charging system (WTF)

[krazykyle]

OK something is messed up.i fired up the car and the charge lite stays on and gets brighter when i give the car gas.i even went out and got another alternator for the **** of it.the alternator is energized when the key is on,but it's not charging the battery.get this one i turn the key backwards while the car is running to shut it off,the ****ing car keeps running with the key in the off position.i have to disconnect the battery to shut t he car off.

 

[crucial118]

Info? What have you done new? Recent swap?

 

[Bonnewagon]

Amp's go up with rpm's is voltage regulator. Running with key off means voltage is backfeeding the ignition. Or you have MSD and the diode that prevents this is missing or blown? Ironicly, the MSD gets backfed through the alternator brown wire.

 

[krazykyle]

i do have a msd ignition.what the **** did i blow in that thing.i have a 6a box with a super coil.ENGINE RUN-ON
If your engine continues to run even when the ignition is turned Off you are experiencing
engine Run-On. This usually only occurs on older vehicles with an external voltage regulator.
Because the MSD receives power directly from the battery, it does not require much current
to keep the unit energized. If you are experiencing run-on, it is due to a small amount of
voltage going through the charging lamp indicator and feeding the small Red wire even if
the key is turned off.
Early Ford and GM: To solve the Run-On problem, a Diode is supplied with the MSD in the
parts bag. By installing this Diode in-line of the wire that goes to the Charging indicator, the
voltage is kept from entering the MSD. Figure 6 shows the proper installation for early Ford
and GM vehicles.
Noteiodes are used to allow voltage to flow only one way. Make sure the Diode is installed
facing the proper direction (as shown in Figure 6).
Ford: Install the Diode inline to the wire going to the #1 terminal.
GM: Install the Diode in-line to the wire going to terminal #4.
Figure 6 Installing the Diode to fix Run-On.
GM 1973 - 1983 with Delcotron Alternators
GM Delcotron Alternators use an internal voltage regulator. Install the Diode in-line on the
smallest wire exiting the alternator (Figure 6). It is usually a Brown wire.

 

[krazykyle]

ok even with the diode not in place and the car running it still should be charging the alternator? because when i check the battery with my meter it's still at 12.3 volts with no change.

 

[Bonnewagon]

Didn't you post before that the wiring wasn't hooked up or the bulb was missing? There's your reason the car shut off OK before. Now that the circuit is complete, you get run-on without the diode, or if it's blown. I'm pretty sure running the alt hooked up wrong for any length of time can fry the regulator. Radical idea, but can you get a known good alternator off a good running car to test against your's? I've seen rebuilt alts and carbs go back 3 or 4 times before I get a really good one.

 

[krazykyle]

the funny thing is that my car has been running for months without that bulb in place.i remember taking it out when i first got the motor in and the check engine lite was on along with the charge lite.i thought it was just from me taking the ecm out of the car.figuring that's what controlled those lites.i'm going to find a diode today and wire it in line with the lite and alternator and see what happens.

 

[Bonnewagon]

A good speed shop that carries MSD stuff will have the diode. It's about a buck last time I needed one.If they don't have one, get the spec and try Radio Shack.

 

[pontiacgp]

if you took out the indicator lite then I don't understand how the battery was ever charged

"Dashboard Indicator Light

If you have an alternator and are using the factory style indicator light on your dashboard, it is a pretty helpful thing. It helps kick-start the alternator into working at idle speeds when you first start the car, and it tells you if the alternator is putting out less voltage than the battery has in it, indicating a problem. The light is connected on one side to the field current system inside the alternator and to a switched ignition power source on the other side. When you turn the key on but have not started the car yet, the field acts as a ground and power flows through the light and out to ground - lighting the bulb so you know it works. Once you start the car, the voltage at the field is powered internally by the output of the alternator. If this value is exactly the same as the battery voltage, then you have the exact same voltage on each side of the indicator light and they balance each other out - kind of like a tug of war in reverse. If all goes well, the light never comes on, and you drive happily around knowing all is well with your alternator. If the output of the alternator should drop due to a slipping/broken belt or due to certain kinds of electrical faults inside the alternator itself, there will be less voltage on the field side of the light and more voltage on the switched ignition side of the light. The result is that some amount of electricity will flow through the light and into the field and the light will glow proportional to that voltage difference. This is how a slipping belt or an overloaded alternator will cause the light to glow very dimly, while a full-on failure will cause the light to glow very brightly. Note that if you disconnect (or forget to connect) the wire at the alternator, the light will never come on and the alternator will not charge properly.

The dashboard indicator light circuit also typically has an extra wire with a calibrated resistance in it. This wire is run in parallel to the indicator light and has about a 10ohm resistance. It's purpose is to allow slightly more current to flow to the alternator field current system at initial start-up to make sure the alternator begins producing power as soon as the engine starts. About 1 amp total current is flowing to the field current between the light and the resistance wire, with the resistance wire supplying about 3/4 of an amp. This extra resistance wire does not affect the functionality of the indicator light in any way."

 

[Bonnewagon]

Excellent explanation Steve.