electrical problems--help please

[mobilenuke]

Just purchased Superformance136 with a 1963 427.
After a very hot (110) day of driving eveerything seemed fine. Took the wife out for a ride last evening and noticed that the ammeter was on the - side.
After I turned the lights on it dropped even further.Pulled in to get gas and unable to start after. After a jump drove home with lights and ammeter still on
neg side. Pulled into garage and turned off car, tried to restart and battery not able to revive the beast.
Went out today, pulled battery and had it checked, before trying to remove alternator, and it tested as just needing a charge. Took it home, reinstalled and turned on the key----started right up? Ammeter reading on the plus side with an increase when revs up even when lights on. Engine temp goes up to proper operating temp and ammeter drops to 0 then drops to the neg side
Sorry for the long winded explanation but my question is--- could it be the electronic voltage regulator or possibly the altenator?
Jeff
PS tried to start car when it was at temp and no go---won't turn over

[Jerry Clayton]

Is the cooling fan coming on as thhhhhhe ammeter drops to zero and goes negative?

I have seen several cars with underdrive pulleys which circulates the water more slowly and doesn't turn the alternator fast enough to keep up with cooling fan and lites.

Many will drop to 9 or 10 volts when the fan comes on with an 80 amp alternator with underdrive pulleys.

Jerry

[Excaliber]

Sure sounds like a heat induced problem, this is a head scratcher. When at temp and with the amp reading negative I'd 'by-pass' the regulator to eliminate IT as a variable.

When by-passing (shorting) the WIRES TO the regulator (not the regulator itself) the alternator should put out MAX power, so don't run the test to long. Which wires do you jump to by-pass the regulator? Gotta look it up somewhere, it can also be 'jumped out' at the alternator but it's much harder to get to the wires in that case.

[Rick Parker]

As Jerry hinted at, if the pulleys are underdrive your alternator may not be able to keep up with your electrical demands. However, check your battery for load capacity not just current voltage reading. Then, check alternator output (Which I suspect will be ok) and then voltage regulator ,many auto parts stores such as Auto Zone will do it for no charge. I suspect you have a fan(s) that may be drawing to much current or a short circut that is somehow temprature related and appears only when the fan circuit is activated. Since the amp needle goes positive upon startup (COOL) it would indicate alternator is functioning and regulator working. Keep us posted.

[Excaliber]

Even if the pulleys are underdrive it sounds like the amp draw is WAY high and draining the system to quickly for pulley size to be a factor.

The fan motor does draw some serious amps. You could disconnect it when symptoms appear to see if that is the problem.

[Rick Parker]

Good idea Ernie. A Spal fan draw up to as much as 24 amps.

[vettestr]

You hae been gien great adise already but a couple of steps farther may help your case. Check to see if your regulator output is set properly when at operating temp. Voltage should be a min of 14.2 volts. so alt and reg can each be checked. An inductive meter used to check starter amp dram can be used to check total current demand on the battery and the charging system.
A couple of tricks needed on one of my cars was to run 2 batteries for that demand under the highest conditions. The injection ECM did not like power sages nor doesa MSD ignition controler. I was running multiple fans and electric fuel pumps and a coolant xfer pump etc...
My local alt and starter rebuild shop hot rodded my alt. with an internal modification and also swaped the pulley to increase rpm of the alt at low engine RPM. Ask your local alternator rebuilder to HOT ROD for a higher amp output potential and make it available at low engine RPM. I also hate the underdrive engine pulley kits because they can cause all kinds of trouble. good luck and enjoy.

[mobilenuke]

car cooled off and I went to see if it would start again--- no problem, it was charging as it should but reading at battery was only 12.8 up to 13.4 with rev.
Temp went up, fans kicked on, dropped ammeter-- disconnected first fan with a little improvement, disconnected second and went back to normal charging. Since this was a sudden change, worked fine day before, could there be a short in the fan switch or some other problem?

[Jerry Clayton]

Common problem unfortunately---Check the amp rating on your alternator--probably stamped somewhere--check the size of you pulleys to determine if they are underdriven--if they are aluminum most likely they are underdriven--the crank pulley should be larger than the waterpump pulley and the alternator pully only about 3 inches. Lights and fans will take probably mininum of 100 amp modern one wire alternator to work reasonably well.

Jerry

[Rick Parker]

Disconnect both fans and bring it up to temp where fans normally kick on and see if symptoms still exist. If not, check current draw on each fan individually. Is it possible one of the fans has developed a bad bearing or bushing making it hard to turn?

[mobilenuke]

While looking at the engine compartment trying to figure things out I put my hand on the voltage reg and it was smoking hot. Replaced the reg and things seem to be operating fine now. There is a drop during idle (with lights and fans running)but after 12-1500rpm ammeter reads to the positive. Thanks to all that have replied for your suggestions and I will refer back to them if this doesn't last.
Jeff

[Excaliber]

Actually a standard 60 amp or so alternator is generally fine for Cobras. If you add up the total load it should be under or around that. Nothing wrong with a 100 amp alternator, but they cost more and weigh more and are usually over kill.

[vettestr]

GREAT news but she should not be displaying a neg charge at idle. You may getaway with it running low but this is hard on the electronics to swing or sag low at idle.
Install a smaller diameter ALT. drive pulley to increase idle output or the better route would be to install a higher output ALT. like Ernie suggested and with the smaller pulley too make sure.

[vettestr]

It just dawned on me this is MULVS car. Sorry I ride the verrrrry short bus sometimes. Mulv took great pride in this car and he can tell ya if it has reduction drive pulleys or not. I change stock Alt. pulleys to smaller diameter to increase idle output regardless and also have ALT modified by shop on all cars.

[John S Peterson]

You say you pulled the battery and had it checked......Are you sure whoever checked it did it right? There is no one specification for all batteries Sometimes when parts store people (no put downs intended) charge and load test batteries they fail to follow the proper methods. First, when a battery is charged a very strong surface charge is present across top of the battery which needs to be removed. This is done by applying a 300amp load for 10 15 seconds at which time you should see at least 12.2v or above. If the battery is not charged properly it cannot be tested properly. It's job is to provide the energy necessary to start the car and power the accessories until the engine/alternator takes over. The only time it comes back into play is when your system writes a check your alternator cant cash, then it borrows it from the battery. Ck to make sure you battery is of the right capacity An alternator will only give back to the battery what it thinks it needs to, so if the batt is lying (defective cell) it wont charge properly either.....make sure it was charged and load tested properly (by the book).....ck all connections and cables (voltage drops are your worst enemy) NO crimp connections or those cheap battery connections....solder and shrink wrap battery cables. Use at least #8 wire from alternator to battery source. What your trying to do is make sure is that you are providing a FEAST so to speak of voltage to your most hungry accessories keeping them very satisfied. Follow the basics of what you have read from these guys, remember the words "fiberglass car" and redundant grounds. Also....a good Battery is at 100% potential at 80 degrees f. above and below that it's performance drops dramatically sooooo.

John

[John S Peterson]

I forgot to mention to watch out for your Optima type batteries...usually these type dont like very high amp charge rates found on large shop type units. Stick with low apms for longer periods of time, that works better on all batteries anyway. Also alot of people when they "jump start" their dead car they drive it for a while to charge the battery. That is the worst thing you can do for the charging system. It was designed to replenish only and it seriously overloads the system, besides it would be difficult to fully charge a really dead one, so the vehicle should be taken somewhere and the battery properly charged........you heard it here...........

John