You can also use the 12 Volt outputs
of the supply if the 5 Volts is not driving enough current into you cell. You will have to use diodes or resistors in this case to lower
the Voltage seen by the cell or too much current will flow. The 12 Volt outputs cannot put out as much current as the 5 Volt outputs
but they are still capable of putting out quite a respectable current. Get a meter to measure the current and don't abuse the
supply. It may go into shut down mode if you draw too much current.
A good way to measure the current is to put a low value resistor in series with the line, say 0.01 Ohms. The Voltage measured across this resistor will be related to the current going through it by the formula (Ohms law!!) V = I X R, or if you like I = V/R. If you measure 0.1 Volts across the resistor there will be 10Amps going into cell. Make sure the resistor has high enough Wattage. It should have a minimum wattage = (max. likely current into cell)squared X R. You can make a resistor out of some resistance wire from an old electric fire.
It is possible to put
two of theses supplies in parallel and isolate each supply from the rest by
putting in a diodes into both leads from the supply's. You may have to use identical units (which may be hard to come by) so that
the current is shared equally between units. Do not run the combined units at the max. new possible combined current as the
supplies will probably not share the current equally among themselves.
Another alternative for using computer supplies in parallel is to connect all positives to the anode and connect each negative to a seperate Cathode. The Cathodes should be of equal size and spacing from the Anode and from each other. Diodes should also be placed in each supply to help isolate each supply and stop current being driven into one supply from another.
There is lots of info about using computer power supplies as bench power supplies(cell supply) on the net. See here
There is a useful add-on for a computer power supply here.
There is some useful constant current add-on for a computer power supply here (pdf file).
The color code for the wires is:
Red = +5V, Black = Ground (0V), White = -5V, Yellow = +12V, Blue = -12V, Orange = +3.3V, Purple = +5V Standby (not used), Gray = power is on (output), and Green = Turn DC on (input, tie to Black), Brown = 3.3v sense (tie to Orange), +5VSB (ignore).
Note about computer supplies: One thing about power supplies. In my setup a modified computer PSU works perfect. Old UNIX servers sometimes have PSUs up to 250 A at 5V. While higher output voltage of 6.4 V instead of 5 V is not really a problem, overriding the over- and under-voltage protection can be a pain. With PC-PSUs it sometimes helps to disconnect all other voltages (12V and negatives)at the rectifier diodes to prevent damage. If there is even a under-voltage protection on these you should discard the PSU and look for another one. Follow back the massive copper lines for +5V on the PCB and there will normally be connected one small line for the loop-back (voltage regulation). Disconnect this line and reconnect it with a low ohmic voltage divider (i.e 100 Ohm to ground, 28 Ohm to Output). After that modification the PSU will think to produce 5V while its 6.4 V. ;-)
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