5V USB to 12V DC jack?

Hello.

I'm building a boombox, which I will be using a 10,000 mAh powerbank to power it. I want to use the 5V/2A USB output of the powerbank, to a 12V converter for the amp (TDA7492P Bluetooth 4.0).

I can only find such converters which can hold a max current draw of 800mA. The amp will most likely draw much more than that on 12V on high volume.

Any suggestions of where I can find what i'm looking for, or maybe a smarter way to tackle this?`


Note: A USB jack on the other end of the converter is not necessary, as I can simply solder one in place.
 
It's a question of power - [email protected] = 10W; [email protected] = 9.6W.

Chances are, it would have a hard time at 800mA, since that assumes 96% efficiency, which is tough for a step-up switching power supply.

I think I'd look at Li-ion/polymer packs and separate chargers that are designed for ~12V from someplace like BatterySpace.com. I realize you aren't in the US, but there's probably something similar available on your side of the pond.
 
the only question to answer is how much power does the "boombox" draw?
and, lacking that information, what is the rated power output (total) and what sort of amplifier is it - digital or analog?? (i'm not personally going to look it up...)

Then you can determine what sort of power source is possible.

The other question is how LONG a period of time do you want to run it?

A 10Ah "powerbank" may deliver 1Amp for <10hours, for example. (the last couple of hours may or may not be useful depending on the circuit used to regulate or provide the nominal voltage supplied to the amp.

_-_-
 
Get a straight 12V battery, period.
Add as many packs in series as needed to reach or slightly surpass 12.6V ; up to 14.4V is perfectly acceptable so do the Math.

Forget about powering *any* power amp from an USB outlet.
Except those tiny cute golfball sized PC speakers which are more toys and novelties than anything else, definitely not boombox class.
 
Get a straight 12V battery, period.
Add as many packs in series as needed to reach or slightly surpass 12.6V ; up to 14.4V is perfectly acceptable so do the Math.

Forget about powering *any* power amp from an USB outlet.
Except those tiny cute golfball sized PC speakers which are more toys and novelties than anything else, definitely not boombox class.

I don't want those heavy 12V 7-10 Ah batteries. I want something fairly light, and I will gladly trade that at the cost of playtime. I would be very satisfied with 3-4 hours at moderate to high volume. Anything in mind that you could recommend?
 
I didn´t mention or even hint "lead acid" but more packs same type as you are using now.
Add as many packs in series as needed to reach or slightly surpass 12.6V

I am somewhat puzzled by the "5V USB output" , know no chemistry which is exactly that, so I guess there is some internal converter built in.

Get the raw batteries, no converters, as many as you need to add up to 12 to 14.4 V range, which what most "car/12V" rated amplifiers expect.

If 3.6V packs, you need 4 of them in series for perfect 14.4VDC; 5AH capacity will give you required 4 hours work if feeding a typical bridged out car type amp, nominally 20W RMS into 4 ohms.

There, I did all the Math for you ;)

I have built hundreds of battery powered Musical Instrumentamplifiers and am painfully aware of what you can and can not pull from batteries.
 
I didn´t mention or even hint "lead acid" but more packs same type as you are using now.


I am somewhat puzzled by the "5V USB output" , know no chemistry which is exactly that, so I guess there is some internal converter built in.

Get the raw batteries, no converters, as many as you need to add up to 12 to 14.4 V range, which what most "car/12V" rated amplifiers expect.

If 3.6V packs, you need 4 of them in series for perfect 14.4VDC; 5AH capacity will give you required 4 hours work if feeding a typical bridged out car type amp, nominally 20W RMS into 4 ohms.

There, I did all the Math for you ;)

I have built hundreds of battery powered Musical Instrumentamplifiers and am painfully aware of what you can and can not pull from batteries.


Are you thinking of those 18650 3.6V batteries? If so, do I need a charge controller and other electronics between the batteries and the amp, or could i simply connect them straight to the amp?

I have a voltmeter display, that I can connect to the batteries and monitor the voltage. So i can manually turn off the amp when they are getting low on charge, to prevent overdischarge. I believe some of these batteries already has integrated circuit to prevent this.
 
Last edited:

easp

Member
2016-05-29 9:35 pm
That powerbank might have 4-5 Li-ion cells in series and be close enough in voltage.

ie tap directly from the batteries and use the electronics in the powerbank as a charge controller.

Multi-cell powerbanks that only provide USB output are pretty much always in parallel configuration.

Are you thinking of those 18650 3.6V batteries? If so, do I need a charge controller and other electronics between the batteries and the amp, or could i simply connect them straight to the amp?

I have a voltmeter display, that I can connect to the batteries and monitor the voltage. So i can manually turn off the amp when they are getting low on charge, to prevent overdischarge. I believe some of these batteries already has integrated circuit to prevent this.

For your safety and the longevity of the batteries, you should have a protection circuit in the battery pack. These prevent overdischarge and overcharge.

On packs with multiple cells in series, protection circuits monitor the individual banks of cells to make sure one or more of them isn't overdischarged or overcharged. Many will also balance cells at top of charge, shunting current around cells that are already full and allowing the others to catch up.

In consumer electronics, charge management is typically a separate function from protection, though there are probably integrated solutions at this point.

The only thing I can think of that should solve your problem pretty easily is an external lithium ion battery pack designed for use with laptops that can deliver 14-19v (adjustable). I don't know that they can hit 100W, but they should be able to get you well over 50W, unless they have trouble with transients. They often include USB outputs, but require a laptop power brick for charging. I think they probably have an internal (nominal) voltage of 11.1 or 14.8v and then use a switching supply to deliver the desired voltage.

Other possibilities:

Battery packs intended for RC use. Typically these lack any protection in the pack, but RC chargers do balance charging of packs.

Lithium Ion car "jump starter" packs. These can deliver high currents at ~12V. They are usually packaged like a USB power bank, and often have USB power ports. Inside though, they have the batteries in series. The one I tore down had a proper series charge management / protection circuit, with the important caveat that none of it is engaged when drawing power through the jumpstarting port.

You can also get protected 18650 cells and an appropriate charger and load the charged cells into a battery holder wired in series. The downsides are 1) you should get a matched set of cells to use. 2) protected 18650s can be a bit expensive.

You can also get unprotected 18650s (they are very popular for "vapers"), and find some suitable protection boards on ebay.

It may be tempting to skate by without proper protection or charging. Don't. Enough batteries to power that amp for more than an hour at any sort of power are going to cost a decent amount of money, and are going to be capable of causing significant damage if something goes wrong (like short).