Battery-powered supplies

[UK Dave]

Hi

I thought I'd add to this thread.

I've been looking at the basics of battery powered Gainclones, and I'm focusing on Yuasa (NPC) batteries. Basically because they are easily available in the UK via Maplins (anybody know of a cheaper source in the UK ?).

On their web site you can download a pdf file that goes through all the fundementals of battery type, sizing, and charging methods. Although it's Yuasa specific, the basics should apply to all manufacturers.

http://www.yuasa-sales.co.uk/NPMan1.html (click on the manual)

My questions on gainclone batteries at present are.

1. 12v or 24v supply (2 or 4 batteries). Same rules apply as PSU's ?
2. Can we expect the same difference with 'dual mono' supplies as with dual PSU's. I've just assumed that because dual PSU's are best that dual battery supplies will also be the best by the same margin. Right or wrong on my part ?
3. What are the realistic life cycle of the battery supply. I've seen 500-1000 cycles being quoted, but it seems to depend on depth of discharge. Either way it doesn't seem much for a an amp and could end up expensive in the longer term.
4. Charging method and chargers.

I've done a quick search for DIY charging cicruicts and come up with the following. I haven't checked yet to see how it fits into the specs quoted by Yuasa yet.

http://www.vt52.com/diy/myprojects/other/charger/charger.htm

Also found an application note from TI discussing their UC3906 chip and charging large strings of batteries. again I haven't had time to read up on it yet.

http://www.ti.com/sc/docs/psheets/abstract/apps/slua115.htm

Sorry to drop this on you without proper research, but my time is tight at the moment and wanted to share the info.

 

[protos]

I am about to build my dual mono 24V supply for the gainclone.
I realized that the charger will have to be also at 24V and I need four of them since it will difficult to switch battery connections.
Originally I was planning for a 12v charger until I realized that this wouldn't work at all.
A dual mono 24V PS needs four times the batteries and double the chargers and charging voltage than a 12v supply. Simple isn't it?- but it is much more expensive of course.

 

[Pan]

protos

will you use car batteries or smaller ones?

/Peter

 

[protos]

How about 24v truck batteries! That should keep the gainclone going for a couple of years!
Seriously though you don't need that much amperage.The way I figure it I am playing my gainclone at between 1 and 2 amps most of the time and my four batteries per channel are 4x7AH=28Ah so -if I am not mistaken in my calculations I should have between 14 to 28 hrs continuous use without needing a recharge.

 

[Pan]

Is it really possible/wise to use up all the rated "Ah" of the batterie?

My concern is the internal resistance of the batterie though, maybe a bigger batterie have better bass and better stamina when the going gets tough?? Especially if difficult loads are used.

One other thing that makes me think about using 4 car batteries is that I´m able to listen to my rig even if/when the power is gone. This has happened three times the latest 1.5 years in my block. Since the background noise level is greatly reduced when the power is out (due to the fact that fans and circulation pumps are dead, and also washing machines and fluorescent light) this could be the ultimate time for listening to nice records and really dig into low level candy

/Peter

 

[Steve Eddy]

The way I figure it I am playing my gainclone at between 1 and 2 amps most of the time and my four batteries per channel are 4x7AH=28Ah so -if I am not mistaken in my calculations I should have between 14 to 28 hrs continuous use without needing a recharge.

If you're using a pair of 7 Ah batteries in series to get a 24 volt rail, and using two pairs of these for a +/- 24 volt supply, your effective Ah rating isn't 28, but rather 3.5.

se

 

[Steve Eddy]

Is it really possible/wise to use up all the rated "Ah" of the batterie?

Sure, you can effectively drain the battery. But deep cycling will reduce the life of the battery. So it's best to keep the batteries topped up by having them on the charger whenever you're not listening.

My concern is the internal resistance of the batterie though, maybe a bigger batterie have better bass and better stamina when the going gets tough?? Especially if difficult loads are used.

The internal resistance of even the small Ah SLAs is pretty low. Usually under 100 milliohms. The larger the battery capacity, the lower its internal resistance. A Panasonic 2.3 Ah SLA has an internal resistance of about 70 milliohms. Their 28 Ah SLA is about 6 milliohms.

And of course if you connect batteries in series, their resistances will add.

One other thing that makes me think about using 4 car batteries is that I´m able to listen to my rig even if/when the power is gone. This has happened three times the latest 1.5 years in my block. Since the background noise level is greatly reduced when the power is out (due to the fact that fans and circulation pumps are dead, and also washing machines and fluorescent light) this could be the ultimate time for listening to nice records and really dig into low level candy

Hehehe. True.

And if you want to go the "ultimate" then you'd use solar power to recharge your batteries.

se

 

[Sparhawk]

If you're using a pair of 7 Ah batteries in series to get a 24 volt rail, and using two pairs of these for a +/- 24 volt supply, your effective Ah rating isn't 28, but rather 3.5.

se

I believe the amp-hour rating would be 7 in this case, not 3.5. Putting two batteries in series does not cut their Ah rating in half; it stays the same. Putting them in parallel would double the Ah rating.

 

[Sparhawk]

Is it really possible/wise to use up all the rated "Ah" of the batterie?

/Peter

If you completely drain the battery, it will not last very long. To get the longest lifetime from a lead-acid battery, it shouldn't be cycled much beyond 20% depth of discharge. If you want your batteries to last for a long time, it is best to oversize them so that you are never discharging them very deeply.

Good deep-cycle batteries (NOT the cheap, sealed kind used in UPS units and emergency lights) can last for 10-15 years if properly maintained.

 

[ralf]

very intersting..

i think you need for making a battery supply very much capacitance, when using car batteries (see hiraga le monstre)
then you should everytime see the state of the battery load, because it can easily get damaged.

i like to experience with batteriy supply, but i have too less information howto build a good one .

Has someone experiences with the sound improovement when using batteries?

greets,

Ralf

 

[Steve Eddy]

I believe the amp-hour rating would be 7 in this case, not 3.5. Putting two batteries in series does not cut their Ah rating in half; it stays the same. Putting them in parallel would double the Ah rating.

No, it should be 3.5.

When you double the voltage into a given load, you also double the current. Since each battery's capacity remains the same, then your Ah rating should be cut in half because each battery is delivering twice as much current which means they will deplete twice as fast.

This is fundamentally the same as placing two identical capacitors in series. Your total capacitance is half that of each capacitor on its own.

se

 

[Sparhawk]

No, it should be 3.5.

When you double the voltage into a given load, you also double the current. Since each battery's capacity remains the same, then your Ah rating should be cut in half because each battery is delivering twice as much current which means they will deplete twice as fast.

This is fundamentally the same as placing two identical capacitors in series. Your total capacitance is half that of each capacitor on its own.

se

I have to disagree here.

I agree that, for a given load, the current requirement doubles when you double the voltage. But this has nothing to do with the capacity of the batteries.

A battery rated at 7 Ah can supply 7A for one hour. Or 14A for 1/2 hour, or 3.5A for 2 hours. (Actually this is not quite true, as the curve is not linear. The capacity of a battery is usually specified at a given discharge rate, ie. 7 Ah at the 20 hour rate).

Two 12V, 7Ah batteries in series can supply 24V at 7A for one hour (in theory, if the discharge curve were linear).

Now, if your load requred 7A at 12V, it is going to require 14A at 24V, so you're going to get half the runtime from the batteries. This makes sense, as you have twice as much stored energy, but your load requires four times as much energy with double the supply voltage. Hence, half the runtime.

But this has nothing to do with the capacity of the batteries. The capacity is still 7Ah.

 

[A 8]

Batteries??

I've got my lc audio millenium power amp running on 16 (2x4 per channel) Panasonic 12V 7.2Ah SLA's.
I am using a normal power amp PS to charge ie transformer and the rest results in 2x55 volt per channel which during charge puts 13.75 volts per battery.
This is my second set of batteries using this very simple "charger" and the last one kept the batteries OK for 9 years (then they started to loose voltage and get really warm...)

This is how it looks.........

 

[Steve Eddy]

I have to disagree here.

I agree that, for a given load, the current requirement doubles when you double the voltage. But this has nothing to do with the capacity of the batteries.

A battery rated at 7 Ah can supply 7A for one hour. Or 14A for 1/2 hour, or 3.5A for 2 hours. (Actually this is not quite true, as the curve is not linear. The capacity of a battery is usually specified at a given discharge rate, ie. 7 Ah at the 20 hour rate).

Two 12V, 7Ah batteries in series can supply 24V at 7A for one hour (in theory, if the discharge curve were linear).

Now, if your load requred 7A at 12V, it is going to require 14A at 24V, so you're going to get half the runtime from the batteries. This makes sense, as you have twice as much stored energy, but your load requires four times as much energy with double the supply voltage. Hence, half the runtime.

But this has nothing to do with the capacity of the batteries. The capacity is still 7Ah.

Aye, yes, you're correct. Thanks. Went back and refreshed my memory regarding the derivation of the amphour ratings.

Yes, the amphour rating would remain the same. As does my original point, that stringing batteries in series gives you less time, not more.

se

 

[Pan]

A8,

how does the Millenium on batteries compare to "traditional PS"?

My Zapsolutes would be nice to try on batteries

They draw 700W or so idle so I´ll have to go for like eight Yellow top or similar

/Peter

 

[A 8]

Hi Pan,

There are no huge differences, but still there are some, particularly the midrange gets really clean and very..very (relative description) intense/powerfull.
Other then that it affects both low and high frequencies, the lower gets a bit more solid and paced, upper ranges gets slightly softer and better defined.

All in all it is more fun to listen with the batteries switched on.

NOTE My set up still has 240,000uF when running on batteries and 480,000uF when I run the normal supply. The transformers (one per channel) and half the 480,000uF are in a separate box. The batteries and the rest of the caps are in the poweramp case.
The benefits are still there during charge so I typically run with both supplies going.

 

[protos]

If you're using a pair of 7 Ah batteries in series to get a 24 volt rail, and using two pairs of these for a +/- 24 volt supply, your effective Ah rating isn't 28, but rather 3.5.

se

In a simple circuit according to ohms law the amperage will double with twice the voltage into the same load. So yes if you connect two batteries in series they would only deliver 7ah instead of 14ah.
However.... since we are not talking about a class A circuit with continuous high consumption and since we are not asking the batteries to deliver 24v all the time to the load the actual amperage/current requirements of the gainclone circuit is much much less than this. So we have to look at what volume/voltage output we are actually working at.
Since on 1khz tone at my normal listening levels I have measured between 4-8V into 4ohms I am saying that the circuit is not consuming more than 1 to 2 A average roughly.
Moreover since we are talking about an AC signal this load is split between the two rails so thats why I am counting total Ah on both rails.
Although I defer to more experienced and EE educated members I maintain that my calculations are (roughly) correct.
This means that if I have a total of 28AH battery capacity stated and my circuit consumes 1A then obviously I can run it theoretically for 28 hours until the batteries are technically exhausted.

 

[ppl]

When I first got my LM-3886 based amp up and running on AC power I used 4 12 Volt series connected 3000 mAH Ni-Mh Cells found in Model car packs. ran for I believe 10 hours at normal listening with Optmus LS-5's Nice tight sound compared to AC I would not mind going back to a virtual battery supply on this amp.

 

[Verbal]

In a simple circuit according to ohms law the amperage will double with twice the voltage into the same load. So yes if you connect two batteries in series they would only deliver 7ah instead of 14ah.

Well, yes, but this has nothing to do with the load - it's just that in a series configuration both batteries will supply the full current, while in a parallel connection, (ideally) both will each just supply half the total current.

since we are not asking the batteries to deliver 24v all the time

We may not be asking them, but they'll do anyway (it's not a constant 24V BTW, but will start at about 26V when fully charged and go down to ca. 22V when you should switch them off)

so thats why I am counting total Ah on both rails.

Yes, however, to stay with the example of 4 12V/7Ah batteries to get +/-24V, the total is still 7Ah, as they're all in series.

BTW the AH rating is usually for a discharge period of 20 hours, i.e. a 7Ah battery will deliver 0.35A for 20 hours. If you drain the battery faster, the capacity will decrease. I you e.g. use 10 times the current, capacity will go down to 60%.

 

[vic2]

A8,

Thanks for your response. Could you give some more details on how your charging system is set up?

Thanks,

Vic