how to test if your alternator is healthy
 

my alternator is original as far as i know...109,000 miles on it (83 SC). all seems well at the moment.

i would like to test it to see how healthy it is right now as i have had to depend on this car to get me around alot lately

ive searched around and i see various voltage readings but im not sure what i should be looking for

can anyone write out a step by step routine of how to check it, what type of voltmeter to get (digital cig lighter gauge vs other types), how best to read the voltage (under power, at idle etc..) and what the exact readings should be seen on the meter

i bought a crappy $15 volt meter cig lighter gauge at pep boys, plugged it in and it read something like 5 volts so i went back and got my money back assuming it was broken. i see some online for about $90...anyone have a suggestion on what brand/type to buy?

thanks

At the battery fully charged....
12.5+
13 at idle
13.5-14 at 2500 rpms.

You can get a decent "Fluke" on fleabay for $50.

awsome thanks!

so looks like the fluke hooks up to the battery.

since i will be alone, it will be hard to test at 2500 rpm

if anyone can suggest a high quality accurate cig lighter meter based on your experience with it, that would be great

They make leads that have alligator clips....or you can stick the probe inside the connectors.

Place the fluke on the hood and read it while your behind the wheel. A good Fluke is a valuable tool....I use mine constantly.

ok. ill get one of those. thanks

i would also like to be able to constantly monitor it while im driving though...so if i see a bad reading, i can try to get myself to a safe location off the highway and into a parking lot etc...

does anyone make a meter that will fit into the stock clock location that is dummy-proof as far as the wiring is concerned...as in, one that doesnt require any rewiring. i suck with electrics

Exactly, and just because it is working now, does not mean it'll be working next week...with that kind of age/mileage.

If you want to buy a hand held digital multimeter, $100 will get you a quite a bit. You would like to get one with features like Max/Min Hold and 10A DC; the latter most $50 meters have.

I have a voltmeter that is connected directly to my battery installed in my 993 so that I know exactly what my charging system is really doing at all times.

http://edelweiss.smugmug.com/Cars/Po..._C3Xi8-M-1.jpg

At cruise rpm, my charging voltage is 14.2 to 14.3V.

The OCV (open circuit voltage of batteries varies from 12.65 to 13.0 volts depending on the type (flooded lead acid to AGM or GEL respectively).

A healthy charging system does not guarantee your car to be trouble-free if the battery is the issue. A true battery test involves a load test and a capacity test, the latter is never done at a shop as it is time consuming.

Westach made my custom volt/head temp gauge. They do aircraft stuff, was reasoanble. Those digital meters that hook into the ciggy lighter are inaccurate, but consistent. They will at least alert you to a dip or high spike.

Bet is you tested that gauge against a Fluke it would be as much as .5v off.....:eek:

You might also want to add a battery load tester to your shop.

You can get a 100A load tester at Harbor Freight for under $20 and a variable to 500A carbon pile battery load tester for $80; cheaper when they go on sale.

That battery load tester can be connected to the battery in the vehicle and it'll tell you if your alternator is up to the task of supplying current. You can find the alternator specs in your owner's manual...for example, mine is 115A at 14V. That means the voltage should not drop below 14V when 115A is drawn from the charging system.

You can get a amp clamp for your "Fluke" meter and due the above tests. That's an expensive meter for simple voltage test.

I have tested my Craftsman against my Fluke and honestly they are fairly close except for MV and some Ohm readings. The Fluke also doesn't fluctuate but it is $300 more which could buy and alternator you are testing for.

Craftsman makes a $100 amp clamp meter that is great deal for the money. Somebody also told me Home Depot has great deals on meters but at my local they are locked up behind a cage so I can't view them to check.

I eventually had Hollywood Speedo remove the oil level gauge and replace it with a volt meter...Not cheap but I really like having it there and the oil level gauge was next to useless, and I really like having the clock.

I first had one made that fit into the clock housing but didn't like it much cuz it was/is too small for my liking. It does work fine. I will sell it if you want....PM me..

They're not necessarily inaccurate. If they are accurate, they are reading the voltage at that point which may not be the battery voltage.

If I want to know what the battery voltage is, I do not place a voltmeter in any circuit that has a voltage drop at that point with respect to the battery. Which is why I wired my on-board voltmeter directly to my battery

Although I have a few digital multimeters, I treated myself to a nice Fluke 88V automotive kit last year from National Tool Warehouse. They had the best price.

http://images.nationaltoolwarehouse....K-88-5AKIT.jpg

The simplest alternator test is dynamic...and simple. With the engine idling switch on the headlights and rear heater blower then measure the voltage across the battery posts. Now rev the engine to 2000 RPM and the measured voltage should rise substantially as the alternator picks up the load.

That isn't to say the alternator will not fail in the next the minutes.

Be watchful of the tach jumping/bouncing or the brake light on the dash latching up. Those are clear indications of an alternator or regulator failing.

AAA will come out and test your entire starting/battery system for you, and give you a read out, just tell you are having difficulty starting :D

Turning on everything is NOT the way to test an alternator...now if you want it to fail this is how its done.

"My" Cheap Ass Load Test, is turning on the lights and all accessories and starting the engine. If the lights dip in strength, it's suspect.

Most of the local Kragen's, Pep Boys and such will test for free.....even loan tools. You can't get a fuch'n part w/o a year, make, model and a computer search....but they do have other services.

How then and how does that cause the alternator to fail?

Turning everything on, while not putting a full load on the system, does at least put a partial load on the alternator. I prefer doing a full test using a load tester...no doubts left then.

I remember way back when I first got my SC. Several months had passed and I was taking my first long road trip to Black-hawk Farms a local track here in Illinois. Anyway for some reason during my journey I just started testing everything to see that it worked. Sunroof,AC,CC, everything. Well everything worked and I continued onto my destination but on the return trip my alternator died. Would it have given up the ghost eventually?... yes... just not during my trip.

+1 on install a voltmeter. All cars should come with one. Either a stand alone, or the NH speedo replacement of the oil level one.

I added one to the big empty spot on the center console. Love it.

Kidasters, I must say, you have yourself a very nice little collection there.

Prior to purchasing my'89, I did a lot of "book learning". If I remember correctly the amperage was increased 20-30% around '87, and the "improved" VR/alternators started quitting around 20K miles.
I had an alternator check done as part of my ppi, and no problems were found in my 19.6K car. Luckily my car has a factory installed volt meter because my alternator started failing to the high side on the drive home.
Does your car have room in the center console? That's where the factory put mine.

Porsches run best at 14.2-14.5+
13.75-14 is ok but not really good enough. your car may seem fine but 100% performance happens when voltage is closer to 14.5
A key ground connection is the one between the regulator panel and ground stud behind filter.

This thread discusses the importance of a good connection and the differences even small resistances make.

Alternator Cable

If you want to check your alt output
remove the rear regulator panel and the small 3 fuse panel. look for the big red wire in the three fuse panel.should be the middle one/ that's coming right off the alternator. also it's east to blip the throttle from there.
at idle perfect would be 14.2,the slightest rev takes it to 14+ ,magic number being 14.56especially for carburated cars.A carbed car will not run right at 13.5-13.75.if you hit 14.5+ your car can handle all the accessories without worry. if you have more than 1 volt diff between the rear panel output and the reading at the battery then you have too much resistance somewhere in the line.
Also .don't just take one reading and do everything based on that.take a few readings over a period of time . You will not get a correct reading with a low battery either. A battery has to be at a certain state before it can even accept a full charge. Best to drive the car with NOTHING on for a while and then test it .do that a few times for the most accurate reading of your alternator.

Where does that magic 14.56 come from and why especially for carbureted cars?

Why not and what does a carb have to do with a battery?

Isn't it 0.5V for a 12V system?

no magic .if everything is bang on the system will show 14.56
amperage. the voltage reading is just an indicator .You need a big spark to blow that dump of fuel properly.
13.5-13.75 ign system is not giving a enough amperage to produce the big spark .most noticeable in carbed cars .you get a bawking feeling when you nail it in say second gear.

the voltage reading if all is up to snuff will be 14.5 something . I just know from years of experiance that if you see 14.56 or above.(if alls fine it will never be much higher than that,maybe a fliker) then that is the best you can get and your car runs excellent. at 14-14.2 it runs fine and I'm sure some will argue there is no difference. I'm telling you there is .
It's got to do with the amperage being drawn in the system as the revs increase and the minimum amperage needed to give you the big spark you need.

your right on the .5. I just rounded off to 1 because if there is an issue it is usually closer to a 1 volt difference

I got a cigarette lighter voltmeter from Amazon. Works great and has been a big help in tracking down intermittent alternator problems. Amazon.com: Vector VEC008 Digital LCD Voltmeter, 12 Volt: Automotive

^^^ I think you may have had a weak component somewhere if you needed that voltage to get a good spark.

Regulators regulate at 14.4V for FLA batteries which is what early cars came with and most of the time, the voltage is lower while driving.

I use my radar detector voltameter function , monitored at cig/lighter. This measurement point has been (and continues to be) checked every so often against (compared to) battery terminals to ensure I account for this slight voltage drop. Hope to get a nice analog meter in there soon!!! This setup audibly alerted me to a +16.5 VDC spike...happened once that day,..the next day: again. Installed new alternator and regulator (found the original 1989 factory hardware in there!!!!!!!!!!

BEST!

Doyle

What...WHAT..??

Alternators DO NOT fail as a result of having to supply their maximum rated output current, and alternator internal design aspects do not allow them to exceed that maximum design rating. Excessive voltage output, >16V, but below the maximum output current rating, yes, but only with a failed/failing regulator "commanding" same.

Wow, I feel as if my leg is getting longer and longer.

Battery terminal/(post) voltage with the engine running, charging system operating properly, and low electrical loading is strictly a function of battery SOC. And.... Battery terminal voltage at a specific SOC level, say 70%, will be different in wintertime vs summer.

Automotive charging system regulators use a PWM, Pulse-Width-Modulation, voltage dutycycle to regulate to get an average output voltage. Your voltmeter might read an average of 14.5 when the actual peak voltage is somewhere NORTH of 16 volts.

I once had a shorted phase, one of three, in an alternator and things seemed to work perfectly find except the system voltage ripple content was over 4 volts. I have no idea how long the car had been running that way, I only noticed it when I discovered the alternator case was running extemely HOT.

I cut the stator winding to that one phase as a temporary fix and as far as I know the car went to the "graveyard" that way.