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Charging batteries in boombox while using it

megajonern

May 14, 2017
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May 14, 2017
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Hi!
I'm building a boombox where I have 10, 1.2 Volt AA rechargable batteries in series (12 V total) and I was wondering how I can charge them while still using the boombox and to prevent overcharging, do I need a voltage regulator between the amplifier and batterypack so that I don't go over the amplifiers threshold or do i need to do something else so that I don't completely destroy everything,
I know that I can add a few switches so that the battery disconnects when hooked up to the wall, but I want to make the boombox as user friendly as possible.
The amplifier I use takes between 8 - 25 Volts (link further down)

Amplifier:
http://www.ebay.com/itm/TDA7492P-50...id=100005&rk=6&rkt=6&mehot=ag&sd=271883054265
 

Audioguru

Sep 24, 2016
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The charger for 10 cells will produce 14V to 15V. The maximum voltage for the amplifier is much higher at 25V so a voltage regulator is not needed.
The battery and boom-box must be separated when charging the battery but the battery can be connected to the charger and the boom-box can be connected to the input voltage to the charger.
 

73's de Edd

Aug 21, 2015
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Sir megajonern . . . . .


Considering past amps of that rating, is hard to perceive of that unit with its Lilliputian sized digital to analog filtering networks, of mini inductors and mini canned electrolytics components shown, getting those specs, even in a comical “Music Powered Ratings” at your low end of the power supply's input spectrums, 12VDC power input level.

The thing to do would be to get the unit up and operating, using a stereo audio input and have the unit feeding into your prescribed speakers . . . as its loads.

Then you open the + power supply feed and insert a series arrangement of the test leads of your DVM, being placed into its 10 amp DC current scale.

You then adjust for your normal volume level that you will be using 90% ? of the time and then actually see how much average current , is being consumed.

Then do an increase to the max level that you might use, to then compare its current pull.
" 10, 1.2 Volt AA rechargable batteries " . . . . ( That is not a whole bunch of battery life run time at high volume levels. )


Then you would need to use a series power diode branched into the + supply line to be able to keep your external power supply isolated, yet be able to EITHER be playing “keep up,” with the inserted power level, meeting the power level being being consumed in operation.

OR to gain a bit, and additionally put a bit of a charge into the batteries, if the applied external input voltage was being made even a bit greater.

But watch out on that level, as THAT input level might be of an excessive battery charge level, if the amp was switched off.

This would require an adjustable power supply to do those evaluations with, then, a dedicated one could be built up with that voltage level output.


73’s de Edd
 
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Audioguru

Sep 24, 2016
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A graph in the datasheet for the TDA7492 shows 50W per channel with a 25V supply and horrible-sounding clipping distortion. The minimum voltage on the graph is 15V but I figure 6W per channel into 8 ohm speakers with fairly low distortion when powered by this 12V battery.

Music is never continuously at full blast but its loudest average is 1/5th its 12W maximum which is 2.4W. The IC heats with only 10% more for a new total of 2.64W. The average current is 2.64W/12V= 220mA plus maybe 40mA for the Bluetooth for a total average current of 260mA.

Ni-MH AA batteries are 2300mAh so a charge will play loudly for about 2300/260= 8.8 hours but the volume must be turned down a little as the battery voltage runs down.

Modern Ni-MH batteries must not be continuously charged, the charger circuit must detect a full charge then turn off the charging. Then the amplifier must be disconnected from the battery with a diode when the battery is charging.
 

megajonern

May 14, 2017
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May 14, 2017
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the project is just made by parts I have laying around and got for free at my university... the amplifier is something i got from school while the batteries are just a ten pack that was laying around at the workshop... batterypack WILL be upgraded later, but i wanted to test with a 12 V batterypack at first just to see how it works... but thanks for the answers!
 
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