ALL ABOUT BIG BATTERIES

1. ALL ABOUT BIG BATTERIES Batteries Use for Emergency or Field Power – “auto” and “marine” batteries

2. FIRST • Batteries are not long term power supplies UNLESS • There is a readily available way to recharge them. • Generator • Solar Panels • Commercial Mains

3. WHAT WE WILL COVER • Chemistry of Batteries (how they work, so we understand the other parts of this) • What kills batteries • Different kinds of batteries (flooded cell, Gel cell, AGM) • How to keep your battery healthy and prolong its life • We will kill some wives tales along the way

4. Lead Acid Batteries This presentation covers the following type of large batteries – Lead Acid Batteries – most often used by Hams • Automotive “cranking” batteries • “Marine” Batteries (also known as deep cycle or RV) • Gel Cells • AGM (Absorbed Glass Mat) They are big and heavy

5. THE EXTREME BASICS • Lead, lead oxide and sulfuric acid react to make electricity. • There are plates of lead, plates of lead oxide and a solution of very strong sulfuric acid. • These are housed in a plastic case with “terminals” on the outside.

6. MAKING ELECTRICITY

7. Each plate generates about 1.02 volts, for a total of 2.04 volts • Lead Sulphate is deposited on both plates.

8. How To Get “12 Volts” • So we have a cell that makes 2.04 volts! • Connect six cells in series • Cells in series add their voltage • 6 X 2.04 = 12.24 volts • This is why a “12 volt” battery will actually show a higher voltage than “12”. • That is why they are called “batteries” and not cells, they are a battery of cells.

11. THE REACTION CAN BE REVERSED By applying a voltage to the terminals higher than what the cells put out.

12. CHARGING

13. Pb SO4 + 2 H2O Pb + PbO2 + 1 H+ + 2 H2O NOTE: NO HYDROGEN GAS IS MADE IN THIS REACTION ! Hydrogen is only formed when the water itself is broken apart (electrolysis).

14. ELECTROLYSIS?? • Now what is this??? • When a voltage is applied to water, it is broken down into hydrogen gas and oxygen gas. • This happens at a lower voltage that the charging voltage. • As long as there is lots material for the lead/lead oxide/sulfuric acid reaction, that will be favored over the electrolysis reaction. • But if to much voltage is applied, then both lead/lead oxide/sulfuric reaction and the electrolysis reaction can take place.

15. CHARGING VOLTAGESnot all batteries need the same voltage • WHY? • Materials added to the plates causes small differences in the voltage required to recharge • Why would there be other materials added to the plates? • Add Strength or inhibit Hydrogen formation.

16. Plate Additives • Antimony: makes the plates stronger BUT adds to creation of hydrogen (charging voltage about 13.8 volts) • Calcium: helps make plates a little stronger, BUT it reduces or eliminates hydrogen gas formation • BUT it requires a higher charging voltage (usually about 14. 2 volts)

17. Plate Additives • Antimony: because of hydrogen gas formation, the cells have “access” (caps) so that water can be replenished and gas (HYDROGEN) can vent (“off gassing”). • Calcium: These are usually seen as “sealed” or “maintenance free” batteries. • WHY?

18. Hydrogen gas is formed when a higher voltage is applied than required to completely recharge the battery. • ALSO: The sulfuric acid solution gets hot and boils, thus loosing water. • AND: The water itself is broken down by electrolysis.

19. SO, THE RECHARGING VOLTAGE OF DIFFERENT BATTERIES IS IMPORTANT. • More on this later.

20. CHARGING RATE

21. But First • AMPS and VOLTS are related • E = (I) x (R) • Amps (I) = amount of electrons flowing • (R) = resistance in the circuit • E = Pressure (like water pressure) • If we have more amps (flow) then we must push the electrons harder (higher voltage) • It takes a higher voltage to charge at 10 amps that to charge at 2 amps! Important later.

22. CHARGING RATE Approximately one tenth the amp hour rating

23. Examples • 20 amp hour charging rate = 2 amps • 7 amp hour charging rate = 0.7 amps • 70 amp hour charging rate = 7 amps

24. CHARGERS • Simple “manual” chargers have a charging voltage of about 15 volts. BE CAREFUL and do not over charge the battery or cause formation of hydrogen gas. • “Smart Chargers” will start the charging at a higher voltage (13.9 – 14.5) and as the battery gets closer to full charge, reduces the charging voltage. Some will then change to a “float charge” voltage.

25. In Your Vehicle or Boat • Automotive (“cranking”) batteries designed to provide big discharge, for short period, and then immediately recharged. • Why is our radio equipment designed for 13.8 volts? • That is the “float” voltage for most batteries. • The alternator in your vehicle puts out a higher voltage when the battery needs recharging, then reduces to 13.8 volts to “float” it. • When the battery is charged, the alternator is actually supplying the electrical power for the vehicle, and also “holding” the charge in the battery for when it is needed later.

26. BUT WE MISSED SOME OTHER CHEMISTRY THAT GOES ON IN A BATTERY!

27. Two Other Activities • First • Small side reaction: Pure sulfur deposits on the plates (sulfination). • Sulfur does not conduct electricity • Sulfur coats the plate surfaces and prevents the chemical reactions, and insulates conductive surfaces.

28. SULFINATION • Sulfination is happening all the time. • Worse in two cases • Worse when battery is left sitting and not used (discharged or charged) • Recharging helps knock off the sulfur from the plates • Vibration and sloshing also helps (like when in a car, boat, truck, RV)

29. Low Voltage • The chemical reaction that causes sulfination is faster when the battery is discharged below 11.5 volts.

30. Lead Sulfate • Second • During discharge, lead sulfate is deposited on the plates (remember) • A little bit of this falls off the plates and settles in the bottom of the battery • When the lead sulfate is not on the plate, it cannot be turned back into lead and lead oxide, thus the battery eventually will not be able to take much of a charge, or eventually will take no charge.

31. CAPACITIES OF BATTERIES

32. AMP HOURS • Definition: The number of amps the battery can deliver at a reasonable discharge rate, for a designated amount of time, at a voltage not below 11.5 volts.

33. Amp Hours Examples 20 amp hours = 1 amp for 20 hours, or, 2 amps for 10 hours, or 20 amps for one hour, 40 amps for ½ hour, etc. 7 amp hours = 1 amp for 7 hours, 3.5 amps for 3.5 hours, 7 amps for 1 hour, etc. 70 amp hours = well, you get the picture.

34. About one tenth the amp hour rating 20 amp hour battery = 2 amps 70 amp hour battery = 7 amps Lead Acid batteries can provide much higher discharge rates (i.e., more amps) but sometimes at a cost. “Reasonable Rate of Discharge”???

35. DISCHARGE DON’TS • Max discharge rate before harming the battery is about one fourth the amp hours rating • 20 amp hour battery = 5 amps before harm • 70 amp hour battery = 17.6 amps before harm • 7 amp hour battery = 1.75 amps before harm • “Harm” is not death, just shortened life.

36. DISCHARGE DON’TS CON’T • Don’t leave partially or heavily discharged batteries sit for a long period before recharging. • This increases the sulfination process and allows more time for the lead sulfate to fall of the plates. • This shortens the life of the battery

37. OTHER HARM • High discharge rate causes: • Heating of battery • Over heating can damage plates and connectors of cells – warping & shorts & braking • Overheating can boil sulfuric acid solution All these either reduce the life of the battery, In the worse case, it can be destroyed.

38. BUT DON’T BE AFRAID • Automotive batteries and marine batteries can handle short periods of very large discharge rates without significantly reducing the life of the battery. • We will talk about how to prolong the life of the battery in a little bit.

39. BATTERY SIZES • Most automotive “cranking” batteries are about 45 amp hours • Most “marine” (or RV or Deep Cycle) batteries or 70 to 100 amp hours • Most smaller batteries, such as those found in UPSs, alarm backups, etc. are about 5 to 10 amp hours. • Most motorcycle and lawn tractor batteries are about 10 – 15 amp hours.

40. DIFFERENT KINDS OF BATTERIES

41. “FLOODED CELL” • So far we have been looking at what is called a “flooded cell” or “wet” battery • The sulfuric acid in solution is a liquid sloshing around between the plates. • Sealed or Maintenance Free batteries have plates with calcium which does not allow “off gassing” thus no need to put water in the battery • Other flooded cells need periodic replenishment of the water in the sulfuric acid solution -- due to evaporation, off gassing, and just plain old use.

42. GEL CELLS • Same chemistry and same plates, but the sulfuric acid solution is made into a gel, like jello. • More efficient since the ions in the electrolyte is physically closer to the plates • Do not off gas unless recharged at an over voltage • Sometimes can be installed on side or upside down -- consult manufacturer info. • Act more like a deep cycle battery, can be discharged below 11.5 volts with less harm. • Requires a slower recharge rate than flooded cell - can be damaged easier. • Requires a little higher recharge voltage than flooded cell -- Calcium added to the plates.

43. AGM • Absorbed Glass Mat • The sulfuric acid solution is absorbed on a fiberglass mat and held against the plates. • Strongest construction method - can take more bashing. • Also acts more like a deep cycle battery • Takes a little slower recharge rate than flooded cell – can be damaged easier • Require a little higher initial recharging voltage than a flooded cell -- also Calcium. • Can be mounted in any position (including upside down)

44. Differences Between Auto and Marine Batteries • Auto designed differently than marine • Remember the “do not go below 11.5 volts” in the chemistry section? • Sulfination and loss of lead sulfate • But the “deep cycle” can mean drawing those amps from the battery that are available below 11.5 volts. • WHY AND HOW?????

45. Bigger IS Better • Average life of auto battery is about 5 years (+/- depending on how well built) • To over come the added sulfination and loss of lead sulfate, they just put bigger plates into marine (RV, deep cycle, etc.) batteries, so that they also last about 5 years. • Life expectancy of a lead acid battery is directly related to the plate size and discharge/charging usage. • Use a battery designed for the load.

46. PROLONGING THE LIFE OF YOUR LEAD ACID BATTERYUSE IT OR LOOSE IT

47. DON’TS 1. Leave a battery sitting unused for a long time (even if left fully charged at first) • Leave a discharged or partially discharged battery sitting for a long time. Recharge as soon a possible. • Disuse is the biggest killer of batteries. • WHY? The sulfination process can chug along, uninterrupted.

48. DON’Ts 3. Over charge (to fast, to long). • Boil the sulfuric acid. • Over heat the battery causing mechanical failure • Use the correct charging amperage • Under charge • Use the correct charging voltage (amperage) • Does not drive the reaction to completion and causes sulfation and loss of lead sulfate

49. DOs

50. Stratification: (flooded cell only) The acid solution at the bottom is strong and at the top weak. This messes up battery chemistry. • Strong recharging stirs up the acid solution as it warms up -- but don’t boil or over heat. • Movement (like driving around in our car) sloshes the acid solution around.