Need help selecting a DC-DC isolated converter.

[Jack.Straw]

Hi guys. I'm looking to purchase a DC-DC isolated converter to help solve a ground loop noise problem in a bluetooth module and amplifier. The power supply is 6x 18650 li-ion batteries in 3S2P setup, so the voltage can vary from something like 8.7v to 12.5v. At times I use a 13v wall wart, so lets call the range 8.7v-13v. Both the amplier and bluetooth modules are fine with this voltage range, but after some experimenting, I can say that the bluetooth module will not run on 5v.

How picky are the DC-DC isolated converters about voltage? Can i get away with a straight 12v-12v converter?

I do see that they make converters that accept a range of voltage inputs, but they are considerably more expensive. For example I see one that accepts 4.5v-18v and outputs 12v. I'm concerned about efficiency/battery life. The converter is constantly going to be stepping the voltage up or down, depending on the state of the batteries. Would it be more efficient to use some kind of bucking switch converter to stabilize the voltage before feeding the DC-DC converter?

I'm also noticing that the DC-DC converters have an output power and current rating. I really have no idea about the wattage or current requirements of the module, and I don't have a way to test it (that i know of). Is anyone able to make an educated guess? The ebay listing gives lots of specs, but oddly nothing concerning power requirements. This is the module:

**broken link removed**

Thanks for any advice you can offer!

 

[audioguru]

The Chinese no-name-brand module has no audio spec's and no electrical spec's.
It should at least say what is its power supply voltage and current.

 

[Jack.Straw]

The Chinese no-name-brand module has no audio spec's and no electrical spec's.
It should at least say what is its power supply voltage and current.

True. I've sent him a message asking for those details, but i'm not hopeful. I've tried a number of the Chinese no-name-brand modules and they pretty much all sucked. Except the older version of this module that is. I can't get my hands on it anymore, and there is a very bad ground loop issue with this new version.

 

[Jack.Straw]

So I sent messages to several people selling this module online and none of them could tell me the wattage or current requirements. The voltage range is quite wide though: 6v-36v, 12v optimal.