how to test if your alternator is healthy

[ramonesfreak]

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

[Joe Bob]

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.

[ramonesfreak]

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

[Joe Bob]

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.

[ramonesfreak]

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

[Traveller]

Originally Posted by ramonesfreak

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

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.



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.

[Joe Bob]

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.....

[Traveller]

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.

[WANNA930]

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.

[Drdogface]

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..

[Traveller]

Originally Posted by Joe Bob

Those digital meters that hook into the ciggy lighter are inaccurate, but consistent.

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.

[wwest]

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.

[DRACO A5OG]

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

[scoe911]

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

[Joe Bob]

"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.

[Traveller]

Originally Posted by scoe911

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

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.

[scoe911]

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.

[Kidasters]

+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.

[scoe911]

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

[vracer]

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.