battery power supplies

[cowanrg]

i was just wondering what everyone here thought about battery power supplies? you can buy some nice gel cell (lead acid ) batteries surplus for around $20. get a couple of them together, and you could easily power a cd player or a pre-amp for hours. and when its off, a relay switches on and starts charging...

for an amp it wouldnt be TOO wise, because power drain is too much. but from what i understand, a good battery bank could yield around 10 hours of playback before recharging. even if you had a slow trickle charger, after watching a 3 hour movie or something, it would take 6 hours to charge. BUT, you would techinically be still left with 7 hours anyway... 10 hours is a LONG time to listen to a stereo continuious. you would at least take a few hour break!

this would eliminate quite of a bit of the cost of making a higher end power supply section for a cd player or preamp, would it not? a simple battery pack could be a perfect power source, and be relatively easy and cheap to build, not to mention would rival many extreme power supply designs.

let me know what you all think!

[dlharmon]

I powered an amp off some 17AH 12V lead acids out of a UPS while I was waiting on the transformers to come. It was a SOZ so it was more like listen for an hour charge overnight. I just took the batteries to the garage and charged them with a car battery charger. It worked well. You wouldn't need much in the way of caps. For a preamp you could run for days at a time if not weeks.

Darrell Harmon

[cowanrg]

what about a cd player? do you thin that would be a good idea?

im replacing the whole power supply section anyway, so its either new caps/transformer, OR just do it battery powered....

[dlharmon]

I think with the cd it would be best just to beef up caps on the analog section. The digital can be left alone. I open up my cd (Onkyo DXC-370) and was impressed with most of the insides. The output actually was class A with some TO-220 parts on heatsinks. I was thinking of finding the output of the dac and building a new preamp, but I decided not to because it was good already.

Darrell Harmon

[cowanrg]

well, its an NAD, its already got all panasonic caps in there. it could use black gates, but thats another step.

im trying to make this as high end as i can. clock will be replaced, new PS, beefed up analog section, dampening, etc.

ill give it a though on the battery supply. allelectronics has some cheap lead acids for like $6. one or two would be fine for a couple hours of playback. could be a cheap alternative.

[dlharmon]

Originally posted by cowanrg
well, its an NAD, its already got all panasonic caps in there. it could use black gates, but thats another step.

I though it was a cheap cd player. You might want to think about building one of the diy dac's instead. I'm wanting to do that for mine.

Darrell Harmon

[cowanrg]

im actually planning on it. its a decent cd player to begin with. i wanted to start with a solid player from scratch, upgrade the mechanics (casing, transport, etc...), then electronically.

an external DAC will eventually come. thats why im pondering the battery supply. that too could power the DAC...

[kiwi_abroad]

My last DAC project used battery supplies. I used 5x 1.2AH Sealed Lead Acid batteries to produce dual +/-12V supplies to power the DAC's and the output Op-amps and a single supply for the rest of the digital circuitry. The Op-amps were connected directly to the batteries, but the DAC's had regulators to reduce it to +/-5V.
A few points:

I set the charging arrangement up so when I turned the DAC off, it really just turned on the charger, and the circuitry worked continiously. All fine except when you unplug it from the mains for a long time. I would have to open the DAC up and disconnect all 5 batteries, otherwise they would go dead flat. Not good for the life of the battery.

You will need some supply capacitance near the circuitry, as you need to lower the PS impedance at higher frequencies. All they have to do is supply power at higher frequencies, not to filter out ripple.

When rating the batteries, to improve their service life, make sure you never get them close to being discharged. A fully charged battery is 13.6V, and can be considered fully discharged at around 11.5V Don't let them go below 12V if you can help it.

Experiement and enjoy, it is a very viable option to improve performance, especially in lower powered equipment

Cheers, Adrian

[cowanrg]

sounds perfect.

i was going to do a few things...

have a trickle charger on them, so when the source is turned off (or just when the cd player or whatever is turned off), the charger initiates. basically, when off, the batteries would be completely disconnected from the player. and, when at full power, they would be disconnected from charger and player.

dual VU meters would be on the front panel, measuring both amperage and volts. this would ensure proper battery life. i would probably just overkill the batteries, so i could listen for hours without a problem.

hum, i think the cd player needs a bigger case :-)

[cowanrg]

when you say i need caps near the source, you just mean some smaller value (2200uf or so) caps right before the board, just so it reduces impedance? i dont need like HUGE values right?