5-Channel LiPo-Cell Electronic Load Tester Kit (LELTx5) PART NO

Transcription

1 5-Channel LiPo-Cell Electronic Load Tester Kit (LELTx5) PART NO Configured as five independent (up to) 100.0mA constant current loads (each), the LELTx5 is a versatile and valuable piece of test equipment for any experimenter working with the quickly expanding Lithium-Ion and Lithium-Polymer (LiPo) battery technologies and their many varied applications and circuits. Using on-board switches, it can present constant current loads of: 100.0mA, 200.0mA, 300.0mA, 400.0mA, and 500mA, per LELTx5 board. Two LELTx5 kits will get the loading up to 1.0Ampere; four will get 2.0Amperes, etc. WHY: Characterizing the discharge behavior of batteries is an important task for optimally selecting the best solution for many battery-operated applications, including (but, by no means limited to): medical and healthcare devices including a huge assortment of Wearable small to medium size robots, a wide-spectrum of wireless sensors with ISM radio-based communications (think: RF-digital, Wi-Fi, Bluetooth, XBee, Active-RFID, ZigBee, Radio Modems, et.al), even the exploding field of UAV to mention just a few. A simple resistor-load will NOT do. Unlike active circuits (microcontrollers, radio transceivers, sensing system and some low-power actuators), resistors do NOT "look like" constant (on average) loads to batteries and/or cells since the current drawn by them drops as the voltage drops over time. The purpose of Electronic Loads in battery testing systems is to present an unchanging current-or-power drain regardless of the battery or cell's voltage level, emulating the power drain of the (future) application circuitry. HOW: The useful voltage range in most LiPo-cell-powered circuits is +4.2volts maximum (for a 3.7volt rated cell just after it has been completely recharged) down to +3.2volts minimum (just starting into the sharp knee drop-off towards total discharge). So, as a minimum design goal, it would be ideal for an Electronic Load to maintain a constant loading on the cell down to at least 3.2volts if it is to perform as a practical Electronic Load for LiPo cell testing and performance analysis purposes. This is a perfect task for a low-dropout linear voltage regulator. The LELTx5, per channel, consists of a low-dropout regulator that maintains a constant voltage on a fixed resistor (and LED) load regardless of the voltage input applied to it, at least down to 3.2volts. Non-precision resistors can be used because the actual voltage output is adjusted so that exactly 100.0mA is flowing into the LELT-channel circuitry, compensating for variations in component values due to wide-tolerances. This enables precision operations from extremely inexpensive components. As shown in both the block diagram and the schematic in the figure with this brief, the Green (jumbo, 10mm) LED, whose actual forward voltage drop varies significantly from unit to unit, is in parallel with a series resistor string composed of 5% tolerance resistors. When the Green LED(s) turn(s) off, the LiPo-cell being discharged by the one or more LELTx5 devices has dropped its output voltage to the point where its integrated Protection Circuit Board [PCB] has electronically disconnected the cell from its wiring to prevent over-discharging the cell(s). More details about the PCB s can be found in the Owner s Manual for the LiBaC kit. BREADBOARD VERSION: The "ELOAD#" voltage levels for the breadboard version of the LELTx5, after per channel calibration to exactly 100.0mA loading each, measured from a low of +2.66volts to a high of +2.69volts. For the LP2951, the typical 'headroom' when controlling 100mA is nominally 400mV (at 25C) and goes up to about 430mV (at 50C). This means that 100mA loading can be maintained when the LiPo-cell voltage drains down to a low of +3.09volts (at 25C), which is well into the drop-off knee for a typical discharge curve. The LELTx5 channels can be adjusted for lower constant-current loadings, with a low of 50mA already tested during the LiBaC development. Additional data regarding non-100ma-per-channel operations are included in the kit instructions.

2 When running the LELTx5 per-channel load levels at the maximum of 100.0mA (each), the maximum "V+" input voltage (in case the kit-builder wants to use it for other battery and cell testing purposes) is: +14volts (at 25C), or 12volts (at 50C) or a low of about 8volts (at 85C). There are more details about how the LELTx5 works, including a couple of classic-form discharge curves, in the LiBaC Instructions, steps 38, 41, and 49. More curves are included in the instruction set for this kit as Performance Data. THRU-HOLE ONLY = BEGINNER LEVEL: All of the Jameco-only components for the LELTx5 are thru-hole components, making this kit easy to build, even as a very first kit, for the beginner kit-builder. Assembly time is about an hour, not including calibration. Any voltage source greater than 3.2volts (LiPo-cell, 9volt battery, power supply, car battery, etc.) with a Multimeter that has a 200mA ammeter scale is all that is needed to calibrate each channel (one at a time) of the LELTx5 after assembly. WARNING: If you are unsure of the dangers involved with your particular project, consult with someone who is experienced. Always wear eye protection and gloves. FAILURE TO INITIATE AND FOLLOW YOUR OWN SAFETY PROCEDURES MAY RESULT IN BODILY INJURY OR DEATH! Time Required: 1 hour maximum depending on experience Experience Level: Beginner Required tools and parts: Soldering Iron with solder, flux, and cleaners. Side or Flush cutters for trimming excess leads. (that's all really, for building the LELTx5). CALIBRATION: 1) Any voltage source from about 3.3volts to about 8volts, including (of course) LiPo-Cells, other batteries, or a bench power supply in this voltage range. 2) An ammeter capable of displaying 100mA +/- 20mA, like the 200mA range found on most multimeters. 3) Small flat-blade screwdriver for adjusting the five voltage-output potentiometers. Bill of Materials: Qty Jameco SKU Component Name uf 50 Volt Monolithic, Epoxy Dipped Radial Capacitor on 0.2" pitch LED Uni-Color Green 565nm 2-Pin, 10mm (JUMBO) Switch Slide Min Single Pole Double Throw On-On PCB Mount 50 Volt 0.5 Amps Lead 4mm ADJUSTABLE MICROPOWER VOLTAGE REGULATOR DIP-8, 100mA max., 1.24v to 29v output Resistor Carbon Film 10 Ohm 1/4 Watt 5% (In Bags of 10) Resistor Carbon Film 150 Ohm 1/4 Watt 5% (In Bags of 10) Resistor Carbon Film 10k Ohm 1/4 Watt 5% (In Bags of 10) Connector Terminal Blocks 2 Position 5mm Solder Straight Thru-Hole 16A, blue /2 Watt Square Cermet Potentiometer 3/8 Inch 25K Ohm 10% 20 Turns, Top Adjust Step 1 - Step 1: Assembly Drawing Components Placement.

3 Step 2 - Step 2: Assembly of 10 Ohms Resistors. Step 3 - Step 3: Assembly of 10k Ohms Resistors. Step 4 - Step 4: Assembly of 150 Ohms Resistors. Step 5 - Step 5: Assembly of Integrated Circuits. THESE PARTS MUST BE INSTALLED CORRECTLY!

4 Step 6 - Step 6: Assembly of Filter Capacitors Step 7 - Step 7: Assembly of Switches Step 8 - Step 8: Assembly of Potentiometers NOTE: was replaced to due to low inventory. Step 9 - Step 9: Assembly of Green "JUMBO" LEDs

5 Step 10 - Step 10: Assembly of Input Terminal Block Step 11 - Step 11 Technical Calibration Procedure for the LELTx5 *** Reference the Picture with this step *** EQUIPMENT HOOKUP: EQUIPMENT NEEDED: The "Required Tools or Supplies" portion of the Overview identified two pieces of 'equipment' that are needed to perform the calibration procedure on the LELTx5: a) Any voltage source ranging from about +3.3volts to about +8volts (assumes that the channels are going to be calibrated to be 100.0mA loads). This voltage source, of course, can be any 3.7v (nominal, rated) LiPo-Cell that is not near full discharge, any other kind of battery source (3 AA battery pack, 9-volt battery, et.al), or even a Wall-wart or (fixed or variable) bench power supply. Whatever kind of voltage source is used, it just needs to be capable of delivering at least 100mA current. b) Any digital ammeter that can display 100mA or (better still) 100.0mA (or higher resolution). The most common bench test equipment, the multimeter, generally has a 200mA full-scale DC Ammeter range, and this will work just fine for these calibrations. WIRING EQUIPMENT: *** STUDY THE PICTURE FOR THIS PORTION *** i) TURN-OFF the Voltage source before wiring ii) Connect the positive output of the voltage source (shown with a red plus sign in the picture for this step) to the positive AMMETER input (usually a dedicated banana jack, often yellow, on many multimeters). iii) Connect the negative AMMETER (output, usually the shared "COM" black banana jack on most multimeters) to the "V+" input of the LELTx5. Note that this is the right wiring cage on the 2-position terminal block. iv) Connect the Voltage Source "common" or "return" (shown with a black minus sign in the picture for this step) to the "GND" (left wiring cage) on the 2-position terminal block on the LELTx5. v) Move all FIVE of the SPDT slide switches to their "OFF" positions. CALIBRATION: These sub-steps should be repeated for each channel of the LELTx5 to be calibrated. Note that these sub-steps assume that the kit-builder is using each channel at its maximum load capability of 100.0mA, and not some lower value (which is possible, of course, if desired, as shown in Step 19). 1) Turn on the Multimeter or other form of Digital Ammeter, ensuring that the DC Ammeter function is selected and that a scale is chosen that includes 100.0mA. 2) TURN-ON the voltage source. 3) Move the slide switch for the channel to be calibrated from the "OFF" position to the "ON" position. Do not be concerned if the Green LED does not immediately light-up since the output voltage on the regulator may not be high enough (yet) if the potentiometer has not yet been adjusted. 3) Rotate the adjustment screw for the potentiometer for the channel being adjusted until the ammeter reading is 100.0mA. Ensure that the Green LED is lit (it will be if it was not installed backwards). After allowing the LELTx5 to drain your voltage source for about a minute. 4) Turn OFF the channel control slide switch, briefly, and turn it back ON again, verifying that the ammeter still displays 100.0mA. There is a brief warm-up period until the resistive loads are dissipating their 'normal' heat levels, during which their resistance values change slightly. After running for a couple of minutes, the adjustment potentiometer can be adjusted again if it is needed to bring the load 'current' level back to 100.0mA. 5) Turn OFF the channel's control slide switch (again). 6) Repeat sub-steps 3 through 5 for each channel to be adjusted on the LELTx5 until all five of them are calibrated. 7) Turn OFF the voltage source and the ammeter (multimeter) and disconnect all the wiring performed in the beginning.

6 YOUR "new" LELTx5 is ready to go to work for you. See the Technical Section's "Other Currents" in step 19, and see the Performance Results (steps ) in this document for some typical operational results. Step 12 - Step 12 Technical Overview of LELTx5 *** Reference the Picture with this step *** TOP RIGHT CORNER: Block Diagram of 1 Channel of the LELTx5 TOP LEFT CORNER: Schematic of 1 Channel of the LELTx5. The full schematic for the LELTx5 is shown in the next (#13) step. BOTTOM RIGHT CORNER: Printed Circuit Board (2.85" x 2.85") with Components. You should be fairly familiar with this after having built the LELTx5 in the first 10 steps. BOTTOM LEFT CORNER: Assembled Printed Circuit Board version of LELTx5. The five-channel breadboard version was developed and used during Performance Evaluation of the LiBaC (Lithium-Ion Polymer: LiPo Battery-cell Charger kit also available from Jameco). The Performance Data acquired and presented in the last section, starting with step #20, was acquired using the breadboard version. Step 13 - Step 13 Technical Schematic of LELTx5 *** Study the Picture as this step *** This design was developed using EAGLE PRO tools. The LELTx5.sch (schematic) and LELTx5.brd (layout) files are available for the asking if the kit builder wishes to use this design as a basis for their own modifications. This design (because it is so simple) can be viewed and modified in the free downloadable version of EAGLE.

7 Step 14 - Step 14 Technical Bottom Copper Layout of LELTx5 Note, the 'view' pictured is an X-Ray view, as the bottom copper appears from the top looking through the board. 86.0% of the bottom of the board is copper. This design was developed using EAGLE PRO tools. The LELTx5.sch (schematic) and LELTx5.brd (layout) files are available for the asking if the kit builder wishes to use this design as a basis for their own modifications. This design (because it is so simple) can be viewed and modified in the free downloadable version of EAGLE. The printed circuit board measures 72.39mm (2.85") per side, and is only a 2-layer board with no surface mount pads (all thru-hole). There are 32 signals routed with 131 wires and 3 polygons (copper pours). The smallest 'pour' is the "V+" connections on the bottom of the board, with the other two copper polygon pours (one on top and one on bottom) being "GND" connections. There are 157 'drills' total, 9 for Via's and 148 for 'pads' (including the four 3.3mm grounded mounting holes). With the bottom left corner being the sizing reference of 0.0(X) x 0.0(Y), these four 0.130" mounting holes are located at: 1) 0.20" x 0.20" 2) 2.65" x 0.20" 3) 6.15" x 2.67" 4) 0.65" x 2.67" Either short standoffs or stick-on rubber feet can be used to raise the bottom of the board off of any potentially-conductive surface. Remember, these four mounting holes are all electrically connected to GND. Step 15 - Step 15 Technical Top Copper Layout of LELTx5 78.7% of the top of the board is copper. (Repeat of more text from step 14, in case you skipped it): This design was developed using EAGLE PRO tools. The LELTx5.sch (schematic) and LELTx5.brd (layout) files are available for the asking if the kit builder wishes to use this design as a basis for their own modifications. This design (because it is so simple) can be viewed and modified in the free downloadable version of EAGLE. The printed circuit board measures 72.39mm (2.85") per side, and is only a 2-layer board with no surface mount pads (all thru-hole). There are 32 signals routed with 131 wires and 3 polygons (copper pours). The smallest 'pour' is the "V+" connections on the bottom of the board, with the other two copper polygon pours (one on top and one on bottom) being "GND" connections. There are 157 'drills' total, 9 for Via's and 148 for 'pads' (including the four 3.3mm grounded mounting holes). With the bottom left corner being the sizing reference of 0.0(X) x 0.0(Y), these four 0.130" mounting holes are located at: 1) 0.20" x 0.20" 2) 2.65" x 0.20" 3) 6.15" x 2.67" 4) 0.65" x 2.67" Either short standoffs or stick-on rubber feet can be used to raise the bottom of the board off of any potentially-conductive surface. Remember, these four mounting holes are all electrically connected to GND.

8 Step 16 - Step 16 Technical Assembly Photographs of LELTx5 Steps 2 through 5 This step presents technical assembly view information only. No tasks are associated with it. Step 17 - Step 17 Technical Assembly Photographs of LELTx5 Steps 6 through 9 This step presents technical assembly view information only. No tasks are associated with it. Step 18 - Step 18 Technical Assembly Photographs of LELTx5 ALL Steps through 10 This step presents technical assembly view information only. No tasks are associated with it. Step 19 - Step 19 Technical Other Calibration-currents for the LELTx5 The picture for this step is a tabulation of the measurements taken for the 'results' presented in this step. *** Reference the Picture with this step *** Reference Step 11 for the test setup and procedure executed, where only the current values where changed (from 100.0mA) where needed. By way of reminder, the "Eload" reference is the output voltage from each of the five LP2951 regulators. The "Eload" voltage tabulated was that measured after the input current was adjusted to the desired level shown (100.0mA, 80.0mA, 60.0mA, and 50.0mA). The variations in voltage levels is due to the wide variations (+/- 5% each) in the resistances used as loads, as well as the (even wider range) forward voltage drop of the jumbo Green LEDs used. To a lesser degree, variations are also attributable to the 'headroom' voltage dropout (of regulation) exhibited by individual LP2951 IC's, and the resolution and accuracy of the meters used for the test and calibration procedures.

9 ********** Depending upon the ambient light, and the channel involved, the five green LEDs became very dim at around 65mA-to-75mA of load current. This is the reason for the note between the 80mA range and the 60mA range in the table in the picture for this step. The minimum constant currents for these five channels were also recorded (as a matter of interest), and are: 1) 42.1mA 2) 42.6mA 3) 42.7mA 4) 42.8mA, and 5) 42.7mA The minimum constant current is a function of the calibration potentiometer's end-position where the output voltage (at 'Eload') equals the reference voltage of (about) +1.23volts. The quiescent current, when ALL 5 channels are OFF, was measured at 832uA (166uA average, each regulator). Keep this in mind when attaching the LELTx5 to any kind of battery, in that it will increase the discharge rate of the battery/cell slightly, even when all five constant current electronic loads are turned off. Step 20 - Step 20 PERFORMANCE: LELTx5 Discharging 700mAh LiPo at 300mA rate. The picture for this step is a presentation of the data acquired by a Commercial-Grade WinDaq Data Acquisition System (DAS) and plotted as a full-test-view. The actual test, performed 3Jul15, was in support of performance testing of the LiBaC, the Generic Lithium-Ion- Polymer Battery-Cell Charger kit. There are no additional 'tasks' associated with this step.