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Re: One more question about alternator Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 13 Nov 2002 14:45:53
In Reply to: One more question about alternator, Jeff Cunningham, Wed, 13 Nov 2002 10:03:58 Members do not see ads below this line. - Help Keep This Site Online - Signup |
JimBlake has it right (no, no flames)- The alternator pushes out electrons.
Electrons are like water - they only flow if there is a reason, and they flow 'downhill'. Downhill is the same as voltage. A flat surface, and water doesn't flow very much - no voltage difference. If there is a BIG voltage difference, it's like a very steep slope or a cliff - lots of water will flow.
Current flows from the higher voltage to the lower voltage. So if the battery is at a lower voltage than the alternator, electrons will flow to the battery, charging it. Once the battery is fully charged, it's the same voltage as the alternator, so no current flows from the alt to the battery. All the alternator current flow is available for the car's loads. If the car's electrical load requires more current than the alternator can provide, the voltage output of the alternator drops, and since the battery voltage is higher, the battery will source electrons to help supply the car's electrical load.
The voltage regulator on the alternator adjusts the alternator's output to meet the load of charging the battery and running the car.
Say you have a fully charged battery. It has plates made of lead (negative) and lead dioxide (positive) in a bath of sulphuric acid. If you pull current (electrons) out of the battery, the lead dioxide combines with the sulphur and free protons (the opposite of electrons) in the acid to form lead sulphate. When you look at the chemistry, lead sulphate has fewer electrons in it than the amout of lead and sulphuric acid.
Where did the electrons go? They flowed out of the battery. When they come back in the negative side, they also form lead sulphate and some protons. Those protons swim through the acid to the positive side to provide the protons for the equation on the other side.
If you keep discharging the battery, you end up with thin plates and a soup of lead sulphate in a weak acid bath.
If you charge the battery, you're adding energy into it. Those extra electrons break the lead sulphate down into lead and sulphur. The lead electroplates back onto the metal plates, and the sulphur combines with the positive ions and hydrogen in the soup to become sulphuric acid.
The energy in the battery is stored as various chemicals. Some chemical compounds have more energy than others. If you split the high energy compounds apart, you get extra electrons and some low-energy compounds. If you have extra energy, you can supply electrons and reverse the chemical process. There are a bunch of these reversable chemical reactions - lead-acid, nickle-cadmium, etc. Those are used for rechargeable batteries. There are other reactions that don't reverse, like zinc-carbon and certain alkaline compounds. Those tend to have a higher engergy density than the rechargables, but can't be recharged.
Oooh! Ask me about why a wide spark plug gap at high boost causes misfiring! I love to go on endlessly about Mean Free Path.
posted by 192.249....
, Wed, 13 Nov 2002 14:45:53 <-- Viewing This Message
, Wed, 13 Nov 2002 10:56:06, Tue, 12 Nov 2002 11:52:23, Wed, 13 Nov 2002 09:04:12
, Tue, 12 Nov 2002 13:18:20
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