Battery Operated Supply

It has been a wish of mine to try out battery operated supplies
i plan on using 2 12volts 7.2Ah battery to power my phonostage of opamps.
i was reading from many places that i should insert caps between the battery(jean hiraga mc ps)
the caps that are recommended 2*333mf,2*30mf, 2.2uf , 10nf
can I used this for my opa2601 ?
what is the advantage of using so much caps in the ps
how do i go about charging the battery?
since the battery a - is tied to battery b + to form the ground
this leaves + of battery a and - of battery b to supply the +-12volts
to charge the battery can i just use a +/-12 volt supply using lm7812 and lm7912 circuit capable of 1.5 amp current supply? and if this works how would the connections go ?+ 12 volts to the + of battery a and -12 volts to battery b-
or do i need a separate battery charger
 

paulb

Member
2001-06-01 4:53 pm
Calgary
What kind of batteries are you using?
If they are gel cells, you can just "float" them at a constant voltage (not the quickest, but the safest). The recommended voltage is probably 14V or so, check the manufacturer data.
If they are Ni-cad or Ni-MH, a constant voltage is not appropriate. Find some battery charger literature.
(Hint: you can buy a charger cheaper than you can build one).
Don't charge them while you're using them to power your amp.
The caps are to reduce the impedance of the batteries and are a really good idea.
 
As for the charging of the batterys, you will want to charge them while they are disconnected of the pre-amp. If you don't, you will delete any noise advantage that the battterys may give you.

If you try to charge the batterys using two seprate 12 volt chargers you may run in to difficalty over having the two isolated (you have to connect + to - remember) Also if the chargers are charging at diffrent rates you might end up with batterys at different voltages.

A far easier way to tackle the problem is to get a constant current charger that has a 24 to 28 volt supply. You leave the batterys connected end to end (-ve of batt A to +ve of batt B) like they are when you power the preamp. But then connect the -ve of the constant current to batt B -ve, and +ve of the constant current to batt A +ve. Set the current to about 600mA and the batterys will be charged in 12 hours :)

A constant current can be built buy simply getting a junkbox LM718 and putting a resistor in feedback from the output to the adjust.

Don't ask me if batterys are better though, never tried it. Caps near the op-amp are always a good idea.

Remember to always be carefull will grounds!