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Friday, July 11, 2014

Nothings Shocking Now: An Electrical Primer (Part 3)

I get it, I have heard it for years.  Batteries, alternators, switches and wiring are intimidating.  Guess what: even for us in the know, its still tough, its still frustrating and annoying, its still brain- racking to find and diagnose electrical problems. 

 Its a complicated system we have created, but I truly think that everyone can get the basic concepts and at least help with diagnosis of electrical problems, if not fix them outright, without the need for special training or knowledge.  Together we will follow the basic flow of electricity thru a cars electrical system in a simplified way to analyze every aspect of it.  

The idea is to progress through electrical components of storage and generation, then go into loads; lights, fans, actuators, etc...  In the last article we went through some of the reasons that electrical diagnosis is so difficult.  Now lets start a journey of discovery back to how to do just that, difficult or not. 

Lets dive into a nice vat of sulfuric acid shall we?  No?  Well ok, but as a thought baby, lets do it in our minds.  That acid vat is the source of the power that we use in our cars (motorcycles, ATV's, Snowmobiles, watercraft, riding mowers...) to start the engine, run lights and accessories, and provide power when engine speed drops to idle where alternator output may not cover the needs of the system. 

The lead- acid battery has been around and storing energy for us for just over 150 years officially (Wikipedia link) and accounts for most of the battery tech used for automobiles, trucks, submarines and ships, and all manner of engine starting battery and backup power storage.  My homestead and many other off-grid homes and businesses, as well as computer, telecom, and communications backup systems store power in lead acid batteries, using massive banks of big heavy batteries to store hours or even days worth of power.

  A lead acid battery is full of metal plates stacked alternatively one then the other of pure lead in one plate and lead oxide in the other plate.  These plates are submerged in sulfuric acid contained in a tough plastic box.  A chemical reaction in the battery from one plate to the next and through the acid, releases hydrogen gas and electricity as it converts both plates to lead sulfate and the acid to water.  This reversible chemical reaction is known commonly as discharging and then recharging the battery.

A process called sulfation is the number one killer of lead acid batteries right after heat and cold temperatures.  Long term, all lead acid batteries will succumb to sulfation.  As the conversion of lead or lead oxide to lead sulfate happens, a small portion of that lead sulfate sticks and stays through the next recharge cycle to become a permanent crystalline layer built up inside the battery.  This layer of sulfate insulates the plates electrically and prevents the reaction from occurring at that location anymore.  Lead sulfate is 'dead' and cannot participate in any reactions that produce power- thus the term 'dead battery'.  

Anytime a battery is discharging it is creating sulfation naturally.  The longer a battery is allowed to remain in a sulfated, partly discharged state, the more permanent the sulfation becomes.  Sulfation causes a battery to lose holding capacity, drop voltage under load more quickly, and get hotter from use (waste more energy charging or discharging as heat).  Recharging a dead battery quickly reduces the amount of sulfation that stays behind after charging, but can never eliminate it completely.

 You can drastically increase the life of said batteries by never leaving them even partly discharged- recharge them fully as soon as possible. Another way to prevent early sulfation death is to never drain the battery below 75% capacity.  This simply means that less of the plate area is accessible to become sulfated, and therefore will likely last much longer that its over-discharged cousin.  

Once frozen, most lead acid batteries are in a world of hurt and bound for the recyclers.  In a fully charged battery, the acid prevents freezing until temperatures well below the freezing point of water.  As a battery discharges tho, and the acid is changed into water, the freezing point of the liquid electrolyte becomes higher and higher until it can freeze solid.  When water freezes, it expands with a force of over 40,000psi and compresses or crushes everything in its way.  In this case, the soft lead is crushed and cracked, mashed and ruined by the force of nature in a confined space.  

Corrosion is a major issue for lead acid batteries.  Corrosion stops power from entering or leaving the battery because of added resistance in the circuit.  This corrosion and its associated power loss can ruin the battery itself, the alternator, and a myriad of other components too.  The terminals will get coated with thick white, green, or sometimes black, fuzzy, crystalline, dusty, crust that must be removed.  A small wire brush will remove most of this from the outside of the terminal, but to get it all truly as clean as it can be, which is always best, a bit of disassembly is required.  Remove the terminal by loosening the bolt and then use the wire brush to clean the lead contact area, then the lead, copper or brass of the wire end terminals.  Clean all the small wire ends with the brush as well.  If the corrosion is really bad, use some baking soda mixed with a bit of water to neutralize any leftover acid on the metal terminals, then rinse well with water.  After the terminals are all dry again, use a good grease to seal the connections from moisture and acid fumes and reassemble

Thats all for the immediate battery thoughts, hope it helps some curious people out there.  Cheers to your machines, MW out. 

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