======================COMPONENTS_BATTERY======================================= ANODE: where oxidation happens cell's negative electrode = anode discharging, negative electrode = cathode when being charged BATTERY: cells connected to form a single unit. C-RATE: rate charge or disharge in amperes equal to the capacity of the battery in ampere hours. CATHODE: cell plate reduction region occurs. positive electrode = cathode when discharging, = anode when being charged. CELL: electrochemical energy-storage device consisting of two electrodes, or plates; an electrolyte; and (usually) a separator. ELECTROLYTE: the ionic conductor, typically a liquid, provides the internal connection between plates of cell. must not an electronic conductor lest short-circuit cell. LIFE: time before it needs to be replaced. FLOAT CHARGING: keeping battery ready by means of continuous, long-term constant-voltage, limited the charging regime. MEMORY The reduction in capacity of a nickel-cadmium due to repeated partial discharge-charge cycles. POWER DENSITY: the volumetric power density of a battery, usuallyexpressed in watts per liter. PRIMARY CELL: can be discharged only once. SECONDARY CELL: rechargeable celi. SEPARATOR: nonconductous material between, the plates of cell permeablile to ionic conductivity SPECIFIC ENERGY: the gravimetric energy storage density of a battery, expressed in watt-hour per kilogram. lead-acid batt 25 Wh/kg 60 Wh/l. Lithium batte 400 Wh/kg 1000 Wh/l. gasoline 13,540 Wh/kg 9613 Wh/l SECIFIC POWER: the gravimetric density of a battery, usually expred in watts/gm six-volt battery three cells connected in series. GAS GAGE FUEL GAGE measures amount charge remaining in cell SELF-DISCHARGE loss of useful capacity during storage due to internal chemical reactions, such as drying out. SERVICE LIFE time a battery provides useful current and voltage, SHELF LIFE time a battery can be stored SMART BATTERY contains one or more chemistry self identification, charge control, fuel gaging, and a communications port. Defibrillator, Users Guide, Battery Pack, Battery pack 18 VDC 1300 mAH lithium. Disposable, recyclable, long-life, primary cells. Typically 100 shocks or 5 hours operating time. -------------------------------------------------------------------------------------- Electrochemical Cells spontaneously produce electrical current callede Electromotive Force (EMF) result of the electrical potential involve (reduction) an (oxidation). Voltaic Cells also called Galvanic Cells Electrolytic Cells Galvanic cells voltaic cells = basically batteries. copper in solution of silver nitrate grayish white silver deposit formed on the copper solution turns blue because of copper (II) nitrate. 2Ag+ + Cu ==> Cu2+ + 2Ag produce electricity if it was placed in a galvanic cell. galvanic cell consists of two containers with a salt bridge between them. each containers store half-reactions reduction: Ag+ + e- ==> Ag oxidation: Cu ==> Cu2+ + 2e- Voltaic Cells (Galvanic) Cells two "half cells" electrolyte solutions and electrodes oxidation occur at anode electrode atoms lose electrons electrons -> anode -> circuit -> Cathode . reduction occur at cathode electrode attracts ions gets electrons from circuit "salt bridge" permits ions to enter or leave the two half reactions generate a cell potential -------------------------------------------------------------------------------------- <- electrons flow __________________________________ | | | Cathode Anode | \|/ (+) (-) | v Ag+ +e- => Ag Cu => Cu+2 +2e- _____/\ ___________ Cell Diagrams | \/ | | Salt bridge | | _______ | | | _____ | | Cathode | || || | Anode (+)|~~~|~~~~~||~| |~||~~~~~~|~~~| (-) | _| || | | || |_ | | | | | | | | | | | | | | | | | | |_| AgNO3 | |Cu(NO3)2 |_| | |____________| |_____________| NO3 -> anode oxidation occurs (remember "an ox" ). cathode reduction occurs (remember "red cat"). electron flow anode to cathode = electricity. galvanic cell cathode =positive , anode =negative, electrolytic cell cathode =negative , anode =positive. -------------------------------------------------------------------------------------- half-cells solutions both compartments remain electrically neutral. salt bridge permits ions to enter or leave . voltaic cell at 25 C: Cu_elec/Cu+2(1M) Ag+(.01M)/ Ag_elec Ag+ + e- ---> Ags E0red = + 0.80 v Cu+2 + 2e- ---->Cus E0red = + 0.337 v Reversing half cell direction make Copper half reaction oxidation reduction potential =>oxidation potential: Cu(s) ---> Cu+2 + 2 e- E0ox = -0.337 v two half reactions together: 2Ag+ + 2e- ---> 2Ags E0red = + 0.80 v Cu(s) ---> Cu+2 + 2 e- E0ox = -0.337 v ------------------------------------------- 2Ag+ + Cu(s) ---> 2Ags + Cu+2 E0cell = E0red + E0ox = 0.80 + (-0.337) = 0.563 v -------------------------------------------------------------------------------------- Nernst Equation Bcause ion concentation seldom at 1 Molar and 1 atm. Ecell = E0cell - (.0591 / n)*log Q (Nernst Equatio) Q = [products]^coeff /[Reactants]^coeff n = electron exchange (balancing electrons gained and lost) (0.0591 = combination of ... 2.303(R)(T)/F R = gas constant = 8.31 J/mole-K T = 298 K F = Faradays Constant = 96,500 Coulombs/Joules/V mole electrons 2.303 = conversion factor the natural log the common log -------------------------------------------------------------------------------------- Express Q Q = [Ag(s)]^2 [Cu+2] / [Cu(s)] [Ag+]^2 All solids or pure liquids would drop out their volumes incompressible. molar conce remain fixed will not influence the value of Q. Q = [Cu+2] / [Ag+]^2 [Cu+2] = 1.0 M [Ag+] = .01 M Q = (1.0) / (.01)2 = 1.0 / .0001 = 1 X 104 -------------------------------------------------------------------------------------- cell potential. Ecell = E0cell - (.0591 / n )*log Q = 0.563 - (.0591 / 2 )*[log (1 X 104)] = 0.563 - (.02 = 0.445 v -------------------------------------------------------------------------------------- Daniell Cell: electrode -> Zn/Zn+2 <=saltbridge=> Cu+2/Cu <-electrode Zinc ion more easily oxidized and the Copper ion more easily reduced. Zinc electrode anode (where oxidation occurs) half reaction Zn(s) -> Zn+2 + 2 e- Copper electrode Cathode (where Reduction occurs) a half reaction Cu+2 + 2e- -> Cu(s) External electrons from anode electrons received by oxidized atoms to cathode electrons given to reduced atoms in the external circuit. Internal electrons travel from cathode to anode through salt bridge. cell potential adding potential of two half cells Daniel Cell... Gravity Cell. Zn_solid + Cu+2 => Zn+2 +Cu_solid When ZnSO4_aq layered over concentration of CuSO4_aq, cell has internal resistance. -------------------------------------------------------------------------------------- COPPER-ZINC ELECTROCHEMI CELL. 1.10 volts process is reversible. discharging zinc oxidizes into zinc-sulphate electrolyte, zinc tend to reduce at -0.76 volts coppgr reduces out of copper-sulphate electrolyte. Copper like toreduce by 0.34 volts. zinc copper cell 0.34 - (-0.76) = 1.10 volts. Cadmium-Nickel Cd_solid +2OH-1_aq => 0.76eV => Cd(OH)2 + 2e-1 NiO2 +2H2O + 2e-1 => 0.49eV => Ni(OH)2 + 2OH-1_aq Cd_solid +NiO2 +2H2O => 1.25eV => Cd(OH)2 + Ni(OH)2 Lithium Battery Li_solid => eV => Li+1 + e-1 MnO2_solid +Li+1 +e-1 => eV => LiMnO2 Li_solid +MnO2_solid => 2.5eV => LiMnO2 Defibrillator, Users Guide, Battery Pack, Battery pack 18 VDC 1300 mAH lithium. Disposable, recyclable, long-life, primary cells. Typically 100 shocks or 5 hours operating time. -------------------------------------------------------------------------------------- half-cell zero potential defined as zero for hydrogenelectrode 2H+1 +2e-1 => H2_gas 1 atm,25C and 1M Hydrogen Electrode 2H+1 +2e-1 => 0eV => H2_gas half-cell reactions written as reductions. Magnitude measure tendency to proceed from left to right reactions that proceed assigned a positive voltage). reference half cell compartment composed of Hydrogen ion 1 Molar conc with Hydrogen gas 1 atmosphere and Platinum electrode. called Stardard Hydrogen Electrode. Met_electrode/Met_ion <=saltbridge=> H+,H2/Pt_electrode -------------------------------------------------------------------------------------- pH meter is a voltaic cell produces millivolt related to Hydrogen ion concentration PH = (.76 - Ecell) / .0592 electrode used is a combination of a reference electrode and an indicator electrode. reference electrode has a constant voltage potential .76 v. Br2 E0red = +1.07 MnO4-2 E0red = +1.49 Ni+2 E0red = -0.23 F2 E0red = +2.87 Na+ + OH- --> NaOH (sodium hydroxide) Na+ + Cl- --> NaCl (salt) 3H+ + PO43- --> H3PO4 (phosphoric acid) 2Na+ + S2O32- --> Na2S2O3 3Mg(OH)2 + 2H3PO4 --> Mg3(PO4)2 + 6H2O -------------------------------------------------------------------------------------- Zinc half cell Hydrogen half cell connected: Pt_elec/H+,H2 Zn+2(1M)/Zn_elec voltage -.763 volts E0red = -0.763 v for the Zinc ion. -------------------------------------------------------------------------------------- Copper half cell Cu_elec/Cu+2(1M) H+(1M),H2(1atm)/Pt_elec E0red = +0.337 v for the Copper ion. net cell add up the two half cells Zn(s) + Cu+2 ----> Zn+2 + Cu(s) E0cell = E0red + E0ox = 0.337 + 0.763 = 1.100 v -------------------------------------------------------------------------------------- Nernst equation E_cell = e(0) -(0.591/n)*log( Q ) e(0) is the standard cell potential and n is number of electrons needed to balance half-cells. Find half-reactions which can be combined to yield the desired reaction. Fe+3 + 3e-1 => ??eV => Fe_solid Fe+3 + 1e-1 => 0.77eV => Fe+2 Fe+ + 2e-1 <= 0.41eV <= Fe_solid -------------------------------------------------------------------------------------- free energy change for each reaction Delta[ G(0)_1 ] = -n_1*F*e(0)_1 Delta[ G(0)_2 ] = -n_2*F*e(0)_2 Delta[ G(0)_0 ] = Delta[ G(0)_1 ] - Delta[ G(0)_2 ] = n* F*e(0) e(0) = ( n_1*e(0)_1 + n_1*e(0)_1)/n e(0) = ( n_1*e(0)_1 + n_1*e(0)_1)/n = ( 1*0.77V + 2*(-0.41V) )/3 = -0.0167V -------------------------------------------------------------------------------------- pH Equation Henderson-Hasselbach Equation pH = p*K_a +log([base]/[acid]) Equilibri Constant If C_a << K_a, assume complete dissociation and use the charge balance equation. If , solve the equilibrium expression. If C_a �=' K_a �=' 1e7, use the exact solution K_p =K_c(R*T)^delta(n) Fe+3, Fe+2 || H+1 MnO4-1 Mn+2 The half-cell equations are 8H+1 +MnO4-1 +5e-1 => 1.49eV => Mn+2 +4H20 5Fe+2 <= 0.77eV <= 5Fe+3 +5e-1 _________________________________________________ 8H+1 +MnO4-1 +5Fe+2 => 0.72eV => Mn+2 +5Fe+3 +4H20 -------------------------------------------------------------------------------------- Lead Storage Bat Pb_solid+SO4-2_aq => 0.356eV =>PbSO4+2e-1+PbO2+SO4-2_aq+4H+1 +2e-1 => 1.685eV => PbSO4 +2H2O Pb_solid+PbO2+2SO4-2_aq+4H+1 => 2.041eV =>2PbSO4 +2H2O anode lead(IV) oxide, cathode spongy lead, electroyte mod dilute sulfuric acid - + | | | | |~~~|~~~~~~~~~~~|~~~| | _|_ _|_ | | | | max | | | | | | H2SO4 | | | | | | | | | | | | min | | | | |___| H20 |___| | Charged | Pb PbO2 | | | |___________________| - + | | | | |~~~|~~~~~~~~~~~|~~~| | ##### ##### | | ## ## min ## ## | | ## ## H2SO4 ## ## | | ## ## ## ## | | ## ## max ## ## | | ##### H20 ##### | DisCharged | Pb PbO2 | | PbS04 PbS04 | |___________________| storage cell. discharging cycle, lead cathode is oxidized to Pb++ ions which thcn form lead(II) sulfate, PbSO4 , precipitate on thc cathode: Pb - 2 e- -> Pb++ Pb++ + S04= -> PbS04 (solid) summarized: Pb - 2 e- + S04= -> PbS04 (solid) Simultancously at anodc, H2O+ ions may be reduced and may then, rcduce PbO2 to PbO forming water in the process. sulfuric acid Reaction = lead(II)sulfate+ water Lead(II) sulfate precipitates on the anode. 2 H30+ + 2 e- -> 2 H20 +2 H 2 H + PbO2 -> PbO + H20 PbO+ 2 H30+ + S04= -> PbS04 (solid) + 3 H20 summarized: 4H2O+ +2e- +PbO2 +S04= -> PbS04 (solid) + 6 H20 (Electric Storage Battery) (cathode)Pb -2e-1 + S04-2 => PbS04_solid (anode) 4H30+1+2e-1+Pb02+S04-2 => PbS04_solid 6H20 _______________________________________________________ (cell) Pb +Pb02 + 4H30+1+2S04- => 2PbS04_solid + 6H20 during discharge electrods ogidatiodate cathode flow extcrnal to anode where reduction occurs. constitutes electric currcnt During charging lead(II) sulfate cathode reduccd to element, lead. PbS04 + 2e-1 => Pb + S04-2 (cathode) PbSO4 + 2e-a => Pb + S04-2 (anode) PbSO4 + 6H20 - 2e-1 => PbO2 + 4H30+1 + S04-2 ____________________________________________________ (cell) 2PbS04 + 6H20 => Pb +Pb02 + 4H30+1 + 2S04-2 at anode, lead(II) sulfate -ox-> lead(IV) oride. PbS04 - 2e-1 + 6H20 => Pb02 + 4H30+1 + S04-2 charging electrons supplied to cathode , and removed from anode, by external source of electric energy. is reverse of the discharging action. charging --------> <-------- discharging 2PbS04 + 6H2O <=> Pb + Pb02 + 4H3O+1 + 2S04-2 charging, sulfuric acid is formed and water is decomposed. specific gravity acid 1.300 for fully-charged cell. discharging, sulfuric acid is used up and water is formed. specific grarity completely discharged 1.100. Batteries Wear Out lead sulfate on both plates separated into lead(Pb) and sulfate(SO4). su3fa~e (S04) leaves both the plates hydrrogen(H) in electrolyte form sulfuxic acid (H2SO4). oxy~en(O) in electrolyte combines with lead (Pb) at positive plate form lead oxide (PbO2) and negative plate to form of lead (Pb). plate naterial expands slightly dischexge contract~to norma1 size charge. many cycles eventually plate to loosen and flake off of grid, resulting in a won-out battery. all batteries weax out Other include Po~itFre Plate Giid Growth/Oxidation accelerated by high temperatues -------------------------------------------------------------------------------------- Battery(1) Anode Cathode Volt theor/typ Amp-hrs/kg Ammonia Mg m-DNB 2.2(1.7) 1.400 cadmium-Air(c) cd 02 1.2(0.8) 475 Cuprouschloride Mg CuCI 1.5(1.4) 240 Edison (C) Fe NiO 1.5((.2) 195 H2-O2(C) H2 02 1.23(0.8) 3,000 Lead-Acid(C) Pb Pb02 2.1(2.0) 55 Leclance(NC Zn Mn02 1.6(1.2) 230 Lithium- 350'C, Li S 2.1 11.8) 885 with fused salt Magnesium (NC) Mg Mn02 2.0(1.5) 270 Mercury (NC) Zn HgO 1.34(1.2) 185 Mercad(NC) Cd HgO 0.8(0.85) 165 Mn02 alkaline(NC) Zn Mn02 1.5(1.15) 230 NiCad(C) Cd NiO 1.35(1.2) l65 Organic Cath.(NC Mg m-DNB 1.8 (1.15) 1,400 SilverCadmium (C) Cd AgO 1.4(1.05) 230 Silver Chloride Mg AgCI 1.6 (1.5) 170 SilverOxide Zn AgO 1.8511.5) 285 Silver-Poly Ag Polyiod 0.66(0.6) 180? Sodium -300'C, with Na S 2.2(1.8) 1,150 B-alumina electrolyta Thermal Ca Fuel 2.8(2.6) 240 Zinc-Air(NC) Zn 02 1.6(1.1) 815 Zinc-Nickel(C) Zn Nioxid 1.75(1.6) 185 Zinc-SilverOx Zn AgO 1.85(1.5) 285 Fuel Cells: Hydrogen H2 02 1.23(0.7) 26,000 Hydrazine N2H4 02 1.5(0.7) 2,100 Methanol CH2OH 02 1.3(0.8) 1,400 (NC) Primary Cell and cannot be recharged. (C) Secondary Cell and can be recharged. Amp-hr/kg theoretical capacity of the cell. -------------------------------------------------------------------------------------- AA_batteries Alkaline NiCad NiMH Li-ion price $0.25 $1 $3.25 $10 energy density Whr/kg 125 30 55 90 energy density Whr/l 350 105 160 voltage nominal 1.5 1.2 1.2 3.6 voltage end 0.9 1.0 1.0 1.8 self-discharge_I_uA 10 200 300 70 High_discharge_rate 1.2 6 5 1 Internal_R_mohm 500 20 10 200 Weight_gram 23 22 21 15 Number of charges 20 2000 1000 1000. -------------------------------------------------------------------------------------- NiCad Rechargeable: AAA CH12ABP-2 10024 1.2 180 milliamp-hours AA CH15 10015 1.2 500 milliamp-hours C CH35 10014 1.2 1.2 ampere-hours Sub C CH1.2 10022 1.2 1.2 ampere-hours D cH50 10013 1.2 1.2 ampere-hourr D CH4 10013HC 1.2 4 ampere-hours N CH150 10910 1.2 150 milliamp-hours CH22 8.4 8O milliamp-hours CF rechargeable is Fast Charge, CH Standard Charge at a rate of 1/10 amp-hour for 10 hours Anode Cathode V A-hr/Kg C size AH 9 volt AH Alkaline Zn MnO2 1.5 230 37.5mA*160hr 6 18ma*33hr 0.6 NiCad Cd NiO 1.35 165 1.2 Amp hours 1.2 -------------------------------------------------------------------------------------- Mercury batteries incredibly stable, and can last decades. usually develop a white leakage residue long before they expire, Shelflife typically 5 years from date of manufacture. alkaline 1.5V 150Whr/kg at 14W/kg at .3% diard per month Alkaline-Manganese: AAA E92 24A 1.5 37.5 ma @ 25 hrs leadacid 2.0V 35Whr/kg at 200W/kg at 4% diard per month nicad 1.2V 60Whr/kg at 130W/kg at 10% diard per month Anode Cathode V A-hr/Kg C size AH 9 volt AH Alkaline Zn MnO2 1.5 230 37.5mA*160hr 6 18ma*33hr 0.6 NiCad Cd NiO 1.35 165 1.2 Amp hr 1.2 Internal "Open" Type ResistanceVoltage Capacity @ Capacity @Size Mass (ohm) (V)(mAh) mA (mAh) mA (in)(gm) Le Clanche 35 9 300 1 160 10 0.65 x 1.0 x 1.9 35 Heavy Duty 35 9 400 1 180 10 " 40 Alkaline 2 9 500 1 470 10 " 55 Lithium 18 9 1000 25 950 80 " 38 Alkaline Cells: D 0.1 1.5 10000 10 800010 1.3D x 2.2L 125 C 0.2 1.5 4500 " 3200 " 1.0D x 1.8L 64 AA 0.4 1.5 1400 " 1000 " 0.55D x 1.9L 22 AAA 0.6 1.5 600 " 400 " 0.4D x 1.7L 12 watt_hour_limit_portables -------------------------------------------------------------------------------------- Battery MinW-hr/cell MaxW-hr/cell Battery energy range W-hr Nickel-cadmium <1 6 <1 to 60 Nickel-hydride <1 7 <1 to 70 Lithimum-ion <1 14 <1 to 35 Lithimum-polymer <1 NA NA Zink_air 4 30 20 to 300 Nickel-cadmium <1 6 <1 to 60 -------------------------------------------------------------------------------------- battery available % temperature F 100 80 90 50 80, 30 75 20 61 0 cold cranking amps 43 -20 (CCA) Cold-cranking amps are read at a temperature of OF. -------------------------------------------------------------------------------------- capattery 30F/gram means 11V 0.47F is 1 in cube C_cell_capatitor 10-Ahr*3600 =36000F large cap 5.5volt 1F capatttery is .5in^3.. 11vot/.5F is 1in^3 -------------------------------------------------------------------------------------- Standard D size except Zinc in flat rectanglar 6v 3cell lead acid 1.3Ar at 0.06ohms AAA nicad 0.18Ahr at 0.021ohms .24in^3 10grams AA nicad 0.55Ahr at 0.011ohms .48in^3 24grams C nicad 1.8Ahr at 0.00445ohms 1.6in^3 80grams D nicad 4Ahr at 0.00341ohms 3.4in^3 160grams AAA alkaline 1.2Ahr AA 2.5, C 7.5 D 16.4 N 0.9Ahr resistance 0.6 ohms except D with .07ohm -------------------------------------------------------------------------------------- alkaline 1.5V 150Whr/kg at 14W/kg at .3% diard per month leadacid 2.0V 35Whr/kg at 200W/kg at 4% diard per month nicad 1.2V 60Whr/kg at 130W/kg at 10% diard per month 3->6% -------------------------------------------------------------------------------------- Anode Cathode V A-hr/Kg C size AH 9 volt AH Alkaline Zn MnO2 1.5 230 37.5mA*160hr 6 18ma*33hr 0.6 NiCad Cd NiO 1.35 165 1.2 Amp hours 1.2 -------------------------------------------------------------------------------------- Size Eveready# NEDA# Volt Capacity Carbon Zinc Cells: AAA 912 24F 1.5 20 ma @ 21 hrs AA 915 15F 1.5 54 ma @ 20 hrs C 935 14F 1.5 20 ma @ 140 hrs C 1235 14D 1.5 37.5 ma @ 97 hrs D 850 13F 1.5 20 ma @ 360 hrs D 1150 13C 1.5 375 ma @ 15.8 hrs D 1250 13D 1.5 60 ma @ 138 hrs N W4 910F 1.S 20 ma @ 22 hrs WO 201 1.5 0.1 ma @ 650 hrs 750 7W 3.0 20 ma @ 37 hrs 715 903 4.5 120 ma @ 90hrs 724 2 6.0 60 ma @ 175hrs 509 908 6.0 187 ma @ 40 hrs 109 206 .1611 9 12 ma @ 40 hrs 127 226 1600 9 12 ma @ 61 hrs 276 1M)3 9 20 ma @ 350 hrs 117 216 1604 9 9 ma @ 50 hrs 228 1810 12 12 ma @ 59 hrs 420 225 22.5 5 ma @ 60) hrs 482 207 45 40 ms @ 125 hrs 490 204 90 10 ma @ 63 hrs Alkaline-Manganese: AAA E92 24A 1.5 37.5 ma @ 25 hrs AA E91 lsn 1.s 20 ma @ 107 hrs C E93 14A 1.5 37 5 ma @ 160 hrs D E95 13A 1.5 50 ma @ 270 hrs G 520 930A 6.0 375 ma @ 59 hrs N E90 910A 1.5 9 ma @ 90 hrs 532 1308AP 3.0 20 ma @ 35 hrs 531 1307AP 4.5 20 ma @ 35 hrs 522 1601A 9.0 18 ma @ 33 hrs 539 6.0 18 MA @ 30.5 hrs Twelve-volt six cells. fully charged lead storage cell -------------------------------------------------------------------------------------- Space Power Miniature_Radioisotope_Power_Source About the size of a small flashlight, a proposed unit could power small instruments for years. 16.5cm _________________________________ | Radioisotope 7 AA LiTiS2 Cells | + _|__ _____ _______ _______ | | |==| | |_______||_______| | _ _|__|==|_____| |_______||_______| | 4.7cm | Insulate |_______||_______| | |_________________________________| PowerController and Thermalpile NASA's Jet Propulsion LaboratorL: Pasadena, California A proposed miniature power source would generate electricity for years without addition of fuel or dependence on sunlight. Called the powerstick, it would be relatively inexpensive lightweight, and rugged in comparison with other radioisotope thermoelectric generators that have been designed in recent years. The powerstick could supply power to small vehicles or scientific instruments in remote locations on Earth or in outer space. Some envisioned uses include Mars miniature rovers and monitoring equipment for toxic or nuclear storage sites. The powerstick consists of a radioisotope heater unit, a thermopile made of state-of-the-art thermoelectric material, a rechargeable battery, and control circuitry (see figure). During a full discharge from an initial full charge, the battery could supply 28 W.h of energy (1 A.h at 28 V). The total mass of the power stick would be approximately 380 grams. The radioisotope heater unit is a spot heater, produced by the U.S. Department of Energy, that contains a relatively small amount of radioisotope fuel and is commonly used on spacecraft. This unit provides 1 W of thermal power. Multilayer thermal insulation would direct most of the heat flux toward the thermopile, battery, and control circuitly, where it would not only supply energy for thermoelectric conversion, but would also maintain the battery and circuitry at the proper operating temperature. The thenopile would convert some of this thermal power to 40 mW of continuous electric power, which would be used to trickle-charge the batte�y. It would take about one month to fully recharge the battery after full discharge. The thermopile consists of about 1000 bismuth telluride legs that are 3 cm long and have a square cross section of 1/3 mm on a side. The battery in the powerstick would consist of fourteen LiTiS2 rechargeable cells of standard AA size, characterized by low self-discharge rate. The energy densities of these cells are 120 W.h/kg - about four times that of nickel/cadmium cells. The 28-V output of the battery could be downregulated by a microchip regulator or a dc-dc converter to various lesser voltages with an efficiency of about 85 percent. This work was done by Artur B. Chmielewski of Caltech for NASA's Jet Propulsion Laboratory. For further information, write in 25 on the TSP Request Card. NPO- 19339