[dave-r]

CHARGING SYSTEMS
Early vehicles were made with 6 volt electrical systems. Although some were negative earth the standard was in fact positive earth.
The early battery charging systems were D.C. generators with cut out relays. Later models used more sophisticated voltage regulators that regulated both the voltage and the current being supplied to the battery.

In the mid '50s auto. manufacturers switched over to 12 volt systems with a negative earth but still used D.C. generators to replenish the battery.
It was in the early '60s when manufacturers started using alternators. These produce A.C. current which cannot be directly used to recharge a battery without first being "rectified" to convert it to D.C. current. This is normally accomplished using diodes.

The advantage of using an alternator is that it can provide enough voltage to the battery even at idle. A generator needs to be spinning faster than it would at idle to produce a comparable amount of electricity.

An alternator MUST have battery voltage present to produce a magnetic field in the spinning rotor or there is no output. A generator will produce electricity as soon as it starts spinning fast enough. It needs no external voltage to get it operating. This means that if a cars battery is completely flat, and it uses an alternator, then it is impossible to push-start the vehicle.

Voltage regulators are used between the generator/alternator and the battery to provide a constant charging voltage.
Early regulators were mechanical and could be adjusted for output. Chrysler were the first to employ solid state electronic regulators in the late '60s. All of these early types were mounted on the inner fender or bulkhead.

When G.M. switched to electronic regulators they housed them inside the alternator itself. These alternators tend to put out a bit more voltage than their predecessors because they are designed to work with maintenance free batteries which require a higher charging voltage. If you use the old type of battery with one of these alternators you will boil the water out of the acid at a higher rate then would normally be the case.

To test your cars charging system connect a voltmeter across the battery with the engine running. Charging voltage should be approximately 14.4 volts. If the voltmeter reads above 15.0 volts then the charging system is overcharging the battery.

[shawna]

Help! Ever since we swapped the 318 out for a 340 and somewhere along the line changed the point distributer to electronic, I cant keep a battery in it. When we first put the 340 in, of course it was mildly built, I went through 3 batterys in the first 6 months. of course I also went through a couple altenators and at least 2 starters. Now, 7 years down the road, Im still having the battery problem, of course there might be 1500 miles on the engine(I was in the Army for 6 years), but it seems that I get a new battery, and 6 month later the battery cant even hold its own charge. It starts out great and slowly every time I go to start it it drags a little more until I cant even jump start the dang thing. Ive tried every battery there is, from a Mallory to a diehard marine battery. Ive done all the normal things, like change cables, checked for grounds, and alot of things anyone could think of looking for, but its been a bust...anyone live near Dallas that wants to help me with this possesed challenger?

[ted]

bad voltage regulator.

[dave-r]

You keep the battery on a trickle charge when the car is stowed right?

If the regulator is ok be sure not to let the battery stand for a long time without being charged up. Batterys don't like being left to run down.

[dave-r]

Also don't use low maintenance or maintenance free batteries. These take more voltage to charge them than the original alt/regulator will supply.

Have you got 14.4 volts accross your battery with the engine running? You did not say if you had done the test described above.

[Shawna]

Thanks Ted and Dave for the info, Unfortunetly, I dont know to check the regulator but Im sure one of you all could tell me..and, Im sorry to say, I let the car sit around maybe three weeks to a month before I start it, and then I usually only let it run at an idle, guess I expected more out of my battery than I should. I also let it sit with full charge on at all times. I just thought that maybe it was an electrical wiring problem, since my headlights hardly stay lit at an idle and my blinkers dont work at an idle either. This car is quite the nightmare for a poor divorcee girl with out a garage and my ex has all the tools....ahhhhh po me...lol.

[dave-r]

Sigh.
Take a volt meter and measure the voltage across the battery with the engine running!
Am I talking to myself I wonder!

[dave-r]

CORRECTION!

I just looked up my own advice on batteries and found I had remembered it wrong (how unlike me).

LOW MANTAINANCE is the one to go for. They still have filler caps (like normal lead/acid) but require topping up less often and have a better shelf life than normal lead/acid.

AVOID mantainance-free batteries completely in old cars.

[Dave-R (Roppa440)]

I realise now that I have not really described the Mopar charging circuit in detail.

I will try to post a simple diagram tonight.

An alternator does not put out a constant voltage. The faster it spins the more it puts out. So it has to be regulated to avoid over-charging the battery and burning out all your wiring. The output is controled buy the voltage in the field coil wrapped around the outside of the alt. casing. If you lower the voltage in this field coil then the output drops too.

The system is designed so that it is just able to charge the battery at idle with 12 volts running through the field coil from the regulator.

As the speed of the alt. increases, it's output goes up. When the output goes up the voltage in the cars wiring goes up too. The regulator is like a variable resistor that goes to ground but it's resistance depends on the voltage on it.

When you only have 12 volts on the regulator it has no connection to ground. But as voltage increases it starts to short to ground. This drops the voltage going to the field coil in the alt. That then drops the output to the battery.

So the system regulates itself by controling the voltage in the field coil.

To describe the actual wiring;

There is a blue wire that comes from the ignition switch (the 'run' circuit) that connects directly to the uppermost field coil connection on the alternator (although in practice it makes no difference which of the two field connectors it is)

The lower connector has a green wire on it that comes back to the upper pin on the voltage regulator. The lower pin (and the regulator casing) is connected to ground (earth/chassis).

Make sure there is a good ground between the regulator casing and the bodywork.

The main output from the alt. goes to the battery of course but usually through an ammeter first (if your car has one) and sometimes via the starter motor.

[David Robson (Admin)]

As promised. I know there is at least one person out there this will help. I hope so anyway.