Battery-powered supplies

[fdegrove]

Hi,

So you're just out for a cheap troll.

Loosing our sense of humour when it suits us, are we?

[Verbal]

Originally posted by Steve Eddy


Typical SLAs already have internal resistances well below 100 milliohms. Why would you need to add a big gob of capacitance?

se

A 12V/7Ah will typically have ca 100mOhms, not well below. And remember you'll usually have to put several in series to get your desired voltage, so this will add up. How important this is depends of course on the application, but I'd say for a class B or AB amp drawing substantial current peaks, this is more than you'd probably want. IMHO, YMMV, etc...

[A 8]

Originally posted by Verbal

A 12V/7Ah will typically have ca 100mOhms, not well below. And remember you'll usually have to put several in series to get your desired voltage, so this will add up. How important this is depends of course on the application, but I'd say for a class B or AB amp drawing substantial current peaks, this is more than you'd probably want. IMHO, YMMV, etc...

Anyone know how linear their ESR are over a wider frequency range...say 10hz>100,00kHz?

I found I needed to add both electrolyts and film caps.

[sangram]

I've always been skeptical of battery power.

Also, batteries are expensive - a single 12V 7AH SLA costs almost as much as a nice 255VA 25-0-25V transformer. Thsoe who follow my regular ranting will figure out quickly enough that I don't have access to toroids, well, I do, if I need a thousand of them.

I've been testing some new STK4191 amps using a discman. All of yesterday the tests have been through the mains adapter. Just so I could drain some Nicd AA batteries which were laying about, I powered the discman through them.

Suffice it to say that I am now looking for batteries for another amp of mine...

[vic2]

Check this out:

www.batterymart.com/battery.mv?c=sla

[Bill F.]

I don't have firsthand experience with batteries, but it seems to me that they would make excellent power supply filters.

I've been wondering about using constantly charged battery power--IOW, inserting batteries in series with the + and - of an otherwise noisy dc power supply.

Since batteries function by the relatively slow process of ion diffusion, wouldn't series batteries remove all but extremely low-frequency ripple?

If this is so, why not use a battery supply that is constantly being supplied by a simple float charging circuit? You could skip the concerns of charging cycles.

Would the batteries pass noise? Anyone ever scope the output of a battery in series with noisy DC?

[vic2]

Interesting idea but how would you implement that? If the charger is hooked up to the batteries wouldn't you get the output of your charger across the terminals and thus as your power supply.

Ion diffusion is actually extremely fast. It is charge diffusion that actually occurs, not the movement of individual ions.

Vic

[Steve Eddy]

Originally posted by Verbal
A 12V/7Ah will typically have ca 100mOhms, not well below.

Well, the Panasonic LC-R127P has an internal resistance of 26 milliohms. I don't know about you, but I'd consider 26 to be well below 100. And the higher the Ah rating, the lower the internal resistance. Their 28Ah LC-XC1228AP has an internal resistance of 6 millioms.

And remember you'll usually have to put several in series to get your desired voltage, so this will add up.

Ok, with 3 in series, that's 78 milliohms. Still nothing to lose sleep over in my opinion.

How important this is depends of course on the application, but I'd say for a class B or AB amp drawing substantial current peaks, this is more than you'd probably want. IMHO, YMMV, etc...

What's the class of operation have to do with anything?

se

[Steve Eddy]

Originally posted by A 8
Anyone know how linear their ESR are over a wider frequency range...say 10hz>100,00kHz?

100,000kHz? Do you mean 100kHz?

What on earth are you reproducing up at that frequency range?

I found I needed to add both electrolyts and film caps.

I haven't found any such need so far. Though I do use a small amount of bypass capacitance at the opamp to nullify lead inductance.

se

[Bill F.]

Interesting idea but how would you implement that?

I was just picturing two batteries, one in series with each rail of the power supply (+,-) with a seperate ground between. Sort of using them like filter caps (in addition to caps, that is).

Ion diffusion is actually extremely fast. It is charge diffusion that actually occurs, not the movement of individual ions.

So are you saying that batteries may pass higher-frequency ripple?