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Battery power/power supply from wall charger for BT speaker
Battery power/power supply from wall charger for BT speaker
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Old 30th June 2015, 07:48 PM   #1
satx is offline satx  United States
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Default Battery power/power supply from wall charger for BT speaker

Hi, I've started a small semi portable bluetooth speaker build and I'm having a hard time figuring out the powering and charging scheme. I've read and searched like crazy for the last few weeks, but I've seen a number of conflicting comments.

First of all the speaker is a dayton RS100-04/ND16FA two way in 1.7L that ends up at about 83db sensitivity after the xo. It's just one speaker so I will try to feed it a mono signal.

The items that I've purchased for it so far are a separate BT 4.0 module and a couple of little mono amp modules that use the TDA203A. I also ordered an integrated BT 4.0 and 25+25 watt amp module that uses the TDA7294P. I'd only use one of course, but I didn't know what to expect as far as the quality and functionality of the BT modules and also if I'd have ground loop issues if using a single power supply with separate modules.

I pickup up a 9.6V Nimh 2000mah Tenergy battery and accompaning wall charger that is 12v 400ma. This battery and power supply exceeds the minimum power requirements for all the boards and doesn't exceed any of the max voltage/amp ratings.

I also have a variety of plugs, rocker switches, barrel jacks and female DC jacks with 3 pin connections.

The issue I'm having is if I can connect the battery and wall charger to the modules in parallel without safety or longevity issues? That way the unit can run from the battery and/or wall charger and also charge the battery when the current draw from the amp isn't too high. There will be a rocker switch to power on/off the units. I realize the wall charger is probably under rated, amp wise, but so far the little 2030a's seem to run fine from it after I eliminated the noise the supply was introducing. I could switch to a 12v 2A charger if needed. Everything hooks up and powers up fine when I've connected the battery and charger to the amp at the same time and the battery is also receiving charging voltage with the speaker playing at moderate levels.

What I don't understand is the potential problems with this setup. I'm worried that the charger will not properly read the batteries charge state because of the draw from the amp and will either continue charging it to overcharge and cause damage or danger. Or that it will limit current when the battery's fully charged and shut off the amp (this is a less concerning outcome).

I've tried to figure out a wiring scheme that could use the floating third pin of the female dc jack in conjunction with the unneeded third pin of the rocker switch to use battery with no wall power connected, use the wall power when connected and disconnect the battery and charge the battery when the rocker switch is in the off position, but I can't figure it out.

So, any help would be greatly appreciated. I'm completely new to using and charging batteries in any of my projects. And I apologize for the novel, but the more info the better!

Thanks
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Old 30th June 2015, 08:50 PM   #2
infinia is offline infinia  United States
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all depends 12V at 400mA charger and the "audio load". The heavier the "audio load" is will use up the charger current 1st.
is the charger a smart charger? then you should be OK for max V at 3*4.2V.

Why not play it safe and move the battery around, unless your looking for an "audio UPS".
until then you could figure it out yourself with a couple of cheap DMMs.
start out with a discharged battery scenario, and monitor charger current and chart the voltage keeping an eye out for abs max limit.
next try a fully charged batt. and repeat. best to study up on the battery chemistries you have selected, lots of resources on the web.( the only warning I can give you is your series conn battery will need "balancing" for each cell at some point!) does your charger do that?
I reckon the only danger is slow to recharge batts depending on the load. and increased ripple and noise with charger connected.
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Last edited by infinia; 30th June 2015 at 09:12 PM.
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Old 30th June 2015, 10:37 PM   #3
infinia is offline infinia  United States
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oh yeah these Li batteries have a shorted life being kept at full charge.
when not being discharged best to store batteries between 3.7-3.8V per cell..
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Old 30th June 2015, 10:50 PM   #4
satx is offline satx  United States
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Quote:
Originally Posted by infinia View Post
all depends 12V at 400mA charger and the "audio load". The heavier the "audio load" is will use up the charger current 1st.
is the charger a smart charger? then you should be OK for max V at 3*4.2V.

Why not play it safe and move the battery around, unless your looking for an "audio UPS".
until then you could figure it out yourself with a couple of cheap DMMs.
start out with a discharged battery scenario, and monitor charger current and chart the voltage keeping an eye out for abs max limit.
next try a fully charged batt. and repeat. best to study up on the battery chemistries you have selected, lots of resources on the web.( the only warning I can give you is your series conn battery will need "balancing" for each cell at some point!) does your charger do that?
I reckon the only danger is slow to recharge batts depending on the load. and increased ripple and noise with charger connected.
Thanks Infinia. Some of your terminology is a little over my head, but I got most of it.....I think What's a DMM? Usually I know its a meter, but you said I'd need a couple? I have a Digital multi meter. And what's the ABS max limit?

I don't wan't to move the battery around because I want an all enclosed system if possible.

I don't know if the charger's a smart charger, but for the price I paid, I doubt it. This is what I have http://www.amazon.com/Tenergy-9-6V-B.../dp/B005ZKSSZO

I've read a number papers about the different batteries types. From what I understand, the Nimh are less efficient, but safer and somewhat less critical about charging than the LI batteries. That and lower price are why I decided to start there.

I did connect the battery, charger and amp in parallel and played a source at fairly high levels (for that little amp) for a couple of hours. Beginning voltage on the battery was 9.8v I believe and the voltage after a couple of hours was 11.4v. It's a 9.6v battery, but it was at around 11.8v when I received it and reviews said it gets close to 12v when fully charged. The battery and charger never got warm at all really.

I did monitor voltage at the amp, battery throughout, but I don' tknow what I I should be looking for. The Voltage at the battery when charging started at around 11.2v and ended up at 11.5v. The amp had similar numbers I believe. The amp was drawing .02ma and the battery was drawing .01ma.

Also I got some extra noise (EMI) with the charger connected, but after a ferrite core and backing off the gain on the amp very slightly it disappeared.
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Old 1st July 2015, 12:01 AM   #5
infinia is offline infinia  United States
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Quote:
Made with 8xAA 2000mAh TENERGY high capacity and high power NiMH Batteries
sorry I was mistaken your batteries for LiPo hobby packs. please research "care and feeding of AA NiMH batteries". here's a start
http://batteryuniversity.com/learn/a..._metal_hydride
Quote:
Charging Directions: It will take 7 hours to fully charge this 2000mah battery pack -- manually unplug the unit after the 7 hour period.
well you do follow directions?
I reckon if they aren't heating up that's good. Without knowledge and monitoring things I wouldn't expect much long term success for your set up. that's the tradeoff for an all-in-one sealed system.
IMO next time consider a 3 cell 18650 external pack for portability.
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Last edited by infinia; 1st July 2015 at 12:25 AM.
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Old 1st July 2015, 02:27 AM   #6
satx is offline satx  United States
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Yes, I actually do follow directions, thanks. I don't remember seeing what you posted as I bought the battery a while back. The package said follow directions, but there were none included. The directions aren't exactly going to outline how to wire up a bluetooth module, amp and implement charging anyways. I can plug the thing into the wall and unplug it when it's charged, that's why I didn't ask how to do that

It seems to me that there are more options than just connecting everything in parallel, that's what I'm asking for. Do I need an internal charging circuit, different wall charger. I don't really see how long term success is compromised by an all in one setup. Many, many commercial products are just that. You don't have to remove the battery to charge the unit. I'm hoping to understand how they do that.

A different battery isn't a problem if that's what's needed.
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Old 1st July 2015, 03:11 AM   #7
sofaspud is offline sofaspud  United States
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There is usually a smart charge circuit built into the unit or charger. You could have a look at TI's line of chemistry-specific charge IC's to investigate this further.
I might not be too concerned with simultaneous play-charge. Several use and performance questions would need answers.
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Old 1st July 2015, 04:23 AM   #8
infinia is offline infinia  United States
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you don't have a smart charger. the best ones are implemented inside the battery pack like on a laptop. yours is purely time based without even a simple timer shutoff, so its manual only. Laptops battery packs have built-in complex circuitry based on series connected cells, using combination hardware, software, and balancing each cell, etc,) Charge time is estimated by the amount of discharge and the condition of the cells. So on yours, with brand new cells completely discharged and all the current available ( not running extra stuff ) it's 7 hrs. This time is adjusted for mAH and current so YOU cant run it in parallel with your extra stuff running and expect predictable charging or good lifetime. As the battery wears out the time is adjusted down due to decreased capacity. They talk about this in the link I gave you , did you read it? If you leave everthing in parallel like you want its likely to ruin your batt. pack in a year or less.
my advice, select good power supply with a DC plug then add the same plug on your battery pack and use either one, one at a time. then when the battery pack is discharged unplug it and use the supplied cheap charger according to the directions.
you may be able to use 2 switches or a multi pole switch to charge an internal battery and disconnect the audio.
but IMO all that buys you is using the same crappy charger to run the audio or charge the battery, but not at the same time.
Sorry but a good charger scheme for series connected cells and running your stuff is probably more complex than your entire project.
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Last edited by infinia; 1st July 2015 at 04:52 AM.
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Old 1st July 2015, 04:24 AM   #9
satx is offline satx  United States
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Quote:
Originally Posted by sofaspud View Post
There is usually a smart charge circuit built into the unit or charger. You could have a look at TI's line of chemistry-specific charge IC's to investigate this further.
I might not be too concerned with simultaneous play-charge. Several use and performance questions would need answers.
That was my thinking too. The charger does have a red light when charging that turns green when it's charged so that would imply some level of monitoring to me. Part of my confusion is that I don't know if the draw from the amp and BT module will confuse the monitoring built into the charger.

Now that i have actually hooked everything up, I think that a battery with it's own protection circuit would be the safer way to go. That way it's self regulated. Something like the Li-ion that infinia recommended.

As for use and performance questions. What do you need to know? The amps and BT boards all accept PS between 7-15v. The amps are fairly low powered and the speaker is fairly insensitive, but sims show xmax is exceeded with only about 7 watts so I figure 15-25W music power should be about right. I'm really only looking for maybe 88-90db max in room.

Run time: I'm hoping for a least 6-8 hours at normal listing levels.

I've noticed with the little 2030A boards that distortion sets in pretty fast at higher volume. Doesn't matter if it's running off the battery or 12v 2A supply. I even tried a 12v 5A supply and it's about the same. The same PS connected to a Lepai 2020a does much better with the speaker.

Maybe I need to add some capacitance in line with the supply? I'm very new to the electronics end of audio so please correct me if I'm wrong.

Anything else?
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Old 1st July 2015, 04:32 AM   #10
satx is offline satx  United States
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Quote:
Originally Posted by infinia View Post
you don't have a smart charger. the best ones are (sort of complex circuitry based on series cells, software, and balancing etc,) implemented inside the battery pack like a laptop. yours is purely time based without even a simple timer shutoff, so its manual only. Time is estimated by the amount of discharge and the condition of the cells. So with brand new cells completely discharged and all the current available ( not running extra stuff ) it's 7 hrs. the time is adjusted for mAH and current so YOU cant run it in parallel with your extra stuff running and expect predictable charging or good lifetime. they talk about this in the link I gave you , did you read it?
my advice, select good power supply with a DC plug then add the same plug on your battery pack and use either one, one at a time. then when the battery pack is discharged unplug it and use the supplied cheap charger according to the directions.
Sorry but a good charger scheme for series connect cells and running your stuff is probably more complex than your entire project.
Understood. No I haven't gotten to it yet, but I will.

What about 12v 2A charger designed for 9.6v nimh batteries? Then using a switch scheme that uses the charger/PS to run the components with the battery out of the circuit and when the unit is turned off the charger connects to the battery? I guess I would still need to manually monitor and unplug it when it's charged.
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