driver for low volt parallelo-cell Project Page 1

my first professional-like project. i know some things are sub-par, but its built, it works, and it looks pretty nice! this houses my dc-DC converter.  last thing left to do is label input/output plugs and the pot for voltage adjust.

input to this box is automotive voltage (10-14 DCV). it steps down the voltage from 0.8 to 5.5 DCV. this is perfect for my apparatus, as raising the DCV raises my amperage. as per my other project folder, you can see the MS paint pictures for final setup and wiring. i choose to put my cells in parallel of each other in order to regulate the amperage via the input voltage.

one thing i've noticed is that the resistance of the cell changes with the applied voltage.  i was noticing that at two volts, i could barely draw a few ampheres- 3 or 4 amps max. when i stepped the voltage up to 5.0 dcv, the amperage went through the roof, 25-30 amps. well, simple math shows a difference of resistance.

@ 2 DCV:
  E      2(DCV) / 4(amps)= .5 ohms.
------
I | R

@ 5 DCV

5(dcv) / 25 (amps) = .2 ohms.

same cell, same electrolyte. tests were taken minutes apart.

it was chemelec who first made me realize this phenomenon.

well, boyce says to use 0.25 amps per sq in of active plate area. that is the highest efficiency method. if you want to drive the cell harder, use 0.5 amps per sq in.  i actually use the average of these two methods. long story short, i desire to drive the cells  @ 12 amps each.  my power supply is limited @ 25 ampheres, which is convenient the way the math works out.

i have a Voltage output adjust and a fairly accurate ammeter. i would like to put an Amp Total gauge, and another amp gauge on each cell to be sure one isnt pulling more amps than the other cell.

either way, i simply turn on my driver, and slowly turn up the voltage until the cell draws about 20 amps cold.

the best part about this system, is that even pulling maximum current into this driver, still uses less current than most electrolysers. putting out 5 DCV and 25 ampheres, this unit only draws 13.5 ampheres from the car itself. and i know the voltage will be less than 5.0 dcv, since 5.0 volts on one single cell draws about 25 amps. this is two cells wired in parallel.

these are the cells i'm driving. smacks booster style switch outlet covers spaced about 1mm apart. two positive plates on the inside, two negatives on the outside. all plates have been cross-hatch sanded and used in previous projects. the cells have a balance tube and an outlet tube. yes the one cell is not finished, its brand new. a random spark blew the housing to pieces. these containers are better than pelican cases for our purposes, since pelican cvases are almost always vented- and these are clear, cheap, and available in two sizes. this is the smaller, $6 case. maybe $7 cant reemember. available at walmart in the camping section.

i can also get a much bigger case from the BX in the photography section for $14. its come cheap china made thingy.

for bench testing, i use my radioshack 13.8DCV input, 3 amp rated power supply.

yes, its fan cooled. the manufacturer says it doesnt need any heatsink nor cooling fan, however it does get warm, to about 130*F i think. either way- adding a simple fan couldnt hurt. so i did. whenever the unit gets power, the fan is on. its pretty quiet. i had an on-off switch, but it created such a voltage drop across it, that it needed to be used in conjunction with a relay. and with the unit only drawing around 7 amps normally and 13 maximum, theres no need for all that.

turning the unit on, with the Voltage Output knob turned all the way down, the driver puts out around .8 volts.