Author Topic: Sun Alternator Tester - Diagnostic Procedure  (Read 1497 times)

Online goodfellow

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Sun Alternator Tester - Diagnostic Procedure
« on: October 10, 2020, 11:34:39 AM »
Note: These threads are old. I managed to restore these Sun Automotive Equipment threads from backups that I had made several years ago.
Hope you like them -

Yesterday I posted the acquisition of my Sun Alternator Service Center workbench. Well, the thought ocurred to me that most folks probably have never seen one of these things in action.

First -- is the machine 

The front dials turn on the tester overhead logo light, the motor, a dial for alternator pulley diameter, and a field control rheostat dial round out the controls

This is the alternator -- my recently rebuilt Lucas unit and it is installed on the testing fixture

The big spade terminals are the DC Output, while the two small terminals under the black cover are for Field + and Field - , the only other connection is a insulated connector at 11 o'clock that is the terminal for the alternator warning light.

First the connection:

The SASC has four leads on the front panel -- Red = battery POS , Black = battery NEG , Green = field NEG, and Blue = field POS

BATTERY LEADS:  POS lead is hooked to the alternator output terminal, and the battery NEG lead is hooked to the alternator frame or (if present), the alternator NEG terminal.

FIELD LEADS: this is tricky because alternators are mostly designated either as "A" field or "B" field types

"A" fields are externally grounded alternator circuits (usually grouded through the voltage regulator) and have an external terminal marked "Field", or "F", or "FLD"

"B" fields are grounded to the alternator housing, and are energized through the voltage regulator.

So, the voltage regulator is key here (doesn't matter if the regulator is internal or external) -- In an  "A" fields it provides grounding, and in "B" fields it energizes. In my case, I have "field" terminals; hence it's an "A" type; meaning it's grounded through my external Lucas voltage regulator.

Here is the alternator all hooked up -

The VAT's large POS and NEG clamps are hooked to the SASC external POS and NEG connectors (notice the large connections on the side of the main cabinet)

.. and the VAT inductive pickup is hooked around the BAT POS lead on the front panel of the tester (that's the lead that is currently attached to the alternator output terminal)

With the connections set, a fresh 12v battery is hooked up the SASC's rear battery terminals (the SASC requires an external 12v power source) to measure charging rates.

As an intial test, the field circuit is tested by turning the SASC "Field Control" knob from "open" to "direct". That tells me if my field connections are good and the windings are being energized. In my case, I'm good -- the AMP meter registers current

Next, the pulley diamter on the alternator is set on the machine -- mine is 2-3/4"

The VAT is set at the 100 amp and 18v test ranges (middle ranges)

Then the fixture is locked and the motor turned on to register RPM -- in my case I'm testing at 3000 RPM. That's in the recommended range for an older model alternator

Now, to limit any excessive output voltage (this is necessary because this alternator doesn't have an internal voltage regulator), the VAT load dial is increased to show 1/3rd of battery voltage -- or 4v

then the SASC "field current" dial is turned from "open" to "direct" to energize the fields and at the same time the VAT load dial is decreased from 4v to 12v. At that time the alternator output is read off the VAT's AMP scale -- in my case it reads steady at 60 AMPS.

The alternator rebuild was a success -- it's right on the money.

Now wasn't that easy?  ;)  - well maybe not the first time, but the procedure is pretty straight forward and easily remembered.