5v battery & step-up circuit - current draw?

[pliens]

Hello everybody!
I've been searching the threads for long now...but i still can't make this up ...

i'm planning for a kit where i'm going to use an AMP32-PS going into an 8ohm speaker.

The kit is going to be portable and lightweight.

i have to use a 5v battery and i'm thinking of using the 5to12v step-up module from 41hz. (http://shop.41hz.com/shop/item.asp?catid=10&itemid=78)

as far as i have understood the average current draw of the amp is ~300mA.
Is that assumption correct?
Will the step-up circuit draw more juice?

I've concerned using a battery like this one: http://www.bixnet.com/5v7libapa.html
According to the specs, the capacity of the battery is 26.6Wh .
I guess that equals to 26.6wh / 5v = 5.32Ah. right?

If that is correct, that means that battery's "life" is going to be (5.32/0.3) ~17 hours?!!!
or the step-up circuit will draw more current?

any help would be really appreciated.

thank you for your time!

thomas

[V-bro]

Hi Thomas and welcome!

The amp draws 300mA on average, but up to 3A peak current and there is no way in the world the 5V to 12V converter will hold up. It will just distort like crazy...

For that price there are MUCH better battery choices available and if you're not afraid of the fire hazard and don't mind to invest in a proper charger (like a Multiplex LN5014) then choose for three cells of LIPO and feed the amp with them directly.

Also a converter like the 5V to 12V step up works with simple linear math. 12V and 100mA out is 5V and 240mA on the input. Current is simply traded for voltage and likewise....

By the way, what's the application?

[Scratchy]

What V-bro said - 100mA is not enough for this amp.

The PS8 converts 5V to +/-12V. Outputs are regulated. Maximum current, 2x100mA.

[pliens]

V-bro and Scratchy, thank you very much!

I'm a sound-artist and i'm preparing an installation where i will have multiple channels of audio in a room.
The sound will be transmitted from a main server to multiple boards like the BeagleBoard (http://beagleboard.org/)
and from there, to their t.amps. So, i'm gonna have multiple 1-channel kits with board+amp+speaker+battery .
BeagleBoard needs 5v to function, so i find myself in the situation where i have to power 2 different voltage systems.
5v for the BeagleBoard and 12v for the amp.
That's why, in the beginning, the converter seemed as a good idea.
So, as far as i can understand maybe i should better look for 2 different batteries ... but that's not the most
ergonomic solution, me thinks.
Also, a LIPO solution looks a little bit dangerous, since the batteries will be recharged at night, in the installation place with
nobody around.
hmmm ...
what do you think, is it better to go for a higher-current converter?..if that exists..

thank you for your help!

thomas

[krilli]

Interesting stuff ...

How much power / current does the BeagleBoard need?

[Jan]

Hi Thomas and welcome!
Also a converter like the 5V to 12V step up works with simple linear math. 12V and 100mA out is 5V and 240mA on the input. Current is simply traded for voltage and likewise....

But add some for losses as the efficiency is not 100% but maybe between 70% and 90%

PS8 is intended for pre-amps, mixers and similar, not for power amps.

[pliens]

Hey krilli!

the beagleboard draws max 800mA at 5v ... it needs some ...
though i don't think that i will need that much, because i will exclude some functions and keep only the audio stuff .
i keep that number in mind though ... as a design parameter ..

thanks for the clarification JanAf, i'll keep it in mind for the future.

[V-bro]

Take a down converter and use just one battery then? This is most oftenly done....

[krilli]

I would take this ~12V 3300mAh LiFePO4 battery from Batteryspace.com, and this charger for it. (Or this 6600mAh battery, and this stronger charger for it.)

LiFePO4 or 'Lithium ferrophosphate' batteries are safe (they basically just don't explode or catch fire), they have quite good capacity, last for thousands of charges (!), put out HEAPS of current, and are easy to charge – these are as perfect as can be for powering always-on Tripath amps.

Then add a 12V-to-5V converter of about 10W. This one would do nicely for $30 – they probably come in smaller and/or cheaper packages too.

Edit ---

This ~12V-to-5V converter search on Farnell should also be useful! I hope the link is shareable ... If it isn't I searched under DC-DC modules, with these limits. The battery+charger combo will put out voltages from just above 9V at low-battery to around 15-16V (?) when charging, so the 5V generator will have to accept that range. (Looking at the limits again, I see that they are a little too loose in the input range.)

[Scratchy]

Link works fine Krilli....

@pliens.
See how much more helpful information you receive when you tell us what your are doing, rather that asking for a specific solution. In this case it makes far more sense to use a 12V supply and derive the 5V for the beagle-boards from that.
Generally it's cheaper and you have more options when down-converting a voltage than upconverting.
The links Krilli posted is a great start. There are other threads on this forum discussing the virtues of LiFePO4 batteries.
They are a much different animal than LiPo or Li-Ion batteries.