Testing an Alternator on a SUN SASC Test Bench

[goodfellow]

A few years ago 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.


 

[Der Bugmeister]

I could have used one of those this week!  Just replaced the alternator in my daughter's 2017 Corolla (which was MUCH easier than what I went through changing the one in my 2011 model).  Had to cross my fingers a bit with the diagnosis though, which a machine like this could have saved me.  Maybe.  It was still putting out 14+ volts at the battery terminal but everything else checked out fine.  Probably a dying diode.

[goodfellow]

I could have used one of those this week!  Just replaced the alternator in my daughter's 2017 Corolla (which was MUCH easier than what I went through changing the one in my 2011 model).  Had to cross my fingers a bit with the diagnosis though, which a machine like this could have saved me.  Maybe.  It was still putting out 14+ volts at the battery terminal but everything else checked out fine.  Probably a dying diode.

Yes, the old machine would have helped isolate the voltage regulator diode issue. It's old school all the way. These days a half decent engine analyzer or scanner will give you much the same info. Back in the day, this was the standard way of testing. I'm old enough to remember these things being standard equipment in advanced auto repair shops where they actually rebuilt customer alternators if there was a problem. In most cases it turned out to be bearings or voltage regulators. Rarely did the windings bite the dust by themselves.

[j.a.f.e.]

Very nice - pretty cool piece of equipment. Can't be many of them left especially in working order.

[Muddy]

I believe I have a dying alternator in my truck right now. While driving it puts out 14.4v. At idle, under load (headlights radio blower motor etc.) it goes down to 12.7v

Sure autozone or advanced does testing but I'd never trust those behind the counter there like I would Goodfellow.

[jabberwoki]

And now days they just throw them away and fit another cheap chinese junk one in.
How far we've fallen.

Goodie i`d love to visit your shop and gaze in awe at your wonderful stuff for sure.

[goodfellow]

And now days they just throw them away and fit another cheap chinese junk one in.
How far we've fallen.

Goodie i`d love to visit your shop and gaze in awe at your wonderful stuff for sure.

Thanks Jabber! Back in the mid-1990's/early 2000's you could pick this old testing equipment for free. Saved many of these testers form winding up in the landfill. These days they're considered "antiques" -- who knew? I just had old cars that needed cheap testing equipment to keep them running.

That said, I'm thinking of selling most all of it because I don't have any older every-day drivers anymore. I'm getting up there and my car restoration days are pretty much behind me.

[Uncle Buck]

And now days they just throw them away and fit another cheap chinese junk one in.
How far we've fallen.

Goodie i`d love to visit your shop and gaze in awe at your wonderful stuff for sure.

Thanks Jabber! Back in the mid-1990's/early 2000's you could pick this old testing equipment for free. Saved many of these testers form winding up in the landfill. These days they're considered "antiques" -- who knew? I just had old cars that needed cheap testing equipment to keep them running.

That said, I'm thinking of selling most all of it because I don't have any older every-day drivers anymore. I'm getting up there and my car restoration days are pretty much behind me.

I recall seeing the huge roll around Sun test equipment of 60's-80's with all sorts of wires, hoses and etc. related to the machine at KS State Surplus Property in the 1990's just dirt cheap $100-200 or so. These were not terribly old technology at the time. They were far to big for me to buy at the time. Not to mention not knowing how to use probably half of the features the machines offered.  While I can appreciate an oscilloscope and what it does, I have no clue how to interpret the thing even if I could have hooked the thing up right. At the time for the right guy these would have been an incredible piece of equipment at a great price. Through the years I did snag a few old Sun meters more modest in size that I did understand how to use. I have always been in awe of GF vintage diagnostic  equipment,  and his ability to restore and put to use his machines.

[Uncle Buck]

And now days they just throw them away and fit another cheap chinese junk one in.
How far we've fallen.

Goodie i`d love to visit your shop and gaze in awe at your wonderful stuff for sure.

I recall as a kid having to work with dad on cars which at the time I appreciated as much as a toothache. Had dad been a lot less of an old grump these experiences my not have been as unappreciated as they were at the time. In retrospect,  I am now glad money was tight and dad being a product of the depression did teach me how to rebuild wheel cylinders,  alternators, starters and carburetors. Some of these I have taught my son though not as much as I learned myself.