DIY Battery Power

[JoshK]

OK, I'll bite.

Or you could do like I do and run the UcD400 modules off of 8 12V7ah SLA batteries and a bank of smoothing caps.

If you want to start a new thread about DIY battery power please do so. I think you'll get some very interesting input from our resident power application engineer.

Interested to know Jon's take on battery power in the DIY realm. My own application involves power UcD400 modules off of two APS battery packs ($25/ea on surplus market) which have 4 12V7ah batteries in each and a battery charger. Together they provide the +54/0/-54V rails which derates my said UcD400s a bit as they call for 52V-62V iirc on the rails. This is a non-issue as I am using them for active multi-amping so I do not need 400watts into 4Rs they are spec'd to deliver.

I am still using a bank of "smoothing"/bypass caps, so the SLAs only replace the transformer and rectifiers. In my case 4 channels (mids/highs) are off of SLAs, while the woofer amp channels are off of the grid.

I am curious to know your thoughts on battery power.

[Paul Ebert]

So, how long can you go on a charge or does it charge while in use?

[JoshK]

Actually mine are not quite done, need to finish drilling out the back panel of my case before I finish wiring it up. That said, another buddy of mine did the same thing. He said running his 86db speakers (devore gibbon 8s) he was getting 10-12 hours before voltage had dropped from 54V to 50V and the recharge time was < 20minutes. So not the big hassle some battery powered DIY gear is.

[Dennis H]

Do you need the caps? Batteries are basically giant electrolytic caps and there is no AC ripple that needs to be smoothed unless you are running it with the charger on.

[ThomasW]

Here's a graphic I snagged somewhere (DIY Audio Forum?) showing how 'clean' battery power is .... :wink:

[Occam]

Lucy.... you got some splain'n to do......

Could it be? I do believe that is the famous ALW (who 'appropriated' and makes a Jung/Didden regulator boad/kit) 'scientific' study, that has circulated thoughout the internet. He never did respond to why it has that unusual spike at 50hz and its harmonics (he lives in England).
Luuuucy.... you got some splain'n to do.

[Bent]

Is that into a load, or open circuit?

[Dennis H]

Luuuucy.... you got some splain'n to do.

No sh*t, Sherlock! How does a battery create AC at any frequency? I don't buy that graph for a second unless he's measuring with the charger running. Probably European power and a switching charger given the big 50Hz fundamental and all the HF garbage.

[JoshK]

Do you need the caps? Batteries are basically giant electrolytic caps and there is no AC ripple that needs to be smoothed unless you are running it with the charger on.

Not running with charger on. I have just heard from a number of sources that it subjectively sounds "faster" with bypass caps. That was my only rationale, but I added quick connects so it is no trouble to bypass the bypasses :lol: to make a comparison. Hell I got some 4pdt switches....hmmm...

[ThomasW]

I looked around and found the text that went with the graphic

The plot below is the noise of a sealed lead-acid gel-cell (Yuasa NP series) under no-load and resistive load conditions. For comparison there's a discrete regulated supply. The resistive load represent about a 35mA current drain - it gets worse with increasing load current. Even more inportant the noise doesn't stop when a heavy load is removed, it takes seconds to settle, presumably due to the chemical reaction going on inside the cell.

[Dennis H]

I really question his measurement and/or his shielding methods. If he's in Europe (220V, 50Hz power) and the biggest spike of the "battery noise" is at 50Hz, I think that that tells us something. GIGO.....

[JoshK]

I really question his measurement and/or his shielding methods. If he's in Europe (220V, 50Hz power) and the biggest spike of the "battery noise" is at 50Hz, I think that that tells us something. GIGO.....

Something is definitely fishy. :??

[Occam]

He blinded me with SCIENCE!

Given Mr. Andrew L. Weekes' resounding silence when queried about those anomoulous harmonics on his graph, first posted on DiyAudio, I didn't even bother to ask my question about the condition of the SLA battery. Any SLA that has not been properly maintained is going to have a large amout of hard sulfation, and is going to be as noisey as all get out.
I frankly believe Mr. Weekes was not an 'honest broker', as he obviously has his own agenda (don't we all?). Why no 10uf low esr cap with .1uf metalized polyprop accross the battery? While I don't expect peer review journal quality, that graph and his explanation doesn't qualify for a juniior highshcool science fair project.
That being said, SLA batteries are not a noiseless solution. Any electochemical reaction is going to generate some noise. They need proper passive bypassing, as well as proper maintainence which is rarely provided by typical rechargers. Do a google search on 'desulfator'. But they are keen for low voltage single rail applications, dacs, flea power switching amps..... otherwise I prefer a proper grid sourced supply, with that obligatory balanced power ( I did say we all have our own agendas, didn't I?)

[Paul Ebert]

So, um, Josh... might I persuade you to share info about the batteries? Like, part numbers and where I might be able to purchase a set? This might make the subwoofers I've been contemplating doable.

As to the graph, I never could make any sense of it (but then, I'm a software guy). I would love to see some confirmation and/or an explanation of what's going on.

Paul Ebert

[JoshK]

Unfortunately, when we went back to purchase more (diy buddies & me) then we all bought out. Occam actually had bought these packs and sold them to me as he scrapped his idea to use them. I wish I could point you to where you could also get them but I'm afraid I can't. You could purchase SLAs individually and a charger but that isn't nearly as inexpensive.

[JoshK]

I am still interested in Jon's take on the matter.

[JonMarsh]

Not running with charger on. I have just heard from a number of sources that it subjectively sounds "faster" with bypass caps. That was my only rationale, but I added quick connects so it is no trouble to bypass the bypasses :lol: to make a comparison. Hell I got some 4pdt switches....hmmm...

Batteries by themselves are not the same thing as large electrolytic caps- in fact their intenral impedance, depending on time, charge state, and noise generation, are substantial. Running with the external capacitors is a VERY good idea, the more the merrier. Don't forget to use some good low impedance film types, too, preferably a number in parallel.

Look at the batteries as a way to charge the caps, without the noise issues from more conventional approaches (AC line bridge rectifiers, swithing power supplies, etc).

OTOH, a good choke input supply, aside from the expense and size (which is not that dissimilar from using any type of battery support), can be just as low noise. It doesn't have the "UPS" functionality of batteries, but then it doesn't have the maintainence issues, either. So if operating only when AC power is available is OK, that's the approach I tend to prefer.

This technology approach was used in the Ayre V3 and V1, and in some custome designs I've done for some people, as well as in Cello amplifiers.

~Jon

[JoshK]

Thanks for your feedback Jon. That is what I was thinking, it had to do with impedance, but I didn't know for sure and didn't look it up.

Excuse my ignorance but with a choke supply, where does the choke go in relation to the caps? Is that a CMC?

[Cowanrg]

Josh,

can you explain a bit more about how you wired everything up? the charger charges at 12v, right? but the batteries are wired as +-48 or so. how is that all wired up?

[JoshK]

Well my battery packs are ADS banks made for computer backup I beleive. I got them from a surplus site that no longer has any more. You need to use 2 packs and tie the pos from one to the neg from the other to derive -48/0/48V. Each pack has 4 12V 7ah SLAs. I couldn't honestly tell you if the charger is working at 12V or 48V (though I could look it up for you). I know the packs come already configured for 48V output (~54.5V fully charged). The packs also have a low voltage alarm and a bunch of other safety and informative features built in so it is pretty mindless to maintain.

I just got it all wired up yesterday before an audio gathering meeting. I just didn't have the right connectors so I haven't fired it up except to test all the voltages.

[JoshK]

Jon,

Do you have a choke input supply schematic somewhere that I could have a look at to see what is going on? Just something representative not necessarily any specific one.