Charging system help.

[birdman3131]

Ok I have been having problems with a dead battery. This morning I had to get my roommate to work and ended up starting it by yanking a battery out of my moms truck. I could not leave that battery in because the posts are wrong so I ended up driving on just the alternator.

Now at times my headlights would be very bright and at other times they would dim to almost nothing. It did not seem to be rpm dependent. it could be idle and bright or 4500 rpm and almost nothing


I know my alternator belt seems a little bit loose so that could be it. Also at one point the belts were changed and only one got put back on the alternator pully.

Once places open up I am gonna take the battery down to the parts store to get tested and verify it is not the issue. It could be part of it seeing as it is almost 5 years old

What seems most likely to cause RPM independent alternator output fluctuations? Alternator belt being loose or some other portion of the system.

EDIT: 1984 300D turbo

[vstech]

alternators NEED the battery to be in the circuit. odds are very high, you need an alternator now. also, the alt needs both belts. and they need to be METRIC belts, 10mm, not 9.5mm, and they really need to be a matched set from the same box, as length of the belts needs to be consistent.

[97 SL320]

The battery serves as a buffer to smooth out voltage variations. The "can't run a alternator without a battery" has often been repeated but I don't think it is valid other than the rest of the electrical system seeing occasional overvoltage. There have long been kits to make 120 V DC from a car alternator while retaining 12 V DC operation.

I suspect you were having alternator issues prior to running without a battery.

[Diesel911]

Originally Posted by 97 SL320

The battery serves as a buffer to smooth out voltage variations. The "can't run a alternator without a battery" has often been repeated but I don't think it is valid other than the rest of the electrical system seeing occasional overvoltage. There have long been kits to make 120 V DC from a car alternator while retaining 12 V DC operation.

I suspect you were having alternator issues prior to running without a battery.

This is called an Inverter. However, there is still a limitation as to the Amperage of your Alternator that is going to limit the Watts that the Inverter is going to put out.

If you only run an Inverter on a Battery you can get all the Watts you want but it deadens the Battery fast.

[BillGrissom]

Originally Posted by birdman3131

... I could not leave that battery in because the posts are wrong so I ended up driving on just the alternator.
'''
Now at times my headlights would be very bright and at other times they would dim to almost nothing.

In the 2nd paragraph, are you still driving without a battery? If so, how do you start the car? Better to have the old battery in as a buffer, even if it can't start the car. Autozone and others will load-test your battery in the parking lot. They can also do an alternator test, but I suspect it just looks for "I'm alive" sinusoids and isn't a detailed test.

[97 SL320]

Originally Posted by Diesel911

This is called an Inverter.

No this kit. It consists of moving the alternator output to a house type socket and full fielding the alternator to make 120 VDC ( Volts Direct Current ) This will run lighting and universal motors.

Low cost solid state inverters have surpassed this and motor / generator technology.

[birdman3131]

Originally Posted by BillGrissom

In the 2nd paragraph, are you still driving without a battery? If so, how do you start the car? Better to have the old battery in as a buffer, even if it can't start the car. Autozone and others will load-test your battery in the parking lot. They can also do an alternator test, but I suspect it just looks for "I'm alive" sinusoids and isn't a detailed test.

Yes. I started the car with a battery out of my moms F350 but I could not leave it in there because the posts are on the wrong side. I should have put my old one back in but my roommate was already 15 mins late to work so I was in a hurry.

The battery is currently at autozone being charged and tested.

[birdman3131]

The battery tested good so tomorrow I am gonna try to pull it into work and tighten the alternator belt and see abut getting to the voltage regulator and checking the brushes.

As far as I can tell none of the local parts stores have the voltage regulator as an option so I will be stuck ordering one online if I have to get one.

[whunter]

Originally Posted by birdman3131

Yes. I started the car with a battery out of my moms F350 but I could not leave it in there because the posts are on the wrong side. I should have put my old one back in but my roommate was already 15 mins late to work so I was in a hurry.

The battery is currently at autozone being charged and tested.

NEVER disconnect the battery cables with the engine running.

I have argued this point more than 35 years.

On older pre-electronic cars, this is at best unwise.

On newer electronic cars, this can cause catastrophic damage to the vehicles electrical system.

Regardless:
With an alternator there is a HIGH risk of voltage spike, wrecking at least the voltage regulator and potentially diodes.

More data on this topic, for those interested.
http://www.peachparts.com/shopforum/general-information/273454-never-disconnect-battery-cable-engine-running-test.html

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[barry12345]

If you can turn the pulley fan on the alternator with your finger it is just a loose belt or belts usually.