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A dumb electrical question (please educate me)
I recently experienced headlight fluctuations and an occasional sputter/miss at just off idle. Of course I checked for the obvious (loose ground) and discovered that the negative cable on the battery had worked itself quite loose (must be those momentary flat spots upon start-up on the Billboards :LOL: ).
I admittedly SUCK at electrical. I was always under the impression that once you started the car it was the alternator that generated power to the car, kept things steady, kept the battery charged, etc. How come my headlights were dimming with a really loose connection at the battery? And why would l lose spark at the motor (for a brief instant) during the same condition (once I got going it went away)? I think I need an education on alternator vs voltage regulator vs battery (again) and how they all interact. This getting older thing sucks, too. :LOL: BTW, I re-checked ALL of my other primary grounds and they were clean as a whistle and tight as a drum. -Dean |
There is a RPM that the exciter circuit has to see before the alternator supplies a charge. Below this RPM, there is no charge.
I have a GM 1 wire 160amp alt and have to be above 1200 RPM to charge. If your volt gauge is working, you will see it drop below 14v at idle and jump up with the exciter RPM. If the batt connection was loose, you would see the fluctuance in the headlights when you come to idle and brighter with RPM. HTH |
All electrical must have a reference. Ground or negative is usually it. If the ground is unstable, the electrical will be unstable and funny things happen in an unstable environment.
Once you understand this, all of the rest of the stuff is principle. :D I am not trying to insult you by trivializing your question, but I think this might be enough to grasp the concepts. :D |
Once you get reference down, electrical ( minus a large amount of electronics ) is a matter of pressure, volume and resistance.
You car runs on 13.8 Volts. That is the pressure. You alternator puts out 14 Volt or more of pressure OF 65 to 150 Amps. Amps are the volume. The resistance to the flow of the Amps is called...you guessed it Resistance. Okay, relative to ground, all of your readings with your voltmeter are made with the black lead connected to ground ( your reference ). On the battery not running, 12 to 13 volts. Running will be from 12 to 15 Volts ( the alternator is trying to push more Amps back into the battery ). If you read the voltage at say the fuel pump, it may be lower because the long wire getting to the pump has some resistance in it. These are general concepts that may be helpfull. :D |
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I use an Optima Red Top battery and (I believe) it's a 65amp alternator (it has several wires off the back). The battery is fairly new. |
The battery is more than for starting the car. Think of it as a large reservoir of electrons than can be drawn on any time the alternator is not producing enough to meet your car's needs. That can happen at low RPM when the alternator is producing little or no electrical output, and it can happen when very high loads (e.g., headlights, electric fuel pump, electric fan, windshield wipers, stereo, etc. all on at the same time) exceed the capability of the alternator.
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A lot of people don't realize the battery is your main filtering device for your car's electrical system. Alternators don't by nature supply "clean" power to the system. Alternators produce "pulsed" DC (actually AC run through diodes).
Lots of things on your electrical system produce noise, especially inductive loads like motors and your ignition coil. The battery absorbes all this. |
Loose battery connections can also cause fuses to blow. With an intermittent connection on the battery you have a changing load on the electrical system as a whole. This can cause surges of power, or drains of power. You tend to see more drains when the neg is loose and more surges when the pos is loose, but you can get both issues with either. A sudden surge of power will cause a sudden increase in amps going through a fuse causing it to blow. Certain types of battery connectors will cause this as well. I worked on one Cobra that had a battery connector that did not secure very well to the cable. Changing out the connector fixed the issue.
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Tommy/Ronbo/Joe, thanks for the additional feedback...all good stuff. Whether the battery is a "filter" of sorts or a large reservoir of electrons, I get it.
I learned something new today, so it's been a good day. Thanks. :) |
Another example of free education opportunities from the CC site.
Next week we will discuss the breeding of combat hamsters and amateur brain surgery you can do at home with standard household items. :LOL: :LOL: |
Next Month Dean will be holding classes in electrical wiring.
:LOL: |
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The headlights were a great visual for the fluctuations in demand and supply voltage. I have the typical voltage demands on my car as most of you ....puller cooling fans, headlights, running lights and ignition. In addition to the demands of MSD ignition I am running aftermarket fuel injection.
The sages or drop in system voltage at idle was causing my Holley injection CPU or control unit to freak out if voltage dropped below about 13VDC. I had my 100 amp Alternator hot rodded at my local rebuilder to perform better or supply amperage at a lower RPM. I don't know what he did internal but he also installed a smaller pulley so it now supplies amps at 600 engine RPM. My engine idles at about 950 and will lope to maybe 800 now and then but is well above 600 turn on point. I installed a second battery so I have plenty of amps and does not load the demand at idle now. My lights stay bright and ignition as well as injection CPU purrs right along. The grounds and positive connections need to be sound of course but a second battery and hot rodded alt. made all the difference for me. |
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When I was experiencing that off-idle stumble, essentially what was happening was there was not enough volume of electrons to fire the MSD. It was too low an rpm for the alternator to put out sufficient volume to generate the proper spark, so the system really needed the battery at that point to supply the necessary level of juice. Once I got to higher rpms, the alternator was then supplying enough volume to compensate for the loose negative battery cable condition. Hence the stumble/cutting out immediately went away. Teacher, do I get an 'A' for today? :D |
A little slow on the uptake, but you got it and that is what counts. So I guess an A is justifiable.
The pulley swap will also help. Basically what Vettstr is talking about is changing the pulley to make the alternator spin faster at lower RPMs. I have seen some issues where someone puts under drive pulleys on and then have electrical issues. The under drive pulleys work by UNDER DRIVING the accessories thus having a lower load on the engine. I always recommend that if you put under drive pulleys on, to put an over drive pulley on the alternator to compensate |
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That is a pretty good guide. Enough detail and well explained. I like the self help guide feel as well. The way it is written kind of reminds me of the online courses I have to take to keep up with the changes in technology for work.
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Great stuff...thanks for the link.
-Dean |
One of the first things you would learn in basic electronics is a comparison of water and electricity.
Volts (potential) would be like pressure of water. Amps (volume) would be like volume (gallons lets say). A 4" pipe or a 1/2" pipe, which will deliver 20 gallons faster if both are pressurized at 60 PSI? - This is current. Which car has a better chance of jumping a ditch? The one traveling at 5mph or the one going 30mph? - This is potential. Power is a ratio of both: A 1/2" pipe would deliver the same volume as the 4" if the pressure was 2000psi. If the car traveling 5mph weights 10lbs it would make it across the ditch. (the numers are a guess, but you get the idea) Spark plugs don't work well at 12v @600amps, however 12,000v @.6 amps is just the ticket. The power is the same 7200 Watts. A starter is just the opposite. |
In high school I took four years of Chemistry and was a solid B student mixing potions.
In my senior year I took Physics and discovered the limits of my intelligence, clawing and scratching my way to a C. Same can be said for Trig and Calculus...that C- on my college report card was one of the happiest moments in my life...Passed! I have an MBA and B.A. in Corporate Finance. Some of what you guys are saying right now is killing me. :LOL: 'Nuff said. :D |
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