The Zero Fossil Fuel Constant Current PWM v2.1

This is a slightly modified version of the first PWM. The basic circuit is the same. Some component values have changed. And it's layed out specifically to fit in a Velleman G106 sealed die cast aluminum enclosure measuring 4.5" L x 2.5" W x 1.25" H. Bud and Deltron also make very nive die cast aluminum cases.

Circuit description:

U1 is a LM324N quad op-amp. U1A and U1B form a triangle wave generator. The output voltage swing is approx 1/3-2/3 Vcc. The output is fed to comparator U1C which turns it to square wave based on the threshold voltage at pin 10. The duty cycle threshold is set by VR1. R6 and R7 are calibrated to give full range duty cycle adjustment of VR1. The voltage reference for R7 is normally held at Vcc by the output of current limiting error amp U1D. Gain is set at 1000 (subject to change depending on how stiff I want the current to limit). Any time the source of Q1 draws current a voltage drop occurs across R12. 40 amps will give 120mV, the max setting on VR3. If the voltage drop across R12 exceeds the preset value of VR3, the comparator drops the PWM duty cycle until the average is just less than the preset value. C4 ensures that the current limiting is average not peak.

R12 is a 4.5" piece of 16ga stranded speaker wire or appliance power cord. One end is shorted together. The two leads at the other end are connected to the Source of the MOSFET, AT THE SOURCE TERMINAL, and to the common ground, AT THE COMMON GROUNDING POINT. Also, the PC board terminal at the junction of C4/VR3 connects directly to the common ground and the PC board terminal for R10 connects directly to the MOSFET Source terminal. These steps are very important to observe as unwanted oscillations and instability can occurr.

Here is your detailed parts list.   Adjustment procedure below.

Click image to enlarge

Click image to enlarge

Frequency range is 1KHz-10KHz. Max RMS current should be around 40 amps. You can elevate the max limit if you need to by shortening the wire inside that makes R12.

Pots are 20 turn. Crank the "I" pot fully CW for MAX current. Turn the "%" CW until you just hit 100%, straight DC at the output, or just a hair less. Connect to the cell. Adjust your electrolyte for the target current while cold. Rotate the "I" pot CCW until it Just starts to fold back while still cold. Done!

As the cell heats up, peak current will rise but duty cycle will fold back an equal amount to keep the RMS current constant.

PWM Parts List, v2.1 Unless noted, all resistors are in ohms, 1/4W, 5% tolerance. All capacitors are in uF, 16V minimum Designation P/N Qty Description Mouser Digi-Key Misc vendors U1 LM324 1 Quad Op-Amp 512-LM324N $0.33 ea LM324NFS-ND $0.42 ea U2 7810 1 10V Regulator 512-LM7810ACT $0.31 ea 296-21622-5-ND $0.84 ea  Q1 IRFP064N 1 Power MOSFET 512-HUF75344G3 $2.17 ea, $1.73 ea 10+ IRFP064NPBF-ND $4.12 ea, $2.748 10+   D1 MUR420G or equiv 1 Fast recovery Rectifier 863-MUR420G $0.42 ea MUR420GOS-ND$0.53 eaR12 (note 1) 0.0015 1 Wire Shunt Resistor      R14 10 / 0.5W 1 Resistor 71-RL20S-G-10/R $0.23 ea     R9 100 1 Resistor 71-CCF07100RJKE36 $0.02 ea     R10, R13 1k 2 Resistor 71-CCF07-J-1K $0.02 ea     R1, R7 1.8k 2 Resistor 71-CCF07-J-1.8K $0.02 ea     R6 3.9k 1 Resistor 660-MF1/4LCT52R392J $0.05 ea     R3, R4, R5 10K 3 Resistor 71-CCF0710K0JKE36 $0.02 ea     R2 22k 1 Resistor 71-CCF07-J-22K $0.02 ea     R8 100k 1 Resistor 71-CCF07-J-100K$ 0.02 ea     R11 1M 1 Resistor 71-CCF07-J-1M $0.02 ea     C1 0.022uF 1 Mylar film cap 598-DSF050J223 $0.19 ea     C3 0.047uF 1 Disk ceramic cap 140-100Z5-473Z-TB-RC$0.16 ea     C2, C4 47uF 2 Electrolytic cap 647-UVZ1V470MDD$0.10 ea     C5 4.7uF / 100V 1 Polyester film 5989-100V4.7-F$2.27 ea     C6 .001uF 1 Disk ceramic cap 140-50P2-102K-TB-RC$0.08 ea     C7 12,000uF / 25V 1 Low ESR Electrolytic 661-EKMH250VNN123MP$2.73 ea    

VR3 1K 1 Linear taper pot 652-3006P-1-102-LF $1.55 ea or 652-3296Y-1-102LF $2.20 ea 3006P-102LF-ND $1.73 ea   or 3296Y-102LF-ND $2.50 ea  

VR1 10k 1 Linear taper pot 652-3006P-1-103-LF $1.55 ea or652-3296Y-1-103LF $2.20 ea 3006P-103LF-ND $1.73 ea   or 3296Y-103LF-ND $2.50 ea  

VR2 20K 1 Linear taper pot 652-3006P-1-203-LF $1.55 ea or 652-3296Y-1-203LF $2.20 ea 3006P-203LF-ND $1.73 ea   or 3296Y-203LF-ND $2.50 ea  

TO-247 insulators1 Aluminum oxide wafer 532-4180, $0.70 ea     Mica     MCM 21-1170 $4.21/25

Heat sink compound       526-NTE303 1g $1.77 ea 345-1006-ND 4g $5.04 ea   CPU cooler 5C12B3 1       NewEgg $3.99 + S&H Directron $1.99 ea PC Board   1 Perf board, 0.1"x0.1" hole pattern       Aluminum Die Cast box Velleman G106 or BUD AN-1302 or Deltron 459-0020 1 Velleman US dealer locator Velleman Int'l dealer locator 563-AN-1302 $9.40 ea 400-4591 $7.32 ea 377-1101-ND $9.40 ea Cal-Centron, $8.32 eaFibre shoulder washers  For #10 screw 3 Keystone #3239 or equiv       Fibre flat washers  For #10 screw 3 Keystone #3130 or equiv       #6-32 hardware           #10-24 x 1" screws   3       #10-24 hex nuts   6      #10-24 wingnuts   3        #10 flat washers   6         #10 split lockwashers   6       Crimp lugs   3        Push-In terminals   5 Vector P/N T42-1 574-T42-1/C  $10.68/100 574-T42-1/M  $51.23/1000 V1069-ND  $11.10/100 V1070-ND

$53.27/1000    

Misc: ground lugs, binding posts, stand-offs, hookup wire. R12 is a 6" length of insulated 14ga stranded or solid coper wire. See schematic description for details.

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