New alt, new battery, charge showing18 volt output, too dangerous to drive, now 1st day new battery is drained before I could get it disconnected. Where should I start to get this figured out and not get wiped out before I agree to a repair? I love my Subaru. this is my second one.

Since the alternator and the battery are both new, there should be no reason the battery is not charging while the vehicle is running. Check the B+ or Output of the alternator. You might offend your mechanic by suggesting this, but it is your vehicle, and electrical things usually equal expensive diagnosis. You can kinda see and feel this area from above, but you really need to be underneath. This is the bolt looking thing on the end opposite to the pulley. This bolt is longer than the area the nut sits AND the nut might be a touch loose. The wires that go on that should have an eye-like end that slides over that bolt and will seat on that location. If this connection was not tightened correctly the alternator can not charge the battery. Make sure there is a flat locking washer and a nut on the end of that bolt. Tighten the nut, but don't go crazy. Firm. Then snap on the insulator cap that is attached to that wiring. Push it until both sides snap. If the insulator is not on correctly, it will come loose. The B+ is a pretty warm place and without that insulator it can melt nearby wiring. Makes a bigger mess if it is overlooked.

The ECU has no control on the voltage. Does your vehicle have a separate voltage regulator? If so that's your fault. A lot of alternators have the regulator built into them. The alternator needs to be put on a test rig away from the vehicle and the output tested, this will eliminate the vehicle, You could disconnect the wiring to the alternator, run three fly leads to the alternator and to a separate battery and run the engine and test the voltage on the spare battery. Wire 1: Battery neg to case of alternator Wire 2: Battery pos to + terminal on alt (the thick wire) Wire 3: Battery pos through a 5 watt bulb to the ind terminal (ignition light) 17 volt will blow another battery for sure.

the alternator gets power on big wire battery voltage the wire runs to starter, fuse box .alternator fuse goes to automatic shut down relay to relay control in ecm/pcm the field wire comes from ecm /pcm to alt.other field goes back to automatic shut down relay back to charge battery . if not charging at alt. try new alt. and retest.

The alternator may charge fine but could drain the battery through a bad diode,have you checked the alt for a bad diode?Disconnect the battery positive cable.Put a regular 12v test light between the battery positive post and the positive battery cable.If the test light is bright you do have a drain,if dim it is OK.A dim light may mean the drain is internal in the battery.If you do have a bright light remove a fuse ,one at a time from the fuse box until the light goes dim.Once dim you have identified the bad circuit.If removing all fuses do not dim the light,disconnect the alt charging wire at the alt,if that dims the light,then you do have a bad diode.DO NOT create a drain(bright light) when checking for the drain by turning on the key or opening a door/trunk etc.
Also,do an overnight battery check by disconnecting the battery overnight,if things are fine the next morning after the battery was disconnected then it is a drain in the vehicle,if the battery is dead even after being disconnected overnight,,then the battery is bad.

You need to make sure that your getting good conection to your battery. If your alternator is fine, as you stated, you might not be getting a good conection. Your alternator may be keeping your battery alive just enough when your driving. Check all connections. Hope this helps.

Your alternator dosent work properly rechaange it again

When it is running,put a volt meter across battery terminals. You should see 13 + volts if alternator is working. Also put an ampere meter in series with a battery cable,key off, engine off, and you should see less than 40 to 50 Mili-Amps. If more,start pulling one fuse at a time,untill you find the circuit that is draining the battery

There seems to be a no charge state in this case. i recommend checking the charging system. use the procedure below to isolate this issue.

Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a +positive terminal (red), - negative terminal (black). Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. (Note: never disconnect the battery while the engine is running. If the battery cable is disconnected from the battery a spark can be generated which can cause the battery to explode or a major electrical malfunction to occur.)

To check a battery surface voltage, remove the positive terminal protective cover. Connect the +positive side meter lead (red) to the positive side battery terminal. Connect the - negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts.(You will need to use a voltmeter for this testing procedure)

The alternator is rotated by a drive belt driven by the vehicles engine while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running.(most non charge states will be the cause of a loose belt or a low tension rate, due to a mis-adjusted alternator. make sure you have enough tension in the belt for full rotation of the alt pulley)

Next, you will need to check the alternators output with the Amp meter.

Testing the amperage output of the alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage. Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter is needed. Once the meter is connected start the engine. Next turn on all electrical accessories and raise the engine idle to about 1200 RPM. The alternator should output the max amperage it was designed to produce. Example: a 90 amp alternator should output about 88 amps. Note: An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail. An alternator is designed to operate at max amperage output only for a reasonable amount of time.

((Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive) at engine idle the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing.)))

NOTE_ Ok, if everything checks out Ok with the above inspections, and you charging system is working correctly, this will lead to a battery drain issue. Use thsi procedure below to isolate the drain.

Here is the procedure I use to isolate a battery drain. Remove negative battery cable from the battery. Using a 12-volt test light, hook one end to the negative battery post the other end to the negative battery cable you just disconnected. The test light will glow or "light" if there is a drain. If the "light or glow" is faint, that is probably normal draw for the clock or computer. If the "light or glow" is bright, then there is a large drain. That should be corrected. Now start removing and replacing the fuses one by one until the light goes out; that one will be the circuit with the drain. Remember to hold in the button in the door jam for the interior lights.

change your alternater

Hi. this is defiantly a slow or major drain that is occurring within this vehicle. Here is a test that you can preform that will help you find this battery drain so you can illuminate this issue.



--BATTERY DRAINAGE TEST PROCEDURE--


Using a 12-volt test light, hook one end to the negative battery post the other end to the negative battery cable you just disconnected. The test light will glow or "light" if there is a drain. If the "light or glow" is faint, that is probably normal draw for the clock or computer. If the "light or glow" is bright, then there is a large drain. That should be corrected. Now start removing and replacing the fuses one by one until the light goes out; that one will be the circuit with the drain. Remember to hold in the button in the door jam for the interior lights.


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