Alternator Output ?? AC/Oil Cooling

[brads911sc]

So I upgraded my oil cooling to elephant widemouth with Fan kit, have the upgraded evap Keuhl fan and the ZIMS condenser fender fan.

With AC off and Oil Cooler fan running I am registering 13.2 volts with the car running at 1500 rpms. with AC on full blast its 12.8.

Today I went on a 50 mile drive with it all on (92 degree ambient temps) and then it would not start. Jumped it. Drove home 50 miles without AC and now its fine.

Battery registering 13.0 volts with it all turned off. probably good considering it was discharged enough to not start 50 miles earlier.

What is the conventional wisdom here? Is there a higher output alternator? voltage regulator issue? find it hard to believe that the alternator cant handle an oil cooler fan and a few AC fans.

Belt is fine.
Alternator is a New Paris Rhone with new Voltage Regulator about 1,000 miles ago bought from our host.

I see our host sells a high output 95 amp unit. but its $800 OUCH!

Thoughts?

[Jim Sims]

Recall that an electric fuel pump is also running and when the A/C compressor is engaged the clutch coil is energized drawing current. Do you know the watt or amp ratings of all the motors and coils? Even with everything you've added it wouldn't seem your system is overloaded. I would suspect either an unknown current drain or a failing battery. Battery voltage should be tested under a load; there are procedures for doing this using a large loading resister array. How old is the battery and is it the largest that will fit in the space?

[brads911sc]

Its an optima 34R. Not huge but not a small battery. 850 CCA if I recall. Its a Red Top. Its always on a tender. Never had an issue before. Less than 2 years old.

I also have MSD,MSD Blaster coil, EFI... The AC condenser fans are all on one 20 AMP fuse so together they are less than that. The Kuehl Evap is also on a 20 amp. The fan for the Oil Cooler is on a 10 amp fuse. The AC clutch is triggered off the same fuse that powers the AC condenser fans. I cant wrap my head around it using more than 75 Amps.

[47silver]

brad:
the alternator is not designed to operate at 100 % of the time.
ignition system draw = 10?
fuel system = 10
stock low beams = 10
stock fogs = 10
running lights = 5?
radio = 5?
ac clutch = 10?
condenser fans = 10?
oil cooler fans = 10?
that is roughly 80 amps.
what is the amperage of your alternator? if it is 75 it is way too small
if it is 100 it is marginal. An 80 percent duty cycle will shorten the life of the alternator.
that is why you should always recharge the battery with a charger when the battery is low or dead as the alternator will probably burn out by charging a dead battery for 2 hours straight operation.

when the alternator operates, the extra power generated that is not used by the operating systems is sent to the battery. So a 100 amp alternator witha 50 amp load will only need 50 percent to go to the operating systems and the rest can charge the battery. The voltage regulator shuts off the alternator when the voltage is at this setpoint say 14v. The operating systems then use the battery until the voltage again goes to 13.2. When this occurs the vr allows the alternator to operate to recharge the battery. the battery runs the systems and the cycle continues.
A smaller battery can take less of a charge and may cause the alternator to work more often than it is designed to to do but it should not cause the battery to die if the load is less than the alternator rating.

The on and off duty cycle allows the alternator to cool down, because if it is operating for too long it cannot cool down and it then looses efficiency which begins a slow decline that will cause the battery to discharge and for the alternator to eventually burn out.

In other words i think you need a bigger boat.

[kuehl]

Brad,

I'd say simply based on other 911's (either SC or Carrera), having similar aftermarket improvements, the stock alternator and battery (in good working condition) should be able to handle the loads.

The point that it died while driving is your clue!

Probably doing all the standard tests is the best way to track down the gremlin:

1) Battery Test
2) Alternator Test
3) Check all grounds
4) Parasitic draw (always fun to do).

I just replaced my 4 year old heavy duty (don't know how I fit it in there) battery last month; too many years of monthly recharges finally did her in; parasitic procrastination ...lol.

[brads911sc]

I wasnt using headlights, running lights or fogs. Dont own a radio. So I should have been fine on a 75 amp Alt yesterday.

But your point is well taken. Think I should look at a high output alternator? Voltage regulator play any part of these lower numbers?

Originally Posted by 47silver

brad:
the alternator is not designed to operate at 100 % of the time.
ignition system draw = 10?
fuel system = 10
stock low beams = 10
stock fogs = 10
running lights = 5?
radio = 5?
ac clutch = 10?
condenser fans = 10?
oil cooler fans = 10?
that is roughly 80 amps.
what is the amperage of your alternator? if it is 75 it is way too small
if it is 100 it is marginal. An 80 percent duty cycle will shorten the life of the alternator.
that is why you should always recharge the battery with a charger when the battery is low or dead as the alternator will probably burn out by charging a dead battery for 2 hours straight operation.

when the alternator operates, the extra power generated that is not used by the operating systems is sent to the battery. So a 100 amp alternator witha 50 amp load will only need 50 percent to go to the operating systems and the rest can charge the battery. The voltage regulator shuts off the alternator when the voltage is at this setpoint say 14v. The operating systems then use the battery until the voltage again goes to 13.2. When this occurs the vr allows the alternator to operate to recharge the battery. the battery runs the systems and the cycle continues.
A smaller battery can take less of a charge and may cause the alternator to work more often than it is designed to to do but it should not cause the battery to die if the load is less than the alternator rating.

The on and off duty cycle allows the alternator to cool down, because if it is operating for too long it cannot cool down and it then looses efficiency which begins a slow decline that will cause the battery to discharge and for the alternator to eventually burn out.

In other words i think you need a bigger boat.

[brads911sc]

Hi Kuehl,

Just to clarify, it didnt die when I was driving. Stopped at a store. wouldn't start. Got it jumped and drove home with no issues... well except I didn't run the AC so I was HOT...

when i go home the battery was at 13 volts and started right up. i will have it all tested. but my voltage seemed low with AC running (12.8). Seemed normal with less load (13.2). Ill have it all tested.. Does 13.2 seem right?

Originally Posted by kuehl

Brad,

I'd say simply based on other 911's (either SC or Carrera), having similar aftermarket improvements, the stock alternator and battery (in good working condition) should be able to handle the loads.

The point that it died while driving is your clue!

Probably doing all the standard tests is the best way to track down the gremlin:

1) Battery Test
2) Alternator Test
3) Check all grounds
4) Parasitic draw (always fun to do).

I just replaced my 4 year old heavy duty (don't know how I fit it in there) battery last month; too many years of monthly recharges finally did her in; parasitic procrastination ...lol.

[brads911sc]

Anyone have experience with these guys? They will take your stock alternator and upgrade it to a high output unit. For $275 seems like a good option...

Quality Power
31510 Yucaipa Blvd.
Yucaipa, CA 92399
(909) 794-1600

[adamellis01]

Brad,
I want to share my experience with you as I think it may help (hopefully). I have an 87 Cab with 85K miles, stock and rebuilt at 72K miles (those darn leaky valve guides). My car is pretty solid and runs great. My stereo does have a pretty beefy amp (McIntosh) which I have never had any problems with it.

Three weeks ago my stereo starting kicking on and off while driving. I noticed my battery was now from 2004 - decided to replace it with a BOSCH. This seemed to eliminate my problem. Last week I was 4 hours into a 6 hour trip blasting my stereo with the top down. Pulled off to get gas and couldn't restart my car (dead battery). Finally jumped it and drove the last 2 hours of my trip without issue however I drove with no stereo or lights to be on the safe side.

The next day my brother and I checked the battery and alternator with a volt meter. At idle, the volt meter was reading 12.2 volts. My brother insisted that it should be 13.8 at idle (I didn't know) and that my alternator was bad (newer cars are around 14.4) . Even when I revved it up to 3k RPM's the volts still only went up to 13.2. I took my brothers advice and had a local shop (Brumos in Jacksonville) check it out as I wanted piece of mind on my return trip the next day. They confirmed that the alternator was bad and needed to be replaced. They replaced it with a BOSCH alternator. To fullfill my own couriosity I hooked up the volt meter to the battery again when I got home and at idle it was indeed registering 13.82 volts. I haven't had any problems since.

I certainly don't claim to be an electrical guy but I hope my story helps you out.

Cheers,
Adam

[kuehl]

Brad,

Client stops by today with a 1980 silver SC, lovely car. He has our complete system in it. Helping him resolve a few issues; his shop decided to put stop leak in the system' (solid red, Hawian Punch Red); OMG idiots!.

He goes to drive away and car won't start. Toss on the battery charger for a minute and car starts. He says he had a new alternator put in 2 years ago, battery looks at least 3 years old; probably older. So we toss on a simple volt meter and at idle its about 12.6 v, at 2k rpms same, at idle with ac on about 12.1v. We suggested he have the battery tested and sure enough he's replacing it right now. Probably review the alternator too.

[brads911sc]

Thanks guys. I will have the Alternator and Battery tested. I am hoping its one of the two because i cant wrap my head around $800 for an additional 20 amps.

[kuehl]

"Spray on" solar paint!

[Brorag]

my batt lasted a whole 4 months past it's guarantee--didn't even blink--new batt--all is well.

[brads911sc]

Maybe Reid can market that.

Originally Posted by kuehl

"Spray on" solar paint!

[304065]

Don't Optimas require a special charger? I realize it lives on a tender, but the alternator in the car may not be up to charging it. I ditched my Sonnenschein for this precise reason.

[brads911sc]

no. 3 of the 4 batteries listed top 5 in consumer reports are an optima or diehard platinum or a version of the gel battery.

Originally Posted by 304065

Don't Optimas require a special charger? I realize it lives on a tender, but the alternator in the car may not be up to charging it. I ditched my Sonnenschein for this precise reason.

[brads911sc]

Took the car to my FLAPS. battery tested fine. Alternator failed. So 18 months after i went with the new Valeo, i get to buy a new alternator. out of warranty of course. Bought a new Bosch instead. Hopefully Ill have better luck...