Alternator Voltage regulator - Ford Powerstroke Diesel Forum
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Old 04-03-2007, 08:20 AM Fanatic

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Alternator Voltage regulator

Ok so my regulator shorted out today.

Does anyone know what each of the terminals are on the plug? I see A S I

What does A, S, and I stand for?

Or does that stand for alternator status indicator?


Last edited by ienjoydrifting; 04-03-2007 at 08:24 AM.
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Old 09-23-2012, 07:20 AM
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This may not help you,ienjoydrifting, because its such an old post, but it might provide an answer for some of the folks doing their best to get answers on their own.

The A (battery sense) is used to sense battery voltage. This circuit is used by the regulator to determine generator output. This circuit is also used to supply current to the generator field, which will determine generator (alternator) output.

The S (stator) is used to feed back a voltage signal externally from the generator stator to the regulator. This voltage feedback signal, which is typically half the battery voltage, is used by the regulator to turn off the charging system warning indicator. Diesel engines have usually have an internal stator circuit.

The I (ignition) is used to turn on the voltage regulator. This circuit is powered up with the key in the ON position. This circuit is also used to turn the charging system warning indicator on if there is a fault in the charging system operation.

Typical Operation:
With the key in the ON position, voltage is applied through the warning indicator I circuit to the voltage regulator. This turns the regulator on, allowing current to flow from battery sense A circuit to the generator field coil. When the engine is started, the generator begins to generate alternating current (AC) which is internally converted to direct current (DC). This current is then supplied to the vehicle electrical system through the output circuit B+ terminal of the generator.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the regulator through the stator circuit (S). This voltage feedback signal that is usually half the battery voltage is used to turn off the warning light.

With the system functioning normally, the generator output current is determined by the voltage of the A circuit. The A circuit voltage is compared to a set voltage internal to the regulator. The regulator controls the generator field current to maintain the correct generator output.

The set voltage will vary with temperature and is typically higher in cold temperatures and lower in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.

Oh, the Battery Positive Output Circuit, B+ is the generator output supplied through the battery positive output terminal on the rear of the generator to the battery and the vehicle electrical system.
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Old 09-23-2012, 09:27 AM
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Originally Posted by Lumberg View Post
The I (ignition) is used to turn on the voltage regulator. This circuit is powered up with the key in the ON position. .
Keep in mind though, on our trucks because of the Glow Plugs, the control of the IGN is run by the PCM so that the charging system isn't running at the same time as the GP's to prevent an excessive load. They can draw close to 200A when first activated and that would put a Tremendous Strain on charging the, freshly cranked down, batteries as well as the GP's...

So, what you typically see is No Output from the ALT at first (depending on how long the GP's are on, NOT the WTS light which actually has little to do with them).
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