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Old 01-28-2004, 10:39 AM
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Running better with alternator disconnected?

My SBC engine started running rough the other day. I have gone over everything from carb to vacuum and nothing is working. I checked the voltage at the coil and it was at 7 volts. That is a little low for my Mallory ignition. They like 8-9 volts.

My alternator has a started making a bearing noise. It started when the engine began running rough. I pulled the alternator harness off of the alternator and my engine started running better. Not back to normal, but better. I hooked the harness back up and it started running bad again. Now my voltage is at -12 volts. Anybody have any ideas as to what is going on?

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Old 01-28-2004, 09:30 PM
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My car is running again. The problem ended up being a vacuum leak at the bottom of the intake gaskets. I changed the gasket and it is back to normal.

I don't know why the engine ran better with the harness off.

-12 Volts? What was I thinking?... DC... the tester leads were backwards.
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Old 01-29-2004, 01:48 AM
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Quote:
I don't know why the engine ran better with the harness off.
The reason is that you said your voltage was low, the alternator tries to make up the difference in the load. This creates drag on the motor because the alternator is spinning coils of wire through a magnetic Field, when the current drain get to large the wires try to keep the magnets from passing through. The more load you place on the electrical system the more drag the alternator creates.

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Mark
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Old 01-29-2004, 07:45 PM
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The magnetic lines of flux are always there. Are they what you are talking about? I didn't know there was more drag when the voltage was low. I thought alternators are always running at full potential load, and when the charging system needs more voltage, the regulator lets more current by.
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Old 01-30-2004, 12:52 AM
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The purpose of the regulator is to regulate the amount of current to the field coil of the alt. Think of it as an electromagnet rotor. With no current flowing thru the field, no current is coming from the alt. No load. Thats why you can spin an alternator by hand right out of the box, but if you try to spin it with 12 volts (installed on the car) on the field wire connector, it a lot harder to turn.
Go to this site and read about charging systems and click the link at the bottom on regulation. (interesting reading )http://www.autosite.com/garage/subsys/bachargs.asp
If that link isnt working, go to www.howstuffworks.com and go to the automotive section and look for links to that (autosite) site. This (howstuffworks) is another great site where you can spend HOURS reading tech stuff.

Last edited by 2-manytoyzs; 02-02-2004 at 09:47 AM.
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Old 02-02-2004, 07:17 AM
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When you jump start a car with dead battery, you can hear the alternator load pull down the idle when the jumper cables are installed. That is one of the biggest loads on the electrical system.

Trees
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Old 02-02-2004, 11:40 PM
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Interesting.

I have taken AC and DC theory and motor theory, and the way an alternator works on a DC system has alluded me. I guess I have never really put any thought into it past hooking it up, and having it tested at the local speed shop. I will check that site out.
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Old 02-03-2004, 07:10 AM
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Quote:
Originally posted by lluciano77
Interesting.

I have taken AC and DC theory and motor theory, and the way an alternator works on a DC system has alluded me. I guess I have never really put any thought into it past hooking it up, and having it tested at the local speed shop. I will check that site out.
Because of the in-effecient losses of trying to generate electricity in DC (direct current) form, whether it be for automotive use or home use much more power would be wasted in generating AND transferring DC, higher amperages and larger gauge wires would be needed to counteract the parasitic losses experienced with direct current.

An automotive alternator generates three fields of alternating current, and through the use of diodes the current is converted to a direct current for useage in a direct current system.

Just remember back to when they instructed the theories of generating electricity, and the ways Nicola Tesla wanted alternating current which required lower gauge transmisson lines by using higher voltages as opposed to higher amperages, and Thomas Edison wanted direct current.

Explanation of Tesla's theroy versus Edisons theory.

How an alternator generates its power.

Last edited by M&M CUSTOM; 02-03-2004 at 07:25 AM.
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Old 02-08-2004, 07:01 PM
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Got it thanks.

Wouldn't it have been strange though if they would have kept residential/commericial use all DC? Of course if cost and production weren't an issue.

I have worked in a lot of aviation electronics labs where we had DC rectifiers and DC panels feeding the testing equipment. They use DC a lot on aircraft because of the fact that the components are lighter and take up less space. It is funny, you can't even think about trying to use an inductive analyzing voltage tester. The things will go off before you can even get close to what you are working with.

We were in a DC electrical room and the EMFs were enough to ignite the gasses in the flourescent lights we were holding. It makes you wonder what is happening to your cellular structure while working in there.
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