[sil0nt]

I have seen some people talk about their portable battery power supplies in a few threads recently, and I would like to get a few more details.

I am going to be building a mains powered +/- 12vdc power supply which connects via DIN plug on the amp. What I want to do is make a battery pack that outputs something like +/- 10-12 vdc to a DIN. As you can see, my goal is to be able to transparently switch from home to portable power supply.

My plan is to use 10 NiMH AAA batteries per rail. Does that seem about right in terms of voltage and mAH? I chose AAA for size, cost, and I have other devices that use AAA but nothing that uses AA. I know I would have two sets of 10 wired in series, but how do I wire this so that I have +/- rails? Should I use 20 AAA's in series and a rail splitter?

Also, I see people discussing voltage regulators on battery packs and various passive components like capacitors. What is the benefit to adding such devices to a battery pack?

Last question.. what about a ground? I need the pinout on the battery power supply DIN to exactly match the mains power supply in order for this to work. Should I just omit a ground on both?

Thanks for answering my questions,
brian

 

[sil0nt]

i can understand if people dont know the answers/dont want to answer my questions.. but just for sake of my own curiosity.. does anyone else have questions such as mine.. or am i way out in left field all alone?

hehe.

 

[zhtham]

Yeah, i posted a thread regarding 2x7.2V NiMH a while ago over here. I had 1 response

My final design has 12x1.2V NiMH 850mAH (series/parallel) that squeezed into a portable META42

I hooked it up so that i can charge all batteries as 2x7.2V in parallel. Now i have 5 times the capacity of normal 9V recargebles.

Z.

 

[tangent]

There are a couple of ways you can do it. One is the "20xAA in series plus rail splitter" method. The disadvantage of this method is that you have to add a bit of circuitry to the battery pack box.

The other would be to have two series groups of 10xAA, and wire those two groups in series. Now the point where the two groups join is your "ground" -- it's halfway between either "end" of your battery groups. The disadvantage of this method is that if the power drain is unbalanced on the amp for any reason, the rails will become unbalanced as one group of batteries discharges faster than the other. I'm told that this can "run away" on you, with one group discharging faster and faster so that you end up with something like 0V, 0V and +9V for your rails, which then does nasty things like biasing your op-amp's output to deliver a DC offset relative to your "ground" rail.

On the voltage regulator and capacitor stuff, are you sure the posts aren't talking about wall power supplies?

 

[sil0nt]

I think I will probably go with the 20xAAA in series plus rail splitter. I do not mind adding a rail splitter, especially since I don't have to worry about unbalanced power drain and whatnot.

Regarding the voltage regulator stuff, I *thought* I read about that, but maybe I'm just losing it. hehe.

thanks,
brian

 

[aos]

I would add regulator even with batteries, or at least experiment with it. This was discussed in previous threads. Batteries do give very low noise level but they still have finite internal resistance and their voltage varies with the load changes.

 

[sil0nt]

Would a regulator aid in balancing the power drain on the batteries? Also, would there be any benefit to putting some caps on my battery supply?

 

[tangent]

I'll buy that, aos. The regulator helps control ripple, I see.

No, sil0nt, it won't help control unbalanced battery drain. In the split battery pack scenario, you would use two voltage regulators, which will act independently. In fact, it may make the problem worse as the low side drops out of regulation while the high side is still in regulation. Just speculation here...

On the capacitor thing, again, point me to the thread. You will have capacitors following your power supply already, at least in amps like the META42 and all its predecessors. I'm not sure whether you're talking about adding more of the same or adding some different kind of capacitor to get some benefit that the standard power supply capacitors don't give you.

 

[Ari]

Remember about fuse protection !