Charging two separate batteries with a single power input?

[JohnnyHN]

I recently made my own bluetooth speaker; I have no previous experience with something like that, just thought that it'd be something fun to try. One problem that I encountered was ground loop noise coming from the bluetooth receiver and amplifier being powered from the same 12v battery. I was able to get rid of the noise using a ground loop isolator made by Pyle (PLGI35T), but I also lost some bass from the audio. Now I'm thinking of making another bluetooth speaker, but using two separate batteries (one for the amp and one for the bt receiver) to avoid the ground loop problem, rather than using an isolator and losing some of the audio range. I would like to have a single input for charging the batteries though. I'm thinking that if I throw in a relay that will normally have the two batteries separated and put them in parallel with power applied, that should work. I just wanted to bounce the idea of some folks who are smarter than I am to make sure it was an alright idea and not a recipe for disaster.

 

[BobK]

Ground loop noise normally refers to AC powered circuits. There should be no problem powering both the receiver and amplifier from the same battery. What kind of noise are you getting?

Bob

 

[JohnnyHN]

Bob, I get a hum/buzz kind of noise. If I plug the Bluetooth receiver into external power the noise isn't there, and with the isolator I mentioned it also isn't there. I'm not that smart on audio systems, but besides the DC vs AC thing, it seems like ground loop noise to me. Part of the problem is probably that my speaker is more or less jury rigged, the bt receiver is a $6 generic "add Bluetooth to your car" that runs on 5v through a usb jack, and I just used a car cigarette lighter adapter to convert the 12v from the battery to the 5v. I'm not too concerned with fixing it since the isolator is working. If I do make another speaker though, I'd like it to be a little more professional and to avoid the feedback/noise I was getting. One option I was considering was to use a similar Bluetooth receiver, but a higher quality one with its own built-in battery. That would avoid the noise problem, but I'd need to plug in two cables to charge the separate batteries unless I can wire them together for charging while keeping them separate while operating.