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Universal Charger

Firmware features

Description of the Universal Charger features

The Universal Charger firmware is the natural evolution of the Advanced Charger. The Universal Charger will use the same hardware of the Advanced Charger (HV or not HV) changing only the PIC firmware. For new hardware development we do not recommend the manufacturing of the Advanced Charger but refer to the dedicated hardware developed for Universal Charger. It will fast charge/discharge this types of batteries:

1. Nickel Cadmium
2. Nickel Metal Hydride
3. Lithium Polymer
4. Sealed Lead Acid

Changing the charge maximum cell voltage and the discharge cutoff value this charger can charge and discharge also the Li-Ion cells and in general the Li-xx cells. With the same adjustement the user can manage the VRLA batteries (Valve regulated Leaded Acid - automotive batteries). The key points of this new firmware are the following:
  1. Accurate calibration to meet LiPo cells voltage and current measurement requirements
  2. The usage of the charger does not require the PC, software needed only for advanced users
  3. 12 battery pack profiles stored into the charger
  4. 17 different parameters per battery pack, 5 editable on-the-field, 12 by PC software
  5. Parameters editable on-the-field (directly on charger)
    • Battery pack chemistry
    • Battery pack capacity
    • Number of cells
    • Charge current
    • Discharge current
  6. Parameters editable off-line (via PC software)
    • Cell cutoff voltage (all types)
    • Cell delta peak voltage (NiCd and NiMh)
    • Cell maximum voltage in charge (LiPo and SLA)
    • Charge final current (LiPo and SLA)
    • Maximum pack capacity charge
  7. General charger parameters (via PC software)
    • Selection of battery profile
    • Maximum charge current
    • Maximum discharge current
    • Voltage and current calibration
    • Customizable "hello message"
Please refer to the user manual in the file section for more details.


Charger usage

Description of the charger on-the-field usage

The Universal Charger usage is very easy but some point must be strictly followed in order to avoid any problem in battery and charger management. First read the charger documentation, then follow these recommendations in order to have a good charger usage.



Voltage and current calibration

The charger is a mesurement instrument because has to measure very accurately the voltages and current flows. For this the first step is to calibrate the charger using the "Volt Calibration" and "Ampere Calibration" on the charger. Follow the instructions on this website and on the user manual to perform a good calibration. The calibration process, if the resistors are very different from the default on (R6=12K and R5=47K) can be a bit long process. Take advantage from the key autorepeat during this adjustment or adjust the resistor value using the PC software.




Customization and backup

After the calibration the user can customize all the battery profiles in order to prepare the charge and discharge of the different cell packs. The customization can be performed on three types of parameters:

  • Battery main parameters (editables from the charger or from the PC software)
  • Battery advanced parameters (editables only from the PC software)
  • Charger parameters (editables only from the PC software)


The change of battery advanced parameters or charger parameters must be performed only by expert users. Take expremely care to modify these parameters because the wrong setting can bring to the charger or battery damage.
The user can (backup or restore) the charger complete parameters set (better if after the calibration) with the relevant PC software.

See the "General manager" web site page to a complete reference for the parameters that can be changed.


Battery charge

After the calibration and the customization the user can safely charge a battery pack. Be sure that the selected profile in terms of chemistry, capacity and number of cells matches the battery pack to be charged.
The charge process is performed using a constant current for NiCd and NiMh. For this charge the charger looks at the pack voltage and stores the maximum peak reached: when the cells "comes back" from this peak a certain amount of voltage (delta peak) the charger stops the process because the cells are full. The delta peak used for these cells is the following:
  • NiCd -> 10mV/cell
  • NiMh -> 5mV/cell

The charge process for LiPo and SLA is performed using a constant current until the reaching of the Maximum Voltage, then with a constant Voltage decreasing the current. The charge will finish when the current is under the 5% of the initial current. The maximum voltage for these cells is the following:
  • LiPo -> 4200mV/cell
  • SLA -> 2500mV/cell

All these parameters can be changed using the PC software. The charge current is expressed in terms of cells capacity: 1.0 in the charge parameters means that the cells will be charged at the mA corresponding to the capacity. For a cell of 2000mAh, in the above case, the charge current will be 2 Ampere.
During the charge process the user can display the voltage, current and capacity curves (see figure) using the delivered software tool.


Battery discharge

After the calibration and the customization the user can safely discharge a battery pack. Be sure that the selected profile in terms of chemistry, capacity and number of cells matches the battery pack to be charged.
The discharge process for all battery types is performed using a constant current until the reaching of the Cutoff Voltage, then the discharge will finish. The cutoff voltage for these cells is the following:
  • NiCd -> 800mV/cell
  • NiMh -> 1000mV/cell
  • LiPo -> 3000mV/cell
  • SLA -> 2000mV/cell

All these parameters can be changed using the PC software. The discharge current is expressed in terms of cells capacity: 5.0 in the charge parameters means that the cells will be discharged at five times the mA corresponding to the capacity. For a cell of 2000mAh, in the above case, the discharge current will be 10 Ampere.
During the charge process the user can display the voltage, current and capacity curves (see figure) using the delivered software tool.


Charger calibration

Description of the calibration process to be performed before the charger usage.

The universal charger implements the possibility to calibrate the voltage and ampere readings with a few common components (a charged battery and a tester). The reasons for the implementation of this new features are the following:

  • The management of LiPo and SLA batteries needs a more accurate voltage reading in order to meet the stringent requirements in fact of maximum voltage and cutoff.
  • Avoid the need of the PC for the Universal Charger usage: the Advanced Charger needs to change some parameters in the source code and to recompile the program for calibration. The Universal Charger performs the same operation quickly and easily with only the charger and a tester.

Voltage calibration

The voltage calibration is performed using a charged (charged and with stable voltage) battery, and a tester capable to read the voltage of the battery. With more accurate tester the resulting calibration will be more accurate. To perform the voltage calibration use the following steps:

  • Connect the battery to the charger
  • Connect the tester to the battery to read the voltage (see figure)
  • Wait for a stable reading on the tester
  • Select "Volt Calibration" on the charger
  • If the charger reading is below the tester reading, press the "+ or UP" key on the charger and hold it pressed until the two readings are equal.
  • If the charger reading is above the tester reading, press the "- or DOWN" key on the charger and hold it pressed until the two readings are equal.
  • At the end press "OK" on the charger and disconnect the battery and the tester.

Current calibration

The current calibration is performed using the charger and a tester capable to read a current of at least 2 Ampere. With more accurate tester the resulting calibration will be more accurate. To perform the current calibration use the following steps:

  • Connect the tester to the charger using the "ampere" input (see figure)
  • At this point the tester reads a 0.00 Ampere current
  • Select "Ampere Calibration" on the charger
  • At this point the charger will source a 2.00 Ampere current into the tester.
  • If the charger reading is below the tester reading, press the "+ or UP" key on the charger and hold it pressed until the two readings are equal.
  • If the charger reading is above the tester reading, press the "- or DOWN" key on the charger and hold it pressed until the two readings are equal.
  • At the end press "OK" on the charger and disconnect the tester.


General Manager SW

Short reference for general manager software usage

The Universal Charger "General Manager" software usage is very easy but some point must be evidenced in order to get a very quick startup. Please refer also to the user manual of this software released in the files directory.


COM port selection

The first step is to choose the serial port for charger connection: the COM1 - COM16 ports are displayed on the right bar, with in evidence only the ports available and active on the computer. Select the port that is phisically connected to the charger clicking on the name. Once selected the serial port the user can go to the following steps.



Backup and restore the charger complete configuration

The first page allows the user to backup and restore the complete configuration of the charger. The Backup function copy all the charger parameters on a file, the Restore function copy the parameters from a file to the charger.
The progress bar on the bottom of the page shows the operation progress. The user dialog box propose a “.universal” extension for this backup file but the user can specify an arbitrary name.

Important: the backup of the charger configuration save all the charger parameters and all the profiles parameters, allowing a complete solution to restart the system with a predefined state.

Important: the restore of the charger configuration overwrites the present charger configuration with no recovery possibility.



Change Universal Charger general parameters

This page allows to read/modify the general charger parameters (the parameters common to all the profiles).

The “READ from CHARGER” button reads all the parameters on this page from the charger and display the data. The “WRITE to CHARGER” button writes the data displayed (eventually edited by the user) into the charger. The small progress bar below the buttons shows the progress of the commanded action.

Important: the write operation is composed by a write and a successive read in order to re-display (for check) the data entered by the user, giving a feedback of the charger status.

The following is the list of the general parameters that can be customized:

  • Actual Profile: (0..11) This parameter is the selected profile into the charger. Changing this value has the same effect that a selection performed with the “Profile select” inside the charger. The “actual profile” parameter is used by the charger for charge, discharge or editing.
  • MAX charge current (0..255) Maximum charge current in Ampere. A charge current greater than this parameter will be saturated at this maximum value.
  • MAX discharge current (0..255) Maximum discharge current in Ampere. A discharge current greater than this parameter will be saturated at this maximum value.
  • Buzzer frequency (50..10000) Buzzer frequency in Hertz. This frequency should be adapted the resonant frequency of the charger buzzer.
  • R6 (0..65535) Partitor resistor in Ohm. See the figure on this page for more details.
  • R5 (0..65535) Partitor resistor in Ohm. See the figure on this page for more details.
  • Current pick-up sens. (0..65535) Current pick-up sensitivity in uV/A: LTS-25NP: typical 25000, ACS750-50: typical 40000.
  • Suspended action (0..2) Writing a value different from 0 (idle) in this parameter force the charger to restart a selected action when powered up: 1: charge, 2:discharge
  • First hello line (ASCII) First line of the “Hello message” displayed by the charger when powered up. This string has a length of 16 characters.
  • Second hello line (ASCII) Second line of the “Hello message” displayed by the charger when powered up. This string has a length of 16 characters.

Change single profile parameters

This page allows to read/modify the individual profile charger parameters (the parameters that can be changed profile by profile).

The “READ from CHARGER” button reads all the parameters on this page from the charger and display the data. The “WRITE to CHARGER” button writes the data displayed (eventually edited by the user) into the charger. The small progress bar below the buttons shows the progress of the commanded action.

Important: the write operation is composed by a write and a successive read in order to re-display (for check) the data entered by the user, giving a feedback of the charger status.

The following is the list of the profile parameters that can be customized:
  • Cell chemistry (0..3) Type of cell chemistry for this profile: 0:NiCd, 1:NiMh, 2:LiPo, 3:SLA.
  • Cell capacity (100..25500) Capacity of the cell pack, expressed in mAh. To be specified in multiples of 100mAh.
  • Number of cells (1..19) Number of cells or series elements.
  • Charge current (0.1 .. 25.5) Charge rate, specified as multiplier for the capacity. A rate of 1.0 cause a charge current equal to the capacity expressed in mA. Typical value 1.0: very few batteries allows a charge rate greater than this limit.
  • Discharge current (0.1 .. 25.5) Discharge rate, specified as multiplier for the capacity. A rate of 4.0 cause a charge current equal to 4 times the capacity expressed in mA. Typical value 4.0-6.0 in order to discharge a full charged battery in 10-15 min.
  • Charge peak inhibit. (0 .. 255) The charger inhibit the delta peak control for this specified number of minutes after the start of the charge. Typical value from 5 to 10 min, increase in case of batteries not used for very long time.
  • Cutoff NiCd (0..2550) Minimum voltage for the discharge process expressed in mV/cell. The discharge will terminate when the battery pack voltage is under the (Cutoff*Number of cells). Typical value 700..900 mV.
  • Cutoff NiMh (0..2550) Minimum voltage for the discharge process expressed in mV/cell. The discharge will terminate when the battery pack voltage is under the (Cutoff*Number of cells). Typical value 900..1100 mV.
  • Cutoff LiPo (2500..3500) Minimum voltage for the discharge process expressed in mV/cell. The discharge will terminate when the battery pack voltage is under the (Cutoff*Number of cells). Typical value 3000mV.
  • Cutoff SLA (1500..2500) Minimum voltage for the discharge process expressed in mV/cell. The discharge will terminate when the battery pack voltage is under the (Cutoff*Number of cells). Typical value 2000mV.
  • Delta peak NiCd (0..255) Delta peak (mV/cell) used for the costant current charge finish. Typical value 5..10mV.
  • Delta peak NiMh (0..255) Delta peak (mV/cell) used for the costant current charge finish. Typical value 3..7mV.
  • Max. voltage LiPo (3500..4500) This voltage represent the maximum voltage(in mV) of the cell in the charge process. At this point the charger switches from constant current to constant voltage charge method. Typical value 4200mV.
  • Max. voltage SLA (2000..3000) This voltage represent the maximum voltage(in mV) of the cell in the charge process. At this point the charger switches from constant current to constant voltage charge method. Typical value 2500mV.
  • Final curr. LiPo (0..255) This parameters is expressed in % with respect to the initial charge current, and is used by the charger to stop the charge when in constant voltage mode. Typical value 3..20%.
  • Final curr. SLA (0..255) This parameters is expressed in % with respect to the initial charge current, and is used by the charger to stop the charge when in constant voltage mode. Typical value 3..20%.
  • Maximum charge (0..255) This parameters is expressed in % with respect to the pack capacity. The charge will stops when the charger has passed this capacity to the cells. Used as timeout (typ. value 120) or to shorten the charge time (with not full battery charge) (typ. 70-80 for 45 min. LiPo charge)


Display Manager SW

A short reference for the display manager

The Universal Charger "Display Manager" software usage is very easy but some point must be evidenced in order to get a very quick startup. Please refer also to the user manual of this software released in the files directory.


COM port selection

The first step is to choose the serial port for charger connection: the COM1 - COM16 ports are displayed on the right bar, with in evidence only the ports available and active on the computer. Select the port that is phisically connected to the charger clicking on the name. Once selected the serial port the user can go to display the curves.


Program parameters adjust

Edit the Universal_Charger.ini file, putting the correct values for the hardware used: this is important to show on the screen the correct values.

Universal_Charger.ini:

[Parameters]
R5=47000
R6=12000
Current scale=25000

The R5 and R6 values are in Ohm, the Current Scale is in uV/A and the typical value of sensitivity for the LTS-25NP (Isens) current pick-up is 25000uV/A.
For medium accuracy put the values as defined in the characteristics of R5,R6 and current pick-up. For high accuracy put the values as displayed in the “General manager SW” after the initial calibration process, performed directly on the charger, as described in the “Firmware user manual”.


Display charge and discharge processes

This page shows the charge and discharge curves from the data output from the charger. The connection can be established at any moment, the action on the charger and/or the PC program can be launched in any sequence.

The serial data stream come out from the charger only during the charge and discharge process.

The three main panels shows the voltage, current and capacity charged (or discharged) from the battery pack. The actual value of these 3 panels is replicated on the bottom part of the window, with the same precision and digits as displayed in the charger. The horizontal axis of the panels is the time in seconds.

The “PWM drive” value is the driving of the charge (or discharge) mosfets during the charge (or discharge) phase (maximum value is 1023, for 10-bit PWM). This value is useful to evaluate the capability (and the safety margin) of the charger to sustain a defined charge (or discharge) current.

In the right portion of the screen, below the COM ports there is the “RECORD on FILE” button. When the user press this key is created an ASCII file that contains all the data coming from the charger. The name of this file is automatically generated:

Monitor_hhmmss_DDMMYY.txt

Where “hhmmss” is the time and “DDMMYY” is the date of the key hit. When the key is pressed a second time, the file is closed and ready to be open from the user. The content of the file is the following:

Current; Voltage; Capacity; Minutes; Seconds Drive
2.00; 7.115; 1.9; 0; 7; 817;
2.00; 7.115; 1.9; 0; 8; 819;
2.00; 7.115; 2.0; 0; 8; 819;
2.00; 7.115; 2.0; 0; 8; 819;
2.00; 7.115; 2.1; 0; 8; 819;
2.00; 7.115; 2.1; 0; 8; 817;
2.00; 7.115; 2.1; 0; 8; 819;


and each line is sampled every 16*5ms = 80ms. The format is easily importable in the spreadsheet programs to evaluate the charge or discharge characteristics by macro or direct calculation.

The “Action started from” field represents the duration of this action (from the charger point of view), expressed in minutes and seconds.

The “Clear” button cancel the main panels and restart the visualization of the curves.


Charger hardware


A new hardware implementation for the Advanced Charger or Universal Charger (the two firmwares are completely compatibles) is proposed on this page. This new hardware has the same basic functionning of the old versions but overcomes some limitations and add some new features. The main blocks of this new hardware are the following (at the end of the hardware development I will publish a detailed illustrated "book" on how to build an "Universal Charger"):


Charger enclosure

The selected charger enclosure is the 1598ESGYPBK from Hammond. This case has a dimensions of approx. 160x160x80mm, sufficient to contain the charger (with included DC/DC converter), the display and keys, the heatsink and the fan. There is also the possibility to put inside the AC/DC converter in order to have a complete solution from the 220V. This case is composed by two parts (upper and lower) and two panels (front and rear). The two panels are not used for charger building because they will be substituted by a pre-milled PCB of the same tickness, realized together the PCB for electronics mounting.


Charger front and rear panel

These panels are the front and rear of the charger. They substitutes the ones shipped with the 1598E case. This panels are fabricated in FR4 with 1.6mm thickness (the same of 1598E panels) and finishd with a black solder resist in order to give the same estetic effect that the original pieces. An adhesive label will be developed for better front panel estetic result.
The front panel has the milling for:

  • 16x2 display with led backlight
  • 2+2 - 4mm socket for battery force and sense connection
  • 4 keys, round shaped with a diameter of 12mm
  • One D-sub 9 pin female (socket) connector



The rear panel has the milling for:

  • 70mm,12Vdc fan cooler
  • 2 - 4mm socket for 12VDC power supply
  • Air inlet port for heatsink forced cooling






Charger front PCB (display, keys and connectors)

The front PCB is designed for display, keys and connectors mount. The front PCB will be fixed to the front panel with 4 screws M3 and the right spacers fro display and keys alignement are the types of 10mm height . The front panel PCB has these main components:

  • Display generic, 16x2, 80x36mm, 16 pin connector upper-right
  • Keys MCDTS-2 from Multicomp. (Farnell 9471650)
  • Blue key cap, for UP/DN keys. (Farnell 9561528)
  • Green key cap, for OK keys. (Farnell 9561501)
  • Orange key cap, for RESET keys. (Farnell 9561498)


Other components are the D-sub 9 pin connector (socket) and a 5W 47Ohm resistor for display backlight (LED type).



Charger main PCB

The charger is directly derived from the Advanced Charger. The grounding diagram has been improved allowing the analog to digital conversion to be referenced directly on the battery negative pole. The current and voltage measurement are performed using a 4 separated wires.
The main parts are the following:

  • PIC16F876A PIC microcontroller clocked at 20 MHz, 5 MIPS effective rate
  • Discharge mosfet (TO247) and Charge mosfet (TO220) can be generic type
  • Current pick-up: the PCB is compatible with both LTS25-NP and ACS750
  • MAX232 or equivalent for serial communications
  • Generic electromagnetic buzzer with a diameter of 12-14mm and pin spacing of 6 or 7.6mm.
  • The main PCB for the charger is a single sided, 1.6mm tick printed circuit board.





Heatsink and fan cooler

The heatsink and fan cooler are a very important assembly for the performances of the charger. The selected heatsink is a standard extrusion from Aavid thermalloy, fixed with spring fasteners to the mosfet case (no screws and no holes). This heatsink as a thermal impedance of 0.44 celsius degrees/Watt (in forced air cooling) allowing the dissipation of about 300W. The fan cooler is 12Vdc type, generic brand, 25mm max tickness, 70mm overall dimensions capable to an air flow of 900l/min.



Availability of the components

The most "difficult to find components" will be available directly from this website. In a few weeks we can provide the following items:

  • Enclosure 1598ESGYPBK
  • Front and rear pre-milled panels
  • Front and Main single sided PCB
  • Keys and key caps
  • ACS750 current pick up


Front Panel

Assembly of the charger front panel
We can start to assemble the front panel from the PCB that constitute the panel itself. The new idea in this case is to realize the panels (and its cutouts) with standard PCB panels, without copper traces. It is sufficient to specify with a simple line the profile of the panel and its cutouts and all the web PCB realization services are able to deliver a well finished ready to use panel. For this purpose the GERBER and DXF files are included in the Universal charger assembly file, downloadable from this website. The panel has the cutout for display (16x2), for keys, for the D type connctor (serial communication) and for the 4mm-type sockets for battery connection. The 4mm sockets used are quite large, but the milling is compatible with some other connetors type (FARNELL 871760 e 1176427) and/or found on some eletronic stores. The sockets spacing is 19mm, the standard measure if someone want to connect a shunt between the force and sense connection and use a single wire for battery. The 4 wire connection is preferable because intrisically more accurate eliminating the voltage drop on the cables at high charge or discharge currents. The photo shows the "naked" version of the panel: the user can personalize the aspect using an adhesive label.
This photo shows the panel internal face with the 4mm-type sockets in place. This type of sockets (this version) has a small contact for wire soldering (down oriented), the economical types allows the wire to be soldered directly on the connector body.
Now we start with the assembly of the PCB. This circuit is "U" shaped in order to be fastened to the front panel and to allow the connection of the battery connectors. The first thing to solder is the 16x2 display: the dimensions are 80x36mm and the type is compatible with the APEX rc162051 yfhlyb. Equivalent displays are availables from some other brands or unbranded: the mounted one, for example is marked "Wintek Corp." and WM-C1602M-7GLYc. The display is simply put on the PCB surface making the electronic contacts with 16 wires (or 2.54mm stripe): important to put the display close to the PCB in order to have the right height of the overall assembly (10mm). Then we sold the keys (FARNELL 9471650) with blue covers for "UP/DOWN" (FARNELL 9561528), with green cover for "OK" (FARNELL 9561501) and with red cover for "ABORT" (FARNELL 9561536). Obviously all the colors for keys are equivalent, the only constraint is to follow the panel colors.
Then we mount the 5W, 47 Ohm power resistor for display backlight. The optimal lighting is btained with a voltage of 4.2V on the display LEDs with a current of 150-160mA. Calculate the right resistor with your power supply, the 47 Ohm value is OK for the range 10-18V. Take care for the dissipated power supply on the resistor, soldering the resistor up the PCB with a distance of 0.8-1.2mm.

The other components on the PCB are the connectors: DEM9S (socket) for serial communication and flat cable for panel connection to the main PCB. The DEM9S connector is soldered on the PCB using the (straight) pins, then fastened using the two spacers. The height of this connector is compatible with the overall assembly height. This type of connector allows the usage of female/male serial cables with NO inversion on the 2-3 pins of the wiring. The flat connector is an IDC (insulation displacement connector) type, the type that can be mounted directly on the PCB (FARNELL 1298771): the standard male/female solution is not compatible with the overall assembly height. The economical way is to sold 20 separated wires between the two PCB with very care for wire ordering (pin 1 to pin 1...up to the number 20).

Image of the panel rear with the display milling showing that the display is fastened only using the 16 electrical contacts, different the 9 pin connector that is mechanically fixed using screws and nuts.
The front panel is fixed to the PCB using 4 M3 screws (with conical head - in order to minimize the impact on the front) and with 4 x 10mm-spacers. The optimal result is to make conicals also the holes on the front panel to receive the head of the screws.
The images on the right shows the spacers height of 10mm and the particular of the flat cable exit over the 4mm socket connector. The flat cable can be substituted with 20 separated wires soldered between the MAIN PCB and the PANEL PCB.

The last 4mm socket connector has the wire tab rotated in order to allow the flat cable to exit easily from the assembly. This problem does not exist if the flat is substituted with 20 separated wires.



Heat sink

The heat sink for power elements can be realized in several ways and limits in practice the charge and discharge features of the Universal charger (with the fan cooler). The heatsink dimension shall not exceed 130x70x30mm in order to be right fitted on the charger case. The figure shows the drilling plan for the heatsink, compatible with the PCB assembly. To be noted that the most critical process from the heat dissipation point of view is the discharge that deliver on te heatsink the power of the cell pack voltage multiplied for the discharge current, while the charge dissipate only the power of the difference between the power supply and the battery pack voltage multiplied for the charge current. For example, the discharge of 4 LiPo elements at 20 Amps will delivery a power of 3.7V*4*20=296W when the charge of the same batteries at 4 Amps with 20V power supply will delivery about (20-3.7*4)*4=20.8W.





The power elements must be secured to the heatsink with M3 stainless steel screws. Starting from the left we have the two discharge mosfets in case TO-247 (IRFP044 or IRFP260), then the two charge mosfets in case TO-220 (IRF9540 or IRF 9530), then the schottky diode (MBR1645) in TO-220 case. The power mosfets will be fastened DIRECTLY on the heatsink with a thermal conductive paste (VERY small tickness) and the power diode will be fastened using a isolation kit because it must be electrically isolated from the heatsink. On the heatsink will be present the battery voltage: take VERY care to not make accidental short circuit with other charger parts. Take very care also on the fastening (very tight) of the power elements on the heatsink using a proper screwdriver.



Main PCB

We can start to mount the Main PCB assembly from the resistors and capacitors. The rear side of the PCB is "U" shaped in order to accept the 70mm fan cooler mounted very tight to the heatsink. The PCB is a single side, easy to produce and procure exactly as the other PCB on the Universal Charger. The resistors values are not critical the only important aspect is that the values on the input differential stage (R5,R6,R25 and R26) must be matched (R5=R25 and R6=R26) in order to maximize the differential amplifier performances. All the capacitors (except the two 15-18pF for PIC oscillator load) are 100 nF multilayer ceramic type.
Then we mount the IC sockets (28 pins for PIC, 16 pin for MAX232 (or equivalent) and 14 pins for LM324). Together we can mount th NPN transistor (BC 337 or equivalent), the two 1N4148 diodes, the contrast adjustement trimmer, the 20MHz PIC crystal and the small strip connectors.
Then we mount the TO-220 regulators and transistors, the small capacitance electrolytic capacitors, the electromagnetic buzzer and the current pick-up. Very high care in the positioning of the polarized components, see the reference marking on the top silkscreen of the PCB. The LM7812 (U54) regulator must be mounted only in case the power supply exceed the 15V and we use a 12V fan cooler, in case of power supply lower than 15V the pin 1 and 3 of the regulator must be shorted together. For large power supply voltages (greater than 18-20V) a separate heat sink for 7812 and 7805 must be mounted.
This particular shows the circuital alternative that allows to mount the two current pick-ups, the ACS 750 (752 or 756 are good) from Allegro Micro or LTS25-NP from LEM. The ACS 750 has a bigger sensitivity (40mV/A versus 25mV/A of the LTS25-NP), is cheaper than the LTS device and very easy to mount not requiring a separate high current wiring.
The last two components are the big electrolytic capacitor for power supply regulation and the complete assembly of the power heatsink (not shown). This last phase complete the Universal Charger assembly.


Rear Panel

The rear panel of the Univeral Charger is mainly constituted by the PCB that is the panel itself. All the millings are realized using a standard PCB realization service and all the files for this realization are included in the manufacturing files. The millings presents on the rear panel are for air inlet and outlet, for 4mm socket (power supply) and for fan cooler fastening. The 4mm type connectors used are quite large but the millings are compatibles with more cheaper types (FARNELL 871760 and 1176427) and with some other unbranded types. The fan cooler is a 70mm, 900 liter/min (31 Cubic Feet Minute) from SUNON the KDE1207PTV1, this type has a tickness of 25 mm. In case of less power dissipated (discharge current of 5-10 Amps) is sufficient a 60mm fan cooler more easy to find and cheaper. In case the internal heat sink has a depth greater than 30mm is sufficient to find a fan cooler with a total tickness of 15 or 20mm. The best performances are obtained when the fan cooler air outlet (typically the face with the printed marks) in direction of the charger external side (see figure).


Final assembly

The final charger assembly is started from the already mounted 3 assemblies for front panel, rear panel and main PCB. The Main circuit is connected to the front panel with the 4 battery wires (force and sense for battery positive and negative) of at least 2.5 sqmm or greater (preferred 4 sqmm), and with the flat cable for display, keys and serial communication routing. The rear panel has the power supply wiring of at least 2.5 sqmm or greater and the two wires for fan cooler supply. Keep at minimum all the wirings in order to maximize the charge and discharge capabilities.

Then the 3 assemblies are fitted in the plastic enclosure, the 1598ESGYPBK type from Hammond, without the aluminium front and rear panels. The front and rear FR4 panels are fitted using the small guides on the enclosure. The assembly is very easy and require only to flex the cables in order to fit all the assemblies inside the box.















And hereafter attached some views for the final assembly taken from different point of view:





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UNI_manager.zip
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UNI_manufacturing.zip
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UNI_source.txt
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