Ques: Battery / Altenator

Change the battery and see how ya go from there. To test your alternator take voltage reading wgile engine off, start and retest voltage while no load, should be around 13.8-14.2volts. Turn on evrything that you can, radio, heaters, a/c, main beams, everything while car ideling. Voltage should drop to around the 12.5ish volts, then rev the engine above 2000RPM and the voltage readings should increase to around the 13 or more volts. That will confim your chargeing system is working and the batteries in fair condition. If under load and revving the engine the voltage doesnt creep up then you have a charging system fault.

Hope that helps you out.

Check to see if you have a bad Diode in the alternator that is draining the battery down.Good Lock.

How old is the battery? I am on battery # 3, on a '94 4Runner, and the original alternator.

Bill

An easy alternator test...

1) Charge the battery. 2) Read the battery voltage with a digital voltmeter. 3) Start the engine. 4) Read the battery voltage again.

If the voltage is higher with the engine off than with the engine running, you need alternator repairs. If the voltage is higher with the engine running, the alternator is working and you need a new battery.

Ken

Jas> I have a 1990 toyota -runner. Recently went out to start it and found the

If you do not have a voltmeter handy, then here is another test. Start your vehicle, then disconnect the battery. If the engine continues to run, then your alternator is good. If the car dies, then replace the alternator. If your alternator is good you need to find the source of your battery drain. Start with new accessories installed, radio, car alarm, etc....

Good Luck

This was a good check on older vehicles but is not a good idea on computer controlled vehicles. Unplugging the battery with engine running can cause a surge through the sensors or computers and cause a failure. Also, many charging systems are controlled by a computer and engine will shut off if battery is disonnected even if alternator is good. HTH, davidj92

NO, BAD LUCK!!

DO NOT - I REPEAT, *DO* *NOT* *DO* *THAT* *ON* *PURPOSE*!! /EVER/!!

(How the /hell/ did this craptastic meme ever gain traction...?)

On some cars you can easily get away with disconnecting the battery while it's running - either the alternator can limit itself and keep the car running, or it sees no battery for a voltage reference and shuts down the output, and the car shuts down.

But on certain cars when the battery circuit goes open with the car running, the voltage regulator slams the alternator output to "wide open", and suddenly that 12V nominal system (that should never go over

15V) has 100V or higher running through it - your alternator is more than capable of putting out 150V at high RPM's and full field. Which is extremely bad - you start popping the computers, the fuel pump, all the light bulbs, even run so much current through it that you can light the main wiring harness on fire...

You can TOTAL THE CAR THAT WAY - the parts and repairs to get the car back to normal from that abuse can easily cost far more than the car is worth. Scrap it and buy another one.

Since you never know which way any particular car will go (unless you rebuild alternators for a living), it's far safer to NEVER TRY THIS AT HOME - or anywhere else for that matter, and NEVER allow someone to think it's a viable test method.

If you need to test the alternator or battery, get the proper voltmeters, ammeters and test load boxes for the purpose. Or go to someone who has them.

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