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Alternator conv.

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kcbugeye1275

kcbugeye1275

Jedi Knight
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My friend and I have installed new alt on our cars. We are both in a major redo or the cars wich includes a new wiring harness. The ign. light is always on. Two variables makes for hard troubleshooting, any ideas?
 
How's the belt tension?
 
And what is a voltmeter saying (when the engine is running)across the battery terminals?
Bill
 
Generator light comes on under two conditions.
1. Engine not running and ignition turned on. This allows positive (I'm assuming negative ground) from the ignition switch to the ignition (generator) light which is grounded in the voltage regulator (probably inside the alternator). The light turns off when the generator starts charging and putting positive into what earlier was a ground in the regulator.
2. Engine running and when the ignition is switched off the generator continues to charge a little letting the positive from the regulator to reach the ignition light, which is grounded through the ignition accessories.

If the light stays on when the engine is running, it is either that the regulator is grounding the light through not charging, or that the alternator is trying to charge and the light is grounding on the switch side. This could come from not being connected properly to the ignition switch.

As above, what is the voltage reading. If it is above 13.5 it is certainly charging. If it is below 12.5 it isn't charging.

If the alternator is not charging, it could be through several reasons. If it is new, chances are likely that it is in good condition and operable - but don't always bet on it. It must have a good ground. This is usually through the mounting bolts. Check them! It must have a good power supply both to the main output cable and to the regulator. The latter might be internal within the alternator. A Delco is external. Japanese are usually internal.

If it is charging, somehow the ignition light is grounding on the ignition switch side.
 
Is this just at idle? or does it stay on when the rpms go above 2500?
 
The light usually should not come on with an alternator at idle speed. It used to do that with generators because these units put out energy proportional to their speed. A generator would put out a maximum of 22 amps and therefore at idle speed it was not enough to keep the light off. The alternator puts out a maximum of 70 or more amps. At idle speed it would have enough output to keep the light off. With the alternator, maximum rated charging is available at engine speeds of around 1500. Above that the generating capacity is reduced by the regulator.

The two units work generally the same. Run coil windings past a magnetic field.

With the generator the magnetic field is mounted to the case and the coil windings rotate in the center. By taking only power from the side generating in the correct direction it charges DC. this is done with brushes contacting the rotating part. Therefore the charging current must pass through these carbon brushes.

With the alternator the magnetic field is mounted in the rotating part in the center. The magnetic field is generated here and the stationary part outside generates the charging current. This is then rectified with diodes into DC. The advantage here is that the charging current doesn't have to go through carbon brushes. Therefore it can charge much more ampere. So much more that it can be dimensioned to give 70 ampere at engine speed of 1500 rpm.

At idle speed it might only give out 30 amps, but as long as it is something positive the voltage will (should) be up enough to keep the light off.

D.
 
I only ask because I once bought a remanufactured alternator that would not initially charge until rpms went above 2000. Then it would charge at idle. Then the next time the car was started... same thing. Warm or cold did not matter. Drove for several years that way.
 
Some manufacturers would put hysteresis in the circuits. But probably if the initial primer voltage is not immediately available the alternator would not charge. This is helped by using a higher wattage light for the indicator.

The indicator light provides primer voltage to the regulator. Withoug enough voltage, the regulator doesn't know that it should power the reluctor (rotating field) and it doesn't charge.

What you experienced is that when engine turns fast enough, the residual magnitism in the reluctor causes the stator (stationary armature) to generate just enough to excite the regulator, and then the system works as it should.
 
Interesting...
It never bothered me enough to try and find a solution.

Thanks
 
So are you hooked up Positive or Negative Ground? Might be the reason why. Alternator is usually Negative Ground, if this is a Bugeye they normally would be wired Positive Ground. You may have fired the alternator if wired up backwards.

Never overlook the obvious.
 
Negative ground. It has gotten cold here again and the incentive to start the car up and go outside is a little less than it ws last week.
 
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