So far I've been using a big, bulky, not very portable DC power supply to charge my portable N64 because it charges at about 800ma and that's the only 12v PSU I have that can supply enough power (if it gets too little ma, it doesn't fully charge). But I just found a smaller wall wort that's 12v 830ma but it's AC. I could easily change it to DC with a bridge rectifier but wouldn't that make it oscillate a bit without any extra filtering stuff? Would that be bad for charging NiMH or would it work?
AFAIK, all it would take is a capacitor to completely smooth out the signal from the bridge rectifier.
If you feed 12v ac through a bridge rectifier you wont get 12v out the other end, youll get about 10.6v due to the voltage drops of the diodes. Appart from that, at 800ish ma youd need a very large capacitor to smooth the voltage to something like constant. Have a look for a switch mode wall wart, theyre not too expensive and will be able to supply more current. Moriquendi
Almost, but not quite. After the bridge rectifier and capacitor you'll get 12V * 1.414 - (2*0.7) = 15.568V. There'll be a small amount of ripple depending on the capacitor, but it'll still be above 12V.
I don't think batteries mind being charged with crude DC, providing the average current is in the right range to avoid over-heating. Taking an extreme case, most lead-acid battery chargers are generally just a transformer & rectifier, no smoothing at all. The main value of a capacitor will be to lift the average (RMS) voltage to nearer peak level, as said you need more than 12V to charge a 12V battery. Your problem is getting a safe charge current from an unknown PSU. Needs an ammeter in circuit to check what's happening.
That will be the peak voltage true but in terms of usable voltage you have to work from the RMS which gives about 10.6 as i said. Moriquendi
If you have the bridge rectifier on it's own, yes, but as soon as you add the smoothing capacitor the usable voltage is just under the peak RMS.
peak rms makes no sense, the peak voltage is the highest voltage the wave will ever reach while the rms voltage (Root Mean Square) is a form of average, it is constant for a particular peak value and can only be accuratly applied to a sine wave.. The smoothing capacitor does 'store' the peak voltage reducing the ammount that the output voltage varies (the ripple voltage) Moriquendi
