using nimh or nicad batteries for sonic t amp.

[michelevit]

Power supply for sonic t amp questions.

Just want to say thanks first for all the great advice that I found while lurking here. I went ahead and built up my first sonic t amp and it has been a fun project. I am currently housing the amp in a medium sized project box. I am using a 7-amp hour sealed lead acid battery and charging it from a harbor freight charging unit. The charging circuit is switched so I turn it off when listening to the amp.



I am now going to be building up another Sonic Tamp and have a bunch of AA sized batteries. I know they are 1.2 volts each, so if I 10 of them from end to end I should have 12 volts right? What I was wondering what the amperage would be? They are each rated for 2000 mah, which is 2 amp hours each? If I wire them in series, would I add the amperage? Would the amperage be 20 amp hours? These are Nickel Metal Hydride batteries. This amplifier powers 2 speakers in my home theater and needs to run for no more than 4 hours at a time. We only watch movies maybe twice a week at that.

I know this is an elementary question, but its been a while since my physics electronics class. Also what is the best way of charging this? Would this charger that I use now from harbor freight work with the Nimh batteries.

http://www.harborfreight.com/cpi/cta...emnumber=42292
I can purchase this charger from the wlak in store for less than 5 bucks!

Thanks for the reply in advance. I am hoping to use the batteries and chargers because this is already what I have laying around.

[Tweeker]

Yes, 2000mah is two amp hours, series wiring will not increase amperage, it increases voltage. If they are 1.2V and not 1.5V you could use up to 11 in series (13.2V is fine).

You could also use two strings of batteries in parallel for more mah and current delivery power, ei 2*11. Not sure on the charger, but Id really preffer one for 1.2V batteries.

[michelevit]

is there any advantage to using the AA nicads or nimh
over the more common and larger sealed lead acid?

Weight isn't too much of a concern. I can pick up
a nice panasonic 7amp/hour sealed lead acid
from my electronics surplus store for less than 15 dollars.

just wondering if power from the nicads would be cleaner and faster.

[davidsrsb]

Batteries are noisy, see http://www.tnt-audio.com/clinica/reg..._noise4_e.html
It appears that the change in series resistance of a batery as it discharges is really a smooth curve but actually a series of steps

[scottw]

Batteries are noisy, see http://www.tnt-audio.com/clinica/re...s_noise4_e.html

The bottom graph on that link is suspect because of the 50 Hz spike (and harmonics) from the "battery". There must have been some line voltage leaking in somewhere/somehow.


From the linked site:

several batteries were wired in the test amplifier's positive supply (pink traces in the plots). For reference the bypassed LM337 was used for the negative supply (blue traces).

I'm no EE but to test supply noise and use batteries on one rail and a regulator on the other rail of an amp(looks like at the same time) doesn't seem right. The rails could easily have an effect on one another.

And that only leaves the graph of the "waveform of the battery's output voltage", which is interesting and shows some dips at about 37Hz(?) but doesn't indicate magnitude. Not much to hang your hat on.

I haven't tried batteries on digital stuff, yet. Maybe look into Hawker/Cyclon batteries, spiral wound lead-acid type. Some, far more knowledgable then me, have suggested that these batteries have a lower internal resistance, and perhaps better for audio, than standard plate type Lead-acid batteries.

scottw

[Tweeker]

Some extra capacitance would help with "faster" for transients.

[michelevit]

thanks again for everyones help.

so looks like i'll be sticking with the more common larger
lead acid battery.

any suggestions for a capacitor? the electronics store in my town has lots to choose from. any specs that i should be looking at and
any that i should avoid?

thanks again.

[Narcisse91]

Originally posted by michelevit
is there any advantage to using the AA nicads or nimh
over the more common and larger sealed lead acid?

Weight isn't too much of a concern. I can pick up
a nice panasonic 7amp/hour sealed lead acid
from my electronics surplus store for less than 15 dollars.

just wondering if power from the nicads would be cleaner and faster.

Although it looks like you've already gone for the lead acid in your last post, just to add some info about batteries...

NiCads are picky about how they're recharged. They suffer from voltage depletion if they are not discharged fully and recharged fully, so if you're flipping it on and off, they won't like that.

NiMH are more tolerant of that, but they don't do well being constantly discharged and recharged. They overheat easier, and the heat causes voltage depletion problems. Continuously discharging and recharging without significant time to cool can cause problems.

I tend to see NiMH with higher capacities (larger mAh), but NiCds can typically deliver more peak current, which may be better for a stereo application. Depending on the NiCd in question, and the lead acid in question, however, you will probably get a ton more current on demand from the lead acid. It will also be more durable, and probably more cost effective. Just heavier.