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NEVER EVER disconnect a battery cable while the engine is running. The surge will fry your computer.Here's a link to the proper way to test:

Check with your local auto parts store. Most can check the voltage on the car.

You can also start the motor, while it's running remove neg battery terminal if motor stays runnung your alternator is good.

This technique is best done at night/in the dark. Turn headlights on whilst engine is running. If idle is set correctly, when you press gas pedal you should notice the headlights/dash lights become brighter. If they become brighter your alternator is working.

Another check you can do at night is to observe the headlights with the engine running, then shut off the engine. The headlights should get slightly dimmer. If not then the alternator ( and connections) should be checked further

While the engine is running you can take the positive off of the battery terminal. If the car stalls, it's a good bet your alternator is shot.

re-distribution of electrons is toughMost of these answers don't distinguish between a bad alternator and a bad voltage regulator, the symptoms are often the same. Voltage regulators are cheap and usually easy to replace, depending upon how deep the alternator is buried. Then again a voltmeter only costs a few bucks from harbor freight or radio shack.

Like the drunk searching for his keys under the light pole, (the light is better here) diagnosing electrical problems is best done with the easiest/cheapest jobs done first: Checking voltage drop through connectors and harnesses, Cleaning terminals (especially those on the alternator and main fuse panel), Replacing the voltage regulator, Having the battery and alternator inspected (usually free) by an auto parts chain store, etc..

Your alternator might also be ok but but marginally underpowered for the equipment in the car. This'll happen a lot to cars that are loaded down with aftermarket audio and lighting gear. I'm looking at a weird case like this right now, whenever the AC is on, and I'm just puttering around town, the battery starts sagging down under 12 volts. Since I've little aftermarket stuff in the car, I suspect that either the AC clutch or the aux fan is pulling way more current than it should.

My choices seem to be to put a bigger alternator in, or to hook up amp meters to the suspect components to see if they're pulling more than their rated power.

First buy a multimetre from a an auto store or hardware store, $15-25.

Start the car. As the user above pointed out, pull a battery cable if it continue running, you at least have running alternator. However, the alternator could be not charging enough, or over charging.

Set you multimetre to show voltage flow with at least the accuracy of one decimal place. Place the probes on the correct battery poles, red probe on the positive post and the black on the negative post.

If the multimeter reads below ~13.5 volts, it is not charging your battery, or charging it so slowly it would have to run for quite some time to fully charge; may need to replace the alternator.

A reading of ~13.5 to ~14.5 is somewhere in the norm.

And a reading above ~14.5 is probably a little high and you alternator is overcharging the battery; most likely a cheap-to-replace voltage regulator is the culprit. However, having being overcharged for an extensive amount of time may have damaged the battery.

Finally if you are still not sure, go to a trusted auto store and have them test your alternator; if you don't have a trusted auto store, don't be afraid to get a second opinion.

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โˆ™ 2015-07-16 18:04:50
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Q: How do you test an alternator while still mounted to the engine without using a meter?
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Related Questions

You put new alternator and volt regulator in 1987 f600 370 engine and volt meter says 12.8 with engine off and on?

Check fuseable link on alternator Check fuseable link on alternator

How do you know whether its your battery or your alternator?

Start the engine and using a digital volt meter check the voltage at the battery with the engine running. If the alternator is good you will read from 13.5 to 15.5 volts DC.

Why does a 1998 dodge caravan voltage light stays on?

Perhaps alternator is not charging battery properly - check with a volt meter A fully charged battery should read approx. 12.8 volts without engine running reading should be approx. 14.2 with engine running with good alternator

How do you test an alternator with a volt tester?

Check the voltage with a volt meter at the battery with the engine running at idle. You should read 13.5 to 15.5 volts. Any less and the alternator is not charging properly.

Will bad alternator cause 2.2L to stall?

Yes, once the battery looses it's charge the engine will stall. Check the voltage at the battery with a digital volt meter, engine running. You should read 13.5 to 15.5 volts. Any less and the alternator is bad.

2005 escape engine dies with battery light on?

Bad alternator- not charging battery enough to keep vehicle running check with a volt meter A fully charged battery should read approx. 12.8 volts without engine running With engine running should read approx. 13.8-14.2 volts

Flashing battery symbol while driving?

Check alternator out-put Hook a volt meter up to battery With engine running reading should be 13.8-14.2 If under this alternator not charging battery sufficiently

How many volts should the alternator be sending to the battery on a late model car?

The alternator should be putting out between 13.5 and 16 volts on a good alternator with the engine running as measured with a DC volt meter at the battery posts. Any less or any more and the alternator is defective of the belt is slipping.

Which battery lead do you disconnect to check your alternator?

You don't. Disconnecting a battery cable to "check" the alternator is not a good idea. The removal of a cable with the engine running cuases a voltage spike that can damage the computer system on the car. The proper way to check the alternator is with a volt meter.

Why does the engine shut down when the battery cable is removed on your 2005 ford focus?

Alternator is rated at 110 amps. The alternator should provide the voltage required to run the engine. It should handle the system current load. Check the alternator if there is a charge voltage. Turn the engine off and measure the voltage across the two battery terminals with a DC volt meter. Start the engine and measure the voltage across the battery terminals. Look for an increase in voltage on the volt meter. Typically it can go as high as 14.7 volts. If the voltage stays the same as when measuring the across the terminals with the engine off, the alternator is probably bad. If the voltage is charging but not much higher than when the engine is in the off position, some diodes could have burned out in the alternator. Also check the charging wires and ground wires coming from the battery.

How do you connect a dc amp meter to the alternator and battery?

in series to the battery from the alternator following polarity

I recently installed a new stereo system into my car now my car sounds like my battery is weak is it my battery that I have to change or my alternator?

Check the battery with a vom meter while the engine is running. It should read about 14.5 volts and if so the alternator is working, than have the battery checked Now if the meter does not read 14.5 volts, have the battery, and the alternator checked. If they both check out okay, the problem is in the battery or the alternator circuit on the vehicle.

How do you tell alternator is bad?

The best way is to drive it to your nearest auto parts store and have it tested. You can test it somewhat yourself. Start the engine and use a volt meter to test the voltage that is being supplied by the alternator for the battery. If it is less than 13.5 volts the alternator is bad.

Why does the battery light stay on even after the alternator has replaced?

Find a volt meter, check the battery voltage with the engine stopped, it should be a around 12 V. Now start the engine and the voltage should be around 13.5 V. If the alternator isn't putting out about 13.5 (+/- .5 V) the replacment alternator could be bad or you might have a bad connection somewhere.

How do you check if the alternator is working?

Get yourself a mulitmeter, start the car then attach the meter to the battery.If the alternator is working then the meter should say that there is 13.2 to 14.8 Volts. Under NO CIRCUMSTANCES should you remove a battery cable while the engine is running. This could cause you to DESTROY THE COMPUTOR due to a voltage spike!

How do you test your alternator with volt meter?

There are a number of ways to test an alternator, 1,Set your voltmeter to DC most preferable set the meter to 20volts.2,with the engine running, disconnect one of the battery terminals from the battery head. 2,connect the voltmeter to the battery terminal wires and take your reading.

How can you tell if there is a bad connection between the battery and the alternator?

Use a vom meter, or battery tester and with the engine running voltage should be approximately 14.5 volts.

Why does the check battery light come on 1999 contour if battery is not bad?

Alternator may not be charging battery sufficiently Check with a voltmeter A fully charged battery should read approx. 12.8 volts without engine running With engine running meter should read approx. 13.8-14.2 volts

Why is your check charging system light coming on after you changed your alternator?

Either the alternator you installed is defective or you wired it incorrectly. Check the voltage at the battery with the engine idling. You should read from 13.5 to 15.5 volts with a digital DC volt meter.

How to check an alternator in a Vauxhall omega?

Start the engine, put a volt meter across the battery terminal and have a helper bring the engine RPM up to about what it would be at 30 mph. The meter should show about 13.5 to 14 Volts DC. If it won't go that high, its an alternator or regulator problem. If it does, great, now move on to the next step. Turn on EVERYTHING, lights, blower motor, rear window defroster and watch the volt meter. It shouldn't drop significantly and if it DOES drop slightly, a few extra RPM should bring it right back up. If the alternator has a serious problem keeping the voltage up to that level, you should have the alternator tested by a qualified shop.

How do you tell if your alternator is done?

The alternator is here to give power to / recharge the battery while the engine is running. the alternator, when wired correctly isn't charging with the engine running, then you can tell it is not working anymore. how to know : ideally you'll need a volt meter to controle voltage on the battery +/- plug while engine is doing ~1200rev. bit more elaborated : follow the + cable from the battery to the alternator connection, then with the engine running mesure voltage between the alternator connection and any negative ( - ) spot that you are 100% sure of (i.e. the head of a bolt screw onto the car) a good alternator will give you a reading around 14 for a 12V system (most popular) What happen when the alternator is not working properly : Your battery keeps on diying.

What voltage should be expected when testing an alternator on a 1974 Chevy 454?

Idling with headlights off, around 14.5 to 14.9 volts if it's OK. Start the engine and have a friend bring the engine up to about 800 to 1000 RPM and use a meter to test the battery voltage. With the engine running, the alternator should be generating between 13.5 and 14.5 Volts.

New battery and new alternator still charging at 8 amps?

Possibly a bad connection between the alternator and battrie. use a volt meter. put one lead on the possitive post of the battrie and one lead on the alternator b+ terminal. run the engine, put the fan on and lights on. the meter should not read above .02v roughly. if it does theres a problem with the cable or connections. do the same on the ground circuit. or use jupper cables between the alternator and battrie.

How do you know when alternator is not working?

The easiest way to check is apply a volt meter to the battery terminals. With the engine off the voltage should read around 12 volts. With the engine running there should be an increase in the voltage to around 14 volts. If the voltage reading stays at or decreases from the engine off level then the alternator is probably not working. I would then remove the alternator and take it to an auto parts store and have it bench tested to check it for proper operation.

How do you check an alternator?

Start the engine and connect a volt meter set on 20 Volts DC to the battery posts. Red probe to positive and black to negative. You should get a reading of from 13.5 to 16 volts. Any less or more and the alternator is defective.