Lemon Batteries Connected in a Series/Parallel Configuration Charging a 4.4 Farad Capacitor. SECTION #1 - The experimental setup

Transcription

1 Lemon Batteries Connected in a Series/Parallel Configuration Charging a 4.4 Farad Capacitor SECTION #1 The experimental setup 1. The goal of this experiment is to see if I can connect 6 lemons together in a series/parallel configuration to make one battery which will charge up two 2.2 Farad Super Capacitors. 2. A diagram of the battery configuration is presented at the end of the document. Experiment #1: 6 lemons in series/parallel{2 banks, 3 cells/bank}, two 2.2F capacitors in parallel. Experiment #2: 6 lemons in series/parallel{2 banks, 3 cells/bank}, retest of one 2.2F capacitor. 3. The lemons were frozen over night and then allowed to thaw for several hours before the experiment. 4. The negative electrodes are Zn plated washers, 3.7cm diameter (part #2645). It should be noted that the diameter of these washers are slightly larger than the diameter of the silver coins used as the positive electrode. Thus, these electrodes provide a larger surface area from which Zn can provide a current. I got these washers from Home Depot. At the Zn electrode, the Zn metal (Zn 0 ) is dissolving (becomes oxidized) and forms Zn ions (Zn 2 ) and two electrons (e ) as follows: Zn 0 Zn 2 2e 5. Positive electrodes are Canadian Silver Dollars (80%Ag / 20%Cu), years 1958 through I connected two 2.2 Farad electrolytic Super Capacitors to my lemon battery configuration, which theoretically should be able to store 4.4 Farads of charge (or 4,400,000 μf or 4.4 million microfarads). The device number: 2.5DMB2R2M8X16 CAP, ALU ELEC: Manufacturer specifications: 2.5 Volts. Also, these devices have a polarity and MUST be connected into the circuit in the correct orientation. 7. The experiment used the following load resistor: 4700Ω nominal. 8. Experiments were run continuously, i.e., once connected to the battery, the experiment was allowed to run for the indicated time period before the positive terminal of the battery was disconnected. 9. My design also uses a germanium diode at the negative side of my battery configuration. The device number is 1N34A. I measured the V F (forward voltage) and found it to be Volts. 10. Electrical measurements were taken at several points: (i) Circuit current at point "a" (I circuit ). (ii) Voltage across each capacitor, V cap1 and V cap2. (iii) Charging current (I charging ) at point "b". (iv) Battery voltage (a) before start of experiment and (b) at 46 minutes into the experiment and (c) at the end of the experiment. (v) Resistance of each cell, before the start of the experiment. 11. Table 1a contains data from a previous post, i.e., experiment #10 lemons charging a 2.2F Super Capacitor, specifically, the header cells are in pink shading. 12. Additionally, when the current at point "b" is equal to the current at point "a", I will assume that the capacitor is fully charged, or at least very close to fully charged. 13. At the end of each experiment, the charge was drained from the capacitor by disconnecting the Positive terminal and by using an additional resistor of lower value, in parallel with the load resistor, in order to SAFELY drain off the stored up charge. I use the symbol " " to mean "in parallel with". 14. Discharge experiments used the following resistor: 100Ω nominal. 15. The number of Couls of charge and Capacitance is reported at the end of this document (done in Excel). 16. Also reported is the charging ratio (I charging / I circuit, max ) x 100, as a percent. At the beginning of the experiment, the percentage >>> 100% and as the percentage approaches 100%, the capacitor approached being fully charged. 17. A second experiment was done to retest one of the Super Capacitors and this will be explained later. Experiment #2: 6 lemons in series/parallel{2 banks, 3 cells/bank}, retest of one 2.2F capacitor. 18. Table 1c contains discharge data from the current experiment, i.e., 6 lemons in Series/Parallel with Zn plated washers, under the grey header and data from a previous post, i.e., 6 lemons in Series/Parallel with Zn plated nails. 19. Table 4a contains data from all experiments to date with the 2.2 Farad Super Capacitor.

2 SECTION #2: Data for Experiment #1 Table 1a Six Lemons in Series/Parallel, Zn Plated Washers, 4700 Ohm Resistance, 2 x 2.2 Farad Capacitors. Time (min) I "b"; ma Experiment #10,, V cap1 V cap2 6 cells/p 6 cells/p 6 cells/p V cap I "b" I "a"; ma Instantaneous {OL} Table 1b: Experiment #1 Battery Data start: V cell 1 = 1.05V, V cell 2 = 1.0V, V cell 3 = 1.0V, V cell 4 = 1.0V, V cell 5 = 0.97V, V cell 6 = 1.03V start: R cell 1 = 75Ω, R cell 2 = 120Ω, R cell 3 = 100Ω, R cell 4 = 100Ω, R cell 5 = 170Ω, R cell 6 = 100Ω I charge / I ciruit, max = 0.374/0.282 = 133% Voltage (V d ) across 1N34A 38 min = 0.27V {Analog meter} Voltage across battery before start of experiment, V battery = 2.8V {Analog meter} Voltage across battery, V battery = 46 minutes {Analog meter} Voltage across battery at end of experiment, V battery = 2.65V {Analog meter} Estimated # Couls & Farads: Charge = Couls, V = Volts, Capacitance = 2.24 Farads

3 SECTION #2: Data for Experiment #1, continued Table 1c Experiment #1: Discharge of 2.2 Farad Capacitor through 4700 Ohm 100 Ohm, ( 96.7Ω) Discharge Time (minutes) V cap (Volts) I circuit, "a"; ma Power (μw) Current expt ; 6 cells S/P Instantaneous , SECTION #2: Discussion of Data for Experiment #1, Six Lemon Battery (Series/Parallel) 1. The data in Table 1a, under the gray headers is from the current experiment (using Zn plated washers) and the data under the pink headers is from the previous post (using Zn plated nails). 2. Firstly it is noted that the voltage across the first capacitor (V cap1 ) is not changing; thus, the capacitor is not charging. More on this later. 3. The voltage across the second capacitor (V cap2 ) is changing, thus, is charging up. 4. Additionally, V cap1 is very similar to the voltage across the capacitor in the previous post (V cap ) under the pink header within the first minute of the experiment, i.e., V cap2 = 0.050V and 0.078V versus 0.052V and 0.073V for V cap. Thus, the Zn plated nails are producing about the same level of current as the Zn plated washers at this point. 5. But, that is where the similarity ends. From 3 minutes onwards, V cap2 rapidly exceeds the voltage across V cap, e.g., at 40 minutes, V cap2 = 1.024V; whereas, it takes 90 minutes for V cap to reach at least 1V (1.006V). 6. Thus, the Zn plated washers are providing a much greater current than the Zn plated nails. 7. This is further supported by the current data, i.e., at 1 minute, the current for the Zn plated nail battery has dropped to just about 1 ma (1.036mA); whereas, the battery with the Zn plated washers is still producing about 1mA (1.034mA) 14 minutes later (15 minute time point)! 8. Thus, the battery with the Zn plated washers is performing much better than the Zn plated nails. 9. After 130 minutes, the voltage across V cap2 = 1.356V. This is the highest voltage that I have ever obtained, see Table 4a, Line # As well, the charging ratio, I charging / I circuit, max x 100, is 133%, which is the closest that I have come to fully charging a Super Cap, see Table 4a, Line # The measured voltage across the battery at the start of the experiment is 2.8V, which is very close to the theoretical voltage of 3.0V. 12. The measured voltage across the battery at the end of the experiment is 2.65V, which is still 95% of the starting voltage, thus, I feel that this configuration could still have produced more charging current. 13. It should be noted that the starting resistance for each cell ranged from 75120Ω, which is much less than any battery resistance I have ever measured in past posts and is a very good battery characteristic for this model. Most commercial batteries have internal resistances of about 0.51Ω. 14. It should be noted that the voltage across the battery at 46 minutes is 1.4V. Considering the voltage at 45 minutes, 1.063V, and the voltage across the diode at 38 minutes, 0.27V: = 1.33V, which is very close to the measured voltage of 1.4V. 15. Total voltage at end of experiment: 1.356V (V cap2 ) 0.27V (diode) = 1.626V. 16. The estimated number of Coulombs of charge transferred during the experiment is Couls! 17. Taking into account that the final voltage across the capacitor is 1.356V, this means that 2.24 Farads of Capacitance have been stored. This is consistent with the rating of 2.5V.

4 SECTION #2: Discussion of Data for Experiment #1, Discharge Experiment, Table 1c 1. From Table 1c, it can be seen that at the instant the discharge was initiated, the power dissipated is 14,300μW (14.3mW)! That is a significant amount of power and is consistent with a large amount of charge stored in the capacitor. 2. At 1 minute into the discharge experiment, the capacitor is still delivering about 9.5mW (9563μW) of power. 3. This is about twice the amount of power delivered by the Zn plated nails experiment, i.e., Zn plated washers = 9563μW versus Zn plated nails = 4547μW 4. Five minutes later, the capacitor is still delivering about 1mW of power (962μW). Considering the fact that many "small" solar powered projects require power on the μw scale, this configuration should be able to store enough energy to drive those types of projects. 5. Also, one must consider the fact that I am discharging the capacitor through a vey "high" load (i.e., low resistance), of approximately 100Ω. SECTION #3: Discussion of Data for Experiment #2, Retest of One of the Super Capacitors 28Feb From Table 1a, column labeled V cap1, it can be seen that the voltage across capacitor #1 remains the same throughout the experiment; thus, the capacitor is not being charged. 2. One potential reason for this is that all manufactured components have tolerances due to the manufacturing process and therefore, all capacitors will have slightly different electrical characteristics. 3. Super Capacitors have an internal resistance, just like batteries, therefore, V cap2 might have a lower internal resistance than V cap1, thus taking up all of the current produced by the lemon battery configuration. 4. Even though this is a potential reason, I expected that after V cap2 was fully charged, then V cap1 would start to charge up, but that never happened. Thus, I am not sure of the explanation for this result. 5. I wondered if I had destroyed V cap1 somehow; thus, I set up a new circuit that had only V cap1 in the circuit. The data is presented in Table 3a below, under the yellow headers and data from Table 1a above for V cap2 is presented under the grey headers. 6. At the 30 minute time point, the voltages and currents for V cap1 in this experiment are very similar to that of V cap2 from the first experiment presented in Table 1a, i.e., versus and versus Thus, it appears that there is nothing wrong with capacitor #1, i.e., the result in Table 1a is not due to a faulty capacitor. 8. In a future experiment, I will try to "balance" the capacitors, i.e., I will insert a potentiometer (i.e., a variable resistor, also called a "pot") into the circuit to see if I can match the electrical characteristics of capacitor #1 to that of capacitor #2. If successful, both capacitors should charge up at the same time. SECTION #3: Data for Experiment #2, Retest of One of the Super Capacitors Table 3a Experiment #2: Retest of One Super Capacitor Time (min) I "b"; ma V cap1 6 cells/p I "a"; ma V cap2 6 cells/p I "a"; ma Voltage across diode (V d 14 minutes = 0.33V

5 SECTION #4: Summary of Current Experiment and Previous Posts Table 4a Summary of Data from Series and Series/Parallel Battery Configurations, 2.2Farad Capacitors # Configuration # of Cells V cap 1 Series/Parallel, Zn washers 6 {2 banks, 3 cells/bank} I charging / I circuit, max x 100 Time (min) Coulombs # of Electrons transferred Farads % x Series, Series, Series, Series/Parallel, Series/Parallel, % x % x % x {2 banks, 2 cells/bank} 6 {2 banks, 3 cells/bank} % x % x SECTION #4: Discussion of Data from all Experiments with 2.2 Farad Super Capacitors 28Feb From Table 4a, line #1, it can be seen that this battery configuration, i.e., 6 lemons in a series/parallel configuration, using Zn plated washers, is the best result of all of the experiments to date, i.e., I was able to reach 1.356V and store 3 Couls of charge. The only caveat being that it is also the longest experiment that I ran (130 minutes). 2. Also from line #1, the charging ratio is 133%, which is the highest level obtained to date; thus, represents that highest level of charging of the capacitors to date. Not a bad result at all! 3. It can be seen that I was able to approach the rated Capacitance of 2.2 Farads, the range for all experiments being Farads. 4. Furthermore, it is noted that Capacitance has two variables, Voltage and Charge (Couls); thus, capacitance is only relevant when each characteristic in known, i.e., for line #1, I was able to store 3 Couls of a voltage of Volts. 5. Similarly, in line #6, I was able to store Couls of a voltage of Volts. SECTION #5: Lessons Learned 1. The Zn plated washers, part number #2645, used as the negative electrode in a series/parallel configuration of 6 lemons (2 banks, 3 cells per bank) has provided the best battery characteristics to date. 2. The resistance of each cell with the Zn plated washers was very low, i.e. on the order of 100Ω, compared to several hundreds of ohms to thousands of ohms in past battery designs. 3. My current battery design can successfully charge a Super Capacitor to its rated capacitance, anywhere from Volts. 4. The current design can store 3 Couls of charge and can provide 100s of μw of power for extended periods of time. 5. The Super Capacitors have significantly different electrical characteristics, thus, may require some balancing circuitry in order to charge up capacitors connected in parallel.

6 SECTION #6: Calculations of Coulombs & Farads, 6 Cells in Series/Parallel Table XX: Battery Using Zn Plated Washers EXPERIMENT #11 # 1 time b a diff in Curr Curr in Amp time, sec Coul Total Coul Volts Farads 2.24 CONTINUED ON NEXT PAGE

7 SECTION #7: Equivalent Circuit 1. Six Lemon Battery in Series/Parallel Configuration, using Zn plated Washers A = Ammeter, point "a" A = Ammeter, point "b" A A V cap2 V cap1