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Lead Acid Battery basics:
1) They all rely on the same basic chemistry to convert electrical energy to and from chemical energy. Inside, a series of lead and lead peroxide plates (electrodes) are alternately arranged and submerged in sulfuric acid (electrolyte) to form a cell. During discharge the both plate sets are converted to lead sulfate and the acid is converted to water. The nominal voltage of the cell is 2 volts. Placing an electrical load across the cell discharges it and applying a voltage of approximately 2.5 volts across the cell charges it. At the end of the charging cycle oxygen and hydrogen are produced at the electrodes due to electrolysis of the water in the electrolyte. If these gasses accumulate they can recombine suddenly with unpleasant results (think Hindenberg).
2) They are all vented to relieve internal pressure.
3) A "sealed" or "SLA" battery means you can't (easily) add water.
4) "Immobilized Electrolyte" means that the fluid inside the battery (sulfuric acid and water) is not free to slosh about. It can be gelled (like Jello) or sopped up in a fibrous matt (like blotter paper).
5) "Recombinant" refers to the ability to recombine the gasses produced before they accumulate. This is accomplished by fine tuning the chemical reaction with additives.
6) All batteries have internal resistance that limits the peak current they produce. A typical internal resistance for a 6 cell battery (12 volts) may be 30 milliohms (0.030 ohms). If the terminals were shorted with a 0 ohm conductor the battery could produce a maximum of 400 amps.
7) Batteries are rated for their energy storage capacity in terms of Amp Hours (AH). Typically the ratings are based on a 20 hour rate so a 12 volt, 20 amp hour battery will produce 1 amp for 20 hours at about 12 volts, or about 240 watt hours of energy. This battery WILL NOT produce 20 amps for 1 hour. It will produce 20 amps for about 36 minutes, 144 watt hours or about 60% of the rated capacity. At 200 amps (typical engine cranking current) you will be lucky to get 35% of the energy out of the battery, about 120 seconds or 80 watt hours.
8) A good alternator voltage regulator is essential to battery health and longevity. The B&C linear regulator is recommended.
The best battery for the buck is the Panasonic SLA. Period. This battery has immobilized electrolyte and is gas recombinant. They are available from B&C or Digikey. A 12 volt, 33 AH battery weighs 26.5 Lbs, costs $57 (DigiKey) and will easily start your TSIO 550 on a cold day in Denver. My bird is 28V so I use 2 each 12 V 17AH batteries connected in series. These batteries can be mounted in any orientation and do not produce corrosive fumes so you can put them wherever you want. I made a 4 sided box that bolts to the firewall out of epoxy and e-glass with a carbon reinforcing strap. A 6 bid flat cover and the firewall make the other two sides of the box. The batteries are quite happy sitting at the 14 degree angle of the firewall. I replace them every 24 months and have NEVER had a dead battery or insufficient cranking power.
I used these batteries in the Battlebots we built. To qualify them for that application I drop tested the battery from 6 feet onto concrete covered with a 1/2 inch foam pad (a 200 G shock). After the drop test there was no decrease in performance. Try that with a wet cell. Better yet, don't.
Strong, cheap, light, powerfull.......battery nirvana.
Regards
Brent Regan
LML website: http://members.olsusa.com/mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
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Please send your photos and drawings to marvkaye@olsusa.com.
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