12SI alternator troublshooting: DOH: the ignominious denoument

I had already reassembled the 12SI when most of the discussion here took place. Saturday morning I decided to reinstall it into the car.

First, I checked and the tan/brown wire had zippo voltage on it with the key off. Then I installed the alternator and the same problem: increased current draw with the two-pin connector.

THEN I had the horrible realization.

In mid-December, my battery went bad. It was old, and one of the side terminals had leaked and corroded the connection. I also made sure that the aged wiring to the alternator was corrosion-free.

To clean the regulator connections, I popped the wires and connectors from the plastic body, doused them with contact cleaner, and replaced them.

You can probably see this coming: when reinserting the wires into the plastic connector, I swapped 1 and 2. This results with relatively normal alternator operation, except for a higher key-off drain. I switched the wires to the way they're supposed to be, and now my key- off draw is 10mA with the alternator all connected, and 9mA with the two-pin pulled. A great improvement on the 300mA draw before. And the alternator charged fine; no dead shorts to ground either.

So tomorrow I'll go to the auto electric places and get new bearings pressed in, and also collect a proper 12SI rectifier bridge. Then hopefully I can ignore this alternator for the likely remaining life of the car.

Question though: how do you determine if there's excessive voltage drop in the wiring? I turned on the blower on high and the back defrost on. Trying to read the voltage between the battery and alternator B+ terminal was frustrating, with the readins flipping all around the 0.03V range, sometimes going up to 0.06 but sometimes going a bit negative.

What I'm trying to figure out is why the alternator keeps the voltage up when the car has recently been started, no matter if all the accessories are on. After a while, the voltage will drop at idle with a full electrical load. Is this just increased resistance in the alternator when it gets hot?

....Ed

Reply to
Ed Treijs
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Your regulator is well... regulating. It's normal for your voltage to go up to 14V+ or so right after starting the battery. My assumption is that starting puts a heavy drain on the battery which is then brought back up to charge/voltage by the alternator. The battery voltage will drop back down to 13.2V or so after a few seconds.

Reply to
dsi1

Sorry, I wasn't being clear.

There is a decrease in overall voltage levels as everything warms up, and the overall voltage levels are lower in summer than in winter. As you say, that's to be expected from the regulator.

However, when the car is first started and is cold, say the (not-too- accurate 1978-vintage) voltmeter shows 15.5V with no load. I turn on the lights, heater blower, rear defrost, etc--I fully-load the electrical system. The voltmeter continues to show 15.5V, maybe a touch lower.

Let the engine warm up, and the voltmeter shows say 15.0V with no load. (It consistently reads high. So did the gas gauge--so I ran out of gas at 1/8 tank showing!) It'll stay at about 15.0 with a light load, but once I put enough electrical accessories on, it'll drop to

14.0V or lower. For sure, rear defrost, blower motor, and headlights on, it won't maintain voltage at idle or even at 1200 RPM.

Obviously fast idle with the choke on makes this comparison difficult, but sometimes the motor will come off fast idle pretty quickly, and I see this happening. It's almost like the alternator gets tired! Well, hot, anyway.

....Ed

Reply to
Ed Treijs

15.5V with no load seems awfully high - maybe your regulator is faulty? I would think your battery would be damaged with voltages that high.

Anyway with a full load, it would seem normal if your voltage falls - your alternator is not able to keep up with the load. I think that most automotive charging systems are not designed to be able to handle all the load that your car might throw at it under all conditions which is one of the reasons for a battery. Anyway that sounds normal. Your voltage regulation does not.

Reply to
dsi1

15.5V on the factory dash voltmeter corresponds to low-to-mid 14.xV measured with a proper meter across the battery terminals (or alt B+ to ground). It doesn't help that the voltmeter is far to the right of my line of sight, so parallax error probably adds half a volt, in addition to its inherent inaccuracy. But that's how they made Trans Ams in the 1970s.

I could come up with a correspondence table, and read it by leaning over the transmission tunnel to avoid parallax error, but that sounds like a lot of work. Anyway, I've checked that the system isn't overcharging. But the way I see if the system is working "normally" is to glance at the dash to see if the gauge is pointing to where I expect it to.

I will however double-check cold and warm voltages once I reinstall everything--I'm on the way to the electrical shop to get a new rectifier bridge and bearings. Anyway, I have two regulators, both of which are not obviously faulty.

....Ed

Reply to
Ed Treijs

I like those old cars with the voltmeters. If you had an ampmeter like my mom's old car, you'd see the needle swing to the plus side for a short time while the battery was charging every time the engine was started or you'd see the needle blip when the lights were turned on. Of course, this gave some indication of what the voltage was doing.

My old 67 Barracuda had a big, vac gauge on the dash marked with ranges for power and fuel economy. It was my favorite gauge of all time and gave me an awareness of the most efficient technique of using the accelerator pedal as well as engine problems. My least favorite was the big single tach directly in front of the driver on an Alfa Romeo.

I'm used to digital read-out of voltages. You have to ignore the markings on dash voltmeters and instead learn to read the normal range travel but that's the way it's always been with these gauges.

Reply to
dsi1

One of the fun things about working on cars is you go into shops that are a bit of history.

I went to an auto electrical place. Big shop, full of parts and assemblies and tools and meters. One really old guy (he said something about being 80) sitting in the office, otherwise no activity. I said I needed a rectifier bridge and I wanted new bearings. He wound up giving me a preassembled 12SI end frame, including rectifier bridge, new regulator and brushes, new bearing, new diode trio. And a drive end bearing. All for $20. (If anyone in the Toronto area is interesting, the shop is Starter King, on Lockport, off Shorncliffe, south of Dundas.)

I did have to go back, because the drive end bearing he gave me was the wrong size. Got the right one, and he showed me how to press it in using the hand press. Much easier than my basement-wall-stud destroying technique to press the old bearing out.

I won't get around to installing the re-rebuilt alternator until Saturday. At least I know the bearings are good, and I really cleaned up the slip rings. New electronic components--should work great. And I've learned about alternator construction. All for $20. Can't beat that.

Reply to
Ed Treijs

You sure can't. We had a shop called "Starters and Alternator" right down our street and I loved that place. One time the guy rebuilt my alternator (or was it a starter?) and another time he swapped me for one on the shelf. Unfortunately, they moved away soon after. That's the breaks.

Reply to
dsi1

I *so* wish I had a place like that around here. I need to get a VW Corrado alternator rebuilt, and the only places I know that'd do it for me are in Annapolis or Springfield. "ordering" a reman from the parts store is approaching the value of the car.

nate

Reply to
Nate Nagel

I like all of those gauges :) The tach front and center is nice for a sports/racing car where you actually care more about how fast the engine is turning than you are making sure you're not attracting the attention of the po-po.

In my pickemup truck I swapped the gauge cluster for one with a tach, and also hung a 3-gauge cluster under the dash with oil press (never could get the stupid Ford "idiot gauge" to register properly, even after following the instructions I found on the helping friendly interwebs) vacuum and trans temp. I also have a tach strapped on the steering column of my '55 Stude and have a vacuum gauge and voltmeter under the dash. (it already had pretty good gauges stock; it has a 4-gauge multi cluster thing with fuel, oil press, engine temp, and amps) One of these days I'll rig up an oil temp gauge (that one's a 4-speed, so I need to find a "useful" gauge to fill the empty hole. I already have all the gauges I "need," but there's an empty hole in the add-on panel!)

The older a vehicle is, the more gauges I like to have. Makes me a little more comfortable getting in it and driving long distances (or through bad neighborhoods)

nate

Reply to
Nate Nagel

Can the alternator shop around the corner do a Corrado rebuild? More importantly, can anybody do a rebuild on the supercharger on these? Now that's a scary question! Other than that, I'd sure love to have one of those but I suppose in my case, it's better to wish for one than to actually have that dream come true.

Reply to
dsi1

I've got two G-laders for this car, one supposedly "good used" and one rebuilt by BBM maybe 20K miles ago but passing more oil than I'd like. Kompressor Kanada or Bahn Brenner will rebuild 'em for you. Come on down, bring a trailer. I need the garage space for my '55 and need to convince the girl to either buy my 944 or find herself a car.

I can help make your dream a reality! Low low prices! (hell, if the title were in my name, it'd be yours for a case of decent beer just to get rid of the thing.)

nate

Reply to
Nate Nagel

My guess is that the older I get, the less gauges the better. Due to the deterioration of my faculties and eyesight and god knows what else, it takes me longer to read and comprehend gauges these days. Idiot lights are now more my speed. That's the breaks. :-)

Reply to
dsi1

Ha ha. I know how you feel. Your cars are wonderful examples of engineering and design but they have a great need for money to get them into fighting shape. If I lived next to you, I'd be happy to help you work on them. Of course, owning one of those would be another thing! I've learned my lesson... :-)

Reply to
dsi1

come on down. I hate working on cars, hard as that may be to believe. I just like driving nice cars.

Only real headache cars that I've owned, believe it or not, were an '86 BMW 535i with about 200K miles (I could have sorted it, but I couldn't afford to) and a '89 GTI 16V (I think it was an '89? might have been an '88?) that had sat unused for about 10 years. That one did eventually get sorted and was sold to a friend who drove it for several years before passing it on. The Corrado, although not technically mine, is also a bit of a PITA but I think part of that is that no mechanic wants to touch it. The 944 and all my other VWs have been surprisingly trouble free, although I have had some persistent problems with my 944 that I've had to resolve myself simply because again I don't think mechanics like working on cars that old and don't really take them seriously.

nate

Reply to
N8N

Sounds like you need to find a foreign car repair shop that has an old guy named "Fritz." :-) The 944 is a nice ride that one hardly ever sees anymore and I think will be a highly sought-after car in the near future.

Reply to
dsi1

Heh, I knew of one owned by a guy named Rainer Wetzling, but unfortunately he passed on a while back. He also was a bit on the particular side; he refused to work on my Scirocco because it had an aftermarket suspension on it.

I agree that 944s are fun cars but I suspect that they'll end up becoming the next 914 - loved by a few nutcases, but never getting any real respect, and consistently available used for less than $5K and therefore not worth restoring for anyone but the hard core.

nate

Reply to
N8N

What is the deal with German auto mechanics! :-)

You're probably in a better position to judge the future of the 944. My brother had a very nice 914 that he fixed up. It was painted a shiny orangy yellowish but he sold it. You are right about the nutcase aspect of it though... :-)

Reply to
dsi1

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