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Friday, February 10, 2012

How a lead acid battery works

Well, I presume you all should be vaguely familiar with lead-acid batteries. And yes I am referring to batteries like what is used in your cars and trucks. Now it can get rather complicated without an advanced degree in chemistry and electrical engineering so I am going to attempt to explain it the best I can.

First of all in any type of battery out there what makes it work more or less is its electrolyte solution. In lead acid batteries this electrolyte is sulfuric acid, chemical formula H2SO4. So, now that we have the electrolyte spoken for we need to talk about their construction a little more. As the name implies they contain a fair amount of lead. You see in any battery you first need an electrolyte then you need a cathode as well as an anode. The lead in your car battery functions as BOTH the anode and cathode.

The anode and cathode make up the + (positive) and - (negative) leads of such battery. Now the premise that all lead acid batteries work under is something from electrochemistry. In fact it could be said that all batteries are an electrochemical device. The anode and cathode are indirectly connected through the electrolyte in the battery. See, if they were directly connected to one another it would cause a dead short in the battery and it would do no good for you at all. The power flows out from the cathode and back into the anode.

Now that we have the basic premise down, now I will have to introduce you to lead dioxide. You see the anode is made purely from lead while the cathode is made primarily from lead dioxide. As power is discharged from the battery, both the anode and cathode undergo a chemical reaction that progressively changes them into lead sulfate. Now lead sulfate is a bad thing when dealing with lead acid batteries, because over time after many charging cycles the battery may become 'sulfated' and fail to work properly.

During recharging this reaction is just reversed, thereby reversing the electrochemical reaction.

Lead acid batteries are an 18th century technology and thus may be said to be rather rudimentary. They have very poor power to size ratio, but on the up side of things can deliver enormous amounts of power for the starter motors of our vehicles. Join me next time when I talk about nickle metal hydride, nickle cadmium, as well as lithium based batteries.

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  1. Yes! Finally someone writes about miscellaneous.
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    1. It is not at all miscellaneous; a rather descriptive piece if you ask me. A rather complex terminology and chemistry broken down so that lay people can have an understanding of it

  2. Oh I know what you're thinking -- it's those incredibly thermodynamically unstable lithium ion batteries up to their old tricks again. Wrong!! This culprint in this case was a lead acid battery for a lift truck.

  3. This article was just an fyi for the uneducated amongst us