after the session and now it works just fine.

I'm thinking I'm overheating/overspinning the alternator and cooking it. The car has a CAI, Kooks headers with Jet-Hot coating and DEI titanium wrap, Kooks X pipe dumped before the transmission, no thermostat, radiator bypass blocked off, no heater, and the stock hood. I'm thinking the radiator and oil cooler are working better than a stock car and dumping more heat into the air that's then getting trapped under the hood and overheating the alternator.

Thoughts? Solutions? I'd rather not spend $2,000 right now on a vented hood or $600 on a "race" alternator that may or may not fix the issue... I'm not opposed to cutting up my OEM hood, but most of the louvers I've seen are so expensive I might as well buy a new hood.

Thanks in advance gents!

ErnieN85

I have had the same type of problem
here is how I solved it.
1 New 170 amp Billet tech alternator.
2 new heavier power lead to the fuse box, I had a 1 volt drop across this under heavy load
3 air duct from the shroud infant of the radiator

fleming23

I cooked the delco alternator on my LS3 at COTA earlier this year.

I had a very intermittent issue where the current would drop when it got hot. I pulled it off and took it to be tested and it checked out fine. Put it back in, gauge read 12-13 volts, thought it must have been a fluke. Once I hit the track, it would quickly drop to 10 or less, basically running off the battery.

Bad thing is none of the part stores carry the damn thing! Would have thought it would be a relatively common part but apparently not.

Dubstep Shep

1) Yea, unfortunately they aren't cheap and I am.
I want to get one eventually, but it isn't in the budget at the moment.
2) In looking through a few threads, I'm thinking that may be part of the issue. I'm also going to check my starter and see if the connection there is a problem.
3) You mean like run a duct to the alternator? I'd think cutting some vents in the hood would work even better.

That's basically what mine is doing. And yea, I ran around to three different stores last weekend to get alternators.

mikeCsix

You might also have a resistive connection to the fuse box and/or alternator which would certainly heat the alternator. Alternators will fail if their leads are disconnected while the engine is running. Ernie had about an 8% voltage drop between the alternator and fuse block, going to the larger wire will increase charging efficiency and help keep the alternator running cooler, going to a higher output alternator won't help much, it will consume more horsepower at higher rpm's, and could also consume more hp at lower - depending on the charge curve. You can make the OEM alternator more efficient by going to larger wire, also don't forget, the ground is the other half of the circuit and also has to be clean and dry.

Dubstep Shep

This is sort of the exact reason I didn't want to just slap on a bigger and better alternator and call it a day... That may just be a cover up for the real issue here.

I'm planning on running a few voltage tests this evening to see what sort of voltage drops I'm getting in different places.

It's an easy thing to just run better wire everywhere. Power, ground, etc. I'd like to make sure that's the issue before I do it, especially if something like my starter is messed up.

froggy47

My 95 BMW M3 had a cooling duct to the alt, cheap plastic but worked.

This might be stupid, but since the regulator fixes the volts put out anyway, how about spinning it (alt) slower (pully size) like they do with power steering pumps?

Dubstep Shep

That works up to the point that the alternator can't keep up at lower RPMs. I'm already having my voltage drop at idle, so I don't think that'll work for me.

froggy47

Right, good luck, post what you end up doing.

TrackAire

A lot of aftermarket alternators that claim to be "higher amperage" than stock but are built in the same case size as the stock unit often times run much hotter and fail much sooner than a stock alternator. It's no different than having a stock Z06 motor and pumping up the horsepower 30%...it's going to create a lot more heat. Most of the cheap "upgraded" alternators that are built in the stock case have much lower than stock amperage output at idle and only put out the max amperage at higher rpms....but then they start to get hot and the amperage output starts to fall.

Correctly designed alternators that do have upgraded amperage ratings often times have larger cases and additional cooling fins built into them to cope with the extra heat developed. And they usually come with a very high price tag compared to the stock cased units.

Just what I've found working in the 12 volt world for the last 16 years.

Dubstep Shep

Ran a couple quick measurements yesterday with my multimeter. The car wasn't fully warmed up but here's what I got.

With the A/C off:
Across battery at battery posts:14.49
Fuse box power to engine block: 14.58
Alternator B+ to alternator case: 12.58
Fuse Box power to alternator case: 14.52
Alternator B+ to engine block: 14.80
Battery positive post to ground bolt: 14.38
Gauges: 14.3-14.4

With the A/C on:
Across battery at battery posts: 13.20
Fuse box power to engine block: 13.60
Alternator B+ to alternator case: 13.55
Fuse Box power to alternator case: 13.65
Alternator B+ to engine block: 13.55
Battery positive post to ground bolt: 13.20
Gauges: 13.0-13.2

What's weird to me is that the voltage is higher across the alternator with the A/C on... No idea why that's happening but I'm going to get the car up to running temp tonight and recheck all these.

ErnieN85

ok food for thought, the idle speed is bumped up a bit with the air on.
next to check the condition of the connections from the alternator to the fuse box you need to connect to the B+ at the alternator and B+ at the fuse box.
Also it will not show a bad connection or(voltage drop) unless it is under a heavy load, Car Hot, Air and cabin blower on High and also the Cooling fan on High. in my case I have an A6 so it was in gear with the brake lights on.
So a very heavy load on the system when I had a loss of voltage across the feed wire from the alternator.

Dubstep Shep

Yea, that's one reason I was planning to get it up to temp.

Still, the voltage drop on the alternator concerns me. I want to repeat that to make sure it's correct.

TrackAire

Also, never trust your battery is doing ok....even if it shows full voltage of 12.8 or more volts. I have seen a lot of defective batteries (both new and used) that tested fine, had the correct voltage but once put into service they would either short out internally, cause the alternator to run hot due to resistance, etc. The trigger could be the cars vibration, engine heat or the charging circuit itself causing heat which then causes the battery to short out due to being defective. Unfortunately testing the battery with an amp load tester does not always mimic the actual under hood conditions.

If you have a spare battery, install is and see if that makes a difference, it is a very cheap way to diagnose the issue and rule out the battery as being at fault.

Good luck.

Dubstep Shep

Had the starter and alternator checked out off the car. Both worked.

Checked all the connections. Alternator B+, battery positive and negative, negative to frame, starter connections, ground to block, and the fuse box.

Car runs at 13 volts at idle, which seems low to me... it used to run at a higher voltage.

I'm getting about a 0.3 volt drop from alternator to battery.

My guess is that the alternator is overcharging, or was. I'm gonna run it around and see what happens.

Dubstep Shep

Welp, the alternator is intermittently working. It runs at idle, but then turns off as I start to drive.

Side note, possibly related, but my horn sounds really weak...

mikeCsix

It doesn't look like anyone has mentioned this yet, but Alternator +B appears to control the output of the alternator. IOW, when +B is lower at 12.58, alternator voltage rises to 14+,
As +B rises, alternator output drops.

In the multi-step systems I've worked on in the past, this is pretty normal operation. There is a time element that isn't being observed here too. +B usually has to rise to a max voltage for a fixed amount of time and then will shut off to keep from the alternator from overcharging the batteries and to regulate the voltage of the system.

The best float voltage (for all those battery tenders we use in winter) is from 13.02 - 13.2 volts. That is just enough voltage to keep the plates in a lead acid battery from sulfating (coating the plates with sulfur) which stops the flow of electrons. The modern "smart chargers" will drive the battery up to 14.2+ for a period of time with maximum current, then taper the current and maintain the high voltage, then drop the voltage to a maintenance level (13.2 typically).

So that's for your standard lead acid battery. AGM batteries and gel cells may be a different matter altogether, and beyond my experience other than I've used battery maintainers on both but not to the extend of the typical lead-acid batteries.

It appears on some level and depending on the sophistication of the alternator testing, the alternator works within a parameter, ie, +B varies and output varies. what isn't known is if the relationship between alternator rpm's and voltage/current output has changed. If you look at the difference in diameters between the crank/balancer pulley and the alternator pulley, you can get a ratio and hence, a real alternator rpm. From that you can go to a chart and see what the output should be. I don't have access to this information otherwise I would share it here.

At least at this point, you know your connections are good. If you have a conventional lead/acid battery that is in good shape, I would suspect the alternator may be a little off, but not enough to cause immediate issues. I think it may lead to premature battery failure if your system doesn't spend a lot of time at the 14.2+ level where much of the bulk charging takes place. By premature, you may lose a year off a fresh battery if the voltages don't get high enough, long enough to break sulfation of lead plates in a lead acid battery.

From Ernie's post, there is a small connector on top of the alternator, I'm not sure what those small wires are connected to, but could be used for additional alternator sensing or control. You might PM Danno, he seems to have a lot of background info on things like this.

HTH

Dubstep Shep

Here's the wiring diagram for the charging system.



I went back and rechecked my voltages. The low 12.5 volt across the alternator appears to be a false reading. I'm getting a little under a half volt of drop max from the alternator to anywhere else in the system.

Dubstep Shep

Any ideas? Anyone?

froggy47

Did you already try it with another known good battery? Not just readings on yours.



I recall a guy whose abs went nuts racing. Turns out his battery would short out only during race use. New batt fixed all.