[marklivia]

I've got a couple of battery powered pieces in my system and was thinking of using larger batteries for both of them. On my dac I already went from 1.2 AH to 5 AH and noticed a difference. My questions are regarding the use of caps on the batteries. 1) Are they needed and what exactly do they do? 2) How does one determine which caps, values and how are the placed in the circuit?
I'm thinking of going from 5 AH to 100 AH on my amp and from 5 AH to 18 AH on my dac.  Thanks,  Mark

[JoshK]

I think the cap is to filter out the HF noise that batteries generate.  It might also have something to do with impedance of the battery banks, but I don't really know.

[woodsyi]

On another thread a while back I got some answers.  I hope it helps.

http://www.audiocircle.com/index.php?topic=29196.0

[marklivia]

Thanks for the replies so far. Does anyone know how to determine the values needed for the caps?

[rajacat]

I think that the caps hooked up in parallel are to provide a reserve for surges in demand which could overwhelm undersized batteries. I power my Trends 10.1s with batteries and I soldered (12) 1500uf electrolytic caps between the positive and negative poles of each battery for my independently DC powered amps. There was a thread on Audiogon somewhere that discussed this issue. I'll try to find it.

--Roy

[richidoo]

When mikorsmith's Altmann DAC came around on tour last year, mgalusha had added a switchable (10k uF?) cap to the power cord. We couldn't hear any effect. We were using a optima 800Ah battery, maybe it is quieter than traditional lead plates, or maybe the capacity gives more headroom so the cap makes less difference. Mike's SLA motorcycle battery that came with the DAC was dead so we couldn't try the cap on that battery.
Rich

[marklivia]

Thanks Rajacat, it would be great if you could point me in the right direction.  Mark

[jules]

Hi Mark,

have a look at this:

http://www.audiocircle.com/index.php?topic=17661.msg157273#msg157273

to quote Hugh in part:

Batteries are very interesting devices.  They are not quite what people imagine them to be;  there are other issues when powering amplifiers.  While noise is not an issue as it is with AC supplies, the source impedance of lead acid gel cels increases abruptly from 10KHz with frequency.  For a Class A this is not a problem (though energy consumption is, of course), but it is anathema for a Class AB, where short, fast-moving stabs of current are extracted from the supply.  The rising impedance with both current and frequency is an issue, resulting in current starvation at the output stage unless an inordinately large battery is used, and this forces an unpleasant situation.  You have to use storage caps, just like an AC supply.

jules

[DaveC113]

I noticed an improvement using caps on my Optima when powering the Trends amp. I used 6 2200 uF Nichicon electrolytics, and a couple of random film caps I found at the surplus store. The main effect was that it makes the frequency response more extended, especially the highs. I also got a surplus linear regulated power supply, which was just as good as the battery with caps, and less of a hassle. 

[Gordy]

When mikorsmith's Altmann DAC came around on tour last year, mgalusha had added a switchable (10k uF?) cap to the power cord. We couldn't hear any effect. We were using a optima 800Ah battery...
Rich

Yes, it was a 10k uF cap!  I took the small battery (7ah?) set-up to a NY Rave where we did some a/b'ing with the cap and most didn't pick out a difference, though one listener was quite definite that he preferred the sound without the cap.  In my own system I never did find a preference.

As for amps, I ran UcD400 hypex modules with individual 48v battery supplies for over a year, direct comparisons with and without ~10k uF per rail (Bruno's recommendation for linear supplies iirc) proved the need for caps imo.  Can't say the upper freq. was extended (50+ y.o. ears), though dynamics were nicely enhanced. 

[JoshK]

I too ran some UcD 400's off the same battery packs that Gordy tried.  I never really took it to the extent that Gordy did, but there was something always odd about the sound as I had it set up.  I couldn't place my figures on it but it sounded really artificial.  Maybe I am just used to noise.  But Hughes' explanation above makes some sense to why it might be, although I was using storage caps.

In the end it wasn't worth the hassle, but I may try it again some day as I still have the battery packs.